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Dopaminergic (DAnergic) dysfunction and imbalanced dopamine (DA) levels are known contributors to the pathogenesis of numerous psychiatric and neurodegenerative disorders. Of the many identified risk factors for DA‐associated disorders, nuclear receptor subfamily 4 group A2 (NR4A2; or nuclear receptor related‐1 protein (NURR1)), a transcription factor involved in DAnergic differentiation, has been associated with Parkinson's disease and attention deficit hyperactive disorder (ADHD). In zebrafish, transient loss of nr4a2 was previously shown to decrease tyrosine hydroxylase (TH) expression and impair locomotion. To further characterize the roles of the two zebrafish nr4a2 paralogs, nr4a2a, and nr4a2b, we produced targeted loss‐of‐function mutants and examined DAnergic neuron regeneration, oxidative respiration, and behavioral traits. The loss of nr4a2a function more closely recapitulated Parkinsonian phenotypes and affected neurotrophic factor gene expression. Conversely, nr4a2b mutants displayed behavioral symptoms reminiscent of mice deficient in Nr4a2 with increased neurotrophic output. In contrast, nr4a2b mutants also displayed increased metabolic input from non‐mitochondrial sources indicative of high cytosolic reactive oxygen species and perturbed mitochondrial function. The nr4a2a mutants also showed increased maximal respiration, which may suggest a compensatory mechanism to meet the metabolic requirements of DAnergic neuron health. Overall, the zebrafish mutants generated in this study helped uncover molecular mechanisms involved in DA‐related disease pathologies, and in the regeneration of DAnergic neurons. [ABSTRACT FROM AUTHOR]

Medial Forebrain Bundle Deep Brain Stimulation (MFB‐DBS) can have rapid and long lasting antidepressant effects in Treatment Resistant Depression (TRD) patients. The mechanisms are not well understood, but one hypothesis stipulates that modulation of the dopaminergic (DAergic) fibers contribute to the therapeutic outcome. Acute DBS effects on DA release have been studied; however, longitudinal studies with acute‐repetitive DBS are lacking. Long‐Evans accumbal DA release and Ventral Tegmental Area (VTA) calcium tonic and phasic signaling to different mfb‐DBS parameters were measured using fiber photometry over 8 weeks, following acute and repetitive stimulation in behaving and non‐behaving animals. DBS‐induced release was observed in both targets, with increased frequency and DBS duration. 130 Hz stimulation increased phasic and tonic DA response over time, with the latter being a potential mechanism for its long‐term clinical effectiveness. VTA calcium transients decreased, while phasic activity increased with frequency. Pulse width (PW)‐mediated differential peak release timing also suggests potential parallel activation of diverse fiber types. Additionally, decreased DA transients rate during Elevated Plus Maze (EPM) suggests context and stimulation duration‐dependent DA release. The data confirm chronic antidromic/orthodromic DAergic responses with stimulation parameter dependent variability, providing novel insights into temporal adaptations, connectivity and fiber recruitment on mfb DBS. [ABSTRACT FROM AUTHOR]

The nematode Caenorhabditis elegans is well known for its ability to support forward genetic screens to identify molecules involved in neuronal viability and signaling. The proteins involved in C. elegans dopamine (DA) regulation are highly conserved across evolution, with prior work demonstrating that the model can serve as an efficient platform to identify novel genes involved in disease‐associated processes. To identify novel players in DA signaling, we took advantage of a recently developed library of pre‐sequenced mutant nematodes arising from the million mutation project (MMP) to identify strains that display the DA‐dependent swimming‐induced‐paralysis phenotype (Swip). Our screen identified novel mutations in the dopamine transporter encoding gene dat‐1, whose loss was previously used to identify the Swip phenotype, as well as multiple genes with previously unknown connections to DA signaling. Here, we present our isolation and characterization of one of these genes, bbs‐1, previously linked to the function of primary cilia in worms and higher organisms, including humans, and where loss‐of‐function mutations result in a human disorder known as Bardet–Biedl syndrome. Our studies of C. elegans BBS‐1 protein, as well as other proteins that are known to be assembled into a higher order complex (the BBSome) reveal that functional or structural disruption of this complex leads to exaggerated C. elegans DA signaling to produce Swip via a cell‐autonomous mechanism. We provide evidence that not only does the proper function of cilia in C. elegans DA neurons support normal swimming behavior, but also that bbs‐1 maintains normal levels of DAT‐1 trafficking or function via a RHO‐1 and SWIP‐13/MAPK‐15 dependent pathway where mutants may contribute to Swip independent of altered ciliary function. Together, these studies demonstrate novel contributors to DA neuron function in the worm and demonstrate the utility and efficiency of forward genetic screens using the MMP library. [ABSTRACT FROM AUTHOR]

The regulation of dopamine (DA) removal from the synaptic cleft is a crucial process in neurotransmission and is facilitated by the sodium‐ and chloride‐coupled dopamine transporter DAT. Psychostimulant drugs, cocaine, and amphetamine, both block the uptake of DA, while amphetamine also triggers the release of DA. As a result, they prolong or even amplify neurotransmitter signaling. Atypical inhibitors of DAT lack cocaine‐like rewarding effects and offer a promising strategy for the treatment of drug use disorders. Here, we present the 3.2 Å resolution cryo‐electron microscopy structure of the Drosophila melanogaster dopamine transporter (dDAT) in complex with the atypical non‐competitive inhibitor AC‐4‐248. The inhibitor partially binds at the central binding site, extending into the extracellular vestibule, and locks the transporter in an outward open conformation. Our findings propose mechanisms for the non‐competitive inhibition of DAT and attenuation of cocaine potency by AC‐4‐248 and provide a basis for the rational design of more efficacious atypical inhibitors. [ABSTRACT FROM AUTHOR]

The dopamine transporter (DAT) is a transmembrane protein that regulates dopamine (DA) neurotransmission by binding to and moving DA from the synaptic cleft back into the neurons. Besides moving DA and other endogenous monoamines, DAT is also a neuronal carrier for exogenous compounds such as the psychostimulant amphetamine (Amph), and several studies have shown that Amph‐induced behaviors require a functional DAT. Here, we demonstrate that exposure to Amph during early development causes behavioral, functional, and epigenetic modifications at the Caenorhabditis elegans DAT gene homolog, dat‐1, in C. elegans offspring. Specifically, we show that, while embryos exposed to Amph generate adults that produce offspring with no obvious behavioral alterations, both adults and offspring exhibit an increased behavioral response when challenged with Amph. Our functional studies suggest that a decrease in DAT‐1 expression underlies the increased behavioral response to Amph seen in offspring. Moreover, our epigenetic data suggest that histone methylation is a mechanism utilized by Amph to maintain changes in DAT‐1 expression in offspring. Taken together, our data reveal that Amph, by altering the epigenetic landscape of DAT, propagates long‐lasting functional and behavioral changes in offspring. [ABSTRACT FROM AUTHOR]

Xanthurenic acid (XA) raises a growing multidisciplinary interest based upon its oxidizing properties, its ability to complex certain metal ions, and its detoxifier capacity of 3‐hydroxykynurenine (3‐HK), its brain precursor. However, little is still known about the role and mechanisms of action of XA in the central nervous system (CNS). Therefore, many research groups have recently investigated XA and its central functions extensively. The present paper critically reviews and discusses all major data related to XA properties and neuronal activities to contribute to the improvement of the current knowledge on XA's central roles and mechanisms of action. In particular, our data showed the existence of a specific G‐protein‐coupled receptor (GPCR) for XA localized exclusively in brain neurons exhibiting Ca2+‐dependent dendritic release and specific electrophysiological responses. XA properties and central activities suggest a role for this compound in brain intercellular signaling. Indeed, XA stimulates cerebral dopamine (DA) release contrary to its structural analog, kynurenic acid (KYNA). Thus, KYNA/XA ratio could be fundamental in the regulation of brain glutamate and DA release. Cerebral XA may also represent an homeostatic signal between the periphery and several brain regions where XA accumulates easily after peripheral administration. Therefore, XA status in certain psychoses or neurodegenerative diseases seems to be reinforced by its brain‐specific properties in balance with its formation and peripheral inputs. [ABSTRACT FROM AUTHOR]

Depressive disorders are a common and debilitating form of mental illness with significant impacts on individuals and society. Despite the high prevalence, the underlying causes and mechanisms of depressive disorders are still poorly understood. Neurochemical systems, including serotonin, norepinephrine, and dopamine, have been implicated in the development and perpetuation of depressive symptoms. Current treatments for depression target these neuromodulator systems, but there is a need for a better understanding of their role in order to develop more effective treatments. Monitoring neurochemical dynamics during depressive symptoms is crucial for gaining a better a understanding of their involvement in depressive disorders. Genetically encoded sensors have emerged recently that offer high spatial–temporal resolution and the ability to monitor neurochemical dynamics in real time. This review explores the neurochemical systems involved in depression and discusses the applications and limitations of current monitoring tools for neurochemical dynamics. It also highlights the potential of genetically encoded sensors for better characterizing neurochemical dynamics in depression‐related behaviors. Furthermore, potential improvements to current sensors are discussed in order to meet the requirements of depression research. [ABSTRACT FROM AUTHOR]

Despite the advent of combination anti‐retroviral therapy (cART), nearly half of people infected with HIV treated with cART still exhibit HIV‐associated neurocognitive disorders (HAND). HAND can be worsened by co‐morbid opioid use disorder. The basal ganglia are particularly vulnerable to HIV‐1 and exhibit higher viral loads and more severe pathology, which can be exacerbated by co‐exposure to opioids. Evidence suggests that dopaminergic neurotransmission is disrupted by HIV exposure, however, little is known about whether co‐exposure to opioids may alter neurotransmitter levels in the striatum and if this in turn influences behavior. Therefore, we assayed motor, anxiety‐like, novelty‐seeking, exploratory, and social behaviors, and levels of monoamines and their metabolites following 2 weeks and 2 months of Tat and/or morphine exposure in transgenic mice. Morphine decreased dopamine levels, but significantly elevated norepinephrine, the dopamine metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and the serotonin metabolite 5‐hydroxyindoleacetic acid, which typically correlated with increased locomotor behavior. The combination of Tat and morphine altered dopamine, DOPAC, and HVA concentrations differently depending on the neurotransmitter/metabolite and duration of exposure but did not affect the numbers of tyrosine hydroxylase‐positive neurons in the mesencephalon. Tat exposure increased the latency to interact with novel conspecifics, but not other novel objects, suggesting the viral protein inhibits exploratory behavior initiation in a context‐dependent manner. By contrast, and consistent with prior findings that opioid misuse can increase novelty‐seeking behavior, morphine exposure increased the time spent exploring a novel environment. Finally, Tat and morphine interacted to affect locomotor activity in a time‐dependent manner, while grip strength and rotarod performance were unaffected. Together, our results provide novel insight into the unique effects of HIV‐1 Tat and morphine on monoamine neurochemistry that may underlie their divergent effects on motor and exploratory behavior. [ABSTRACT FROM AUTHOR]

The striatum can be divided into four anatomically and functionally distinct domains: the dorsolateral, dorsomedial, ventral and the more recently identified caudolateral (tail) striatum. Dopamine transmission in these striatal domains underlies many important behaviours, yet little is known about this phenomenon in the tail striatum. Furthermore, the tail is divided anatomically into four divisions (dorsal, medial, intermediate and lateral) based on the profile of D1 and D2 dopamine receptor‐expressing medium spiny neurons, something that is not seen elsewhere in the striatum. Considering this organisation, how dopamine transmission occurs in the tail striatum is of great interest. We recorded evoked dopamine release in the four tail divisions, with comparison to the dorsolateral striatum, using fast‐scan cyclic voltammetry in rat brain slices. Contributions of clearance mechanisms were investigated using dopamine transporter knockout (DAT‐KO) rats, pharmacological transporter inhibitors and dextran. Evoked dopamine release in all tail divisions was smaller in amplitude than in the dorsolateral striatum and, importantly, regional variation was observed: dorsolateral ≈ lateral > medial > dorsal ≈ intermediate. Release amplitudes in the lateral division were 300% of that in the intermediate division, which also exhibited uniquely slow peak dopamine clearance velocity. Dopamine clearance in the intermediate division was most dependent on DAT, and no alternative dopamine transporters investigated (organic cation transporter‐3, norepinephrine transporter and serotonin transporter) contributed significantly to dopamine clearance in any tail division. Our findings confirm that the tail striatum is not only a distinct dopamine domain but also that each tail division has unique dopamine transmission characteristics. This supports that the divisions are not only anatomically but also functionally distinct. How this segregation relates to the overall function of the tail striatum, particularly the processing of multisensory information, is yet to be determined. [ABSTRACT FROM AUTHOR]

L‐Dopa, while treating motor symptoms of Parkinson's disease, can lead to debilitating L‐Dopa‐induced dyskinesias, limiting its use. To investigate the causative relationship between neuro‐inflammation and dyskinesias, we assessed if striatal M1 and M2 microglia numbers correlated with dyskinesia severity and whether the anti‐inflammatories, minocycline and indomethacin, reverse these numbers and mitigate against dyskinesia. In 6‐OHDA lesioned mice, we used stereology to assess numbers of striatal M1 and M2 microglia populations in non‐lesioned (naïve) and lesioned mice that either received no L‐Dopa (PD), remained non‐dyskinetic even after L‐Dopa (non‐LID) or became dyskinetic after L‐Dopa treatment (LID). We also assessed the effect of minocycline/indomethacin treatment on striatal M1 and M2 microglia and its anti‐dyskinetic potential via AIMs scoring. We report that L‐Dopa treatment leading to LIDs exacerbates activated microglia numbers beyond that associated with the PD state; the severity of LIDs is strongly correlated to the ratio of the striatal M1 to M2 microglial numbers; in non‐dyskinetic mice, there is no M1/M2 microglia ratio increase above that seen in PD mice; and reducing M1/M2 microglia ratio using anti‐inflammatories is anti‐dyskinetic. Parkinson's disease is associated with increased inflammation, but this is insufficient to underpin dyskinesia. Given that L‐Dopa‐treated non‐LID mice show the same ratio of M1/M2 microglia as PD mice that received no L‐Dopa, and, given minocycline/indomethacin reduces both the ratio of M1/M2 microglia and dyskinesia severity, our data suggest the increased microglial M1/M2 ratio that occurs following L‐Dopa treatment is a contributing cause of dyskinesias. [ABSTRACT FROM AUTHOR]

After ischemic stroke, the cortex directly adjacent to the ischemic core (i.e., the peri‐infarct cortex, PIC) undergoes plastic changes that facilitate motor recovery. Dopaminergic signaling is thought to support this process. However, ischemic stroke also leads to the remote degeneration of dopaminergic midbrain neurons, possibly interfering with this beneficial effect. In this study, we assessed the reorganization of dopaminergic innervation of the PIC in a rat model of focal cortical stroke. Adult Sprague–Dawley rats either received a photothrombotic stroke (PTS) in the primary motor cortex (M1) or a sham operation. 30 days after PTS or sham procedure, the retrograde tracer Micro Ruby (MR) was injected into the PIC of stroke animals or into homotopic cortical areas of matched sham rats. Thus, dopaminergic midbrain neurons projecting into the PIC were identified based on MR signal and immunoreactivity against tyrosine hydroxylase (TH), a marker for dopaminergic neurons. The density of dopaminergic innervation within the PIC was assessed by quantification of dopaminergic boutons indicated by TH‐immunoreactivity. Regarding postsynaptic processes, expression of dopamine receptors (D1‐ and D2) and a marker of the functional signal cascade (DARPP‐32) were visualized histologically. Despite a 25% ipsilesional loss of dopaminergic midbrain neurons after PTS, the number and spatial distribution of dopaminergic neurons projecting to the PIC was not different compared to sham controls. Moreover, the density of dopaminergic innervation in the PIC was significantly higher than in homotopic cortical areas of the sham group. Within the PIC, D1‐receptors were expressed in neurons, whereas D2‐receptors were confined to astrocytes. The intensity of D1‐ and DARPP‐32 expression appeared to be higher in the PIC compared to the contralesional homotopic cortex. Our data suggest a sprouting of dopaminergic fibers into the PIC and point to a role for dopaminergic signaling in reparative mechanisms post‐stroke, potentially related to recovery. [ABSTRACT FROM AUTHOR]

Tyrosine hydroxylase catalyzes the initial and rate‐limiting step in the biosynthesis of the neurotransmitter dopamine. The phosphorylation state of Ser40 and Ser31 is believed to exert a direct effect on the enzymatic activity of tyrosine hydroxylase. Interestingly, some studies report that Ser31 phosphorylation affects Ser40 phosphorylation, while Ser40 phosphorylation has no effect on Ser31 phosphorylation, a process named hierarchical phosphorylation. Here, we provide a detailed investigation into the signal transduction mechanisms regulating Ser40 and Ser31 phosphorylation in dopaminergic mouse MN9D and Neuro2A cells. We find that cyclic nucleotide signaling drives Ser40 phosphorylation, and that Ser31 phosphorylation is strongly regulated by ERK signaling. Inhibition of ERK1/2 with UO126 or PD98059 reduced Ser31 phosphorylation, but surprisingly had no effect on Ser40 phosphorylation, contradicting a role for Ser31 in the regulation of Ser40. Moreover, to elucidate a possible hierarchical mechanism controlling tyrosine hydroxylase phosphorylation, we introduced tyrosine hydroxylase variants in Neuro2A mouse neuroblastoma cells that mimic either phosphorylated or unphosphorylated serine residues. When we introduced a Ser40Ala tyrosine hydroxylase variant, Ser31 phosphorylation was completely absent. Additionally, neither the tyrosine hydroxylase variant Ser31Asp, nor the variant Ser31Ala had any significant effect on basal Ser40 phosphorylation levels. These results suggest that tyrosine hydroxylase is not controlled by hierarchical phosphorylation in the sense that first Ser31 has to be phosphorylated and subsequently Ser40, but, conversely, that Ser40 phosphorylation is essential for Ser31 phosphorylation. Overall our study suggests that Ser40 is the crucial residue to target so as to modulate tyrosine hydroxylase activity. [ABSTRACT FROM AUTHOR]

Vitamin D has been identified as a key factor in dopaminergic neurogenesis and differentiation. Consequently, developmental vitamin D (DVD) deficiency has been linked to disorders of abnormal dopamine signalling with a neurodevelopmental basis such as schizophrenia. Here we provide further evidence of vitamin D's role as a mediator of dopaminergic development by showing that it increases neurite outgrowth, neurite branching, presynaptic protein re‐distribution, dopamine production and functional release in various in vitro models of developing dopaminergic cells including SH‐SY5Y cells, primary mesencephalic cultures and mesencephalic/striatal explant co‐cultures. This study continues to establish vitamin D as an important differentiation agent for developing dopamine neurons, and now for the first time shows chronic exposure to the active vitamin D hormone increases the capacity of developing neurons to release dopamine. This study also has implications for understanding mechanisms behind the link between DVD deficiency and schizophrenia. [ABSTRACT FROM AUTHOR]

Apolipoprotein E signaling in Alzheimer's disease: Mechanisms and novel drug targets Abdel Ali Belaidi, Ashley Bush, Scott Ayton The University of Melbourne, The Florey Institute of Neuroscience and Mental Health, Melbourn... Apolipoprotein E (apoE) is best known for its lipid transport capacity in the brain but also for its association with healthy aging and age-related neuronal disorders including Alzheimer's disease (AD). Combining neurotransmission and myelination reporters along single developing axons revealed that the onset of myelination coincided with the emergence of axonal vesicle fusion. Next, we leveraged deep brain 1-photon calcium imaging through endoscopic lenses during Pavlovian conditioning tasks with positive and negative outcomes to understand the functional involvement of NAc neurons in associative learning. These results identify a novel "feedforward" mechanism operating in specific neurons whereby myelination drives the activity-regulated signal, axonal vesicle fusion, that in turn consolidates myelin growth. [Extracted from the article]

Studies have reported associations between environmental manganese (Mn) exposure and impaired cognition, attention, impulse control, and fine motor function in children. Our recent rodent studies established that elevated Mn exposure causes these impairments. Here, rats were exposed orally to 0, 25, or 50 mg Mn kg-1  day-1 during early postnatal life (PND 1-21) or lifelong to determine whether early life Mn exposure causes heightened behavioral reactivity in the open field, lasting changes in the catecholaminergic systems in the medial prefrontal cortex (mPFC), altered dendritic spine density, and whether lifelong exposure exacerbates these effects. We also assessed astrocyte reactivity (glial fibrillary acidic protein, GFAP), and astrocyte complement C3 and S100A10 protein levels as markers of A1 proinflammatory or A2 anti-inflammatory reactive astrocytes. Postnatal Mn exposure caused heightened behavioral reactivity during the first 5-10 min intervals of daily open field test sessions, consistent with impairments in arousal regulation. Mn exposure reduced the evoked release of norepinephrine (NE) and caused decreased protein levels of tyrosine hydroxylase (TH), dopamine (DA) and NE transporters, and DA D1 receptors, along with increased DA D2 receptors. Mn also caused a lasting increase in reactive astrocytes (GFAP) exhibiting increased A1 and A2 phenotypes, with a greater induction of the A1 proinflammatory phenotype. These results demonstrate that early life Mn exposure causes broad lasting hypofunctioning of the mPFC catecholaminergic systems, consistent with the impaired arousal regulation, attention, impulse control, and fine motor function reported in these animals, suggesting that mPFC catecholaminergic dysfunction may underlie similar impairments reported in Mn-exposed children.

Dopamine (DA) is involved in neurological and physiological functions such as motor control. L‐3,4‐dihydroxyphenylalanine (L‐DOPA), a precursor of DA, is conventionally believed to be an inert amino acid precursor of DA, and its major therapeutic effects in Parkinson's disease (PD) are mediated through its conversion to DA. On the contrary, accumulating evidence suggests that L‐DOPA itself is a neurotransmitter. We here show that L‐DOPA potentiates DA D2 receptor (DRD2) signaling through GPR143, the gene product of X‐linked ocular albinism 1, a G‐protein‐coupled receptor for L‐DOPA. In Gpr143‐gene‐deficient (Gpr143−/y) mice, quinpirole, a DRD2/DRD3 agonist, ‐induced hypolocomotion was attenuated compared to wild‐type (WT) mice. Administration of non‐effective dose of L‐DOPA methyl ester augmented the quinpirole‐induced hypolocomotion in WT mice but not in Gpr143−/y mice. In cells co‐expressing GPR143 and DRD2, L‐DOPA enhanced the interaction between GPR143 and DRD2 and augmented quinpirole‐induced decrease in cAMP levels. This augmentation by L‐DOPA was not observed in cells co‐expressing GPR143 and DRD1 or DRD3. Chimeric analysis in which the domain of GPR143 was replaced with GPR37 revealed that GPR143 interacted with DRD2 at the fifth transmembrane domain. Intracerebroventricular administration of a peptide that disrupted the interaction mitigated quinpirole‐induced behavioral changes in WT mice but not in Gpr143−/y mice. These findings provide evidence that coupling between GPR143 and DRD2 is required for selective DRD2 modulation by L‐DOPA in the dorsal striatum. [ABSTRACT FROM AUTHOR]

While the illicit use and misuse of stimulants like cocaine and methylphenidate (MP) has increased, there remains no FDA‐approved treatments for psychostimulant use disorders (PSUD). Oxytocin (OT) has shown promise as a potential pharmacotherapy for PSUD. Dopamine (DA) neurotransmission plays a significant role in PSUD. We have recently shown that OT blunts the reinforcing effects of MP but, surprisingly, enhanced MP‐induced stimulation of DA levels. Such effects have been suggested as a result of activation of OT receptors or, alternatively, could be mediated by direct actions of OT on MP blockade of the DA transporter. Here, we employed fast scan cyclic voltammetry (FSCV) to investigate the effects of systemic OT on MP‐induced changes in the dynamics of DA, phasic release and uptake, in the nucleus accumbens shell (NAS) of Sprague–Dawley rats. We also tested the systemic effects of an antagonist of OT receptors, atosiban, to counteract the OT enhancement of dopaminergic effects of MP under microdialysis procedures in the NAS in rats. Administration of OT alone (2 mg/kg; i.p.) did not significantly modify evoked NAS DA dynamics measured by FSCV, and when administered 10 min before MP (0.1, 0.3, 1.0 mg/kg; i.v.), OT did not potentiate MP‐induced increases in phasic DA release and did not alter DA clearance rate, suggesting no direct interactions of OT with the MP‐induced blockade of DA uptake. Also, OT alone did not elicit significant changes in tonic, extracellular NAS DA levels measured by microdialysis. However, consistent with previous studies, we observed that OT pretreatments (2 mg/kg; i.p.) potentiated MP‐induced (0.1, 0.3, 1.0 mg/kg; i.v.) efflux of extracellular NAS DA levels. This effect was abolished when rats were pretreated with atosiban (2 mg/kg; i.p.), suggesting that OT receptors mediate this OT action. Overall, our results suggest that OT receptors mediated OT potentiation of MP‐induced stimulation of extracellular NAS DA levels, likely driven by modulation of DA receptor signaling pathways, without affecting MP blockade of DAT. [ABSTRACT FROM AUTHOR]

Noradrenergic neurotransmission is a critical mediator of stress responses. In turn, exposure to stress induces noradrenergic system adaptations, some of which are implicated in the etiology of stress‐related disorders. Adrenergic receptors (ARs) in the ventral tegmental area (VTA) have been demonstrated to regulate phasic dopamine (DA) release in the forebrain, necessary for behavioral responses to conditional cues. However, the impact of stress on noradrenergic modulation of the VTA has not been previously explored. We demonstrate that ARs in the VTA regulate dopaminergic activity in the VTA–BLA (basolateral amygdala) circuit, a key system for processing stress‐related stimuli; and that such control is altered by acute stress. We utilized fast‐scan cyclic voltammetry to assess the effects of intra‐VTA microinfusion of α1‐AR and α2‐AR antagonists (terazosin and RX‐821002, respectively), on electrically evoked phasic DA release in the BLA in stress‐naïve and stressed (unavoidable electric shocks – UES) anesthetized male Sprague–Dawley rats. In addition, we used western blotting to explore UES‐induced alterations in AR protein level in the VTA. Intra‐VTA terazosin or RX‐821002 dose‐dependently attenuated DA release in the BLA. Interestingly, UES decreased the effects of intra‐VTA α2‐AR blockade on DA release (24 h but not 7 days after stress), while the effects of terazosin were unchanged. Despite changes in α2‐AR physiological function in the VTA, UES did not alter α2‐AR protein levels in either intracellular or membrane fractions. These findings demonstrate that NA‐ergic modulation of the VTA–BLA circuit undergoes significant alterations in response to acute stress, with α2‐AR signaling indicated as a key target. [ABSTRACT FROM AUTHOR]

Parkinson's disease (PD) and other neurodegenerative parkinsonisms are characterised by loss of striatal dopaminergic neurons. Dopamine functional deficits can be measured in vivo using positron emission tomography (PET) and single‐photon emission computed tomography (SPECT) ligands assessing either presynaptic (e.g. dopamine synthesis and storage, transporter density) or postsynaptic terminals (i.e. D2 receptors availability). Nuclear medicine imaging thus helps the clinician to separate degenerative forms of parkinsonism with other neurological conditions, e.g. essential tremor or drug‐induced parkinsonism. With the present study, we aimed at summarizing the current evidence about dopaminergic molecular imaging in the diagnostic evaluation of PD, atypical parkinsonian syndromes and dementia with Lewy bodies (DLB), as well as its potential to distinguish these conditions and to estimate disease progression. In fact, PET/SPECT methods are clinically validated and have been increasingly integrated into diagnostic guidelines (e.g. for PD and DLB). In addition, there is novel evidence on the classification properties of extrastriatal signal. Finally, dopamine imaging has an outstanding potential to detect neurodegeneration at the premotor stage, including REM‐sleep behavior disorder and olfactory loss. Therefore, inclusion of subjects at an early stage for clinical trials can largely benefit from a validated in vivo biomarker such as presynaptic dopamine pathways PET/SPECT assessment. [ABSTRACT FROM AUTHOR]

Parkinson's disease (PD) is a heterogeneous multi‐systemic disorder unique to humans characterized by motor and non‐motor symptoms. Preclinical experimental models of PD present limitations and inconsistent neurochemical, histological, and behavioral readouts. The 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) mouse model of PD is the most common in vivo screening platform for novel drug therapies; nonetheless, behavioral endpoints yielded amongst laboratories are often discordant and inconclusive. In this study, we characterized neurochemically, histologically, and behaviorally three different MPTP mouse models of PD to identify translational traits reminiscent of PD symptomatology. MPTP was intraperitoneally (i.p.) administered in three different regimens: (i) acute—four injections of 20 mg/kg of MPTP every 2 h; (ii) sub‐acute—one daily injection of 30 mg/kg of MPTP for 5 consecutive days; and (iii) chronic—one daily injection of 4 mg/kg of MPTP for 28 consecutive days. A series of behavioral tests were conducted to assess motor and non‐motor behavioral changes including anxiety, endurance, gait, motor deficits, cognitive impairment, circadian rhythm and food consumption. Impairments in balance and gait were confirmed in the chronic and acute models, respectively, with the latter showing significant correlation with lesion size. The sub‐acute model, by contrast, presented with generalized hyperactivity. Both, motor and non‐motor changes were identified in the acute and sub‐acute regime where habituation to a novel environment was significantly reduced. Moreover, we report increased water and food intake across all three models. Overall, the acute model displayed the most severe lesion size, while across the three models striatal dopamine content (DA) did not correlate with the behavioral performance. The present study demonstrates that detection of behavioral changes following MPTP exposure is challenging and does not correlate with the dopaminergic lesion extent. [ABSTRACT FROM AUTHOR]

A distinct population of dopamine neurons in the substantia nigra pars lateralis (SNL) has a unique projection to the most caudolateral (tail) region of the striatum. Here, using two electrochemical techniques to measure basal dopamine and electrically evoked dopamine release in anesthetized rats, we characterized this pathway, and compared it with the 'classic' nigrostriatal pathway from neighboring substantia nigra pars compacta (SNc) dopamine neurons to the dorsolateral striatum. We found that the tail striatum constitutes a distinct dopamine domain compared with the dorsolateral striatum, with consistently lower basal and evoked dopamine, and diverse dopamine release kinetics. Importantly, electrical stimulation of the SNL and SNc evoked dopamine release in entirely separate striatal regions; the tail and dorsolateral striatum, respectively. Furthermore, we showed that stimulation of the subthalamic nucleus (STN) evoked dopamine release exclusively in the tail striatum, likely via the SNL, consistent with previous anatomical evidence of STN afferents to SNL dopamine neurons. Our work identifies the STN as an important modulator of dopamine release in a novel dopamine pathway to the tail striatum, largely independent of the classic nigrostriatal pathway, which necessitates a revision of the basal ganglia circuitry with the STN positioned as a central integrator of striatal information. [ABSTRACT FROM AUTHOR]

Mechanisms that determine the survival of midbrain dopaminergic (mDA) neurons in the adult central nervous system (CNS) are not fully understood. Netrins are a family of secreted proteins that are essential for normal neural development. In the mature CNS, mDA neurons express particularly high levels of netrin‐1 and its receptor Deleted in Colorectal Cancer (DCC). Recent findings indicate that overexpressing netrin‐1 protects mDA neurons in animal models of Parkinson's disease (PD), with a proposed pro‐apoptotic dependence function for DCC that triggers cell death in the absence of a ligand. Here, we sought to determine if DCC expression influences mDA neuron survival in young adult and ageing mice. To circumvent the perinatal lethality of DCC null mice, we selectively deleted DCC from mDA neurons utilizing DATcre/loxP gene‐targeting and examined neuronal survival in adult and aged animals. Reduced numbers of mDA neurons were detected in the substantia nigra pars compacta (SNc) of young adult DATcre/DCCfl/fl mice, with further reduction in aged DATcre/DCCfl/fl animals. In contrast to young adults, aged mice also exhibited a gene dosage effect, with fewer SNc mDA neurons in DCC heterozygotes (DATcre/DCCfl/wt). Notably, loss of mDA neurons in the SN was not uniform. Neuronal loss in the SN was limited to ventral tier mDA neurons, while mDA neurons in the dorsal tier of the SN, which resist degeneration in PD, were spared from the effect of DCC deletion in both young and aged mice. In the ventral tegmental area (VTA), young adult mice with conditional deletion of DCC had normal mDA neuronal numbers, while significant loss occurred in aged DATcre/DCCfl/fl and DATcre/DCCfl/wt mice compared to age‐matched wild‐type mice. Our results indicate that expression of DCC is required for the survival of subpopulations of mDA neurons and may be relevant to the degenerative processes in PD. [ABSTRACT FROM AUTHOR]

The olfactory tubercle (OT), an important component of the ventral striatum and limbic system, is involved in multi‐sensory integration of reward‐related information in the brain. However, its functional roles are often overshadowed by the neighboring nucleus accumbens. Increasing evidence has highlighted that dense dopamine (DA) innervation of the OT from the ventral tegmental area (VTA) is implicated in encoding reward, natural reinforcers, and motivated behaviors. Recent studies have further suggested that OT subregions may have distinct roles in these processes due to their heterogeneous DA transmission. Currently, very little is known about regulation (release and clearance) of extracellular DA across OT subregions due to its limited anatomical accessibility and proximity to other DA‐rich brain regions, making it difficult to isolate VTA–DA signaling in the OT with conventional methods. Herein, we characterized heterogeneous VTA–DA regulation in the medial (m) and lateral (l) OT in "wild‐type," urethane‐anesthetized rats by integrating in vivo fast‐scan cyclic voltammetry with cell‐type specific optogenetics to stimulate VTA–DA neurons. Channelrhodopsin‐2 was selectively expressed in the VTA–DA neurons of wild‐type rats and optical stimulating parameters were optimized to determine VTA–DA transmission across the OT. Our anatomical, neurochemical, and pharmacological results show that VTA–DA regulation in the mOT is less dependent on DA transporters and has greater DA transmission than the lOT. These findings establish the OT as a unique, compartmentalized structure and will aid in future behavioral characterization of the roles of VTA–DA signaling in the OT subregions in reward, drug addiction, and encoding behavioral outputs necessary for survival. [ABSTRACT FROM AUTHOR]

Striatal dopamine release is key for learning and motivation and is composed of subregions including the dorsal striatum (DS), nucleus accumbens core, and the nucleus accumbens shell. Spontaneously occurring dopamine release was compared across these subregions. Dopamine release/uptake dynamics differ across striatal subregions, with dopamine transient release amplitude and release frequency greatest in male mice, and the largest signals observed in the DS. Surprisingly, female mice exhibited little regional differences in dopamine release for DS and nucleus accumbens core regions, but lower release in the nucleus accumbens shell. Blocking voltage‐gated K+ channel (Kv channels) with 4‐aminopyridine enhanced dopamine detection without affecting reuptake. The 4‐aminopyridine effects were greatest in ventral regions of female mice, suggesting regional differences in Kv channel expression. The dopamine transporter blocker cocaine also enhanced detection across subregions in both sexes, with greater overall increased release in females than males. Thus, sex differences in dopamine transmission are apparent and likely include differences in the Kv channel and dopamine transporter function. The lack of regional differences in dopamine release observed in females indicates differential regulation of spontaneous and evoked dopamine release. [ABSTRACT FROM AUTHOR]

Environmental reward-predictive stimuli provide a major source of motivation for instrumental reward-seeking activity and this has been linked to dopamine signaling in the nucleus accumbens (NAc) core. This cue-induced incentive motivation can be quite general, not restricted to instrumental actions that earn the same unique reward, and is also typically regulated by one's current need state, such that cues only motivate actions when this is adaptive. But it remains unknown whether cue-evoked dopamine signaling is similarly regulated by need state. Here, we used fast-scan cyclic voltammetry to monitor dopamine concentration changes in the NAc core of rats during a Pavlovian-to-instrumental transfer task in which the motivating influence of two cues, each signaling a distinct food reward (sucrose or food pellets), over an action earning a third unique food reward (polycose) was assessed in a state of hunger and of satiety. Both cues elicited a robust NAc dopamine response when hungry. The magnitude of the sucrose cue-evoked dopamine response correlated with the Pavlovian-to-instrumental transfer effect that was selectively induced by this stimulus. Satiety attenuated these cue-evoked dopamine responses and behavioral responding, even though rats had never experienced the specific food rewards in this state. These data demonstrate that cue-evoked NAc core responses are sensitive to current need state, one critical variable that determines the current adaptive utility of cue-motivated behavior. Food-predictive stimuli motivate food-seeking behavior. Here, we show that food cues evoke a robust nucleus accumbens core dopamine response when hungry that correlates with the cue's ability to invigorate general food seeking. This response is attenuated when sated, demonstrating that food cue-evoked accumbens dopamine responses are sensitive to the need state information that determines the current adaptive utility of cue-motivated action.

Methcathinone (MCAT) is a psychostimulant of abuse that can cause both persistent striatal dopaminergic and serotonergic, as well as hippocampal serotonergic, deficits. Evidence suggests that the rapid effects of stimulants that are structurally and mechanistically similar to MCAT on monoamine transporter function may contribute to the abuse liability and/or persistent monoaminergic deficits caused by these agents. Thus, effects of MCAT on 1) striatal dopamine (DA) transporter (DAT); and 2) striatal and hippocampal serotonin transporter (SERT) function, as determined in tissues from adult male rats, were assessed. As reported previously, a single administration of MCAT rapidly (within 1 hr) decreases striatal [3H]DA uptake. Similarly, incubation of rat synaptosomes with MCAT at 37℃ (but not 4˚C) decreased striatal [3H]DA uptake. Incubation with MCAT likewise decreased [3H]5HT but not vesicular [3H]DA uptake. MCAT incubation in vitro was without effect on [3H]DA uptake in striatal synaptosomes prepared from MCAT‐treated rats. The decrease in [3H]DA uptake caused by MCAT incubation: (a) reflected a decrease in Vmax, with minimal change in Km, and (b) was attenuated by co‐incubation with the cell‐permeable calcium chelator, N,N'‐[1,2‐ethanediylbis(oxy‐2,1‐phenylene)]bis[N‐[2‐[(acetyloxy)methoxy]‐2‐oxoethyl]‐1,1'‐bis[(acetyloxy)methyl] ester‐glycine (BAPTA‐AM), as well as the non‐selective protein kinase‐C (PKC) inhibitors bisindolylmaleimide‐1 (BIM‐1) and 2‐[1‐3(Aminopropyl)indol‐3‐yl]‐3(1‐methyl‐1H‐indol‐3‐yl)maleimide (or Bisindolylmaleimide VIII; Ro‐31‐7549). Taken together, these results suggest that in vitro MCAT incubation may model important aspects of MCAT administration in vivo, and that calcium and PKC contribute to the in vitro effects of MCAT on DAT. [ABSTRACT FROM AUTHOR]

Neuropeptide cocaine‐ and amphetamine‐regulated transcript (CART) is known to influence the activity of the canonical mesolimbic dopaminergic pathway and modulate reward seeking behaviour. CART neurons of the lateral hypothalamus (LH) send afferents to the ventral tegmental area (VTA) and paraventricular thalamic nucleus (PVT) and these nuclei, in turn, send secondary projections to nucleus accumbens. We try to dissect the precise sites of CART's action in these circuits in promoting reward. Rats were implanted with bipolar electrode targeted at the lateral hypothalamus‐medial forebrain bundle (LH‐MFB) and trained to press the lever through intracranial self‐stimulation (ICSS) protocol. CART (55–102) administered directly into posterior VTA (pVTA) or PVT of the conditioned rats significantly increased the number of lever presses, indicating reward‐promoting activity of the peptide. Concomitant increase in dopamine (DA) and 3, 4‐dihydroxyphenylacetic acid (DOPAC) efflux was noted in the microdialysate collected from the nucleus accumbens shell (AcbSh). On the other hand, immunoneutralization of endogenous CART with CART antibodies injected directly in the pVTA or PVT reduced the lever press activity as well as DA and DOPAC efflux in the AcbSh. Injection of CART (1–39) in pVTA or PVT was ineffective. We suggest that CART cells in the LH‐MFB area send afferents to (a) pVTA and influence dopaminergic neurons projecting to AcbSh and (b) PVT, from where the secondary neurons may feed into the AcbSh. Excitation of the CARTergic pathway to the pVTA as well as the PVT seems to promote DA release in the AcbSh and contribute to the generation of reward. [ABSTRACT FROM AUTHOR]

Methamphetamine (METH) is a potent psychostimulant that exerts many of its physiological and psychomotor effects by increasing extracellular dopamine (DA) concentrations in limbic brain regions. While several studies have focused on how potent, neurotoxic doses of METH augment or attenuate DA transmission, the acute effects of lower and behaviorally activating doses of METH on modulating DA regulation (release and clearance) through DA D2 autoreceptors and transporters remain to be elucidated. In this study, we investigated how systemic administration of escalating, subneurotoxic doses of METH (0.5–5 mg/kg, IP) alter extracellular DA regulation in the nucleus accumbens (NAc), in both anesthetized and awake‐behaving rats through the use of in vivo fast‐scan cyclic voltammetry. Pharmacological, electrochemical, and behavioral evidence show that lower doses (≤2.0 mg/kg, IP) of METH enhance extracellular phasic DA concentrations and locomotion as well as stereotypies. In contrast, higher doses (≥5.0 mg/kg) further increase both phasic and baseline DA concentrations and stereotypies but decrease horizontal locomotion. Importantly, our results suggest that acute METH‐induced enhancement of extracellular DA concentrations dose dependently activates D2 autoreceptors. Therefore, these different METH dose‐dependent effects on mesolimbic DA transmission may distinctly impact METH‐induced behavioral changes. This study provides valuable insights regarding how low METH doses alter DA transmission and paves the way for future clinical studies on the reinforcing effects of METH. [ABSTRACT FROM AUTHOR]

In Parkinson's disease, dopamine‐containing nigrostriatal neurons undergo profound degeneration. Tyrosine hydroxylase (TH) is the rate‐limiting enzyme in dopamine biosynthesis. TH increases in vitro formation of reactive oxygen species, and previous animal studies have reported links between cytosolic dopamine build‐up and oxidative stress. To examine effects of increased TH activity in catecholaminergic neurons in vivo, we generated TH‐over‐expressing mice (TH‐HI) using a BAC‐transgenic approach that results in over‐expression of TH with endogenous patterns of expression. The transgenic mice were characterized by western blot, qPCR, and immunohistochemistry. Tissue contents of dopamine, its metabolites, and markers of oxidative stress were evaluated. TH‐HI mice had a 3‐fold increase in total and phosphorylated TH levels and an increased rate of dopamine synthesis. Coincident with elevated dopamine turnover, TH‐HI mice showed increased striatal production of H2O2 and reduced glutathione levels. In addition, TH‐HI mice had elevated striatal levels of the neurotoxic dopamine metabolites 3,4‐dihydroxyphenylacetaldehyde and 5‐S‐cysteinyl‐dopamine and were more susceptible than wild‐type mice to the effects of amphetamine and methamphetamine. These results demonstrate that increased TH alone is sufficient to produce oxidative stress in vivo, build up autotoxic dopamine metabolites, and augment toxicity. [ABSTRACT FROM AUTHOR]

The actions of dopamine are essential to relapse to drug seeking but we still lack a precise understanding of how dopamine achieves these effects. Here we review recent advances from animal models in understanding how dopamine controls relapse to drug seeking. These advances have been enabled by important developments in understanding the basic neurochemical, molecular, anatomical, physiological and functional properties of the major dopamine pathways in the mammalian brain. The literature shows that although different forms of relapse to seeking different drugs of abuse each depend on dopamine, there are distinct dopamine mechanisms for relapse. Different circuit‐level mechanisms, different populations of dopamine neurons and different activity profiles within these dopamine neurons, are important for driving different forms of relapse. This diversity highlights the need to better understand when, where and how dopamine contributes to relapse behaviours. [ABSTRACT FROM AUTHOR]

The addiction‐relevant molecular, cellular, and behavioral actions of nicotine are derived from its stimulatory effects on neuronal nicotinic acetylcholine receptors (nAChRs) in the central nervous system. nAChRs expressed by dopamine‐containing neurons in the ventral midbrain, most notably in the ventral tegmental area (VTA), contribute to the reward‐enhancing properties of nicotine that motivate the use of tobacco products. nAChRs are also expressed by neurons in brain circuits that regulate aversion. In particular, nAChRs expressed by neurons in the medial habenula (mHb) and the interpeduncular nucleus (IPn) to which the mHb almost exclusively projects regulate the "set‐point" for nicotine aversion and control nicotine intake. Different nAChR subtypes are expressed in brain reward and aversion circuits and nicotine intake is titrated to maximally engage reward‐enhancing nAChRs while minimizing the recruitment of aversion‐promoting nAChRs. With repeated exposure to nicotine, reward‐ and aversion‐related nAChRs and the brain circuits in which they are expressed undergo adaptations that influence whether tobacco use will transition from occasional to habitual. Genetic variation that influences the sensitivity of addiction‐relevant brain circuits to the actions of nicotine also influence the propensity to develop habitual tobacco use. Here, we review some of the key advances in our understanding of the mechanisms by which nicotine acts on brain reward and aversion circuits and the adaptations that occur in these circuits that may drive addiction to nicotine‐containing tobacco products. [ABSTRACT FROM AUTHOR]

Drug compulsion manifests in some but not all individuals and implicates multifaceted processes including failures in top‐down cognitive control as drivers for the hazardous pursuit of drug use in some individuals. As a closely related construct, impulsivity encompasses rash or risky behaviour without foresight and underlies most forms of drug taking behaviour, including drug use during adverse emotional states (i.e., negative urgency). While impulsive behavioural dimensions emerge from drug‐induced brain plasticity, burgeoning evidence suggests that impulsivity also predates the emergence of compulsive drug use. Although the neural substrates underlying the apparently causal relationship between trait impulsivity and drug compulsion are poorly understood, significant advances have come from the interrogation of defined limbic cortico‐striatal circuits involved in motivated behaviour and response inhibition, together with chemical neuromodulatory influences from the ascending neurotransmitter systems. We review what is presently known about the neurochemical mediation of impulsivity, in its various forms, and ask whether commonalities exist in the neurochemistry of compulsive drug‐motivated behaviours that might explain individual risk for addiction. [ABSTRACT FROM AUTHOR]

Methylenedioxymethamphetamine (MDMA) is an amphetamine analogue that preferentially stimulates the release of serotonin (5HT) and results in relatively small increases in synaptic dopamine (DA). The ratio of drug‐stimulated increases in synaptic DA, relative to 5HT, predicts the abuse liability; drugs with higher DA:5HT ratios are more likely to be abused. Nonetheless, MDMA is a drug that is misused. Clinical and preclinical studies have suggested that repeated MDMA exposure produces neuroadaptive responses in both 5HT and DA neurotransmission that might explain the development and maintenance of MDMA self‐administration in some laboratory animals and the development of a substance use disorder in some humans. In this paper, we describe the research that has demonstrated an inhibitory effect of 5HT on the acquisition of MDMA self‐administration and the critical role of DA in the maintenance of MDMA self‐administration in laboratory animals. We then describe the circuitry and 5HT receptors that are positioned to modulate DA activity and review the limited research on the effects of MDMA exposure on these receptor mechanisms. [ABSTRACT FROM AUTHOR]

Alcohol addiction is a chronic relapsing brain disease characterized by an impaired ability to stop or control alcohol use despite adverse consequences. A main challenge of addiction treatment is to prevent relapse, which occurs in more than >50% of newly abstinent patients with alcohol disorder within 3 months. In people suffering from alcohol addiction, stressful events, drug‐associated cues and contexts, or re‐exposure to a small amount of alcohol trigger a chain of behaviors that frequently culminates in relapse. In this review, we first present the preclinical models that were developed for the study of alcohol seeking behavior, namely the reinstatement model of alcohol relapse and compulsive alcohol seeking under a chained schedule of reinforcement. We then provide an overview of the neurobiological findings obtained using these animal models, focusing on the role of opioids systems, corticotropin‐release hormone and neurokinins, followed by dopaminergic, glutamatergic, and GABAergic neurotransmissions in alcohol seeking behavior. [ABSTRACT FROM AUTHOR]

Human TPH2 (hTPH2) catalyzes the rate-limiting step in CNS serotonin biosynthesis. We characterized a single-nucleotide polymorphism (C2755A) in the hTPH2 gene that substitutes tyrosine for serine at position 41 in the regulatory domain of the enzyme. This polymorphism is associated with bipolar disorder and peripartum depression in a Chinese population. Recombinant h TPH2 human proteins were expressed in bacteria and also stably expressed in PC12 cells. Following bacterial expression and purification, the tyrosine for serine substitution at position 41 (S41Y) polymorphic enzyme displayed increased Vmax with unchanged Km values. By contrast, enzyme stability was decreased in vitro from 32 min to 4 min (37°C) for the S41Y enzyme (as compared to the wild-type enzyme). The S41Y polymorphism decreased cyclic AMP-dependent protein kinase A-mediated phosphorylation ~ 50% relative to wild-type hTPH2, suggesting that the S41Y mutation may disrupt the post-translational regulation of this enzyme. Transfected PC12 cells expressed hTPH2 mRNA, active protein, and synthesized and released serotonin. Paradoxically, while S41Y-transfected PC12 cells expressed higher levels of hTPH2 than wild type, they synthesized less serotonin. These findings suggest a modified regulation of the S41Y gene variant leading to altered regulation and reduced neurotransmitter synthesis that may contribute to association of the polymorphism with bipolar disorder and depression. © 2014 International Society for Neurochemistry.

Transporters of the solute carrier 6 (SLC6) family mediate the reuptake of neurotransmitters such as dopamine, norepinephrine, serotonin, GABA, and glycine. SLC6 family members are 12 transmembrane helix‐spanning proteins that operate using the transmembrane sodium gradient for transport. These transporters assume various quaternary arrangements ranging from monomers to complex stoichiometries with multiple subunits. Dopamine and serotonin transporter oligomerization has been implicated in trafficking of newly formed proteins from the endoplasmic reticulum to the plasma membrane with a pre‐fixed assembly. Once at the plasma membrane, oligomers are kept fixed in their quaternary assembly by interaction with phosphoinositides. While it remains unclear how oligomer formation precisely affects physiological transporter function, it has been shown that oligomerization supports the activity of release‐type psychostimulants. Most recently, single molecule microscopy experiments unveiled that the stoichiometry differs between individual members of the SLC6 family. The present overview summarizes our understanding of the influence of plasma membrane constituents on transporter oligomerization, describes the known interfaces between protomers and discusses open questions. [ABSTRACT FROM AUTHOR]

Apoptotic endoplasmic reticulum (ER) stress is a major mechanism for dopaminergic (DA) loss in Parkinson's disease (PD). We assessed if low doses of the partial α4β2 nicotinic acetylcholine receptor agonist, cytisine attenuates apoptotic ER stress and exerts neuroprotection in substantia nigra pars compacta (SNc) DA neurons. Alternate day intraperitoneal injections of 0.2 mg/kg cytisine were administered to female and male mice with 6‐hydroxydopamine (6‐OHDA) lesions in the dorsolateral striatum, which caused unilateral degeneration of SNc DA neurons. Cytisine attenuated 6‐OHDA‐induced PD‐related behaviors in female, but not in male mice. We also found significant reductions in tyrosine hydroxylase (TH) loss within the lesioned SNc of female, but not male mice. In contrast to female mice, DA neurons within the lesioned SNc of male mice showed a cytisine‐induced pathological increase in the nuclear translocation of the pro‐apoptotic ER stress protein, C/EBP homologous protein (CHOP). To assess the role of estrogen in cytisine neuroprotection in female mice, we exposed primary mouse DA cultures to either 10 nM 17‐β‐estradiol and 200 nM cytisine or 10 nM 17‐β‐estradiol alone. 17‐β‐estradiol reduced expression of CHOP, whereas cytisine exposure reduced 6‐OHDA‐mediated nuclear translocation of two other ER stress proteins, activating transcription factor 6 and x‐box‐binding protein 1, but not CHOP. Taken together, these data show that cytisine and 17‐β‐estradiol work in combination to inhibit all three arms (activating transcription factor 6, x‐box‐binding protein 1, and CHOP) of apoptotic ER stress signaling in DA neurons, which can explain the neuroprotective effect of low‐dose cytisine in female mice. [ABSTRACT FROM AUTHOR]

Dopamine (DA) has important roles in learning, memory, and motivational processes and is highly susceptible to oxidation. In addition to dementia, Alzheimer's disease (AD) patients frequently exhibit decreased motivation, anhedonia, and sleep disorders, suggesting deficits in dopaminergic neurotransmission. Vitamin C (ascorbate, ASC) is a critical antioxidant in the brain and is often depleted in AD patients as a result of disease‐related oxidative stress and dietary deficiencies. To probe the effects of ASC deficiency and AD pathology on the DAergic system, gulo–/– mice, which like humans depend on dietary ASC to maintain adequate tissue levels, were crossed with APP/PSEN1 mice and provided sufficient or depleted ASC supplementation from weaning until 12 months of age. Ex vivo fast‐scan cyclic voltammetry showed that chronic ASC depletion and APP/PSEN1 genotype both independently decreased dopamine release in the nucleus accumbens, a hub for motivational behavior and reward, while DA clearance was similar across all groups. In striatal tissue containing nucleus accumbens, low ASC treatment led to decreased levels of DA and its metabolites 3,4‐dihydroxyohenyl‐acetic acid (DOPAC), 3‐methoxytyramine (3‐MT), and homovanillic acid (HVA). Decreased enzyme activity observed through lower pTH/TH ratio was driven by a cumulative effect of ASC depletion and APP/PSEN1 genotype. Together the data show that deficits in dopaminergic neurotransmission resulting from age and disease status are magnified in conditions of low ASC which decrease DA availability during synaptic transmission. Such deficits may contribute to the non‐cognitive behavioral changes observed in AD including decreased motivation, anhedonia, and sleep disorders. [ABSTRACT FROM AUTHOR]

Successful completion of daily activities relies on the ability to select the relevant features of the environment for memory and recall. Disruption to these processes can lead to various disorders, such as attention‐deficit hyperactivity disorder (ADHD). Dopamine is a neurotransmitter implicated in the regulation of several processes, including attention. In addition to the higher‐order brain function, dopamine is implicated in the regulation of adult neurogenesis. Previously, we generated mice lacking Shati, an N‐acetyltransferase‐8‐like protein on a C57BL/6J genetic background (Shati/Nat8l−/−). These mice showed a series of changes in the dopamine system and ADHD‐like behavioral phenotypes. Therefore, we hypothesized that deficiency of Shati/Nat8l would affect neurogenesis and attentional behavior in mice. We found aberrant morphology of neurons and impaired neurogenesis in the dentate gyrus of Shati/Nat8l−/− mice. Additionally, research has suggested that impaired neurogenesis might be because of the reduction of dopamine in the hippocampus. Galantamine (GAL) attenuated the attentional impairment observed in the object‐based attention test via increasing the dopamine release in the hippocampus of Shati/Nat8l−/− mice. The α7 nicotinic acetylcholine receptor antagonist, methyllycaconitine, and dopamine D1 receptor antagonist, SCH23390, blocked the ameliorating effect of GAL on attentional impairment in Shati/Nat8l−/− mice. These results suggest that the ameliorating effect of GAL on Shati/Nat8l−/− attentional impairment is associated with activation of D1 receptors following increased dopamine release in the hippocampus via α7 nicotinic acetylcholine receptor. In summary, Shati/Nat8l is important in both morphogenesis and neurogenesis in the dentate gyrus and attention, possible via modulation of dopaminergic transmission. Cover Image for this issue: https://doi.org/10.1111/jnc.15061. [ABSTRACT FROM AUTHOR]

A contribution of α‐Synuclein (α‐Syn) to etiology of Parkinson´s disease (PD) and Dementia with Lewy bodies (DLB) is currently undisputed, while the impact of the closely related β‐Synuclein (β‐Syn) on these disorders remains enigmatic. β‐Syn has long been considered to be an attenuator of the neurotoxic effects of α‐Syn, but in a rodent model of PD β‐Syn induced robust neurodegeneration in dopaminergic neurons of the substantia nigra. Given that dopaminergic nigral neurons are selectively vulnerable to neurodegeneration in PD, we now investigated if dopamine can promote the neurodegenerative potential of β‐Syn. We show that in cultured rodent and human neurons a dopaminergic neurotransmitter phenotype substantially enhanced β‐Syn‐induced neurodegeneration, irrespective if dopamine is synthesized within neurons or up‐taken from extracellular space. Nuclear magnetic resonance interaction and thioflavin‐T incorporation studies demonstrated that dopamine and its oxidized metabolites 3,4‐dihydroxyphenylacetaldehyde (DOPAL) and dopaminochrome (DCH) directly interact with β‐Syn, thereby enabling structural and functional modifications. Interaction of DCH with β‐Syn inhibits its aggregation, which might result in increased levels of neurotoxic oligomeric β‐Syn. Since protection of outer mitochondrial membrane integrity prevented the additive neurodegenerative effect of dopamine and β‐Syn, such oligomers might act at a mitochondrial level similar to what is suggested for α‐Syn. In conclusion, our results suggest that β‐Syn can play a significant pathophysiological role in etiology of PD through its interaction with dopamine metabolites and thus should be re‐considered as a disease‐relevant factor, at least for those symptoms of PD that depend on degeneration of nigral dopaminergic neurons. [ABSTRACT FROM AUTHOR]

This study examined whether insulin modulates the neurochemical effects of nicotine in the mesolimbic pathway of diabetic rats. The rats received vehicle or streptozotocin (STZ) to induce hypoinsulinemia. A subset of STZ‐treated rats was implanted with insulin pellets that rapidly normalized glucose levels. Two‐weeks later, dialysis probes were implanted into the nucleus accumbens (NAc) and ipsilateral ventral tegmental area (VTA). The next day, dialysate samples were collected during baseline and then following systemic administration of nicotine. Samples were also collected following intra‐VTA administration of the gamma‐aminobutyric acid (GABA)A receptor antagonist, bicuculline. Dopamine, GABA, glutamate, and acetylcholine (ACh) levels were assessed using liquid chromatography/mass spectrometry (LC/MS). The results revealed that vehicle‐treated rats displayed a nicotine‐induced increase in NAc dopamine levels. In contrast, STZ‐treated rats did not display any changes in NAc dopamine following nicotine administration, an effect that was likely related to a concomitant increase in GABA and decrease in glutamate levels in both the NAc and VTA. Intra‐VTA administration of bicuculline increased NAc dopamine in vehicle‐treated rats, and this effect was absent in STZ‐treated rats. Vehicle‐treated rats displayed a nicotine‐induced increase in ACh levels in the NAc (but not VTA), an effect that was lower in the NAc of STZ‐treated rats. Insulin supplementation normalized the neurochemical effects of nicotine in the NAc and VTA of STZ‐treated rats, suggesting that insulin modulates the neurochemical effects of nicotine in the mesolimbic pathway of diabetic rats. [ABSTRACT FROM AUTHOR]

Regulation of axonal dopamine release by local microcircuitry is at the hub of several biological processes that govern the timing and magnitude of signaling events in reward‐related brain regions. An important characteristic of dopamine release from axon terminals in the striatum is that it is rapidly modulated by local regulatory mechanisms. These processes can occur via homosynaptic mechanisms—such as presynaptic dopamine autoreceptors and dopamine transporters ‐ as well heterosynaptic mechanisms such as retrograde signaling from postsynaptic cholinergic and dynorphin systems, among others. Additionally, modulation of dopamine release via diffusible messengers, such as nitric oxide and hydrogen peroxide, allows for various metabolic factors to quickly and efficiently regulate dopamine release and subsequent signaling. Here we review how these mechanisms work in concert to influence the timing and magnitude of striatal dopamine signaling, independent of action potential activity at the level of dopaminergic cell bodies in the midbrain, thereby providing a parallel pathway by which dopamine can be modulated. Understanding the complexities of local regulation of dopamine signaling is required for building comprehensive frameworks of how activity throughout the dopamine system is integrated to drive signaling and control behavior. [ABSTRACT FROM AUTHOR]

The ghrelin system was previously proposed to mediate an independent branch of the stress response that curbs fear processing. Interestingly, the ghrelin system was also shown to control the activity of midbrain dopamine neurons. Given that dopamine neurons of the ventral tegmental area appear to have a critical role in fear processing, we aimed to investigate their contribution to the effects of ghrelin on fear processing. Our data show that systemic administration of the ghrelin receptor agonist MK0677, in a dose that induces food intake, has no significant effect on auditory fear processing and does not significantly affect dopamine release in the nucleus accumbens of male C57BL/6J mice. Local administration of the ghrelin receptor agonist MK0677 into the ventral tegmental area significantly increases food intake and it also significantly increased dopamine release in the nucleus accumbens, the medial prefrontal cortex and the amygdala. Nevertheless, it did not significantly affect auditory fear extinction. Our data indicate that pharmacological activation of midbrain dopamine neurons using a ghrelin receptor agonist does not affect auditory fear extinction. We also investigated the effect of non‐pharmacological manipulation of the ghrelin system on auditory fear processing. However, we found that neither overnight food deprivation nor genetic ablation of the ghrelin receptor had a significant effect on auditory fear extinction. We conclude that the effects of manipulation of the ghrelin system on fear processing are subject to boundary conditions that remain poorly understood. [ABSTRACT FROM AUTHOR]

Psychostimulants are widely abused drugs that may cause addiction in vulnerable individuals. While the reward circuitry of the brain is involved in addiction establishment, various pathways in the brain may provide protection at the molecular level that limits the acute and chronic effects of drugs. These targets may be used for strategies designed to prevent and treat addiction. Swiprosin‐1/EF hand domain 2 (EFhd2) is a Ca2+‐binding cytoskeletal adaptor protein involved in sensation‐seeking behaviour, anxiety and alcohol addiction. Here, we tested how EFhd2 contributes to the physiological and behavioural effects of the psychostimulant drugs methamphetamine (METH) and cocaine. An in vivo microdialysis study in EFhd2 knockout mice revealed that EFhd2 controls METH‐ and cocaine‐induced changes in extracellular dopamine, serotonin and noradrenaline levels through different mechanisms in the nucleus accumbens and prefrontal cortex. Electrophysiological recordings in a slice preparation showed that a lack of EFhd2 increases dopaminergic neuronal activity in the ventral tegmental area and increases the sensitivity of neurons to stimulation. We report a role of EFhd2 in METH‐induced locomotor activation and in the conditioned locomotor effects. No role, however, was observed in the establishment of METH‐ or cocaine‐induced conditioned place preference. These findings may suggest that EFhd2 modulates the activity of the dopaminergic system and the neurochemical effects of METH and cocaine, which translate into a modulation of the behavioural effects of these drugs at the level of the acute and conditioned locomotor activity. [ABSTRACT FROM AUTHOR]

Brain endocannabinoids serve as retrograde neurotransmitters, being synthesized in post‐synaptic neurons "on demand" and released to bind pre‐synaptic cannabinoid receptors and suppress glutamatergic or GABAergic transmission. The most abundant brain endocannabinoid, 2 arachidonoyl glycerol (2‐AG), is primarily synthesized by diacylglycerol lipase‐α (DGLα), which is activated by poorly understood mechanisms in response to calcium influx following post‐synaptic depolarization and/or the activation of Gq‐coupled group 1 metabotropic glutamate receptors. However, the impact of other neurotransmitters and their downstream signaling pathways on synaptic 2‐AG signaling has not been intensively studied. Here, we found that DGLα activity in membrane fractions from transfected HEK293T cells was significantly increased by in vitro phosphorylation using cyclic AMP‐dependent protein kinase (PKA). Moreover, PKA directly phosphorylated DGLα at Ser798 in vitro. Elevation of cAMP levels in HEK293 cells expressing DGLα increased Ser798 phosphorylation, as detected using a phospho‐Ser798‐specific antibody, and enhanced DGLα activity; this in situ enhancement of DGLα activity was prevented by mutation of Ser798 to Ala. We investigated the impact of PKA on synaptic 2‐AG mobilization in mouse striatal slices by manipulating D1‐dopamine receptor (D1R) signaling and assessing depolarization‐induced suppression of excitation, a DGLα‐ and 2‐AG‐dependent form of short‐term synaptic depression. The magnitude of depolarization‐enhanced suppression of excitation in direct pathway medium spiny neurons was increased by pre‐incubation with a D1R agonist, and this enhancement was blocked by post‐synaptic inhibition of PKA. Taken together, these findings provide new molecular insights into the complex mechanisms regulating synaptic endocannabinoid signaling. [ABSTRACT FROM AUTHOR]

The caudate nucleus (CN) and the putamen (PUT) as parts of the human striatum are distinguished by a marked heterogeneity in functional, anatomical, and neurochemical patterns. Our study aimed to document in detail the regional diversity in the distribution of dopamine (DA), serotonin, γ‐aminobuturic acid, and choline acetyltransferase within the CN and PUT. For this purpose we dissected the CN as well as the PUT of 12 post‐mortem brains of human subjects with no evidence of neurological and psychiatric disorders (38–81 years old) into about 80 tissue parts. We then investigated rostro‐caudal, dorso‐ventral, and medio‐lateral gradients of these neurotransmitter markers. All parameters revealed higher levels, turnover rates, or activities in the PUT than in the CN. Within the PUT, DA levels increased continuously from rostral to caudal. In contrast, the lowest molar ratio of homovanillic acid to DA, a marker of DA turnover, coincided with highest DA levels in the caudal PUT, the part of the striatum with the highest loss of DA in Parkinson's disease (N. Engl. J. Med., 318, 1988, 876). Highest DA concentrations were found in the most central areas both in the PUT and CN. We observed an age‐dependent loss of DA in the PUT and CN that did not correspond to the loss described for Parkinson's disease indicating different mechanisms inducing the deficit of DA. Our data demonstrate a marked heterogeneity in the anatomical distribution of neurotransmitter markers in the human dorsal striatum indicating anatomical and functional diversity within this brain structure. [ABSTRACT FROM AUTHOR]

Alcohol use disorder most commonly presents as a polydrug disorder where greater than 85% are estimated to smoke. EtOH and nicotine (NIC) co‐abuse or exposure results in unique neuroadaptations that are linked to behaviors that promote drug use. The current experiments aimed to identify neuroadaptations within the mesolimbic pathway produced by concurrent EtOH and NIC exposure. The experiments used four overall groups of male Wistar rats consisting of vehicle, EtOH or NIC alone, and EtOH+NIC. Drug exposure through direct infusion into the posterior ventral tegmental area (pVTA) stimulated release of glutamate and dopamine in the nucleus accumbens (NAc) shell, which was quantified through high‐performance liquid chromatography. Additionally, brain‐derived neurotrophic factor (BDNF) protein levels were measured via enzyme‐linked immunosorbent assay (ELISA). A second experiment investigated the effects of drug pretreatment within the pVTA on the reinforcing properties of EtOH within the NAc shell through intracranial self‐administration (ICSA). The concluding experiment evaluated the effect of NAc shell pretreatment with BDNF on EtOH reward utilizing ICSA within that region. The data indicated that only EtOH+NIC administration into the pVTA simultaneously increased glutamate, dopamine, and BDNF in the NAc shell. Moreover, only pVTA pretreatment with EtOH+NIC enhanced the reinforcing properties of EtOH in the NAc shell. BDNF pretreatment in the NAc shell was also sufficient to enhance the reinforcing properties of EtOH in the NAc shell. The collected data suggest that concurrent EtOH+NIC exposure results in a distinct neurochemical response and neuroadaptations within the mesolimbic pathway that alter EtOH reward. [ABSTRACT FROM AUTHOR]

The ventral striatum is a collection of brain structures, including the nucleus accumbens, ventral pallidum and the olfactory tubercle (OT). While much attention has been devoted to the nucleus accumbens, a comprehensive understanding of the ventral striatum and its contributions to neurological diseases requires an appreciation for the complex neurochemical makeup of the ventral striatum's other components. This review summarizes the rich neurochemical composition of the OT, including the neurotransmitters, neuromodulators and hormones present. We also address the receptors and transporters involved in each system as well as their putative functional roles. Finally, we end with briefly reviewing select literature regarding neurochemical changes in the OT in the context of neurological disorders, specifically neurodegenerative disorders. By overviewing the vast literature on the neurochemical composition of the OT, this review will serve to aid future research into the neurobiology of the ventral striatum. [ABSTRACT FROM AUTHOR]

Sex differences in behavioural patterns of drug abuse and dependence have been hypothesized to be a consequence of sexual dimorphisms in brain pathways, particularly within the dopaminergic reward circuitry. Yet, how potential sex differences are manifested at a neurochemical level remains unclear. Here, we use a meta‐analysis approach to investigate whether animal studies robustly indicate a different regulation of striatal dopamine transmission in males and females. Data from 39 microdialysis experiments on female rats (n = 676) were extracted and statistically compared with data from 1523 male rats. All drugs of abuse, independent of their molecular mechanisms of action, notably increase extracellular dopamine concentrations in the nucleus accumbens (NAc) and caudate putamen (CPu). No significant sex differences in basal levels or in dopaminergic response to drugs of abuse were found. However, basal dopamine levels in CPu (but not NAc) were significantly altered by ovariectomy. In conclusion, there are no sex‐dependent differences in basal dopamine levels within the NAc and CPu. Previously reported sex differences in the CPu seem to be a result of ovariectomy and may only to a lesser, non‐significant degree be attributed to a sexual duality. [ABSTRACT FROM AUTHOR]

The striatum with a number of dopamine containing neurons, receiving projections from the substantia nigra and ventral tegmental area; plays a critical role in neurodegenerative diseases of motor and memory function. Additionally, oxidative damage to nucleic acid may be vital in the development of age‐associated neurodegeneration. The metabolism of dopamine is recognized as one of the sources of reactive oxygen species through the Fenton mechanism. The proposed interactions of oxidative insults and dopamine in the striatum during the progression of diseases are the hypotheses of most interest to our study. This study investigated the possibility of significant interactions between these molecules that are involved in the late‐stage of Alzheimer's disease (AD), Parkinson disease (PD), Parkinson disease dementia, dementia with Lewy bodies, and controls using ELISA assays, autoradiography, and mRNA in situ hybridization assay. Interestingly, lower DNA/RNA oxidative adducts levels in the caudate and putamen of diseased brains were observed with the exception of an increased DNA oxidative product in the caudate of AD brains. Similar changes were found for dopamine concentration and vesicular monoamine transporter 2 densities. We also found that downstream pre‐synaptic dopamine D1 Receptor binding correlated with dopamine loss in Lewy body disease groups, and RNA damage and β‐site APP cleaving enzyme 1 in the caudate of AD. This is the first demonstration of region‐specific alterations of DNA/RNA oxidative damage which cannot be viewed in isolation, but rather in connection with the interrelationship between different neuronal events; chiefly DNA oxidative adducts and density of vesicular monoamine transporter 2 densities in AD and PD patients. [ABSTRACT FROM AUTHOR]