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HSK21542 injection is a new peripheral kappa opioid receptor (KOR) agonist. To evaluate its safety, tolerability, pharmacokinetics and pharmacodynamics, this study was conducted in healthy volunteers, consisting of two parts: a single ascending dose (0.2–3.375 μg/kg, 15‐min infusion) and different infusion durations (0.2 and 1 μg/kg, 2‐ or 15‐min infusion). The area under the plasma concentration‐time curve (AUC) and peak concentration (Cmax) of HSK21542 were dose‐linear among 0.2–3.375 μg/kg. After intravenous injection, HSK21542 was rapidly eliminated with a half‐life (t1/2) of 1.5 h, and the majority (48.02%) of the dose was excreted unchanged in urine. Pharmacodynamic results showed that HSK21542 increased prolactin release and reached a peak at 1–2 h after administration but had no significant effect on vasopressin levels. There was a brief increase in urine volume within the initial 2 h after administration. HSK21542 was well tolerated; most of the adverse effects (AEs) in the trial group were grade 1, and only 2 cases (4.0%) were grade 2. The main AE was paresthesia, which appeared in 42% (21/50) in the trial group. No serious adverse event (SAE) was observed. No subject withdrew early due to AEs. These results suggest that HSK21542 may be a potential treatment for pain and pruritic conditions. [ABSTRACT FROM AUTHOR]

Many drugs of abuse, including alcohol, disrupt long-term synaptic depression (LTD) at dorsal striatal glutamate synapses. This disruption is common to many forms of LTD that are mediated by G protein coupled receptors (GPCRs) that signal through the inhibitory G i/o class of G proteins. A loss of LTD is thought to mediate behavioral changes associated with the development of substance use disorders. We have previously shown in multiple studies that LTD mediated by the G i/o -coupled mu opioid receptor is disrupted by in vivo opioid and alcohol exposure in adolescent and adult mice. One of our previous studies suggested that LTD mediated by delta and kappa opioid receptors was resistant to the LTD-disrupting properties of in vivo opioid exposure. We hypothesized that delta and kappa opioid receptor-mediated LTD would be exceptions to the generalizable observation that forms of dorsal striatal G i/o -coupled receptor LTD are disrupted by drugs of abuse. Specifically, we predicted that these forms of LTD would be resistant to the deleterious effects of alcohol consumption, just as they were resistant to opioid exposure. Indeed, in adult male mice that drank alcohol for 3 weeks, delta and kappa opioid receptor-mediated LTD at glutamatergic inputs to direct pathway and indirect pathway medium spiny neurons in the dorsolateral striatum was unaffected by alcohol. These data demonstrate that alcohol effects on GPCR-mediated LTD are not generalizable across all types of G i/o -coupled GPCRs. • Kappa and delta opioid receptor long-term depression occur at glutamate inputs to both subtypes of medium spiny neurons in dorsolateral striatum. • Neither kappa or delta opioid receptor long-term synaptic depression is sensitive to previous alcohol drinking. • Alcohol effects on opioid long-term depression are not generalizable across all subtypes of opioid receptors. [ABSTRACT FROM AUTHOR]

We recently developed a series of nalfurafine analogs (TK10, TK33, and TK35) that may serve as non-addictive candidate analgesics. These compounds are mixed-action agonists at the kappa and delta opioid receptors (KOR and DOR, respectively) and produce antinociception in a mouse warm-water tail-immersion test while failing to produce typical mu opioid receptor (MOR)-mediated side effects. The warm-water tail-immersion test is an assay of pain-stimulated behavior vulnerable to false-positive analgesic-like effects by drugs that produce motor impairment. Accordingly, this study evaluated TK10, TK33, and TK35 in a recently validated assay of pain-related behavioral depression in mice that are less vulnerable to false-positive effects. For comparison, we also evaluated the effects of the MOR agonist/analgesic hydrocodone (positive control), the neurokinin 1 receptor (NK1R) antagonist aprepitant (negative control), nalfurafine as a selective KOR agonist, SNC80 as a selective DOR agonist, and a nalfurafine/SNC80 mixture. Intraperitoneal injection of dilute lactic acid (IP lactic acid) served as a noxious stimulus to depress vertical and horizontal locomotor activity in male and female ICR mice. IP lactic acid-induced locomotor depression was alleviated by hydrocodone but not by aprepitant, nalfurafine, SNC80, the nalfurafine/SNC80 mixture, or the KOR/DOR agonists. These results suggest that caution is warranted in advancing mixed-action KOR/DOR agonists as candidate analgesics. [ABSTRACT FROM AUTHOR]

Objective: Kappa opioid receptor (KOR) signaling is involved in joint development and inflammation in Osteoarthritis (OA), while the biochemical mechanism remains unclarified. This study aims to investigate downstream molecular events of KOR activation, to provide novel perspectives in OA pathology. Methods: U50,488H, a selective KOR agonist, was intra-articularly injected in mice upon destabilization of the medial meniscus (DMM) as OA models, with PBS injection as control. The behavioral and histological evaluation was assessed by hot plate test and red solid green staining, respectively. Alterations in mRNA and protein expression were assessed by RNA-seq, RT-qPCR, immunohistochemistry and western blotting (WB) in chondrocytes treated with TNF-α or TNF-α + U50,488H. Proteins interacted with KOR were explored using proximity labeling followed by mass spectrometry and then testified by co-immunoprecipitation (Co-IP) assay and immunofluorescence (IF). Results: OA-induced pain was reduced and cartilage degeneration was alleviated upon KOR activation in DMM mice. In chondrocytes, activation of KOR reversed the upregulation of MMPs, IL-6, IL-1β and phosphorylated(p-) STAT3, stimulated by TNF-α, while the expression of NF-κB, MAPKs and AKT signaling weren't reversed. RNA-seq and IF results presented that KOR activation evidently reduced STAT3 nuclear translocation in chondrocytes upon TNF-α stimuli. The reduction may be resulted from the binding of KOR and STAT3 in the plasma membrane, revealed by proximity labeling and Co-IP results. Conclusions: KOR activation protects cartilage from OA, and this protective effect is mainly exerted via sequestering STAT3 on the plasma membrane, resulting in inactivation of STAT3-dependent immune responses which otherwise contributes to OA. [ABSTRACT FROM AUTHOR]

Multiple sclerosis (MS) afflicts millions of people worldwide. While multiple therapeutics have recently been developed and approved as treatment agents, they are not 100% effective. Recent developments investigating the endogenous opioid system involvement in MS has revealed that agonists of the kappa opioid receptor (KOR) have beneficial effects in both animal models of MS (and demyelinating disorders more generally) as well as in vitro models of remyelination. Several groups have contributed to this development. We summarize here the findings of these published studies, with comparisons of the effects and discussion of similarities and differences. The effects of KOR agonists involve both neuroimmunomodulation as well as remyelination, in different populations of cells. The compelling findings in MS model systems using KOR agonists strongly indicate that further investigations at both mechanistic and translational therapeutic levels are warranted. [ABSTRACT FROM AUTHOR]

Kappa opioid receptors (KOPr) are involved in the response to stress. KOPr are also targets for the treatment of stress-related psychiatric disorders including depression, anxiety, and addiction although effects of KOPr are often sex-dependent. Here we investigated c-Fos expression in a range of brain regions in male and female mice following an acute stressor, and a single injection of KOPr agonist. Using adult C57BL/6 c-Fos-GFP transgenic mice and quantitative fluorescence microscopy, we identified brain regions activated in response to a challenge with the KOPr agonist U50,488 (20 mg/kg) or an acute stress (15 min forced swim stress, FSS). In male mice, U50,488 increased expression of c-Fos in the prelimbic area of the prefrontal cortex (PFCx), nucleus accumbens (NAcc), and basolateral nuclei of the amygdala (BLA). In contrast, in female mice U50,488 only activated the BLA but not the PFCx or the NAcc. FSS increased activation of PFCx, NAcc, and BLA in males while there was no activation of the PFCx in female mice. In both sexes, the KOPr antagonist norBNI significantly blocked U50,488-induced, but not stress-induced activation of brain regions. In separate experiments, activated cells were confirmed as non-GABAergic neurons in the PFCx and NAcc. Together these data demonstrate sex differences in activation of brain regions that are key components of the 'reward' circuitry. These differential responses may contribute to sex differences in stress-related psychiatric disorders and in the treatment of depression, anxiety, and addiction. [ABSTRACT FROM AUTHOR]

The macrocyclic tetrapeptide CJ-15,208 (cyclo[Phe-D-Pro-Phe-Trp]) and its D-Trp isomer exhibit kappa opioid receptor (KOR) antagonism which prevents stress-induced reinstatement of extinguished cocaine-conditioned place preference. Here, we evaluated the effects of substitution of Trp and D-Trp on the peptides' opioid activity, antinociceptive tolerance, and the ability to prevent relapse to extinguished drug-CPP. Six analogs were synthesized using a combination of solid-phase peptide synthesis and cyclization in solution. The analogs were evaluated in vitro for opioid receptor affinity in radioligand competition binding assays, efficacy in the [35S]GTPγS assay, metabolic stability in mouse liver microsomes, and for opioid activity and selectivity in vivo in the mouse 55 °C warm-water tail-withdrawal assay. Potential liabilities of locomotor impairment, respiratory depression, acute tolerance, and conditioned place preference (CPP) were also assessed in vivo, and the ameliorating effect of analogs on the reinstatement of extinguished cocaine-place preference was assessed. Substitutions of other D-amino acids for D-Trp did not affect (or in one case increased) KOR affinity, while two of the three substitutions of an L-amino acid for Trp decreased KOR affinity. In contrast, all but one substitution increased mu opioid receptor (MOR) affinity in vitro. The metabolic stabilities of the analogs were similar to those of their respective parent peptides, with analogs containing a D-amino acid being much more rapidly metabolized than those containing an L-amino acid in this position. In vivo, CJ-15,208 analogs demonstrated antinociception, although potencies varied over an 80-fold range and the mediating opioid receptors differed by substitution. KOR antagonism was lost for all but the D-benzothienylalanine analog, and the 2′-naphthylalanine analog instead demonstrated significant delta opioid receptor (DOR) antagonism. Introduction of DOR antagonism coincided with reduced acute opioid antinociceptive tolerance and prevented stress-induced reinstatement of extinguished cocaine-CPP. [ABSTRACT FROM AUTHOR]

Kappa opioid receptor (KOR) agonists have preclinical antipsychostimulant effects; however, adverse side effects have limited their therapeutic development. In this preclinical study, conducted in Sprague Dawley rats, B6-SJL mice, and non-human primates (NHPs), we evaluated the G-protein-biased analogue of salvinorin A (SalA), 16-bromo salvinorin A (16-BrSalA), for its anticocaine effects, side effects, and activation of cellular signaling pathways. 16-BrSalA dose-dependently decreased the cocaine-primed reinstatement of drug-seeking behavior in a KOR-dependent manner. It also decreased cocaine-induced hyperactivity, but had no effect on responding for cocaine on a progressive ratio schedule. Compared to SalA, 16-BrSalA had an improved side effect profile, with no significant effects in the elevated plus maze, light–dark test, forced swim test, sucrose self-administration, or novel object recognition; however, it did exhibit conditioned aversive effects. 16-BrSalA increased dopamine transporter (DAT) activity in HEK-293 cells coexpressing DAT and KOR, as well as in rat nucleus accumbens and dorsal striatal tissue. 16-BrSalA also increased the early phase activation of extracellular-signal-regulated kinases 1 and 2, as well as p38 in a KOR-dependent manner. In NHPs, 16-BrSalA caused dose-dependent increases in the neuroendocrine biomarker prolactin, similar to other KOR agonists, at doses without robust sedative effects. These findings highlight that G-protein-biased structural analogues of SalA can have improved pharmacokinetic profiles and fewer side effects while maintaining their anticocaine effects. [ABSTRACT FROM AUTHOR]

Increased vigilance in settings of potential threats or in states of vulnerability related to pain is important for survival. Pain disrupts sleep and conversely, sleep disruption enhances pain, but the underlying mechanisms remain unknown. Chronic pain engages brain stress circuits and increases secretion of dynorphin, an endogenous ligand of the kappa opioid receptor (KOR). We therefore hypothesized that hypothalamic dynorphin/KOR signalling may be a previously unknown mechanism that is recruited in pathological conditions requiring increased vigilance. We investigated the role of KOR in wakefulness, non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep in freely moving naïve mice and in mice with neuropathic pain induced by partial sciatic nerve ligation using EEG/EMG recordings. Systemic continuous administration of U69,593, a KOR agonist, over 5 days through an osmotic minipump decreased the amount of NREM and REM sleep and increased sleep fragmentation in naïve mice throughout the light-dark sleep cycle. We used KORcre mice to selectively express a Gi-coupled designer receptor activated by designer drugs (Gi-DREADD) in KORcre neurons of the hypothalamic paraventricular nucleus, a key node of the hypothalamic-pituitary-adrenal stress response. Sustained activation of Gi-DREADD with clozapine-N-oxide delivered in drinking water over 4 days, disrupted sleep in these mice in a similar way as systemic U69,593. Mice with chronic neuropathic pain also showed disrupted NREM and total sleep that was normalized by systemic administration of two structurally different KOR antagonists, norbinaltorphimine and NMRA-140, currently in phase II clinical development, or by CRISPR/Cas9 editing of paraventricular nucleus KOR, consistent with endogenous KOR activation disrupting sleep in chronic pain. Unexpectedly, REM sleep was diminished by either systemic KOR antagonist or by CRISPR/Cas9 editing of paraventricular nucleus KOR in sham-operated mice. Our findings reveal previously unknown physiological and pathophysiological roles of dynorphin/KOR in eliciting arousal. Physiologically, dynorphin/KOR signalling affects transitions between sleep stages that promote REM sleep. Furthermore, while KOR antagonists do not promote somnolence in the absence of pain, they normalized disrupted sleep in chronic pain, revealing a pathophysiological role of KOR signalling that is selectively recruited to promote vigilance, increasing chances of survival. Notably, while this mechanism is likely beneficial in the short-term, disruption of the homeostatic need for sleep over longer periods may become maladaptive resulting in sustained pain chronicity. A novel approach for treatment of chronic pain may thus result from normalization of chronic pain-related sleep disruption by KOR antagonism. [ABSTRACT FROM AUTHOR]

The serotonin and kappa opioid receptor (KOR) systems are strongly implicated in disorders of negative affect, such as anxiety and depression. KORs expressed on axon terminals inhibit the release of neurotransmitters, including serotonin. The substantia nigra pars reticulata (SNr) is involved in regulating affective behaviors. It receives the densest serotonergic innervation in the brain and has high KOR expression; however, the influence of KORs on serotonin transmission in this region is yet to be explored. Here, we used ex vivo fast-scan cyclic voltammetry (FSCV) to investigate the effects of a KOR agonist, U50, 488 (U50), and a selective serotonin reuptake inhibitor, escitalopram, on serotonin release and reuptake in the SNr. U50 alone reduced serotonin release and uptake, and escitalopram alone augmented serotonin release and slowed reuptake, while pretreatment with U50 blunted both the release and uptake effects of escitalopram. Here, we show that the KOR influences serotonin signaling in the SNr in multiple ways and short-term activation of the KOR alters serotonin responses to escitalopram. These interactions between KORs and serotonin may contribute to the complexity in the responses to treatments for disorders of negative affect. Ultimately, the KOR system may prove to be a promising pharmacological target, alongside traditional antidepressant treatments. [ABSTRACT FROM AUTHOR]

The natural product Salvinorin A (SalA) was the first nitrogen-lacking agonist discovered for the opioid receptors and exhibits high selectivity for the kappa opioid receptor (KOR) turning SalA into a promising analgesic to overcome the current opioid crisis. Since SalA's suffers from poor pharmacokinetic properties, particularly the absence of gastrointestinal bioavailability, fast metabolic inactivation, and subsequent short duration of action, the rational design of new tailored analogs with improved clinical usability is highly desired. Despite being known for decades, the binding mode of SalA within the KOR remains elusive as several conflicting binding modes of SalA were proposed hindering the rational design of new analgesics. In this study, we rationally determined the binding mode of SalA to the active state KOR by in silico experiments (docking, molecular dynamics simulations, dynophores) in the context of all available mutagenesis studies and structure-activity relationship (SAR) data. To the best of our knowledge, this is the first comprehensive evaluation of SalA's binding mode since the determination of the active state KOR crystal structure. SalA binds above the morphinan binding site with its furan pointing toward the intracellular core while the C2-acetoxy group is oriented toward the extracellular loop 2 (ECL2). SalA is solely stabilized within the binding pocket by hydrogen bonds (C210ECL2, Y3127.35, Y3137.36) and hydrophobic contacts (V1182.63, I1393.33, I2946.55, I3167.39). With the disruption of this interaction pattern or the establishment of additional interactions within the binding site, we were able to rationalize the experimental data for selected analogs. We surmise the C2-substituent interactions as important for SalA and its analogs to be experimentally active, albeit with moderate frequency within MD simulations of SalA. We further identified the non-conserved residues 2.63, 7.35, and 7.36 responsible for the KOR subtype selectivity of SalA. We are confident that the elucidation of the SalA binding mode will promote the understanding of KOR activation and facilitate the development of novel analgesics that are urgently needed. [ABSTRACT FROM AUTHOR]

Background: Adverse pathophysiological and behavioral outcomes related to mild traumatic brain injury (mTBI), posttraumatic stress disorder (PTSD), and chronic pain are common following blast exposure and contribute to decreased quality of life, but underlying mechanisms and prophylactic/treatment options remain limited. The dynorphin/kappa opioid receptor (KOR) system helps regulate behavioral and inflammatory responses to stress and injury; however, it has yet to be investigated as a potential mechanism in either humans or animals exposed to blast. We hypothesized that blast-induced KOR activation mediates adverse outcomes related to inflammation and affective behavioral response.Methods: C57Bl/6 adult male mice were singly or repeatedly exposed to either sham (anesthesia only) or blast delivered by a pneumatic shock tube. The selective KOR antagonist norBNI or vehicle (saline) was administered 72 h prior to repetitive blast or sham exposure. Serum and brain were collected 10 min or 4 h post-exposure for dynorphin A-like immunoreactivity and cytokine measurements, respectively. At 1-month post-exposure, mice were tested in a series of behavioral assays related to adverse outcomes reported by humans with blast trauma.Results: Repetitive but not single blast exposure resulted in increased brain dynorphin A-like immunoreactivity. norBNI pretreatment blocked or significantly reduced blast-induced increase in serum and brain cytokines, including IL-6, at 4 h post exposure and aversive/anxiety-like behavioral dysfunction at 1-month post-exposure.Conclusions: Our findings demonstrate a previously unreported role for the dynorphin/KOR system as a mediator of biochemical and behavioral dysfunction following repetitive blast exposure and highlight this system as a potential prophylactic/therapeutic treatment target. [ABSTRACT FROM AUTHOR]

Immediately following spinal cord injury (SCI) patients experience pain associated with injury to the spinal cord and nerves as well as with accompanying peripheral injuries. This pain is usually treated with opioids, and most commonly with morphine. However, in a rodent model we have shown that, irrespective of the route of administration, morphine administered in the acute phase of SCI undermines long-term locomotor recovery. Our previous data suggest that activation of kappa opioid receptors (KORs) mediates these negative effects. Blocking KORs with norbinaltorphimine (norBNI), prior to a single dose of epidural morphine, prevented the morphine-induced attenuation of locomotor recovery. Because numerous cellular changes occur with chronic opioid administration compared with a single dose, the current study tested whether norBNI was also effective in a more clinically relevant paradigm of repeated, intravenous morphine administration after SCI. We hypothesized that blocking KOR activation during repeated, intravenous morphine administration would also protect recovery. Supporting this hypothesis, we found that blocking KOR activation in young, male rats prevented the negative effects of morphine on locomotor recovery, although neither norBNI nor morphine had an effect on long-term pain at the doses used. We also found that norBNI treatment blocked the adverse effects of morphine on lesion size. These data suggest that a KOR antagonist given in conjunction with morphine may provide a clinical strategy for effective analgesia without compromising locomotor recovery after SCI. [ABSTRACT FROM AUTHOR]

Aim: Endogenous dynorphin signaling via kappa opioid receptors (KORs) plays a key role in producing the depressive and aversive consequences of stress. We investigated the behavioral effects of the dynorphin/KOR system in the ventral pallidum (VP) and studied the underlying mechanisms. Methods: To investigate the effects of dynorphin on the VP, we conducted behavioral experiments after microinjection of drugs or shRNA and brain‐slice electrophysiological recordings. Histological tracing and molecular biological experiments were used to identify the distribution of KORs and the possible sources of dynorphin projections to the VP. Results: An elevated dynorphin concentration and increased KOR activity were observed in the VP after acute stress. Infusion of dynorphin‐A into the VP produced depressive‐like phenotypes including anhedonia and despair and anxiety behaviors, but did not alter locomotor behavior. Mechanistically, dynorphin had an inhibitory effect on VP neurons—reducing their firing rate and inhibiting excitatory transmission—through direct activation of KORs and modulation of downstream G‐protein‐gated inwardly rectifying potassium (GIRK) channels and high‐voltage gated calcium channels (VGCCs). Tracing revealed direct innervation of VP neurons by dynorphin‐positive projections; potential sources of these dynorphinergic projections include the nucleus accumbens, amygdala, and hypothalamus. Blockade of dynorphin/KOR signaling in the VP by drugs or viral knock‐down of KORs significantly reduced despair behavior in rats. Conclusions: Endogenous dynorphinergic modulation of the VP plays a critical role in mediating depressive reactions to stress. [ABSTRACT FROM AUTHOR]

Kappa opioid receptor (KOR) agonists represent promising therapeutics for pain relief due to their analgesic properties along with lower abuse potential than opioids that act at the mu opioid receptor. However, typical KOR agonists produce sedation and dysphoria. Previous studies have shown that G protein signaling-biased KOR agonists may present a means to untangle the desired analgesic properties from undesired side effects. In this paper, we report a new series of G protein signaling-biased KOR agonists entailing –S– → –CH 2 – replacement in a previously reported KOR agonist, triazole 1.1. With an optimized carbon linker in hand, further development of the scaffold was undertaken to investigate the appendages of the triazole core. The structure–activity relationship study of this series is described, including several analogues that display enhanced potency while maintaining G protein-signaling bias compared to triazole 1.1. [Display omitted] • The kappa opioid receptor (KOR) is a target for the treatment of pain and itch. • Most KOR agonists cause dysphoria, a problematic side effect. • Biased KOR agonist selective for G-protein activation reduce dysphoria. • We report carbon-substituted triazoles as biased KOR agonists and examine their SAR. • A binding mode of this class to the KOR is proposed. [ABSTRACT FROM AUTHOR]

Alcohol use disorder (AUD) is a chronic relapsing disease that is deleterious at individual, familial, and societal levels. Although AUD is one of the highest preventable causes of death in the USA, therapies for the treatment of AUD are not sufficient given the heterogeneity of the disorder and the limited number of approved medications. To provide better pharmacological strategies, it is important to understand the neurological underpinnings of AUD. Evidence implicates the endogenous dynorphin (DYN)/κ-opioid receptor (KOR) system recruitment in dysphoric and negative emotional states in AUD to promote maladaptive behavioral regulation. The nucleus accumbens shell (AcbSh), mediating motivational and emotional processes that is a component of the mesolimbic dopamine system and the extended amygdala, is an important site related to alcohol's reinforcing actions (both positive and negative) and neuroadaptations in the AcbSh DYN/KOR system have been documented to induce maladaptive symptoms in AUD. We have previously shown that in other nodes of the extended amygdala, site-specific KOR antagonism can distinguish different symptoms of alcohol dependence and withdrawal. In the current study, we examined the role of the KOR signaling in the AcbSh of male Wistar rats in operant alcohol self-administration, measures of negative affective-like behavior, and physiological symptoms during acute alcohol withdrawal in alcohol-dependence. To induce alcohol dependence, rats were exposed to chronic intermittent ethanol vapor for 14 h/day for three months, during which stable escalation of alcohol self-administration was achieved and pharmacological AcbSh KOR antagonism ensued. The results showed that AcbSh KOR antagonism significantly reduced escalated alcohol intake and negative affective-like states but did not alter somatic symptoms of withdrawal. Understanding the relative contribution of these different drivers is important to understand and inform therapeutic efficacy approaches in alcohol dependence and further emphasis the importance of the KOR/DYN system as a target for AUD therapeutics. • Chronic intermittent alcohol resulted in escalated alcohol self-administration. • KOR antagonism in the AcbSh attenuated escalated alcohol self-administration. • Alcohol withdrawal-induced 22-kHz USVs were ameliorated by AcbSh KOR antagonism. • Symptoms of somatic withdrawal were not impacted by KOR antagonism in the AcbSh. [ABSTRACT FROM AUTHOR]

Mild traumatic brain injury (mTBI) increases the risk of affective disorders, anxiety and substance use disorder. The lateral habenula (LHb) plays an important role in pathophysiology of psychiatric disorders. Recently, we demonstrated a causal link between mTBI-induced LHb hyperactivity due to excitation/inhibition (E/I) imbalance and motivational deficits in male mice using a repetitive closed head injury mTBI model. A major neuromodulatory system that is responsive to traumatic brain injuries, influences affective states and also modulates LHb activity is the dynorphin/kappa opioid receptor (Dyn/KOR) system. However, the effects of mTBI on KOR neuromodulation of LHb function are unknown. Here, we first used retrograde tracing in male and female Cre mouse lines and identified several major KOR-expressing and two prominent Dyn-expressing inputs projecting to the mouse LHb, highlighting the medial prefrontal cortex (mPFC) and the ventromedial nucleus of the hypothalamus (VMH) as the main LHb-projecting Dyn inputs that regulate KOR signaling to the LHb. We then functionally evaluated the effects of in vitro KOR modulation of spontaneous synaptic activity within the LHb of male and female sham and mTBI mice at 4 week post-injury. We observed sex-specific differences in spontaneous release of glutamate and GABA from presynaptic terminals onto LHb neurons with higher levels of presynaptic glutamate and GABA release in females compared to male mice. However, KOR effects on the spontaneous E/I ratios and synaptic drive ratio within the LHb did not differ between male and female sham and mTBI mice. KOR activation generally suppressed spontaneous glutamatergic transmission without altering GABAergic transmission, resulting in a significant but sex-similar reduction in net spontaneous E/I and synaptic drive ratios in LHb neurons of sham mice. Following mTBI, while responses to KOR activation at LHb glutamatergic synapses remained intact, LHb GABAergic synapses acquired an additional sensitivity to KOR-mediated inhibition where we observed a reduction in GABA release probability in response to KOR stimulation in LHb neurons of mTBI mice. Further analysis of percent change in spontaneous synaptic ratios induced by KOR activation revealed that independent of sex mTBI switches KOR-driven synaptic inhibition of LHb neurons (normally observed in sham mice) in a subset of mTBI mice toward synaptic excitation resulting in mTBI-induced divergence of KOR actions within the LHb. Overall, we uncovered the sources of major Dyn/KOR-expressing synaptic inputs projecting to the mouse LHb. We demonstrate that an engagement of intra-LHb Dyn/KOR signaling provides a global KOR-driven synaptic inhibition within the mouse LHb independent of sex. The additional engagement of KOR-mediated action on LHb GABAergic transmission by mTBI could contribute to the E/I imbalance after mTBI, with Dyn/KOR signaling serving as a disinhibitory mechanism for LHb neurons of a subset of mTBI mice. • The mouse LHb receives Dyn/KOR projections from cortical and subcortical regions. • mTBI shifts synaptic E/I toward excitation in the female mouse LHb. • KOR activation suppresses excitatory but not inhibitory synaptic transmission within the LHb. • mTBI engages KOR activation to additionally suppress GABA release within the LHb. • mTBI switches KOR-mediated net synaptic inhibition to excitation within the LHb of a subset of mTBI mice. [ABSTRACT FROM AUTHOR]

Rationale: Opioid use during pregnancy can lead to negative infant health outcomes, including neonatal opioid withdrawal syndrome (NOWS). NOWS comprises gastrointestinal, autonomic nervous system, and neurological dysfunction that manifest during spontaneous withdrawal. Variability in NOWS severity necessitates a more individualized treatment approach. Ultrasonic vocalizations (USVs) in neonatal mice are emitted in isolation as a stress response and are increased during opioid withdrawal, thus modeling a negative affective state that can be utilized to test new treatments.We sought to identify the behavioral and USV profile, brainstem transcriptomic adaptations, and role of kappa opioid receptors in USVs during neonatal opioid withdrawal.We employed a third trimester-approximate opioid exposure model, where neonatal inbred FVB/NJ pups were injected twice-daily with morphine (10mg/kg, s.c.) or saline (0.9%, 20 ul/g, s.c.) from postnatal day(P) 1 to P14. This protocol induces reduced weight gain, hypothermia, thermal hyperalgesia, and increased USVs during spontaneous morphine withdrawal.On P14, there were increased USV emissions and altered USV syllables during withdrawal, including an increase in Complex 3 syllables in FVB/NJ females (but not males). Brainstem bulk mRNA sequencing revealed an upregulation of the kappa opioid receptor (Oprk1), which contributes to withdrawal-induced dysphoria. The kappa opioid receptor (KOR) antagonist, nor-BNI (30 mg/kg, s.c.), significantly reduced USVs in FVB/NJ females, but not males during spontaneous morphine withdrawal. Furthermore, the KOR agonist, U50,488h (0.625 mg/kg, s.c.), was sufficient to increase USVs on P10 (both sexes) and P14 (females only) in FVB/NJ mice.We identified an elevated USV syllable, Complex 3, and a female-specific recruitment of the dynorphin/KOR system in increased USVs associated with neonatal opioid withdrawal severity.Objectives: Opioid use during pregnancy can lead to negative infant health outcomes, including neonatal opioid withdrawal syndrome (NOWS). NOWS comprises gastrointestinal, autonomic nervous system, and neurological dysfunction that manifest during spontaneous withdrawal. Variability in NOWS severity necessitates a more individualized treatment approach. Ultrasonic vocalizations (USVs) in neonatal mice are emitted in isolation as a stress response and are increased during opioid withdrawal, thus modeling a negative affective state that can be utilized to test new treatments.We sought to identify the behavioral and USV profile, brainstem transcriptomic adaptations, and role of kappa opioid receptors in USVs during neonatal opioid withdrawal.We employed a third trimester-approximate opioid exposure model, where neonatal inbred FVB/NJ pups were injected twice-daily with morphine (10mg/kg, s.c.) or saline (0.9%, 20 ul/g, s.c.) from postnatal day(P) 1 to P14. This protocol induces reduced weight gain, hypothermia, thermal hyperalgesia, and increased USVs during spontaneous morphine withdrawal.On P14, there were increased USV emissions and altered USV syllables during withdrawal, including an increase in Complex 3 syllables in FVB/NJ females (but not males). Brainstem bulk mRNA sequencing revealed an upregulation of the kappa opioid receptor (Oprk1), which contributes to withdrawal-induced dysphoria. The kappa opioid receptor (KOR) antagonist, nor-BNI (30 mg/kg, s.c.), significantly reduced USVs in FVB/NJ females, but not males during spontaneous morphine withdrawal. Furthermore, the KOR agonist, U50,488h (0.625 mg/kg, s.c.), was sufficient to increase USVs on P10 (both sexes) and P14 (females only) in FVB/NJ mice.We identified an elevated USV syllable, Complex 3, and a female-specific recruitment of the dynorphin/KOR system in increased USVs associated with neonatal opioid withdrawal severity.Methods: Opioid use during pregnancy can lead to negative infant health outcomes, including neonatal opioid withdrawal syndrome (NOWS). NOWS comprises gastrointestinal, autonomic nervous system, and neurological dysfunction that manifest during spontaneous withdrawal. Variability in NOWS severity necessitates a more individualized treatment approach. Ultrasonic vocalizations (USVs) in neonatal mice are emitted in isolation as a stress response and are increased during opioid withdrawal, thus modeling a negative affective state that can be utilized to test new treatments.We sought to identify the behavioral and USV profile, brainstem transcriptomic adaptations, and role of kappa opioid receptors in USVs during neonatal opioid withdrawal.We employed a third trimester-approximate opioid exposure model, where neonatal inbred FVB/NJ pups were injected twice-daily with morphine (10mg/kg, s.c.) or saline (0.9%, 20 ul/g, s.c.) from postnatal day(P) 1 to P14. This protocol induces reduced weight gain, hypothermia, thermal hyperalgesia, and increased USVs during spontaneous morphine withdrawal.On P14, there were increased USV emissions and altered USV syllables during withdrawal, including an increase in Complex 3 syllables in FVB/NJ females (but not males). Brainstem bulk mRNA sequencing revealed an upregulation of the kappa opioid receptor (Oprk1), which contributes to withdrawal-induced dysphoria. The kappa opioid receptor (KOR) antagonist, nor-BNI (30 mg/kg, s.c.), significantly reduced USVs in FVB/NJ females, but not males during spontaneous morphine withdrawal. Furthermore, the KOR agonist, U50,488h (0.625 mg/kg, s.c.), was sufficient to increase USVs on P10 (both sexes) and P14 (females only) in FVB/NJ mice.We identified an elevated USV syllable, Complex 3, and a female-specific recruitment of the dynorphin/KOR system in increased USVs associated with neonatal opioid withdrawal severity.Results: Opioid use during pregnancy can lead to negative infant health outcomes, including neonatal opioid withdrawal syndrome (NOWS). NOWS comprises gastrointestinal, autonomic nervous system, and neurological dysfunction that manifest during spontaneous withdrawal. Variability in NOWS severity necessitates a more individualized treatment approach. Ultrasonic vocalizations (USVs) in neonatal mice are emitted in isolation as a stress response and are increased during opioid withdrawal, thus modeling a negative affective state that can be utilized to test new treatments.We sought to identify the behavioral and USV profile, brainstem transcriptomic adaptations, and role of kappa opioid receptors in USVs during neonatal opioid withdrawal.We employed a third trimester-approximate opioid exposure model, where neonatal inbred FVB/NJ pups were injected twice-daily with morphine (10mg/kg, s.c.) or saline (0.9%, 20 ul/g, s.c.) from postnatal day(P) 1 to P14. This protocol induces reduced weight gain, hypothermia, thermal hyperalgesia, and increased USVs during spontaneous morphine withdrawal.On P14, there were increased USV emissions and altered USV syllables during withdrawal, including an increase in Complex 3 syllables in FVB/NJ females (but not males). Brainstem bulk mRNA sequencing revealed an upregulation of the kappa opioid receptor (Oprk1), which contributes to withdrawal-induced dysphoria. The kappa opioid receptor (KOR) antagonist, nor-BNI (30 mg/kg, s.c.), significantly reduced USVs in FVB/NJ females, but not males during spontaneous morphine withdrawal. Furthermore, the KOR agonist, U50,488h (0.625 mg/kg, s.c.), was sufficient to increase USVs on P10 (both sexes) and P14 (females only) in FVB/NJ mice.We identified an elevated USV syllable, Complex 3, and a female-specific recruitment of the dynorphin/KOR system in increased USVs associated with neonatal opioid withdrawal severity.Conclusions: Opioid use during pregnancy can lead to negative infant health outcomes, including neonatal opioid withdrawal syndrome (NOWS). NOWS comprises gastrointestinal, autonomic nervous system, and neurological dysfunction that manifest during spontaneous withdrawal. Variability in NOWS severity necessitates a more individualized treatment approach. Ultrasonic vocalizations (USVs) in neonatal mice are emitted in isolation as a stress response and are increased during opioid withdrawal, thus modeling a negative affective state that can be utilized to test new treatments.We sought to identify the behavioral and USV profile, brainstem transcriptomic adaptations, and role of kappa opioid receptors in USVs during neonatal opioid withdrawal.We employed a third trimester-approximate opioid exposure model, where neonatal inbred FVB/NJ pups were injected twice-daily with morphine (10mg/kg, s.c.) or saline (0.9%, 20 ul/g, s.c.) from postnatal day(P) 1 to P14. This protocol induces reduced weight gain, hypothermia, thermal hyperalgesia, and increased USVs during spontaneous morphine withdrawal.On P14, there were increased USV emissions and altered USV syllables during withdrawal, including an increase in Complex 3 syllables in FVB/NJ females (but not males). Brainstem bulk mRNA sequencing revealed an upregulation of the kappa opioid receptor (Oprk1), which contributes to withdrawal-induced dysphoria. The kappa opioid receptor (KOR) antagonist, nor-BNI (30 mg/kg, s.c.), significantly reduced USVs in FVB/NJ females, but not males during spontaneous morphine withdrawal. Furthermore, the KOR agonist, U50,488h (0.625 mg/kg, s.c.), was sufficient to increase USVs on P10 (both sexes) and P14 (females only) in FVB/NJ mice.We identified an elevated USV syllable, Complex 3, and a female-specific recruitment of the dynorphin/KOR system in increased USVs associated with neonatal opioid withdrawal severity. [ABSTRACT FROM AUTHOR]

The dynorphin peptides are the endogenous ligands for the kappa opioid receptor (KOR) and regulate food intake. Administration of dynorphin-A 1-13 (DYN) in the paraventricular hypothalamic nucleus (PVN) increases palatable food intake, and this effect is blocked by co-administration of the orexin-A neuropeptide, which is co-released with DYN in PVN from neurons located in the lateral hypothalamus. While PVN administration of DYN increases palatable food intake, whether it increases food-seeking behaviors has yet to be examined. We tested the effects of DYN and nor BNI (a KOR antagonist) on the seeking and consumption of sucrose using a progressive ratio (PR) and demand curve (DC) tasks. In PVN, DYN did not alter the sucrose breaking point (BP) in the PR task nor the elasticity or intensity of demand for sucrose in the DC task. Still, DYN reduced the delay in obtaining sucrose and increased licks during sucrose intake in the PR task, irrespective of the co-administration of orexin-A. In PVN, nor BNI increased the delay in obtaining sucrose and reduced licks during sucrose intake in the PR task while increasing elasticity without altering intensity of demand in the DC task. However, subcutaneous nor BNI reduced the BP for sucrose and increased the delay in obtaining sucrose in the PR task while reducing the elasticity of demand. Together, these data show different effects of systemic and PVN blockade of KOR on food-seeking, consummatory behaviors, and incentive motivation for sucrose and suggest that KOR activity in PVN is necessary but not sufficient to drive seeking behaviors for palatable food. [ABSTRACT FROM AUTHOR]

This paper is the forty-sixth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2023 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug and alcohol abuse (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18). • This 46th annual review examines opioid molecular-biochemical effects. • It reviews effects upon pain, analgesia, tolerance, dependence and stress. • It reviews effects upon learning, memory, ingestion, abuse and sexual activity. • It reviews effects upon neurophysiological, locomotor and digestive functions. • It reviews effects upon cardiovascular, respiratory and immunological responses. [ABSTRACT FROM AUTHOR]

Selective adult social attachments, or 'pair bonds', represent central relationships for individuals in a number of social species, including humans. Loss of a pair mate has emotional consequences that may or may not diminish over time, and that often translate into impaired psychological and physical health. In this paper, we review the literature on the neuroendocrine mechanisms for the emotional consequences of partner loss, with a special focus on hypothesized interactions between oxytocin, corticotropin-releasing hormone and the κ opioid system. This article is part of the theme issue 'Interplays between oxytocin and other neuromodulators in shaping complex social behaviours'. [ABSTRACT FROM AUTHOR]

Background: The relationship between alcohol and pain is complex. Associations between pain and alcohol use disorder (AUD) vary by race, but the underlying biological basis is not understood. We examined the association of the kappa opioid receptor (KOR) with responses to the cold‐pressor test (CPT), before and after treatment with the opioid antagonist naltrexone, among individuals with AUD who self‐identified as Black or White. Methods: Thirty‐seven individuals (12 Black, 24 White, and 1 Multiracial) with AUD participated in two CPTs, separated by 1 week during which they received naltrexone 100 mg daily. During each CPT, pain reporting threshold (PRT), average pain increase rate (APIR), relative pain recovery (RPR), and alcohol craving were recorded. KOR availability was measured using [11C]‐LY2795050 positron emission tomography (PET) prior to treatment with naltrexone. Results: Black participants reported higher PRT and APIR than White participants during the CPT before, but not after, naltrexone treatment. Among Black participants, KOR availability was positively associated with PRT and APIR before, but not after naltrexone. Greater KOR availability was associated with faster RPR for White, but not Black, participants. The CPT induced more alcohol craving in Black than White participants, particularly in individuals with low KOR availability, an effect that was not attenuated by naltrexone. Conclusions: KOR involvement and naltrexone effects on responses to the CPT were different between Black and White participants. These preliminary findings suggest that further exploration of the differences in the opioid system and pain among Black and White individuals with AUD and their relationship with naltrexone's effects is warranted. [ABSTRACT FROM AUTHOR]

Emerging evidence has implicated the endogenous opioid system in mediating ketamine's antidepressant activity in subjects with major depressive disorder. To date, mu opioid receptors have been suggested as the primary opioid receptor of interest. However, this hypothesis relies primarily on observations that the opioid antagonist naltrexone blocked the effects of ketamine in humans and rodents. This report confirms previous findings that pretreatment with naltrexone (1 mg/kg) just prior to ketamine (10 mg/kg) administration effectively blocks the behavioral effect of ketamine in the mouse forced swim test 24 h post-treatment. Furthermore, pharmacological blockade of kappa opioid receptors prior to ketamine administration with the selective, short-acting antagonist LY2444296 successfully blocked ketamine's effects in the forced swim test. Likewise, the ability of the ketamine metabolite (2R,6R)-hydroxynorketamine to reduce immobility scores in the forced swim test was also blocked following pretreatment with either naltrexone or LY2444296. These data support a potential role of kappa opioid receptors in mediating the behavioral activity of ketamine and its non-dissociate metabolite (2R,6R)-hydroxynorketamine. [ABSTRACT FROM AUTHOR]

While there is high comorbidity of stress-related disorders and alcohol use disorder, few effective treatments are available and elucidating underlying neurobiological mechanisms has been hampered by a general lack of reliable animal models. Here, we use a novel mouse model demonstrating robust and reproducible stress-enhanced alcohol drinking to examine the role of dynorphin/kappa opioid receptor (DYN/KOR) activity within the extended amygdala in mediating this stress-alcohol interaction. Mice received repeated weekly cycles of chronic intermittent ethanol exposure alternating with weekly drinking sessions ± forced swim stress exposure. Pdyn messenger RNA expression was measured in the central amygdala (CeA), and DYN-expressing CeA neurons were then targeted for chemogenetic inhibition. Finally, a KOR antagonist was microinjected into the CeA or bed nucleus of the stria terminalis to examine the role of KOR signaling in promoting stress-enhanced drinking. Stress (forced swim stress) selectively increased alcohol drinking in mice with a history of chronic intermittent ethanol exposure, and this was accompanied by elevated Pdyn messenger RNA levels in the CeA. Targeted chemogenetic silencing of DYN-expressing CeA neurons blocked stress-enhanced drinking, and KOR antagonism in the CeA or bed nucleus of the stria terminalis significantly reduced stress-induced elevated alcohol consumption without altering moderate intake in control mice. Using a novel and robust model of stress-enhanced alcohol drinking, a significant role for DYN/KOR activity within extended amygdala circuitry in mediating this effect was demonstrated, thereby providing further evidence that the DYN/KOR system may be a valuable target in the development of more effective treatments for individuals presenting with comorbidity of stress-related disorders and alcohol use disorder. [ABSTRACT FROM AUTHOR]

Salvia divinorum (Epling and Játiva) is a psychoactive plant traditionally used by the Latinos for various medicinal purposes. Salvinorin A (Sal A), the main bioactive constituent of S. divinorum, is a natural highly selective kappa opioid receptor (KOR) agonist. Considering the anti-inflammatory effect of S. divinorum and endogenous hippocampal dynorphin/kappa opioid receptor (KOR) system playing an anticonvulsant function, we hypothesis that Sal A can be a potential candidate to treat epilepsy. Here, we identified whether Sal A ameliorated epileptic seizures and neuronal damages in animal model and in vitro model and investigated its underlying mechanisms. Mice epilepsy model was induced by pilocarpine following seizures assessed by Racine classification. Hippocampus tissues were obtained for genetic, protein, and histological investigation. Furthermore, lipopolysaccharide (LPS)-activated BV2 microglial cells were utilized to validate the anti-inflammatory and microglia polarization regulation effects of Sal A. Sal A treatment significantly prolonged the latency to status epileptics (SE) and shortened the duration of SE in the pilocarpine-induced model. It also alleviated neuronal damages via activation of the AMPK/JNK/p-38 MAPK pathway and inhibition of apoptosis-related protein in hippocampus tissues. Furthermore, Sal A dose-dependently reduced microglia-mediated expression of pro-inflammatory cytokines and increased anti-inflammatory factors levels in SE mice and LPS-activated BV2 microglial cells by regulating microglia polarization. In addition, the effect of Sal A in vitro was totally blocked by KOR antagonist nor-BNI. Sal A treatment protects against epileptic seizures and neuronal damages in pilocarpine-induced models by suppressing the inflammation response through regulating microglial M1/M2 polarization. This study might serve as a theoretical basis for clinical applications of Sal A and its analogs and provide a new insight into the development of anti-seizure drugs. [Display omitted] • Salvinorin A produced anti-epileptic effect in the pilocarpine-induced model. • Salvinorin A alleviated neuronal damages and inflammation response in the hippocampus of epileptic mice. • Salvinorin A inhibited the polarization of microglia to M1 phenotype and promoted that to M2 phenotype in vivo and in vitro. [ABSTRACT FROM AUTHOR]

Anhedonia and avolition are emotions frequently endorsed by individuals with stress related disorders. Kappa opioid receptor (KOR) activation can induce negative emotions and recent clinical evidence suggests that KOR antagonism can alleviate anhedonia in a transdiagnostic cohort of patients. However, the behavioral consequences of KOR activation and antagonism in modulating motivation, as assessed by schedule-controlled behavioral performance without preexisting conditions (stress or substance use), have not been formally assessed. To address this gap in the literature, this report utilized male and female Sprague Dawley rats to (1) evaluate the impact of the selective KOR agonist U50,488, on the performance of animals responding for sucrose pellets under a progressive ratio (PR) schedule and (2) determine the effects of the short-acting KOR antagonist LY2444296 alone and on U50,488 mediated reductions in PR performance. Overall, U50,488 5 mg/kg significantly reduced the breakpoint and number of rewards obtained by animals. This occurred in the absence of motor impairment and independent of evidence for satiation. LY2444296 did not alter PR performance when administered alone but effectively blocked the deficits induced by U50,488. To further delineate the behavioral alterations that underlie these reductions in responding, a more detailed analysis was conducted on PR performance in the first 15 min of the session, the period of time when animals obtained the most reinforcers. During this period, U50,488 increased the length of the post-reinforcement pause and reduced the running rate on PR schedules. These changes in behavior produced by acute activation of KORs are consistent with a reduction of effort-related motivation in rodents. These data contribute to the understanding of how KORs modulate motivation, which is critical to future efforts to evaluate performance in the context of stress and assess how KOR antagonists alleviate anhedonic behaviors associated with stress. • U50,488 reduced the breakpoint and number of rewards earned in the PR session. • LY2444296 did not alter PR performance but blocked U50,488 induced deficits. • U50,488 increased the post-reinforcement pause duration. • U50,488 decreased the run rates of animals in the PR session. [ABSTRACT FROM AUTHOR]

Prefrontal cortical (PFC) circuits provide top-down control of threat reactivity. This includes ventromedial PFC (vmPFC) circuitry, which plays a role in suppressing fear-related behavioral states. Dynorphin (Dyn) has been implicated in mediating negative affect and maladaptive behaviors induced by severe threats and is expressed in limbic circuits, including the vmPFC. However, there is a critical knowledge gap in our understanding of how vmPFC Dyn-expressing neurons and Dyn transmission detect threats and regulate expression of defensive behaviors. Here, we demonstrate that Dyn cells are broadly activated by threats and release Dyn locally in the vmPFC to limit passive defensive behaviors. We further demonstrate that vmPFC Dyn-mediated signaling promotes a switch of vmPFC networks to a fear-related state. In conclusion, we reveal a previously unknown role of vmPFC Dyn neurons and Dyn neuropeptidergic transmission in suppressing defensive behaviors in response to threats via state-driven changes in vmPFC networks. [Display omitted] • vmPFCDyn neurons are activated by threats and threat-predictive cues • vmPFCDyn neurons rapidly release Dyn in response to threats and their predictors • vmPFCDyn signaling opposes threat-induced passive defensive behaviors • Dyn signaling promotes threat-evoked state transitions in vmPFC networks Wang et al. demonstrate that ventromedial prefrontal cortex (vmPFC) prodynorphin cells are broadly activated by threats and release dynorphin to limit passive defensive behaviors. Furthermore, they demonstrate that dynorphin neuropeptidergic transmission suppresses passive defensive behaviors by facilitating a switch in vmPFC networks to a persistent fear-related state driven by acute threats. [ABSTRACT FROM AUTHOR]

Background: As a class of the opioid receptors, the kappa opioid receptor (KOR) has been verified to be a potential biomarker and therapeutic target for human malignant tumors. However, a thorough understanding of whether KOR affects progression of esophageal squamous cell carcinoma (ESCC) is still lacking. This study focused on exploring the effect of knocking down KOR in ESCC and its underlying mechanism. Methods: Bioinformatics analysis was used to compare the different expression level of OPRK1 (KOR gene) in tumor and adjacent normal tissues, and predict the relationship between KOR expression and overall survival. RNA-sequence analysis was performed to detect the altered functions and mechanisms after down regulating KOR. The in vitro and in vivo assays were used to detect the effects of down-regulated KOR on cell proliferation, migration and invasion. Substrate gel zymography and 3D cell culture assays were used to find the effect of KOR knockdown on the degradation of extracellular matrix (ECM), and immunefluorescence was performed to detect the altered cytoskeleton. Western blotting and immunohistochemistry were used to explore the underlying mechanism pathway. Results: Bioinformatics analysis revealed that the expression of OPRK1 was lower in tumor tissue than that in adjacent normal tissues, and lowered expression of KOR was associated with poorer overall survival. The in vitro assays demonstrated that down-regulation of KOR enhanced ESCC proliferation, metastasis and invasion. Western blotting revealed that down-regulation of KOR could activate PDK1-AKT signaling pathway, which actively regulated the cancer progression. Down-regulation of KOR enhanced the formation of invadopodia, secretion of matrix metalloproteinase-2 (MMP2) and rearrangement of cytoskeleton, which were positively related with the invasion of ESCC. KOR knockdown enhanced the tumor invasion and elevated the AKT phosphorylation in nude mice. The AKT kinase inhibition could reverse the effect of down-regulation of KOR. Conclusion: KOR might act as a tumor suppressor in ESCC and down-regulation of KOR could enhance the ESCC tumor phenotype. 8saryVZK7ypoVwSXab2T6m Video Abstract [ABSTRACT FROM AUTHOR]

Impaired working memory is one symptom contributing to compromised executive function in alcohol use disorder (AUD). Dysregulation of cortical dynorphin (DYN) and κ-opioid receptors (KORs) has been implicated in alcohol dependence-induced impairment in executive function. The present experiments test the hypothesis that dysregulated medial prefrontal cortex (mPFC) KORs contribute to impaired working memory in alcohol dependence. Alcohol dependence was induced in male Wistar rats via 4 months of intermittent ethanol vapor exposure prior to training/testing in an mPFC-dependent working memory task (delayed nonmatching-to-sample task; DNMST). mPFC KOR function in alcohol-naïve rats was compared with that of alcohol-dependent and nondependent rats using a DYN A-stimulated [35S ]GTPγS coupling assay. A functional role for mPFC KORs in the regulation of working memory was assessed via intra-mPFC infusions of a KOR agonist prior to assessment in the DNMST, and the contribution of mPFC KORs to compromised working memory in dependence was assessed via mPFC infusions of the KOR antagonist norbinaltorphimine (nor-BNI). In alcohol-dependent rats, impaired performance in the DNMST confirmed compromised working memory. Furthermore, DYN A-stimulated mPFC KOR function was pathologically increased in alcohol-dependent rats compared with nondependent and alcohol-naïve rats. Additionally, mPFC KOR involvement in working memory was functionally confirmed by intra-mPFC KOR agonist-induced deficits in DNMST performance. Importantly, alcohol dependence-induced impairment in the DNMST was ameliorated by intra-mPFC KOR antagonism. Regulation of working memory by mPFC KORs and alcohol dependence-induced dysregulation of mPFC KOR function identify a novel therapeutic target to treat AUD-related symptoms of working memory impairment. [ABSTRACT FROM AUTHOR]

Abstract: Pain-induced negative affect reduces life quality of patients by increasing psychiatric comorbidities, including alcohol use disorders (AUDs). Indeed, clinical data suggest pain as a risk factor to suffer AUDs, predicting relapse drinking in abstinent patients. Here, we analyse the impact of pain on alcohol relapse and the role of kappa opioid receptor (KOR) activation in mediating these pain-induced effects because KORs play an important role in pain-driven negative affect and AUD. Female and male Sprague-Dawley rats underwent 2 alcohol intermittent access periods separated by a forced abstinence period. The complete Freund adjuvant model of inflammatory pain was introduced during abstinence, and alcohol intake before and after alcohol reintroduction was assessed. In addition, we used behavioural approaches to measure stress and memory impairment and biochemical assays to measure KOR expression in abstinence and reintroduction periods. Only female CFA-treated rats increased alcohol intake during the reintroduction period. Concomitantly, this group showed enhanced anxiety-like behaviour and increased KOR expression in the nucleus accumbens shell that was developed during abstinence and remained during the reintroduction period. Finally, KOR antagonist norbinaltorphimine was administered in the nucleus accumbens shell during abstinence to prevent a pain-induced alcohol deprivation effect, a phenomenon observed in CFA-female rats. The administration of norbinaltorphimine effectively blocked a pain-induced alcohol deprivation effect in female rats. Our data evidenced that inflammatory pain constitutes a risk factor to increase alcohol consumption during a reintroduction phase only in female rats by the rise and maintenance of stress probably mediated by KOR signalling in the nucleus accumbens. [ABSTRACT FROM AUTHOR]

Latent sensitization (LS) of pain engages pronociceptive signaling pathways in the dorsal horn that include NMDA receptor (NMDAR)fiadenylyl cyclase-1 (AC1)fiprotein kinase A (PKA), and exchange proteins directly activated by cyclic AMP (Epacs). To determine whether these pathways operate similarly between males and females or are under the inhibitory control of spinal j opioid receptors (KOR), we allowed hyperalgesia to resolve after plantar incision and then blocked KOR with intrathecal administration of LY2456302, which reinstated hyperalgesia and facilitated touch-evoked immunoreactivity of phosphorylated extracellular signal-regulated kinase (pERK) in neurons (NeuN) but not astrocytes (GFAPs) nor microglia (Iba1). LY2456302 reinstated hyperalgesia even when administered 13months later, indicating that chronic postoperative pain vulnerability persists for over a year in a latent state of remission. In both sexes, intrathecal MK-801 (an NMDAR competitive antagonist) prevented LY2456302-evoked reinstatement of hyperalgesia as did AC1 gene deletion or the AC1 inhibitor NB001. NB001 also prevented stimulus-evoked pERK. In both sexes, the Epac inhibitor ESI-09 prevented reinstatement, whereas the Epac activator 8-CPT reinstated hyperalgesia. By contrast, the PKA inhibitor H89 prevented reinstatement only in male mice, whereas the PKA activator 6-bnz-cAMP itself evoked reinstatement at all doses tested (3-30 nmol, i.t.). In neither sex did incision change gene expression of KOR, GluN1, PKA, or Epac1 in dorsal horn. We conclude that sustained KOR signaling inhibits spinal PKA-dependent mechanisms that drive postoperative LS in a sex-dependent manner. Our findings support the development of AC1, PKA, and Epac inhibitors toward a new pharmacotherapy for chronic postoperative pain. [ABSTRACT FROM AUTHOR]

Rationale: Major depressive disorder is a leading cause of disability worldwide and is likely precipitated by chronic stress. Although many antidepressants are currently available, these drugs require weeks to months of daily administration before reduction of symptoms occurs and many patients remain treatment-resistant despite several courses of treatment. There is a pressing need for new treatments for stress-related disorders. Kappa opioid receptors (KORs) are a promising new therapeutic target for major depressive disorder and anhedonia because acute KOR blockade prevents many effects of stress in rodents. Objectives: The following study assessed whether repeated treatment with the selective KOR antagonist aticaprant (also known as JNJ-67953964, and previously LY-2456302 and CERC-501) was effective in reversing behaviors in rodents following exposure to unpredictable chronic mild stress (UCMS). Methods: Adult male C57BL/6J mice were exposed to 4 weeks of UCMS. After 3 weeks of stress, aticaprant (10 mg/kg) was administered daily for 11 treatments. Behavioral assessments included the sucrose preference test, nesting, forced swim test, hot plate test, light-dark test, and social interaction test. Results: Aticaprant significantly reversed stress-induced deficits produced by UCMS on the SPT, nesting, FST, and hot plate test. The effects of aticaprant persisted through a stress and treatment recovery period. Aticaprant was not effective at reversing behavioral effects caused by stress in the light-dark and social interaction tests. Conclusions: The results support further study of the role of KORs in regulating circuits related to reward, self-care, and cognition when they are disrupted by chronic stress. They are also consistent with the clinical development of aticaprant as a therapeutic for stress-related disorders targeted at anhedonia, such as depression and post-traumatic stress disorder. [ABSTRACT FROM AUTHOR]

Dynantin is a potent and selective synthetic polypeptide kappa opioid receptor antagonist which has potential antidepressant and anxiolytic-like therapeutic applications, however its clinical development has been hampered by plasma stability issues and poor penetration of the blood brain barrier. Targeted liposome delivery systems represent a promising and non-invasive approach to improving the delivery of therapeutic agents across the blood brain barrier. As part of our work focused on targeted drug delivery, we have developed a novel mannosylated liposome system. Herein, we investigate these glycoliposomes for the targeted delivery of dynantin to the central nervous system. Cholesterol was tested and optimized as a formulation excipient, where it improved particle stability as measured via particle size, entrapment and ex vivo plasma stability of dynantin. The in vitro PRESTO-TANGO assay system was used to confirm that glycoliposomal entrapment did not impact the affinity or activity of the peptide at its receptor. Finally, in vivo distribution studies in mice showed that the mannosylated glycoliposomes significantly improved delivery of dynantin to the brain. Overall, the results clearly demonstrate the potential of our glycoliposomes as a targeted delivery system for therapeutic agents of the central nervous system. [ABSTRACT FROM AUTHOR]

Rationale: Cancer patients receiving the antineoplastic drug paclitaxel report higher incidences and longer duration of treatment-resistant depression than patients receiving other classes of chemotherapeutics. Rodents treated with paclitaxel exhibit a suite of changes in affect-like behaviors. Further, paclitaxel causes chemotherapy-induced peripheral neuropathy (CIPN) in humans and rodents. Kappa opioid receptors (KOR) have a well-established role in depression and neuropathy. The contributions of KOR signaling to paclitaxel-induced aversive-like state and CIPN in rodents remain to be explored. Objectives: We aimed to investigate whether dysregulation of the KOR/dynorphin system is associated with paclitaxel-mediated pain-like behavior and depression-like behavior. Methods: Cancer-free male C57BL/6J mice were treated with four injections of vehicle or paclitaxel (32 mg/kg cumulative). The effects of the selective KOR antagonist norbinaltorphimine (norBNI) on paclitaxel-induced sucrose preference deficits and mechanical hypersensitivity were measured. Prodynorphin mRNA and receptor-mediated G protein activation were measured at two time points following the last paclitaxel injection using quantitative real-time polymerase chain reaction and agonist-stimulated [35S]guanosine-5′-O′-(γ-thio)-triphosphate ([35S]GTPγS) binding, respectively, in the nucleus accumbens (NAc), caudate-putamen, amygdala, and spinal cord. Results: Paclitaxel produced a norBNI-reversible sucrose preference deficit, whereas mechanical hypersensitivity was not reversed by norBNI. Paclitaxel treatment increased the levels of mRNA for prodynorphin, a precursor for endogenous KOR agonists, in the NAc. Paclitaxel also had time-dependent effects on KOR-mediated G protein activation in the NAc. Conclusions: These results suggest that KOR signaling mediates an initial aversive component of paclitaxel, but not necessarily paclitaxel-induced mechanical hypersensitivity. [ABSTRACT FROM AUTHOR]

Objective: Selective kappa opioid receptor (KOR) agonists were shown to produce a dose-dependent depression of brain-stimulation reward (BSR) in the rat intracranial self-stimulation (ICSS) tests. However, limited studies using mice produced less conclusive results. Here the effects of U50,488H were re-examined on BSR in mice with a larger cohort of animals. Results: Forty C57BL/6J male mice were implanted with the electrodes in medial forebrain bundle. About a week after surgery, mice were subject to ICSS training. Only eighteen passed the two-phase procedures, at which point they readily spun the wheels to obtain reinforcing effect of BSR, and were used for the ICSS tests. Compared with saline (s.c.), U50,488H (2 mg/kg, s.c.) did not have effects on the BSR thresholds within 1 h post-treatment, while it decreased the maximum wheel-spinning rates in a time-dependent manner. In contrast, cocaine (5 mg/kg, s.c.) decreased the BSR thresholds time-dependently without affecting the maximum wheel-spinning rates in the same cohort of mice, demonstrating the validity of our mouse ICSS models. For comparison, U50,488H (2 mg/kg, s.c.) induced significant conditioned place aversion (CPA) in a different cohort of mice without surgeries. Thus, ICSS may not be an appropriate test for KOR agonist-induced aversion in mice. [ABSTRACT FROM AUTHOR]

Rationale: Agonists of the kappa opioid receptor (KOR) have been shown to block the rewarding effects of drugs of abuse, but with negative side effects. The antipruritic drug nalfurafine, approved in Japan in 2009, is a potent, selective KOR agonist that does not cause significant side effects in humans. Nalfurafine has not been extensively tested for its effect on drug reward and reinforcement in preclinical models. Objectives: The goal of this study was to compare the effects of nalfurafine and a reference KOR agonist for a variety of KOR-mediated endpoints in male C57BL6 mice. Specifically, we aimed to evaluate the "therapeutic window"—doses of agonists lower than those eliciting negative side effects, while still effective for desired therapeutic effects. Methods: In this study, several low doses of nalfurafine and U50,488 were tested for serum prolactin release, rotarod-mediated sedation, and place-conditioning in male C57BL6 mice. These agonists were also tested for effects on intravenous cocaine self-administration, both on an FR1 schedule and on a progressive ratio schedule for 0.5 mg/kg/infusion cocaine. Results: Serum prolactin levels increased following doses of both nalfurafine (3 μg/kg and 10 μg/kg) and U50,488 (3 mg/kg). These doses did not cause sedation in the rotarod assay or aversion in a place-conditioning assay, but blocked conditioned place preference for cocaine. Immediate pretreatment of mice with 10 μg/kg nalfurafine and 3 mg/kg U50,488, however, potentiated cocaine self-administration. Further 10 μg/kg nalfurafine was also observed to potentiate cocaine-seeking behavior as demonstrated by increased progressive ratio break point. Conclusions: Both nalfurafine and U50,488 showed a separation of negative side effects and the modulation of cocaine reward, suggesting this effect of KOR agonists at low doses may be characteristic of the KOR system in general. At higher doses, nalfurafine had similar effects to traditional KOR agonists like U50,488, indicating that its relative potency, rather than differences in KOR signaling, may be responsible for its unique effects in humans. [ABSTRACT FROM AUTHOR]

Preclinical data indicate that selective kappa opioid receptor antagonists reduce nicotine self-administration and withdrawal symptoms. The aim of the current study was to determine whether treatment with CERC-501, an orally available, potent, and selective kappa opioid receptor antagonist, could alleviate nicotine withdrawal and craving and mitigate mood alterations associated with nicotine withdrawal in humans. Healthy, adult cigarette smokers were enrolled into this randomized, multisite, double-blind, placebo-controlled, crossover study. Participants completed two 8-day treatment phases during which they received either CERC-501 (15 mg, p.o., once daily) or placebo. On the seventh day of each dosing phase, participants were admitted as inpatients for an 18-hour cigarette abstinence period followed by experimental testing. The primary outcome measures were (a) performance on the McKee Smoking Lapse test (ie, latency to smoke in exchange for money) and (b) number of cigarettes self-administered during a 60-minute ad lib smoking period. Other outcomes included measures of craving, mood, anxiety, nicotine withdrawal, and subjective effects of cigarette smoking. A total of 71 participants who smoked an average of approximately 23 cigarettes per day were enrolled, and 56 subjects completed the study. CERC-501 was well tolerated, but it did not significantly alter the latency to start smoking (CERC-501: 16.5 min vs placebo: 17.7 min) or the number of cigarettes smoked (CERC-501: 3.3 cigarettes vs placebo: 3.1 cigarettes). Compared with placebo, CERC-501 also did not affect cigarette craving, mood, anxiety, nicotine withdrawal, or subjective effects of smoking. These findings do not support a role for CERC-501 in the treatment of nicotine use disorder. [ABSTRACT FROM AUTHOR]

Objective To evaluate the role of Kappa opioid receptor(KOR) of mice nucleus accumbens(NAc) in heroin withdrawal depression-like(HW-D) behavior. Methods Mice were intraperitoneally injected with 1 mg/kg of heroin once a day(9:00 AM) for 14 days. The depression-like behaviors were evaluated by open field test(OFT), tail suspension test(TST) and sucrose preference test(SPT) after withdrawal for 3-8 weeks. Mice in heroin group were divided into HW-D susceptible group and HW-D unsusceptible group on the basis of depression-like behaviors. According to the stereotactic map of G.Paxinos mouse brain, the bilateral NAc were isolated. Western blotting was used to detect the expressions of KOR and prodynorphin(PDYN). At the 4 th week after withdrawal, nor-BNI, the KOR antagonist, was microinjected into the NAc of mice with brain stereotaxic apparatus to evaluate its impact on depression-like behaviors. Results After 14 days of injection with heroin, mice were abstinent for 3, 4 and 8 weeks, and the behavior outcomes showed the sucrose preference rate in HW-D susceptible group was decreased(P<0.01) and immobility time of tail suspension was increased(P<0.05) when compared with those in saline group and HW-D unsusceptible group. After withdrawal for 4 and 8 weeks, the protein expression levels of KOR(P<0.05) and PDYN(P<0.05) were increased in HW-D susceptible group than those in saline group and HW-D unsusceptible group. The intervention of nor-BNI enhanced the sucrose preference rate(P<0.05) but reduced the immobility time of tail suspension(P<0.05) in HW-D susceptible group. Conclusion KOR in NAc regulates depression-like behavior of mice after heroin withdrawal for a long time. Administration of KOR antagonists in NAc can attenuate the depression-like behavior. [ABSTRACT FROM AUTHOR]

Rationale: Cocaine addiction is a chronic brain disease characterized by compulsive drug intake and dysregulation of brain reward systems. Few preclinical studies have modeled the natural longitudinal course of cocaine addiction. Extended access self-administration protocols are powerful tools for modeling the advanced stages of addiction; however, few studies have duration of drug access longer than 12 h/session, potentially limiting their construct validity. Identification of changes in cocaine intake patterns during the development of addictive-like states may allow better treatments for vulnerable subjects. The kappa opioid receptor (KOPr) system has been implicated in the neurobiological regulation of addictive states as well as mood and stress disorders, with selective KOPr antagonists proposed as possible pharmacotherapeutic agents. Chronic cocaine exposure increases the expression of KOPr and its endogenous agonists, the dynorphins, in several brain areas in rodents. Objectives: To examine the behavioral pattern of intake during chronic (14 days) 18 h intravenous cocaine self-administration (0.5 mg/kg/infusion) and the effect of a novel short-acting KOPr antagonist LY2444296 HCl (3 mg/kg) administered during sessions 8 to 14 of chronic 18 h/day cocaine self-administration and prior to a single re-exposure session after 2 cocaine-free withdrawal days. Results: Both daily and hourly cocaine intake patterns changed over 14 days of 18 h self-administration. LY pretreatment affected the pattern of self-administration across the second week of extended access cocaine self-administration and prevented the increase in cocaine intake during re-exposure. Conclusions: Overall, the KOPr antagonist attenuated escalated cocaine consumption in a rat model of extended access cocaine self-administration. [ABSTRACT FROM AUTHOR]

Naltrexone is a nonselective opioid receptor antagonist used as a treatment for alcohol use disorder. However, only modest clinical effects have been observed, possibly because of limited knowledge about the biological variables affecting the efficacy of naltrexone. We investigated the potential role of the kappa opioid receptor (KOR) in the therapeutic effect of naltrexone. A total of 48 non-treatment-seeking heavy drinkers (16 women) who met DSM-IV criteria for alcohol dependence participated in two alcohol drinking paradigms (ADPs) separated by a week of open-label naltrexone (100 mg daily). Craving, assessed with the Alcohol Urge Questionnaire and the Yale Craving Scale, and drinking behavior were recorded in each ADP. Prior to naltrexone initiation, KOR availability was determined in the amygdala, hippocampus, pallidum, striatum, cingulate cortex, and prefrontal cortex using positron emission tomography with [11C]LY2795050. Participants reported lower levels of craving (Yale Craving Scale: −11 ± 1, p <.0001; Alcohol Urge Questionnaire: −6 ± 0.6, p <.0001) and consumed fewer drinks (−3.7 ± 4, p <.0001) during the second ADP following naltrexone therapy. The observed reduction in drinking was negatively associated with baseline KOR availability in the striatum (p =.005), pallidum (p =.023), and cingulate cortex (p =.018). Voxelwise analysis identified clusters in the bilateral insula, prefrontal, and cingulate cortex associated with the reduction in drinking (p <.0001). In addition, KOR availability in all evaluated brain regions was associated with craving measured in both ADPs. The KOR is implicated in drinking and craving following naltrexone therapy in alcohol use disorder. [ABSTRACT FROM AUTHOR]

Pain comorbidities include several psychological disorders, such as anxiety and anhedonia. However, the way pain affects male and female individuals and by which mechanism is not well understood. Previous research shows that pain induces alterations in the dynorphinergic pathway within the mesocorticolimbic system (MCLS), together with a relationship between corticotropin-releasing system and dynorphin release in the MCLS. Here, we analyse the sex and time course-dependent effects of pain on negative affect. Additionally, we study the implication of dynorphinergic and corticotropin releasing factor in these pain related behaviours. We used behavioural pharmacology and biochemical tools to characterise negative affective states induced by inflammatory pain in male and female rats, and the alterations in the dynorphinergic and the corticotropin systems within the MCLS. Female rats showed persistent anxiety-like and reversible anhedonia-like behaviours derived from inflammatory pain. Additionally, we found alterations in dynorphin and corticotropin releasing factor in NAc and amygdala, which suggests sex-dependent dynamic adaptations. Finally blockade on the kappa opioid receptor in the NAc confirmed its role in pain-induced anxiety-like behaviour in female rats. Our results show sex and time-dependent anxiety- and anhedonia-like behaviours induced by the presence of pain in female rats. Furthermore, we replicated previous data, pointing to the KOR/DYN recruitment in the NAc as a key neurological substrate mediating pain-induced behavioural alterations. This research studies the mechanisms underlying these behaviours, to better understand the emotional dimension of pain. • Inflammatory pain induces negative affective states in a sex- and time-dependent manner. • Inflammatory pain induces dynamic alterations of the genes an protein expression of dynorphin, KORs and CRFR1. • Inflammatory pain descreases plasma cortisol levels in female rats. • Blockade of KORs in NAc of female rats inhibits negative affective states induced by inflammatory pain. [ABSTRACT FROM AUTHOR]

Migraine is a complex disorder that is characterized by an assortment of neurological and systemic effects. While headache is the most prominent feature of migraine, a host of symptoms affecting many physiological functions are also observed before, during, and after an attack. Furthermore, migraineurs are heterogeneous and have a wide range of responses to migraine therapies. The recent approval of calcitonin gene‐related‐peptide based therapies has opened up the treatment of migraine and generated a renewed interest in migraine research and discovery. Ongoing advances in migraine research have identified a number of other promising therapeutic targets for this disorder. In this review, we highlight emergent treatments within the following biological systems: pituitary adenylate cyclase activating peptdie, 2 non‐mu opioid receptors that have low abuse liability – the delta and kappa opioid receptors, orexin, and nitric oxide‐based therapies. Multiple mechanisms have been identified in the induction and maintenance of migraine symptoms; and this divergent set of targets have highly distinct biological effects. Increasing the mechanistic diversity of the migraine tool box will lead to more treatment options and better patient care. [ABSTRACT FROM AUTHOR]

Diffuse noxious inhibitory controls (DNICs) is a pain-inhibits-pain phenomenon demonstrated in humans and animals. Diffuse noxious inhibitory control is diminished in many chronic pain states, including neuropathic pain. The efficiency of DNIC has been suggested to prospectively predict both the likelihood of pain chronification and treatment response. Little is known as to why DNIC is dysfunctional in neuropathic pain. Here, we evaluated DNIC in the rat L5/L6 spinal nerve ligation (SNL) model of chronic pain using both behavioral and electrophysiological outcomes. For behavior, nociceptive thresholds were determined using response to noxious paw pressure on both hind paws as the test stimulus before, and after, injection of a conditioning stimulus of capsaicin into the left forepaw. Functionally, the spike firing of spinal wide-dynamic-range neuronal activity was evaluated before and during noxious ear pinch, while stimulating the ipsilateral paw with von Frey hairs of increased bending force. In both assays, the DNIC response was significantly diminished in the ipsilateral (ie, injured) paw of SNL animals. However, behavioral loss of DNIC was not observed on the contralateral (ie, uninjured) paw. Systemic application of nor-binaltorphimine, a kappa opioid antagonist, did not ameliorate SNL-induced hyperalgesia but reversed loss of the behavioral DNIC response. Microinjection of nor-binaltorphimine into the right central amygdala (RCeA) of SNL rats did not affect baseline thresholds but restored DNIC both behaviorally and electrophysiologically. Cumulatively, these data suggest that net enhanced descending facilitations may be mediated by kappa opioid receptor signaling from the right central amygdala to promote diminished DNIC after neuropathy. [ABSTRACT FROM AUTHOR]

Abstract Background Experiences of abuse and neglect during childhood are major predictors of the emergence of depressive and suicidal behaviors throughout life. The underlying biological mechanisms, however, remain poorly understood. Here, we focused on the opioid system as a potential brain substrate mediating these effects. Methods Postmortem samples from three brain structures regulating social bonds and emotions were analyzed. Groups were constituted of depressed individuals who died by suicide, with or without a history of severe child abuse, and of psychiatrically healthy control subjects. Expression of opioid peptides and receptors was measured using real-time polymerase chain reaction. DNA methylation, a major epigenetic mark, was investigated using targeted bisulfite sequencing and characterized at functional level using in vitro reporter assays. Finally, oxidative bisulfite sequencing was used to differentiate methylation and hydroxymethylation of DNA. Results A history of child abuse specifically associated in the anterior insula with a downregulation of the kappa opioid receptor (Kappa), as well as decreased DNA methylation in the second intron of the Kappa gene. In vitro assays further showed that this intron functions as a genomic enhancer where glucocorticoid receptor binding regulates Kappa expression, unraveling a new mechanism mediating the well-established interactions between endogenous opioids and stress. Finally, results showed that child abuse is associated in the Kappa intron with a selective reduction in levels of DNA hydroxymethylation, likely mediating the observed downregulation of the receptor. Conclusions Altogether, our findings uncover new facets of Kappa physiology, whereby this receptor may be epigenetically regulated by stressful experiences, in particular as a function of early social life. [ABSTRACT FROM AUTHOR]

The endogenous kappa opioid system has primarily been shown to be involved with a state of dysphoria and aversion. Stress and exposure to drugs of abuse, particularly alcohol, can produce similar states of unease and anxiety, implicating the kappa opioid system as a target of stress and alcohol. Numerous behavioral studies have demonstrated reduced sensitivity to manipulations of the kappa opioid system in early life relative to adulthood, and recent reports have shown that the kappa opioid system is functionally different across ontogeny. Given the global rise in early-life stress and alcohol consumption, understanding how the kappa opioid system responds and adapts to stress and/or alcohol exposure differently in early life and adulthood is imperative. Therefore, the objective of this review is to highlight and discuss studies examining the impact of early-life stress and/or alcohol on the kappa opioid system, with focus on the documented neuroadaptations that may contribute to future vulnerability to stress and/or increase the risk of relapse. We first provide a brief summary of the importance of studying the effects of stress and alcohol during early life (prenatal, neonatal/juvenile, and adolescence). We then discuss the literature on the effects of stress or alcohol during early life and adulthood on the kappa opioid system. Finally, we discuss the few studies that have shown interactions between stress and alcohol on the kappa opioid system and provide some discussion about the need for studies investigating the development of the kappa opioid system. [ABSTRACT FROM AUTHOR]

• This work that builds on a limited but growing body of evidence that dezocine might be useful as a modulator of OUD. • Dezocine is not a controlled substance, and it has a minimum risk of addiction and of respiratory depression. • It is the most used medication for acute pain in China but is currently only administered intravenously (i.v.) at low pH for solubility reasons. • Here we show that i.p. or i.n. Cyc-dezocine, a new neutral pH formulation, reduces oxycodone self-administration in two different paradigms. • The data described in this manuscript are an additional step to determine if Cyc-dezocine can be a step-down treatment of OUD and/or as a safer analgesic than those currently used. Dezocine is a partial mu opioid receptor agonist previously used as an analgesic for perioperative acute pain in the US and is now the most used perioperative analgesic in China. In general, dezocine is well-tolerated, with relatively minimal risk of fatal respiratory depression. To our knowledge, there are no reports of dezocine addiction, which suggests that the abuse liability of dezocine is low. The overarching goal of this study was to determine the efficacy of a novel formulation of dezocine (Cyc-dezocine), developed for intraperitoneal or intranasal administration, to reduce voluntary opioid taking in rats. One cohort of male rats self-administered intravenous oxycodone on a fixed-ratio 5 schedule of reinforcement. Once oxycodone taking stabilized, rats were pretreated with systemic injections of vehicle or Cyc-dezocine. Cyc-dezocine dose-dependently reduced intravenous oxycodone self-administration. A second cohort of male and female rats self-administered oral oxycodone from drinking water. Once oxycodone taking stabilized, rats were pretreated with intra-nasal Cyc-dezocine. Consistent with the effects of i.p. Cyc-dezocine in our intravenous oxycodone studies, intra-nasal Cyc-dezocine attenuated oral oxycodone self-administration. Together, these findings support the need for further studies investigating the therapeutic potential of Cyc-dezocine for treating opioid use disorder. [ABSTRACT FROM AUTHOR]

The opioid receptors (OR) regulate food intake. Still, despite extensive pre-clinical research, the overall effects and individual contribution of the mu (MOR), kappa (KOR), and delta (DOR) OR subtypes to feeding behaviors and food intake remain unclear. To address this, we conducted a pre-registered systematic search and meta-analysis of rodent dose-response studies to evaluate the impact of central and peripheral administration of non-selective and selective OR ligands on intake, motivation, and choice of food. All studies had a high bias risk. Still, the meta-analysis confirmed the overall orexigenic and anorexigenic effects of OR agonists and antagonists, respectively. Our results support a larger orexigenic role for central MOR agonists among OR subtypes and that peripheral OR antagonists reduce motivation for and intake of preferred foods. In binary food choice studies, peripheral OR agonists selectively increase the intake of fat-preferred foods; in contrast, they did not increase the intake of sweet carbohydrate-preferred foods. Overall, these data support that OR regulation of intake, motivation, and choice is influenced by food macronutrient composition. • How opioid receptors regulate feeding behavior and intake remains unclear. • The macronutrient content of foods might influence the effects of opioid receptors on intake. • Central mu-selective agonists might selectively increase intake of fat-enriched foods. • Opioid receptor ligands appear to reduce motivation for food. • Opioid receptor agonists selectively increase intake of preferred fat, but not of sweet carbohydrate foods. [ABSTRACT FROM AUTHOR]

Kappa opioid receptor activation has been linked to stress and anxiety behavior, thus leading to kappa antagonists being popularized in research as potential anxiolytics. However, while these findings may hold true in standard models, the neuromodulatory effects of social defeat may change the behavioral outcome of kappa opioid receptor activation. Previous research has shown that social defeat can lead to hyperactivity of serotonergic neurons in the dorsal raphe nucleus, and that inhibition of this increase blocks the social deficits caused by defeat. Kappa opioid receptor activation in the dorsal raphe nucleus works to decrease serotonergic activity. We injected the kappa opioid receptor U50,488 directly into the dorsal raphe nucleus of male and female, defeat and control adult California mice. Here we show evidence that U50,488 induces anxiety behavior in control male California mice, but helps relieve it in defeated males. Consistent with previous literature, we find little effect in females adding evidence that there are marked and important sex differences in the kappa opioid system. [ABSTRACT FROM AUTHOR]

There is an important emerging role for the endogenous opioid dynorphin (DYN) and the kappa-opioid receptor (KOR) in the treatment of alcohol dependence. Evidence suggests that the DYN/KOR system in the bed nucleus of the stria terminalis (BNST) contributes to maladaptive behavioral regulation during withdrawal in alcohol dependence. The current experiments were designed to assess dysregulation of the BNST DYN/KOR system by evaluating alcohol dependence-induced changes in DYN/KOR gene expression ( Pdyn and Oprk1 , respectively), and the sensitivity of alcohol self-administration, negative affective-like behavior and physiological withdrawal to intra-BNST KOR antagonism during acute withdrawal. Wistar rats trained to self-administer alcohol, or not trained, were subjected to an alcohol dependence induction procedure (14 h alcohol vapor/10 h air) or air-exposure. BNST micropunches from air- and vapor-exposed animals were analyzed using RT-qPCR to quantify dependence-induced changes in Pdyn and Oprk1 mRNA expression. In addition, vapor- and air-exposed groups received an intra-BNST infusion of a KOR antagonist or vehicle prior to measurement of alcohol self-administration. A separate cohort of vapor-exposed rats was assessed for physiological withdrawal and negative affective-like behavior signs following intra-BNST KOR antagonism. During acute withdrawal, following alcohol dependence induction, there was an upregulation in Oprk1 mRNA expression in alcohol self-administering animals, but not non-alcohol self-administering animals, that confirmed dysregulation of the KOR/DYN system within the BNST. Furthermore, intra-BNST KOR antagonism attenuated escalated alcohol self-administration and negative affective-like behavior during acute withdrawal without reliably impacting physiological symptoms of withdrawal. The results confirm KOR system dysregulation in the BNST in alcohol dependence, illustrating the therapeutic potential of targeting the KOR to treat alcohol dependence. [ABSTRACT FROM AUTHOR]

Activation of k opioid receptors (KORs) produces analgesia and aversion via distinct intracellular signaling pathways, but whether G protein-biased KOR agonists can be designed to have clinical utility will depend on abetter understanding of the signaling mechanisms involved. We found that KOR activation produced conditioned place aversion and potentiated CPP for cocaine in male and female C57BL/6N mice. Consistent with this, males and females both showed arrestin-mediated increases in phospho-p38 M APK following KOR activation. Unlike in males, however, KOR activation had inconsistent analgesic effects in females and KOR increased G(By-mediated ERK phosphorylation in males, but not females. KOR desensitization was not responsible for the lack of response in females because neither Grk3 nor Pdyn gene knock-out enhanced analgesia. Instead, responsiveness was estrous cycle dependent because KOR analgesia was evident during low estrogen phases of the cycle and in ovariectomized (OVX) females. Estradiol treatment of OVX females suppressed KOR-mediated analgesia, demonstrating that estradiol was sufficient to blunt G(By-mediated KOR signals. G protein-coupled receptor kinase 2 (GRK2) is known to regulate ERK activation, and we found that the inhibitory, phosphorylated form of GRK2 was significantly higher in intact females. GRK2/3 inhibition by CMPD101 increased KOR stimulation of phospho-ERK in females, decreased sex differences in KOR-mediated inhibition of dopamine release, and enhanced mu opioid receptor and KOR-mediated analgesia in females. In OVX females, estradiol increased the association between GRK2 and G(By. These studies suggest that estradiol, through increased phosphorylation of GRK2 and possible sequestration of G(By by GRK2, blunts G protein-mediated signals. [ABSTRACT FROM AUTHOR]