Search

Flaminia Coluzzi,1,2 Francesca Felicia Caputi,3 Domenico Billeci,4 Antonio Luigi Pastore,1,5 Sanzio Candeletti,3 Monica Rocco,2,6 Patrizia Romualdi3 1Department of Medical and Surgical Sciences and Biotechnologies, Sapienza University of Rome, Polo Pontino, Latina, Italy; 2Unit of Anesthesia, Intensive Care and Pain Medicine, Sant’Andrea University Hospital, Rome, Italy; 3Department of Pharmacy and Biotechnology, Alma Mater Studiorum University, Bologna, Italy; 4Division of Neurosurgery, Ca’Foncello Hospital, ASL Marca Trevigiana, University of Padova, Treviso, Italy; 5Unit of Urology, Sapienza c/o I.C.O.T, Polo Pontino, Latina, Italy; 6Department of Clinical and Surgical Translational Medicine, Sapienza University of Rome, Rome, ItalyCorrespondence: Flaminia ColuzziDepartment of Medical and Surgical Sciences and Biotechnologies, Sapienza University of Rome, Corso della Repubblica 79, Polo Pontino 04100, Latina, ItalyTel +39 06 33775673Email flaminia.coluzzi@uniroma1.itAbstract: In patients suffering from moderate-to-severe chronic kidney disease (CKD) or end-stage renal disease (ESRD), subjected to hemodialysis (HD), pain is very common, but often underestimated. Opioids are still the mainstay of severe chronic pain management; however, their prescription in CKD and HD patients is still significantly low and pain is often under-treated. Altered pharmacokinetics and the lack of clinical trials on the use of opioids in patients with renal impairment increase physicians’ concerns in this specific population. This narrative review focused on the correct and safe use of opioids in patients with CKD and HD. Morphine and codeine are not recommended, because the accumulation of their metabolites may cause neurotoxic symptoms. Oxycodone and hydromorphone can be safely used, but adequate dosage adjustments are required in CKD. In dialyzed patients, these opioids should be considered as second-line agents and patients should be carefully monitored. According to different studies, buprenorphine and fentanyl could be considered first-line opioids in the management of pain in CKD; however, fentanyl is not appropriate in patients undergoing HD. Tapentadol does not need dosage adjustment in mild-to-moderate renal impairment conditions; however, no data are available on its use in ESRD. Opioid-related side effects may be exacerbated by common comorbidities in CKD patients. Opioid-induced constipation can be managed with peripherally-acting-μ-opioid-receptor-antagonists (PAMORA). Unlike the other PAMORA, naldemedine does not require any dose adjustment in CKD and HD patients. Accurate pain diagnosis, opioid titration and tailoring are mandatory to minimize the risks and to improve the outcome of the analgesic therapy.Keywords: opioids, chronic kidney disease, pain, hemodialysis, neuropathic pain, PAMORA

Opioids are the most effective drugs used for the management of moderate to severe pain; however, their chronic use is often associated with numerous adverse effects. Some results indicate the involvement of oxidative stress as well as of proteasome function in the development of some opioid-related side effects including analgesic tolerance, opioid-induced hyperalgesia (OIH) and dependence. Based on the evidence, this study investigated the impact of morphine, buprenorphine or tapentadol on intracellular reactive oxygen species levels (ROS), superoxide dismutase activity/gene expression, as well as β2 and β5 subunit proteasome activity/biosynthesis in SH-SY5Y cells. Results showed that tested opioids differently altered ROS production and SOD activity/biosynthesis. Indeed, the increase in ROS production and the reduction in SOD function elicited by morphine were not shared by the other opioids. Moreover, tested drugs produced distinct changes in β2(trypsin-like) and β5(chymotrypsin-like) proteasome activity and biosynthesis. In fact, while prolonged morphine exposure significantly increased the proteolytic activity of both subunits and β5 mRNA levels, buprenorphine and tapentadol either reduced or did not alter these parameters. These results, showing different actions of the selected opioid drugs on the investigated parameters, suggest that a low µ receptor intrinsic efficacy could be related to a smaller oxidative stress and proteasome activation and could be useful to shed more light on the role of the investigated cellular processes in the occurrence of these opioid drug side effects.

Trazodone is an efficacious atypical antidepressant acting both as an SSRI and a 5HT2A and 5HT2C antagonist. Antagonism to H1-histaminergic and alpha1-adrenergic receptors is responsible for a sleep-promoting action. We studied long-term gene expression modulations induced by chronic trazodone to investigate the molecular underpinning of trazodone efficacy. Rats received acute or chronic treatment with trazodone or citalopram. mRNA expression of growth factor and circadian rhythm genes was evaluated by qPCR in the prefrontal cortex (PFCx), hippocampus, Nucleus Accumbens (NAc), amygdala, and hypothalamus. CREB levels and phosphorylation state were evaluated using Western blotting. BDNF levels were significantly increased in PFCx and hippocampus by trazodone and in the NAc and hypothalamus by citalopram. Likewise, TrkB receptor levels augmented in the PFCx after trazodone and in the amygdala after citalopram. FGF-2 and FGFR2 levels were higher after trazodone in the PFCx. The CREB phosphorylation state was increased by chronic trazodone in the PFCx, hippocampus, and hypothalamus. Bmal1 and Per1 were increased by both antidepressants after acute and chronic treatments, while Per2 levels were specifically augmented by chronic trazodone in the PFCx and NAc, and by citalopram in the PFCx, amygdala, and NAc. These findings show that trazodone affects the expression of neurotrophic factors involved in antidepressant responses and alters circadian rhythm genes implicated in the pathophysiology of depression, thus shedding light on trazodone's molecular mechanism of action.

Chemotherapy-induced neuropathy (CIN) is a major adverse effect associated with many chemotherapeutics, including bortezomib (BTZ). Several mechanisms are involved in CIN, and recently a role has been proposed for prokineticins (PKs), a chemokine family that induces proinflammatory/pro-algogen mediator release and drives the epigenetic control of genes involved in cellular differentiation. The present study evaluated the relationships between epigenetic mechanisms and PKs in a mice model of BTZ-induced painful neuropathy. To this end, spinal cord alterations of histone demethylase KDM6A, nuclear receptors PPARα/PPARγ, PK2, and pro-inflammatory cytokines IL-6 and IL-1β were assessed in neuropathic mice treated with the PK receptors (PKRs) antagonist PC1. BTZ treatment promoted a precocious upregulation of KDM6A, PPARs, and IL-6, and a delayed increase of PK2 and IL-1β. PC1 counteracted allodynia and prevented the increase of PK2 and of IL-1β in BTZ neuropathic mice. The blockade of PKRs signaling also opposed to KDM6A increase and induced an upregulation of PPAR gene transcription. These data showed the involvement of epigenetic modulatory enzymes in spinal tissue phenomena associated with BTZ painful neuropathy and underline a role of PKs in sustaining the increase of proinflammatory cytokines and in exerting an inhibitory control on the expression of PPARs through the regulation of KDM6A gene expression in the spinal cord.

Fabry disease (FD) is an X-linked inherited disorder characterized by glycosphingolipid accumulation due to deficiency of α-galactosidase A (α-Gal A) enzyme. Chronic pain and mood disorders frequently coexist in FD clinical setting, however underlying pathophysiologic mechanisms are still unclear. Here we investigated the mechanical and thermal sensitivity in α-Gal A (-/0) hemizygous male and the α-Gal A (-/-) homozygous female mice. We also characterized the gene expression of dynorphinergic, nociceptinergic and CRFergic systems, known to be involved in pain control and mood disorders, in the prefrontal cortex, amygdala and thalamus of α-Gal A (-/0) hemizygous male and the α-Gal A (-/-) homozygous female mice. Moreover, KOP receptor protein levels were evaluated in the same areas. Fabry knock-out male, but not female, mice displayed a decreased pain threshold in both mechanical and thermal tests compared to their wild type littermates. In the amygdala and prefrontal cortex, we observed a decrease of pDYN mRNA levels in males, whereas an increase was assessed in females, thus suggesting sex-related dysregulation of stress coping and pain mechanisms. Elevated mRNA levels for pDYN/KOP and CRF/CRFR1 systems were observed in male and female thalamus, a critical crossroad for both painful signals and cognitive/emotional processes. KOP receptor protein level changes assessed in the investigated areas, appeared mostly in agreement with KOP gene expression alterations. Our data suggest that α-Gal A enzyme deficiency in male and female mice is associated with distinct neuropeptide gene and protein expression dysregulations of investigated systems, possibly related to the neuroplasticity underlying the neurological features of FD., (Copyright © 2021 Elsevier Inc. All rights reserved.)

This study aimed to investigate DNA methylation levels in patients undergoing major breast surgery under opioid-based general anesthesia. Blood samples were collected from eleven enrolled patients, before, during and after anesthesia. PBMC were isolated and global DNA methylation levels as well as DNA methyltransferase (DNMT) and cytokine gene expression were assessed. DNA methylation levels significantly declined by 26%, reversing the direction after the end of surgery. Likewise, DNMT1a mRNA expression was significantly reduced at all time points, with lowest level of -68%. DNMT3a and DNMT3b decreased by 65 and 71%, respectively. Inflammatory cytokines IL6 and TNFα mRNA levels showed a trend for increased expression at early time-points to end with a significant decrease at 48 h after surgery. This exploratory study revealed for the first time intraoperative global DNA hypomethylation in patients undergoing major breast surgery under general anesthesia with fentanyl. The alterations of global DNA methylation here observed seem to be in agreement with DNMTs gene expression changes. Furthermore, based on perioperative variations of IL6 and TNFα gene expression, we hypothesize that DNA hypomethylation may occur as a response to surgical stress rather than to opiate exposure ., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Caputi, Carboni, Rullo, Alessandrini, Balzani, Melotti, Romualdi, Candeletti and Fanelli.)

3,4-Methylenedioxymethamphetamine (MDMA, "ecstasy") is an amphetamine-related drug that may damage the dopaminergic nigrostriatal system. To investigate the mechanisms that sustain this toxic effect and ascertain their sex-dependence, we evaluated in the nigrostriatal system of MDMA-treated (4 × 20 mg/kg, 2 h apart) male and female mice the activity of superoxide dismutase (SOD), the gene expression of SOD type 1 and 2, together with SOD1/2 co-localization with tyrosine hydroxylase (TH)-positive neurons. In the same mice and brain areas, activity of glutathione peroxidase (GPx) and of β2/β5 subunits of the ubiquitin-proteasome system (UPS) were also evaluated. After MDMA, SOD1 increased in striatal TH-positive terminals, but not nigral neurons, of males and females, while SOD2 increased in striatal TH-positive terminals and nigral neurons of males only. Moreover, after MDMA, SOD1 gene expression increased in the midbrain of males and females, whereas SOD2 increased only in males. Finally, MDMA increased the SOD activity in the midbrain of females, without affecting GPx activity, decreased the β2/β5 activities in the striatum of males and the β2 activity in the midbrain of females. These results suggest that the mechanisms of MDMA-induced neurotoxic effects are sex-dependent and dopaminergic neurons of males could be more sensitive to SOD2- and UPS-mediated toxic effects., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Costa, Caputi, Serra, Simola, Rullo, Stamatakos, Sanna, Germain, Martinoli, Candeletti, Morelli and Romualdi.)

Previous studies have shown that genetically selected Marchigian Sardinian alcohol-preferring (msP) rats consume excessive amounts of ethanol to self-medicate from negative moods and to relieve innate hypersensitivity to stress. This phenotype resembling a subset of alcohol use disorder (AUD) patients, appears to be linked to a dysregulation of the equilibrium between stress and antistress mechanisms in the extended amygdala. Here, comparing water and alcohol exposed msP and Wistar rats we evaluate the transcript expression of the anti-stress opioid-like peptide nociceptin/orphanin FQ (N/OFQ) and its receptor NOP as well as of dynorphin (DYN) and its cognate κ-opioid receptor (KOP). In addition, we measured the transcript levels of corticotropin-releasing factor (CRF), CRF receptor 1 (CRF1R), brain-derived neurotrophic factor (BDNF) and of the tropomyosin receptor kinase B receptor (Trk-B). Results showed an innately up-regulation of the CRFergic system, mediating negative mood and stress responses, as well as an inherent up-regulation of the anti-stress N/OFQ system, both in the amygdala (AMY) and bed nucleus of the stria terminalis (BNST) of msP rats. The up-regulation of this latter system may reflect an attempt to buffer the negative condition elicited by the hyperactivity of pro-stress mechanisms since results showed that voluntary alcohol consumption dampened N/OFQ. Alcohol exposure also reduced the expression of dynorphin and CRF transmissions in the AMY of msP rats. In the BNST, alcohol intake led to a more complex reorganization of these systems increasing receptor transcripts in msP rats, along with an increase of CRF and a decrease of N/OFQ transcripts, respectively. Moreover, mimicking the effects of alcohol in the AMY we observed that the activation of NOP receptor by intracerebroventricular administration of N/OFQ in msP rats caused an increase of BDNF and a decrease of CRF transcripts. Our study indicates that both stress and anti-stress mechanisms are dysregulated in the extended AMY of msP rats. The voluntary alcohol drinking, as well as NOP agonism, have a significant impact on neuropeptidergic systems arrangement, bringing the systems back to normalization.

Oxaliplatin-induced neuropathy (OXAIN) is a major adverse effect of this antineoplastic drug, widely used in the treatment of colorectal cancer. Although its molecular mechanisms remain poorly understood, recent evidence suggest that maladaptive neuroplasticity and oxidative stress may participate to the development of this neuropathy. Given the role played on protein remodeling by ubiquitin-proteasome system (UPS) in response to oxidative stress and in neuropathic pain, we investigated whether oxaliplatin might cause alterations in the UPS-mediated degradation pathway, in order to identify new pharmacological tools useful in OXAIN. In a rat model of OXAIN (2.4 mg kg -1 i.p., daily for 10 days), a significant increase in chymotrypsin-(β5) like activity of the constitutive proteasome 26S was observed in the thalamus (TH) and somatosensory cortex (SSCx). In addition, the selective up-regulation of β5 and LMP7 (β5i) subunit gene expression was assessed in the SSCx. Furthermore, this study revealed that oprozomib, a selective β5 subunit proteasome inhibitor, is able to normalize the spinal prodynorphin gene expression upregulation induced by oxaliplatin, as well as to revert mechanical allodynia and thermal hyperalgesia observed in oxaliplatin-treated rats. These results underline the relevant role of UPS in the OXAIN and suggest new pharmacological targets to counteract this severe adverse effect. This preclinical study reveals the involvement of the proteasome in the oxaliplatin-induced neuropathy and adds useful information to better understand the molecular mechanism underlying this pain condition. Moreover, although further evidence is required, these findings suggest that oprozomib could be a therapeutic option to counteract chemotherapy-induced neuropathy., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Melatonin, a neurohormone that binds to two G protein-coupled receptors MT 1 and MT 2, is involved in pain regulation, but the distinct role of each receptor has yet to be defined. We characterized the nociceptive responses of mice with genetic inactivation of melatonin MT 1 (MT 1 -/- ), or MT 2 (MT 2 -/- ), or both MT 1 /MT 2 (MT 1 -/- /MT 2 -/- ) receptors in the hot plate test (HPT), and the formalin test (FT). In HPT and FT, MT 1 -/- display no differences compared to their wild-type littermates (CTL), whereas both MT 2 -/- and MT 1 -/- /MT 2 -/- mice showed a reduced thermal sensitivity and a decreased tonic nocifensive behavior during phase 2 of the FT in the light phase. The MT 2 partial agonist UCM924 induced an antinociceptive effect in MT 1 -/- but not in MT 2 -/- and MT 1 -/- /MT 2 -/- mice. Also, the competitive opioid antagonist naloxone had no effects in CTL, whereas it induced a decrease of nociceptive thresholds in MT 2 -/- mice. Our results show that the genetic inactivation of melatonin MT 2 , but not MT 1 receptors, produces a distinct effect on nociceptive threshold, suggesting that the melatonin MT 2 receptor subtype is selectively involved in the regulation of pain responses., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background and Purpose: Nociceptin/orphanin FQ (N/OFQ) peptide and its cognate receptor (NOP) are widely expressed in mesolimbic brain regions where they play an important role in modulating reward and motivation. Early evidence suggested that NOP receptor activation attenuates the rewarding effects of drugs of abuse, including alcohol. However, emerging data indicate that NOP receptor blockade also effectively attenuates alcohol drinking and relapse. To advance our understanding of the role of the N/OFQ-NOP receptor system in alcohol abuse, we examined the effect of NOP receptor blockade on voluntary alcohol drinking at the neurocircuitry level., Experimental Approach: Using male and female genetically selected alcohol-preferring Marchigian Sardinian (msP) rats, we initially evaluated the effects of the selective NOP receptor antagonist LY2817412 (3, 10, and 30 mg·kg -1 , p.o.) on alcohol consumption in a two-bottle free-choice paradigm. We then microinjected LY2817412 (3 and 6 μg·μl -1 per rat) in the central nucleus of the amygdala (CeA), ventral tegmental area (VTA), and nucleus accumbens (NAc)., Key Results: Peripheral LY2817412 administration dose-dependently and selectively reduced voluntary alcohol intake in male and female msP rats. Central injections of LY2817412 markedly attenuated voluntary alcohol intake in both sexes following administration in the CeA and VTA but not in the NAc., Conclusion and Implications: The present results revealed that the CeA and VTA are neuroanatomical substrates that mediate the effects of NOP receptor antagonism on alcohol consumption. Overall, our findings support the potential of NOP receptor antagonism as a treatment strategy to attenuate alcohol use and addiction., (© 2019 The British Pharmacological Society.)

An isoform of peroxisome proliferator-activated receptors (PPARs), PPARγ, is the receptor for the thiazolidinedione class of anti-diabetic medications including pioglitazone. Neuroanatomical data indicate PPARγ localization in brain areas involved in drug addiction. Preclinical and clinical data have shown that pioglitazone reduces alcohol and opioid self-administration, relapse to drug seeking, and plays a role in emotional responses. Here, we investigated the behavioral effect of PPARγ manipulation on nicotine withdrawal in male Wistar rats and in male mice with neuron-specific PPARγ deletion (PPARγ (-/-) ) and their littermate wild-type (PPARγ (+/+) ) controls. Real-time quantitative RT-PCR and RNAscope in situ hybridization assays were used for assessing the levels of expression and cell-type localization of PPARγ during nicotine withdrawal. Brain site-specific microinjections of the PPARγ agonist pioglitazone were performed to explore the role of this system on nicotine withdrawal at a neurocircuitry level. Results showed that activation of PPARγ by pioglitazone abolished the expression of somatic and affective nicotine withdrawal signs in rats and in (PPARγ (+/+) ) mice. This effect was blocked by the PPARγ antagonist GW9662. During early withdrawal and protracted abstinence, the expression of PPARγ increased in GABAergic and glutamatergic cells of the amygdala and hippocampus, respectively. Hippocampal microinjections of pioglitazone reduced the expression of the physical signs of withdrawal, whereas excessive anxiety associated with protracted abstinence was prevented by pioglitazone microinjection into the amygdala. Our results demonstrate the implication of the neuronal PPARγ in nicotine withdrawal and indicates that activation of PPARγ may offer an interesting strategy for smoking cessation. SIGNIFICANCE STATEMENT Smoking cessation leads the occurrence of physical and affective withdrawal symptoms representing a major burden to quit tobacco use. Here, we show that activation of PPARγ prevents the expression of both somatic and affective signs of nicotine withdrawal. At molecular levels results show that PPARγ expression increases in GABAergic cells in the hippocampus and in GABA- and glutamate-positive cells in the basolateral amygdala. Hippocampal microinjections of pioglitazone reduce the insurgence of the physical withdrawal signs, whereas anxiety linked to protracted abstinence is attenuated by pioglitazone injected into the amygdala. Our results demonstrate the implication of neuronal PPARγ in nicotine withdrawal and suggest that PPARγ agonism may represent a promising treatment to aid smoking cessation., (Copyright © 2019 the authors.)

It is well known that emotions can interfere with the perception of physical pain, as well as with the development and maintenance of painful conditions. On the other hand, somatic pain can have significant consequences on an individual's affective behavior. Indeed, pain is defined as a complex and multidimensional experience, which includes both sensory and emotional components, thus exhibiting the features of a highly subjective experience. Over the years, neural pathways involved in the modulation of the different components of pain have been identified, indicating the existence of medial and lateral pain systems, which, respectively, project from medial or lateral thalamic nuclei to reach distinct cortex regions relating to specific functions. However, owing to the limited information concerning how mood state and painful input affect each other, pain treatment is frequently unsatisfactory. Different neuromodulators, including endogenous neuropeptides, appear to be involved in pain-related emotion and in its affective influence on pain perception, thus playing key roles in vulnerability and clinical outcome. Hence, this review article focuses on evidence concerning the modulation of the sensory and affective dimensions of pain, with particular attention given to some selected neuropeptidergic system contributions.

The dynorphinergic system is involved in pain transmission at spinal level, where dynorphin exerts antinociceptive or pronociceptive effects, based on its opioid or non-opioid actions. Surprisingly, little evidence is currently available concerning the supraspinal role of the dynorphinergic system in pain conditions. The present study aimed to investigate whether neuropathic pain is accompanied by prodynorphin (Pdyn) and κ-opioid receptor (Oprk1) gene expression alterations in selected mouse brain areas. To this end, mice were subjected to chronic constriction injury of the right sciatic nerve and neuropathic pain behavioral signs were ascertained after 14 days. At this interval, a marked increase in Pdyn mRNA in the anterior cingulate cortex (ACC) and prefrontal cortex (PFC) was observed. Oprk1 gene expression was increased in the PFC, and decreased in the ACC and nucleus accumbens (NAc). No changes were observed in the other investigated regions. Because of the relationship between dynorphin and the brain-derived neurotrophic factor, and the role of this neurotrophin in chronic pain-related neuroplasticity, we investigated brain-derived neurotrophic factor gene (Bdnf) expression in the areas showing Pdyn or Oprk1 mRNAs changes. Bdnf mRNA levels were increased in both the ACC and PFC, whereas no changes were assessed in the NAc. Present data indicate that the dynorphinergic system undergoes quite selective alterations involving the corticostriatal circuitry during neuropathic pain, suggesting a contribution to the negative affective component of pain. Moreover, parallel increases in Pdyn and Bdnf mRNA at cortical level suggest the occurrence of likely interactions between these systems in neuropathic pain maladaptive neuroplasticity., (© 2018 The Authors. Genes, Brain and Behavior published by International Behavioural and Neural Genetics Society and John Wiley & Sons Ltd.)

Background: Early-life stressful events affect the neurobiological maturation of cerebral circuitries including the endogenous opioid system and the effects elicited by adolescent cocaine exposure on this system have been poorly investigated. Here, we evaluated whether cocaine exposure during adolescence causes short- or long-term alterations in mRNAs codifying for selected elements belonging to the opioid system. Moreover, since brain-derived neurotrophic factor (BDNF) may undergo simultaneous alterations with the opioid peptide dynorphin, we also evaluated its signaling pathway as well., Methods: Adolescent male rats were exposed to cocaine (20 mg/kg/day) from post-natal day (PND) 28 to PND42, approximately corresponding to human adolescence. After short- (PND45) or long-term (PND90) abstinence, prodynorphin-κ-opioid receptor (pDYN-KOP) and pronociceptin-nociceptin receptor (pN/OFQ-NOP) gene expression were evaluated in the nucleus accumbens (NAc) and hippocampus (Hip) together with the analysis of BDNF signaling pathways., Results: In the NAc of PND45 rats, pDYN mRNA levels were up-regulated, an effect paralled by increased BDNF signaling. Differently from NAc, pDYN mRNA levels were down-regulated in the Hip of PND45 rats without significant changes of BDNF pathway. At variance from PND45 rats, we did not find any significant alteration of the investigated parameters either in NAc and Hip of PND90 rats., Conclusions: Our results indicate that the short-term withdrawal from adolescent cocaine exposure is characterized by a parallel pDYN mRNA and BDNF signaling increase in the NAc. Given the depressive-like state experienced during short abstinence in humans, we hypothesize that such changes may contribute to promote the risk of cocaine abuse escalation and relapse., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Intracellular signaling mechanisms underlying the opioid system regulation of nociception, neurotransmitters release, stress responses, depression, and the modulation of reward circuitry have been investigated from different points of view. The presence of the ubiquitin proteasome system (UPS) in the synaptic terminations suggest a potential role of ubiquitin-dependent mechanisms in the control of the membrane occupancy by G protein-coupled receptors (GPCRs), including those belonging to the opioid family. In this review, we focused our attention on the role played by the ubiquitination processes and by UPS in the modulation of opioid receptor signaling and in pathological conditions involving the endogenous opioid system. The collective evidence here reported highlights the potential usefulness of proteasome inhibitors in neuropathic pain, addictive behavior, and analgesia since these molecules can reduce pain behavioral signs, heroin self-administration, and the development of morphine analgesic tolerance. Moreover, the complex mechanisms involved in the effects induced by opioid agonists binding to their receptors include the ubiquitination process as a post-translational modification which plays a relevant role in receptor trafficking and degradation. Hence, UPS modulation may offer novel opportunities to control the balance between therapeutic versus adverse effects evoked by opioid receptor activation, thus, representing a promising druggable target.

Chronic pain treatment represents one of the most complex clinical challenges and even though opioids exhibit particular efficacy on nociceptive pain, their use must be controlled to avoid the risk of adverse reactions. A useful approach, aimed at maintaining analgesia and mitigating side effects, is represented by the use of a new class of analgesics endowed of µ-opioid (MOR) receptor agonism and noradrenaline reuptake inhibition (NRI) mechanisms. Tapentadol is the progenitor of this new class of drugs called MOP-NRI. A literature review has been conducted to gain information about the efficacy and the tolerability profile of tapentadol shifting from MOR agonism (acute pain) to NRI activity (chronic pain). The tolerability and therapeutic safety of tapentadol in neuropathic pain models, as well as in clinical settings, has been analyzed showing a good gastrointestinal tolerability profile, a moderate effect on hormone levels (in healthy volunteers and in patients) and on cognitive performance, a lack of significant alteration of the electrocardiogram recording and no changes of the QT/QTc interval, a minimal effect on serotonin reuptake in vivo with a low risk of serotonin syndrome, a longer time for the onset of analgesic tolerance and a less occurrence of abuse liability compared to formulations containing other comparator compounds. Tapentadol represents a great innovation in chronic pain therapy with a unique analgesic profile different form classical opioids, therefore, thanks to its synergistic MOR-NRI action, it may be a good option for the treatment of chronic, neuropathic and mixed pain.

Over the years, the ability of N/OFQ-NOP receptor system in modulating several physiological functions, including the release of neurotransmitters, anxiety-like behavior responses, modulation of the reward circuitry, inflammatory signaling, nociception, and motor function, has been examined in several brain regions and at spinal level. This chapter collects information related to the genes encoding the ppN/OFQ and NOP receptor, their regulation, and relative transcriptional control mechanisms. Furthermore, genetic manipulations, polymorphisms, and epigenetic alterations associated with different pathological conditions are discussed. The evidence here collected indicates that the study of ppN/OFQ and NOP receptor gene expression may offer novel opportunities in the field of personalized therapies and highlights this system as a good "druggable target" for different pathological conditions.

Notwithstanding the experimental evidence indicating Withania somnifera Dunal roots extract (WSE) ability to prolong morphine-elicited analgesia, the mechanisms underlying this effect are largely unknown. With the aim of evaluating a PPARγ-mediated mechanism in such WSE effects, we verified the ability of the PPARγ antagonist GW-9662 to modulate WSE actions. Further, we evaluated the influence of GW-9662 upon WSE / morphine interaction in SH-SY5Y cells since we previously reported that WSE hampers the morphine-induced μ-opioid receptor (MOP) receptor down-regulation. Nociceptive thresholds / tolerance development were assessed in different groups of rats receiving vehicles (control), morphine (10 mg/kg; i.p.), WSE (100 mg/kg, i.p.) and PPARγ antagonist GW-9662 (1 mg/kg; s.c.) in acute and chronic schedules of administration. Moreover, the effects of GW-9662 (5 and 10 μM) applied alone and in combination with morphine (10 μM) and/or WSE (0.25 and 1.00 mg/mL) on the MOP gene expression were investigated in cell cultures. Data analysis revealed a functional effect of the PPARγ antagonist in attenuating the ability of WSE to prolong morphine analgesic effect and to reduce tolerance development after repeated administration. In addition, molecular experiments demonstrated that the blockade of PPARγ by GW-9662 promotes MOP mRNA down-regulation and counteracts the ability of 1.00 mg/mL of WSE to keep an adequate MOP receptor availability. In conclusion, our results support the involvement of a PPARγ-mediated mechanism in the WSE effects on morphine-mediated nociception and the likely usefulness of WSE in lengthening the analgesic efficacy of opioids in chronic therapy., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Background: Behavioral studies demonstrated that the administration of Withania somnifera Dunal roots extract (WSE), prolongs morphine-elicited analgesia and reduces the development of tolerance to the morphine's analgesic effect; however, little is known about the underpinning molecular mechanism(s). In order to shed light on this issue in the present paper we explored whether WSE promotes alterations of μ (MOP) and nociceptin (NOP) opioid receptors gene expression in neuroblastoma SH-SY5Y cells., Methods: A range of WSE concentrations was preliminarily tested to evaluate their effects on cell viability. Subsequently, the effects of 5 h exposure to WSE (0.25, 0.50 and 1.00 mg/ml), applied alone and in combination with morphine or naloxone, on MOP and NOP mRNA levels were investigated., Results: Data analysis revealed that morphine decreased MOP and NOP receptor gene expression, whereas naloxone elicited their up-regulation. In addition, pre-treatment with naloxone prevented the morphine-elicited gene expression alterations. Interestingly, WSE was able to: a) alter MOP but not NOP gene expression; b) counteract, at its highest concentration, morphine-induced MOP down-regulation, and c) hamper naloxone-induced MOP and NOP up-regulation., Conclusion: Present in-vitro data disclose novel evidence about the ability of WSE to influence MOP and NOP opioid receptors gene expression in SH-SY5Y cells. Moreover, our findings suggest that the in-vivo modulation of morphine-mediated analgesia by WSE could be related to the hindering of morphine-elicited opioid receptors down-regulation here observed following WSE pre-treatment at its highest concentration.

Several studies showed that chronic pain causes reorganization and functional alterations of supraspinal brain regions. The nociceptin-NOP receptor system is one of the major systems involved in pain control and much evidence also suggested its implication in stress, anxiety and depression. Therefore, we investigated the nociceptin-NOP system alterations in selected brain regions in a neuropathic pain murine model. Fourteen days after the common sciatic nerve ligature, polymerase chain reaction (PCR) analysis indicated a significant decrease of pronociceptin and NOP receptor mRNA levels in the thalamus; these alterations could contribute to the decrease of the thalamic inhibitory function reported in neuropathic pain condition. Nociceptin peptide and NOP mRNA increased in the anterior cingulate cortex (ACC) and not in the somatosensory cortex, suggesting a peculiar involvement of this system in pain regulating circuitry. Similarly to the ACC, an increase of nociceptin peptide levels was observed in the amygdala. Finally, the pronociceptin and NOP mRNAs decrease observed in the hypothalamus reflects the lack of hypothalamus-pituitary-adrenal axis activation, already reported in neuropathic pain models. Our data indicate that neuropathic pain conditions affect the supraspinal nociceptin-NOP system which is also altered in regions known to play a role in emotional aspects of pain., (© 2016 John Wiley & Sons Ltd and International Behavioural and Neural Genetics Society.)

After decades of uncertainties and drawbacks, the study on the role and significance of acetaldehyde in the effects of ethanol seemed to have found its main paths. Accordingly, the effects of acetaldehyde, after its systemic or central administration and as obtained following ethanol metabolism, looked as they were extensively characterized. However, almost 5 years after this research appeared at its highest momentum, the investigations on this topic have been revitalized on at least three main directions: (1) the role and the behavioral significance of acetaldehyde in different phases of ethanol self-administration and in voluntary ethanol consumption; (2) the distinction, in the central effects of ethanol, between those arising from its non-metabolized fraction and those attributable to ethanol-derived acetaldehyde; and (3) the role of the acetaldehyde-dopamine condensation product, salsolinol. The present review article aims at presenting and discussing prospectively the most recent data accumulated following these three research pathways on this never-ending story in order to offer the most up-to-date synoptic critical view on such still unresolved and exciting topic.

The recreational drug of abuse 3,4-methylenedioxymethamphetamine (MDMA) has been shown to produce neurotoxic damage and long-lasting changes in several brain areas. In addition to the involvement of serotoninergic and dopaminergic systems, little information exists about the contribution of nociceptin/orphaninFQ (N/OFQ)-NOP and dynorphin (DYN)-KOP systems in neuronal adaptations evoked by MDMA. Here we investigated the behavioral and molecular effects induced by acute (8mg/kg) or repeated (8mg/kg twice daily for seven days) MDMA exposure. MDMA exposure affected body weight gain and induced hyperlocomotion; this latter effect progressively decreased after repeated administration. Gene expression analysis indicated a down-regulation of the N/OFQ system and an up-regulation of the DYN system in the nucleus accumbens (NAc), highlighting an opposite systems regulation in response to MDMA exposure. Since histone modifications have been strongly associated to the addiction-related maladaptive changes, we examined two permissive (acH3K9 and me3H3K4) and two repressive transcription marks (me3H3K27 and me2H3K9) at the pertinent opioid gene promoter regions. Chromatin immunoprecipitation assays revealed that acute MDMA increased me3H3K4 at the pN/OFQ, pDYN and NOP promoters. Following acute and repeated treatment a significant decrease of acH3K9 at the pN/OFQ promoter was observed, which correlated with gene expression results. Acute treatment caused an acH3K9 increase and a me2H3K9 decrease at the pDYN promoter which matched its mRNA up-regulation. Our data indicate that the activation of the DYNergic stress system together with the inactivation of the N/OFQergic anti-stress system contribute to the neuroadaptive actions of MDMA and offer novel epigenetic information associated with MDMA abuse., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Background: Ethanol and cocaine are widely abused drugs triggering long-lasting changes in neuronal circuits and synaptic transmission through the regulation of enzyme activity and gene expression. Compelling evidence indicates that the ubiquitin-proteasome system plays a role in the molecular changes induced by addictive substances, impacting on several mechanisms implicated in abuse. The goal of these studies was to evaluate the effects of cocaine or ethanol on proteasome activity in neuroblastoma cells. Moreover, the gene expression of specific subunits was assessed., Methods: Chymotrypsin-like activity was measured after 2 h, 24 h, and 48 h exposure to 5 μM cocaine or 40 mM ethanol. Proteasome subunit transcripts were evaluated by qPCR at the same time-points., Results: Treatments modified proteasome function in opposite directions, since cocaine increased and ethanol reduced chymotrypsin-like activity. Interestingly, we observed gene expression alterations induced by these drugs. In the core particle, the β1 and α5 subunits were mainly up-regulated by cocaine, whereas α6 transcripts were mostly decreased. β2 and β5 did not change. Similarly, ethanol exposure generally increased β1 and α5 mRNAs. Moreover, the β2 subunit was significantly up-regulated by ethanol only. The β5 and α6 subunits were not altered. In the regulatory particle, Rpt3 was increased by cocaine exposure, whereas it was reduced by ethanol. No significant Rpn9 alterations were observed., Conclusions: These findings support the notion that addictive substances regulate proteasome function, contributing to the dysregulations related to drug abuse since the availability of adequate subunit amounts is necessary for proper complex assembly and function., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

Paraquat (PQ) and maneb (MB) are able to induce neurotoxic effects by promoting α-synuclein (α-syn) aggregates and altering tyrosine hydroxylase (TH), thus increasing the risk of Parkinson's disease (PD). These pesticides promote neurotoxic effects also by affecting proteasome function that normally regulate protein turnover. We investigated the effects of the two pesticides exposure on multiple targets involved in PD, using SH-SY5Y cells. First, we evaluated TH and α-syn protein levels following PQ and MB cell exposure and a significant increase of these protein levels was observed. Subsequently, since a relationship between ubiquitin/proteasome and opioid receptors has been proposed, the effects of pesticides on their gene expression have been investigated. A decrease of β1 and Rpt3 proteasome subunit mRNA levels, together with the μ and δ opioid receptor down-regulation, was detected. The reported alterations, here simultaneously observed, help to clarify the involvement of multiple biological markers implicated in PD, often separately evaluated., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Background: Alterations of brain-derived neurotrophic factor (BDNF) have been associated with the development of addiction to different drugs of abuse, including ethanol (EtOH). EtOH exposure activates the BDNF-signaling cascade in dorsal striatum, which in turn affects further EtOH intake. Different alcohol exposures have been widely demonstrated to modulate chromatin remodeling, affecting histone acetylation/deacetylation balance. Recently, class I histone deacetylases (HDACs) inhibition has been reported to modulate BDNF mRNA expression and to attenuate morphological and behavioral phenomena related to EtOH exposure. However, the role played by different HDAC isoforms in EtOH-induced plasticity is still unclear., Methods: We investigated the effects induced by acute EtOH exposure on the protein levels of class I HDAC 1-3 isoforms of wild-type (WT) and BDNF heterozygous mice (BDNF(+/-)), in nuclear and cytoplasmic extracts of specific brain regions associated with EtOH addiction., Results: Nuclear HDAC 1-3 levels were markedly reduced after acute EtOH treatment in the caudate putamen (CPu) of WT mice only. Furthermore, CPu basal levels of nuclear HDAC isoforms were significantly lower in BDNF(+/-) mice compared to WT. With the exception of nuclear HDAC 3, no significant changes were observed after acute EtOH treatment in the prefrontal cortex (PFCx) of BDNF(+/-) and WT mice. In this area, the nuclear HDAC basal levels were significantly different between the two experimental groups., Conclusions: These results provide details about EtOH effects on class I HDAC isoforms and strongly support a correlation between BDNF and class I HDACs, suggesting a possible influence of BNDF on these enzymes., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

The therapeutic use of opioids is limited by the development of tolerance to the analgesic effect and the cellular and molecular mechanisms underlying this phenomenon are still not completely understood. For this reason the search for new analgesic derivatives, endowed with lower tolerance, is always an active field. The newly synthesized 14-O-Methylmorphine-6-sulfate (14-O-MeM6SU) shows high efficacy in in vitro assays and a strong analgesic action in the rat tail flick test. The aim of present work was to investigate: the analgesic effect of 14-O-MeM6SU in mouse tail-flick test; the tolerance to analgesic effect of 14-O-MeM6SU compared to morphine in mice, the effects of test compounds on glutamatergic neurotransmission by measuring spontaneous excitatory postsynaptic currents (sEPSCs) of layer V pyramidal cells from rat prefrontal cortices; and the effect of acute and chronic 14-O-MeM6SU treatments on opioid receptor gene expression in SH-SY5Y neuroblastoma cells expressing μ-opioid (MOP) and nociceptin/opioid receptor-like 1 (NOP) receptors. 14-O-MeM6SU was 17 times more potent than morphine in analgesia and had long duration of action in analgesic dose equipotent to morphine. Mice were treated subcutaneously (s.c.) either with 200 μmol/kg morphine or with 14-O-MeM6SU (12 μmol/kg) twice daily for three days. The magnitude of tolerance or cross-tolerance indicated by the shift in antinociceptive ED50 measured was greater for morphine compared to 14-O-MeM6SU. Subsequent to behavioral testing, patch-clamp experiments in layer V pyramidal neurons of rat prefrontal cortical slices in the presence of bicuculline were performed. Both 14-O-MeM6SU (0.1 μM) and morphine (1 μM) decreased the frequency of sEPSCs, indicating reduction of glutamate release. The effect of the novel compound was reversed by the opioid receptor antagonist naloxone, indicating an opioid mediated action. In contrast, the amplitude was not affected. Finally, gene expression data showed a dose dependent down-regulation of MOP receptor after 24h and 48 h exposure to 14-O-MeM6SU. Interestingly, no changes were detected for NOP receptor gene expression. The specific lack of this effect could be related to the lower tolerance development to analgesic effect of 14-O-MeM6SU. Furthermore, 14-O-MeM6SU displayed high intrinsic efficacy possibly an important factor in the observed effects. Further, the observed inhibition of glutamatergic signaling might be attributed also to the reduction of opioid tolerance. Based on our results the development of a new clinically important, safe analgesic agent might be possible., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Recent studies showed that combination of mu opioid receptor (MOP) agonism and monoamine reuptake inhibition may improve the therapeutic effect of opioids by reducing requirement for MOP activation. Tapentadol, showing such a combined mechanism of action, exhibits delayed analgesic tolerance development compared to pure MOP agonists. Here we investigated how opioid receptors are regulated following different schedules (two ranges of concentrations for 24 and 48 h) of tapentadol exposure in vitro in SH-SY5Y cells. MOP and nociceptin/orphaninFQ (NOP) receptor gene expressions were quantified using qReal-Time PCR. Moreover, studies were performed in U2 cells to assess tapentadol effect on MOP internalization compared with morphine and DAMGO. Ten and 100 nM tapentadol for 48 h induced a significant increase of MOP gene expression; cells exposed to 100 μM tapentadol for 24 and 48 h showed a significant increase of MOP mRNA levels. NOP gene expression showed a significant decrease following tapentadol at all low concentrations used after 24 h and at high concentrations (45 and 60 μM) after 24 h and (60 μM) after 48 h. Differently from DAMGO, tapentadol or morphine showed no effects on MOP internalization. This study suggests that tapentadol affects MOP and NOP gene expression and MOP internalization showing a pattern distinct from classical MOP agonists. Whether these differences can explain the improved therapeutic profile of tapentadol remains to be investigated.

Cocaine induces neurochemical changes of endogenous prodynorphin-kappa opioid receptor (pDYN-KOP) and pronociceptin/orphaninFQ-nociceptin receptor (pN/OFQ-NOP) systems. Both systems play an important role in rewarding mechanisms and addictive stimulus processing by modulating drug-induced dopaminergic activation in the mesocortico-limbic brain areas. They are also involved in regulating stress mechanisms related to addiction. The aim of this study was to investigate possible changes of gene expression of the dynorphinergic and nociceptinergic system components in the nucleus accumbens (NA) and in medial and lateral caudate putamen (mCPu and lCPu, respectively) of rats, following chronic subcutaneous infusion of cocaine. In addition, the epigenetic histone modifications H3K4me3 and H3K27me3 (an activating and a repressive marker, respectively) at the promoter level of the pDYN, KOP, pN/OFQ and NOP genes were investigated. Results showed that cocaine induced pDYN gene expression up-regulation in the NA and lCPu, and its down-regulation in the mCPu, whereas KOP mRNA levels were unchanged. Moreover, cocaine exposure decreased pN/OFQ gene expression in the NA and lCPu, while NOP mRNA levels appeared significantly increased in the NA and decreased in the lCPu. Specific changes of the H3K4me3 and H3K27me3 levels were found at pDYN, pN/OFQ, and NOP gene promoter, consistent with the observed gene expression alterations. The present findings contribute to better define the role of endogenous pDYN-KOP and pN/OFQ-NOP systems in neuroplasticity mechanisms following chronic cocaine treatment. The epigenetic histone modifications underlying the gene expression changes likely mediate the effects of cocaine on transcriptional regulation of specific gene promoters that result in long-lasting drug-induced plasticity., (© 2013.)

Morphine is widely used for the treatment of severe acute and chronic pain, but long-term therapy rapidly leads to tolerance. Morphine effects are mediated by μ opioid receptor (MOP) activation as well as for fentanyl that, in contrast to morphine, induces less tolerance to analgesia. The mechanisms underlying opioid tolerance involve complex processes, such as MOP desensitization, internalization, and/or changes of gene expression. The development of morphine tolerance also involves adaptive changes of the anti-opioid nociceptin/orphanin FQ-nociceptin receptor system, as suggested by the reduction of morphine tolerance in nociceptin opioid receptor (NOP) knockout mice. The aim of the present study was to investigate the MOP and NOP gene expression in the SH-SY5Y cells following morphine and fentanyl exposure. Results showed that cell exposure to 10 μM morphine for 5 h induced a significant decrease of MOP and NOP gene expression and that the MOP downregulation was reverted by the pretreatment with naloxone. Conversely, SH-SY5Y cells exposed to 0.1 and 1 μM fentanyl for 5 and 72 h showed a significant MOP upregulation, also reverted by naloxone pretreatment. Fentanyl induced no changes of NOP gene expression. The present findings showed a different effect by morphine and fentanyl on MOP mRNA levels that contributes to define the role of MOP gene expression changes in the mechanisms underlying the tolerance. Morphine also triggers an altered NOP-related signaling confirming that the nociceptin/orphanin FQ-nociceptin receptor system also plays a significant role in the development of morphine tolerance.

Background: Abuse of heroin and prescription opiate medications has grown to disturbing levels. Opioids mediate their effects through mu opioid receptors (MOR), but minimal information exists regarding MOR-related striatal signaling relevant to the human condition. The striatum is a structure central to reward and habitual behavior and neurobiological changes in this region are thought to underlie the pathophysiology of addiction disorders., Methods: We examined molecular mechanisms related to MOR in postmortem human brain striatal specimens from a homogenous European Caucasian population of heroin abusers and control subjects and in an animal model of heroin self-administration. Expression of ets-like kinase 1 (ELK1) was examined in relation to polymorphism of the MOR gene OPRM1 and drug history., Results: A characteristic feature of heroin abusers was decreased expression of MOR and extracellular regulated kinase signaling networks, concomitant with dysregulation of the downstream transcription factor ELK1. Striatal ELK1 in heroin abusers associated with the polymorphism rs2075572 in OPRM1 in a genotype dose-dependent manner and correlated with documented history of heroin use, an effect reproduced in an animal model that emphasizes a direct relationship between repeated heroin exposure and ELK1 dysregulation. A central role of ELK1 was evidenced by an unbiased whole transcriptome microarray that revealed ~20% of downregulated genes in human heroin abusers are ELK1 targets. Using chromatin immune precipitation, we confirmed decreased ELK1 promoter occupancy of the target gene Use1., Conclusions: ELK1 is a potential key transcriptional regulatory factor in striatal disturbances associated with heroin abuse and relevant to genetic mutation of OPRM1., (© 2013 Society of Biological Psychiatry.)

Molecular mechanisms of adaptive transformations caused by alcohol exposure on opioid dynorphin and nociceptin systems have been investigated in the rat brain. Alcohol was intragastrically administered to rats to resemble human drinking with several hours of exposure: water or alcohol (20% in water) at a dose of 1.5 g/kg three times daily for 1 or 5 days. The development of tolerance and dependence were recorded daily. Brains were dissected 30 minutes (1- and 5-day groups) or 1, 3 or 7 days after the last administration for the three other 5-day groups (groups under withdrawal). Specific alterations in opioid genes expression were ascertained. In the amygdala, an up-regulation of prodynorphin and pronociceptin was observed in the 1-day group; moreover, pronociceptin and the kappa opioid receptor mRNAs in the 5-day group and both peptide precursors in the 1-day withdrawal group were also up-regulated. In the prefrontal cortex, an increase in prodynorhin expression in the 1-day group was detected. These data indicate a relevant role of the dynorphinergic system in the negative hedonic states associated with multiple alcohol exposure. The pattern of alterations observed for the nociceptin system appears to be consistent with its role of functional antagonism towards the actions of ethanol associated with other opioid peptides. Our findings could help to the understanding of how alcohol differentially affects the opioid systems in the brain and also suggest the dynorphin and nociceptin systems as possible targets for the treatment and/or prevention of alcohol dependence., (© 2011 The Authors, Addiction Biology © 2011 Society for the Study of Addiction.)

Several studies demonstrated the role of the endogenous opioid system in the development of susceptibility to alcohol dependence. Recently, we reported that binge intragastric administration of ethanol induces selective alterations of pronociceptin and prodynorphin gene expression in the rat amygdala complex depending on the days of exposures and on the development of tolerance and dependence. The aim of the present study was to investigate the potential epigenetic mechanisms leading to these alcohol-induced changes in gene expression. Specific histone modifications and DNA methylation at opioid peptide precursor promoters were analyzed by chromatin immunoprecipitation and real-time methylation-specific PCR, respectively. We found a linkage between gene expression alterations and epigenetic modulation at pronociceptin and prodynorphin promoters following alcohol treatment. In animals treated for 1 day, we observed a reversed correlation, with a decrease of histone 3 lysine 27 trimethylation (repressive mark) and an increase of histone 3 lysine 9 acetylation (activating mark), associated with both gene expression up-regulation. In rats treated with alcohol for up to 5 days, we found an increase in histone 3 lysine 9 acetylation in the pronociceptin promoter providing further evidence of the already proposed possible role for histone deacetylases for addiction treatment. No significant alterations in DNA methylation and histone 3 lysine 4 trimethylation following different alcohol exposures were present, suggesting the selectivity of epigenetic effects induced by alcohol. These data demonstrate that ethanol induces selective epigenetic changes, thus better defining the role of opioid peptides in the ethanol-induced effects in the amygdala complex.