Orexin A expression and promoter methylation in patients with alcohol dependence comparing acute and protracted withdrawal

A case control study investigating the methylation levels of GHRL and GHSR genes in alcohol use disorder

BACKGROUND

Alcohol use disorder (AUD) is a relapsing disease described as excessive use of alcohol. Evidence of the role of DNA methylation in addiction is accumulating. Ghrelin is an important peptide known as appetite hormone and its role in addictive behavior has been identified. Here we aimed to determine the methylation levels of two crucial genes (GHRL and GHSR) in ghrelin signaling and further investigate the association between methylation ratios and plasma ghrelin levels.

METHODS

Individuals diagnosed with (n = 71) and without (n = 82) AUD were recruited in this study. DNA methylation levels were measured through methylation-sensitive high-resolution melting (MS-HRM). Acylated ghrelin levels were detected by ELISA. The GHRL rs696217 polymorphism was analyzed by the standard PCR-RFLP method.

RESULTS

GHRL was significantly hypermethylated (P < 0.0022) in AUD between 25 and 50% methylation than in control subjects but no significant changes of GHSR methylation were observed. Moreover, GHRL showed significant positive correlation of methylation ratio between 25 and 50% with age. A significant positive correlation between GHSR methylation and ghrelin levels in the AUD group was determined (P = 0.037). The level of GHRL methylation and the ghrelin levels showed a significant association in the control subjects (P = 0.042).

CONCLUSION

GHSR and GHRL methylation levels did not change significantly between control and AUD groups. However, GHRL and GHSR methylations seemed to have associations with plasma ghrelin levels in two groups. This is the first study investigating the DNA methylation of GHRL and GHSR genes in AUD.

The Orexin/Hypocretin System, the Peptidergic Regulator of Vigilance, Orchestrates Adaptation to Stress

The orexin/hypocretin neuropeptide family has emerged as a focal point of neuroscientific research following the discovery that this family plays a crucial role in a variety of physiological and behavioral processes. These neuropeptides serve as powerful neuromodulators, intricately shaping autonomic, endocrine, and behavioral responses across species. Notably, they serve as master regulators of vigilance and stress responses; however, their roles in food intake, metabolism, and thermoregulation appear complementary and warrant further investigation. This narrative review provides a journey through the evolution of our understanding of the orexin system, from its initial discovery to the promising progress made in developing orexin derivatives. It goes beyond conventional boundaries, striving to synthesize the multifaceted activities of orexins. Special emphasis is placed on domains such as stress response, fear, anxiety, and learning, in which the authors have contributed to the literature with original publications. This paper also overviews the advancement of orexin pharmacology, which has already yielded some promising successes, particularly in the treatment of sleep disorders.

Alternative use of suvorexant (Belsomra®) for the prevention of alcohol drinking and seeking in rats with a history of alcohol dependence

Alcohol use disorder (AUD) is one of the most treatment-resistant medical conditions globally. The orexin (Orx) system regulates diverse physiological processes, including stress, and is a system of interest for the development of pharmaceuticals to treat substance use disorders, particularly AUD. The present study tested the ability of the dual orexin receptor antagonist suvorexant (SUV), marketed by Merck as Belsomra^®, for the treatment of insomnia, to decrease alcohol self-administration and the stress-induced reinstatement of alcohol-seeking behavior in male Wistar rats with a history of alcohol dependence. Rats were trained to orally self-administer 10% alcohol (30 min/day for 3 weeks) and were either made dependent via chronic intermittent alcohol vapor exposure (14 h ON, 10 h OFF) for 6 weeks or exposed to air (non-dependent). Starting on week 7, the effect of SUV (0-20 mg/kg, p.o.) was tested on alcohol self-administration at acute abstinence (8 h after vapor was turned OFF) twice weekly. A separate cohort of rats that were prepared in parallel was removed from alcohol vapor exposure and then subjected to extinction training for 14 sessions. Once extinction was achieved, the rats received SUV (0 and 5 mg/kg, p.o.) and were tested for the footshock stress-induced reinstatement of alcohol-seeking behavior. Suvorexant at 5, 10, and 20 mg/kg selectively decreased alcohol intake in dependent rats. Furthermore, 5 mg/kg SUV prevented the stress-induced reinstatement of alcohol-seeking behavior in dependent rats only. These results underscore the significance of targeting the Orx system for the treatment of substance use disorders generally and suggest that repurposing SUV could be an alternative approach for the treatment of AUD.

Acute orexin antagonism selectively modulates anticipatory anxiety in humans: implications for addiction and anxiety

Research indicates that heightened anticipatory anxiety underlies several forms of psychopathology. Anticipatory anxiety can be reliably and objectively measured in the laboratory using the No-Predictable-Unpredictable (NPU) threat paradigm. The NPU paradigm is an ideal research tool for the NIH 'Fast-Fail' approach of screening promising compounds and testing human target engagement. Evidence from preclinical studies suggests that the hypocretin/orexin (ORX) hypothalamic neuropeptide system is a potential means for modulating anticipatory anxiety and disrupting stress-related alcohol use. The current study tested this question using a psychophysiological probe of the ORX system in humans. We examined whether a single dose of suvorexant (SUV; 10 mg; dual ORX receptor antagonist) can effectively and selectively target a well-validated human laboratory index of exaggerated anticipatory anxiety using a within-subjects placebo-controlled design. A total of twenty-one volunteers completed two laboratory sessions during acute administration of 10 mg SUV or placebo. Across sessions, we administered the NPU paradigm probing sustained anticipatory anxiety and fear while startle eyeblink was recorded as an index of aversive reactivity. Questionnaires assessing mood states and subjective drug effects were also collected. Results indicated SUV was well-tolerated. Compared with placebo, SUV was associated with decreased startle reactivity during anticipatory anxiety but not fear or no-threat conditions. Therefore, SUV selectively and effectively reduced objective indicators of anticipatory anxiety in humans and engaged our laboratory target of psychopathology. ORX antagonism may be a promising strategy for modulating human anxiety and potentially, stress-related alcohol use.

Subregional Differences in Alcohol Modulation of Central Amygdala Neurocircuitry

Alcohol use disorder is a highly significant medical condition characterized by an impaired ability to stop or control alcohol use, compulsive alcohol seeking behavior, and withdrawal symptoms in the absence of alcohol. Understanding how alcohol modulates neurocircuitry critical for long term and binge-like alcohol use, such as the central amygdala (CeA), may lead to the development of novel therapeutic strategies to treat alcohol use disorder. In clinical studies, reduction in the volume of the amygdala has been linked with susceptibility to relapse to alcohol use. Preclinical studies have shown the involvement of the CeA in the effects of alcohol use, with lesions of the amygdala showing a reduction in alcohol drinking, and manipulations of cells in the CeA altering alcohol drinking. A great deal of work has shown that acute alcohol, as well as chronic alcohol exposure via intake or dependence models, alters glutamatergic and GABAergic transmission in the CeA. The CeA, however, contains heterogeneous cell populations and distinct subregional differences in neurocircuit architecture which may influence the mechanism by which alcohol modulates CeA function overall. The current review aimed to parse out the differences in alcohol effects on the medial and lateral subregions of the CeA, and what role neuroinflammatory cells and markers, the endocannabinoid system, and the most commonly studied neuropeptide systems play in mediating these effects. A better understanding of alcohol effects on CeA subregional cell type and neurocircuit function may lead to development of more selective pharmacological interventions for alcohol use disorder.

Potential biomarkers of addiction identified by real-time PCR in human peripheral blood lymphocytes: a narrative review

Addiction-related neurobiological factors could be considered as potential biomarkers. The concentration of peripheral biomarkers in tissues like blood lymphocytes may mirror their brain levels. This review is focused on the mRNA expression of potential addiction biomarkers in human peripheral blood lymphocytes (PBLs). PubMed, EMBASE, Web of Science, Scopus and Google Scholar were searched using the keywords 'addiction', 'biomarker', 'peripheral blood lymphocyte', 'gene expression' and 'real-time PCR'. The results showed the alterations in the regulation of genes such as dopamine receptors, opioid receptors, NMDA receptors, cannabinoid receptors, α-synuclein, DYN, MAO-A, FosB and orexin-A as PBLs biomarkers in addiction stages. Such variations could also be found during abstinence and relapse. PBLs biomarkers may help in drug development and have clinical implications.

Understanding the Role of Orexin Neuropeptides in Drug Addiction: Preclinical Studies and Translational Value

Orexins (also known as hypocretins) are neuropeptides that participate in the regulation of energy metabolism, homeostasis, sleep, feeding, stress responses, arousal, and reward. Particularly relevant to the scope of the present review is the involvement of the orexin system in brain mechanisms that regulate motivation, especially highly motivated behavior, arousal, and stress, making it an ideal target for studying addiction and discovering treatments. Drug abuse and misuse are thought to induce maladaptive changes in the orexin system, and these changes might promote and maintain uncontrolled drug intake and contribute to relapse. Dysfunctional changes in this neuropeptidergic system that are caused by drug use might also be responsible for alterations of feeding behavior and the sleep-wake cycle that are commonly disrupted in subjects with substance use disorder. Drug addiction has often been associated with an increase in activity of the orexin system, suggesting that orexin receptor antagonists may be a promising pharmacological treatment for substance use disorder. Substantial evidence has shown that single orexin receptor antagonists that are specific to either orexin receptor 1 or 2 can be beneficial against drug intake and relapse. Interest in the efficacy of dual orexin receptor antagonists, which were primarily developed to treat insomnia, has grown in the field of drug addiction. Treatments that target the orexin system may be a promising strategy to reduce drug intake, mitigate relapse vulnerability, and restore “normal” physiological functions, including feeding and sleep. The present review discusses preclinical and clinical evidence of the involvement of orexins in drug addiction and possible beneficial pharmacotherapeutic effects of orexin receptor antagonists to treat substance use disorder.

Epigenetics of alcohol use disorder-A review of recent advances in DNA methylation profiling

Alcohol use disorder (AUD) is a major contributor to morbidity and mortality worldwide. Although there is a heritable component, the etiology of AUD is complex and can involve environmental exposures like trauma and can be associated with many different patterns of alcohol consumption. Epigenetic modifications, which can mediate the influence of genetic variants and environmental variables on gene expression, have emerged as an important area of AUD research. Over the past decade, the number of studies investigating AUD and DNA methylation, a form of epigenetic modification, has grown rapidly. Yet we are still far from understanding how DNA methylation contributes to or reflects aspects of AUD. In this paper, we reviewed studies of DNA methylation and AUD and discussed how the field has evolved. We found that global DNA and candidate DNA methylation studies did not produce replicable results. To assess whether findings of epigenome-wide association studies (EWAS) were replicated, we aggregated significant findings across studies and identified 184 genes and 15 gene ontological pathways that were differentially methylated in at least two studies and four genes and three gene ontological pathways that were differentially methylated in three studies. These genes and pathways repeatedly found enrichment of immune processes, which is in line with recent developments suggesting that the immune system may be altered in AUD. Finally, we assess the current limitations of studies of DNA methylation and AUD and make recommendations on how to design future studies to resolve outstanding questions.

Epigenetic Regulation of Circadian Clocks and Its Involvement in Drug Addiction

Based on studies describing an increased prevalence of addictive behaviours in several rare sleep disorders and shift workers, a relationship between circadian rhythms and addiction has been hinted for more than a decade. Although circadian rhythm alterations and molecular mechanisms associated with neuropsychiatric conditions are an area of active investigation, success is limited so far, and further investigations are required. Thus, even though compelling evidence connects the circadian clock to addictive behaviour and vice-versa, yet the functional mechanism behind this interaction remains largely unknown. At the molecular level, multiple mechanisms have been proposed to link the circadian timing system to addiction. The molecular mechanism of the circadian clock consists of a transcriptional/translational feedback system, with several regulatory loops, that are also intricately regulated at the epigenetic level. Interestingly, the epigenetic landscape shows profound changes in the addictive brain, with significant alterations in histone modification, DNA methylation, and small regulatory RNAs. The combination of these two observations raises the possibility that epigenetic regulation is a common plot linking the circadian clocks with addiction, though very little evidence has been reported to date. This review provides an elaborate overview of the circadian system and its involvement in addiction, and we hypothesise a possible connection at the epigenetic level that could further link them. Therefore, we think this review may further improve our understanding of the etiology or/and pathology of psychiatric disorders related to drug addiction.

Causal roles of stress kinase JNK2 in DNA methylation and binge alcohol withdrawal-evoked behavioral deficits

Excessive binge alcohol intake is a common drinking pattern in humans, especially during holidays. Cessation of the binge drinking often leads to aberrant withdrawal behaviors, as well as serious heart rhythm abnormalities (clinically diagnosed as Holiday Heart Syndrome (HHS)). In our HHS mouse model with well-characterized binge alcohol withdrawal (BAW)-induced heart phenotypes, BAW leads to anxiety-like behaviors and cognitive impairment. We have previously reported that stress-activated c-Jun NH(2)-terminal kinase (JNK) plays a causal role in BAW-induced heart phenotypes. In the HHS brain, we found that activation of JNK2 (but not JNK1 and JNK3) in the prefrontal cortex (PFC), but not hippocampus and amygdala, led to anxiety-like behaviors and impaired cognition. DNA methylation mediated by a crucial DNA methylation enzyme, DNA methyltransferase1 (DNMT1), is known to be critical in alcohol-associated behavioral deficits. In HHS mice, JNK2 in the PFC (but not hippocampus and amygdala) causally enhanced total genomic DNA methylation via increased DNMT1 expression, which was regulated by enhanced binding of JNK downstream transcriptional factor c-JUN to the DNMT1 promoter. JNK2-specific inhibition either by an inhibitor JNK2I or JNK2 knockout completely offset c-JUN-regulated DNMT1 upregulation and restored the level of DNA methylation in HHS PFC to the baseline levels seen in sham controls. Strikingly, either JNK2-specific inhibition or genetic JNK2 depletion or DNMT1 inhibition (by an inhibitor 5-Azacytidine) completely abolished BAW-evoked behavioral deficits. In conclusion, our studies revealed a novel mechanism by which JNK2 drives BAW-evoked behavioral deficits through a DNMT1-regulated DNA hypermethylation. JNK2 could be a novel therapeutic target for alcohol withdrawal treatment and/or prevention.

Orexin gene expression is downregulated in alcohol dependent rats during acute alcohol withdrawal

Alcohol use disorders (AUD) are chronic relapsing brain disorder characterized by compulsive and heavy alcohol consumption. During acute withdrawal, patients with AUD display excessive daytime sleepiness, a condition linked to serious life-threatening complications, however, the mechanism is not known. Orexin and melanin-concentrating hormone (MCH) are the two hypothalamic neuropeptides that regulate many behaviors including sleep-wakefulness, and alcohol consumption, reinforcement, and reinstatement. Importantly, loss of orexin neurons causes narcolepsy, a severe sleep disorder with excessive daytime sleepiness. Does acute alcohol withdrawal reduce orexin gene expression? To investigate this, male Sprague-Dawley rats were divided in two groups: Rats were either administered with alcohol, mixed with infant formula (alcohol group) or control mixture containing water and infant formula (Controls) by gastric intubation every 8 h for 4 days using Majchrowicz's chronic binge drinking protocol. The doses of alcohol were adjusted depending on degree of intoxication, exhibited by animals, prior to each dose. The animals were euthanized after 12 h of last alcohol/water administration. During withdrawal, the hypothalamus was rapidly dissected out, and the expressions of orexin and MCH genes were examined by Real-time PCR. There was a significant reduction in orexin gene expression in rats subjected to alcohol withdrawal as compared to controls. No such change was observed in the MCH gene expression. These results suggest that downregulation of orexin gene expression may be a possible mechanism responsible for excessive daytime sleepiness associated with alcohol withdrawal in patients with AUD.

Evaluation of the relationship between the gene expression level of orexin-1 receptor in the rat blood and prefrontal cortex, novelty-seeking, and proneness to methamphetamine dependence: A candidate biomarker

BACKGROUND

previous studies have suggested that methamphetamine (METH) abuse may affect orexin regulation. However, the data regarding the relationship between the current level of orexin and the vulnerability to METH abuse are minimal. Here, we have investigated the correlation between the gene expression level of the orexin-1 receptor (OX1R) in the rat prefrontal cortex (PFC) and blood lymphocytes and susceptibility to METH dependence and its impact on novelty-seeking behavior.

METHODS

male Wistar rats were first examined for novelty-seeking behavior by the novel object recognition test, and the expression level of OX1R in their blood lymphocytes was evaluated by real-time PCR. Then, the susceptibility to METH abuse was investigated by voluntary METH oral consumption test. According to the amounts of METH consumption, the animals were divided into two groups of METH preferring and non-preferring. Half of the rats in each group were sacrificed, and the level of OX1R in their blood lymphocytes and PFC tissue was measured. The other half were sacrificed for the same reason after two weeks of drug abstinence.

RESULTS

The indexes of novelty-seeking behavior were significantly higher in the METH- preferring group compared to the non-preferring animals. Furthermore, the expression level of OX1R in the blood lymphocytes and PFC in the preferring group was considerably higher than the non-preferring group.

CONCLUSION

Up-regulation of the mRNA expression level of OX1R in the lymphocytes and PFC may predict vulnerability to the METH consumption and novelty-seeking, which may serve as a potential biomarker for METH abuse.

Targeting the Orexin System for Prescription Opioid Use Disorder

Prescription opioids are potent analgesics that are used for clinical pain management. However, the nonmedical use of these medications has emerged as a major concern because of dramatic increases in abuse and overdose. Therefore, effective strategies to prevent prescription opioid use disorder are urgently needed. The orexin system has been implicated in the regulation of motivation, arousal, and stress, making this system a promising target for the treatment of substance use disorder. This review discusses recent preclinical studies that suggest that orexin receptor blockade could be beneficial for the treatment of prescription opioid use disorder.

Maternal ethanol consumption before paternal fertilization: Stimulation of hypocretin neurogenesis and ethanol intake in zebrafish offspring

There are numerous clinical and pre-clinical studies showing that exposure of the embryo to ethanol markedly affects neuronal development and stimulates alcohol drinking and related behaviors. In rodents and zebrafish, our studies show that embryonic exposure to low-dose ethanol, in addition to increasing voluntary ethanol intake during adolescence, increases the density of hypothalamic hypocretin (hcrt) neurons, a neuropeptide known to regulate reward-related behaviors. The question addressed here in zebrafish is whether maternal ethanol intake before conception also affects neuronal and behavioral development, phenomena suggested by clinical reports but seldom investigated. To determine if preconception maternal ethanol consumption also affects these hcrt neurons and behavior in the offspring, we first standardized a method of measuring voluntary ethanol consumption in AB strain adult and larval zebrafish given gelatin meals containing 10% or 0.1% ethanol, respectively. We found the number of bites of gelatin to be an accurate measure of intake in adults and a strong predictor of blood ethanol levels, and also to be a reliable indicator of intake in larval zebrafish. We then used this feeding paradigm and live imaging to examine the effects of preconception maternal intake of 10% ethanol-gelatin compared to plain-gelatin for 14 days on neuronal development in the offspring. Whereas ethanol consumption by adult female HuC:GFP transgenic zebrafish had no impact on the number of differentiated HuC⁺ neurons at 28 h post-fertilization (hpf), preconception ethanol consumption by adult female hcrt:EGFP zebrafish significantly increased the number of hcrt neurons in the offspring, an effect observed at 28 hpf and confirmed at 6 and 12 days post-fertilization (dpf). This increase in hcrt neurons was primarily present on the left side of the brain, indicating asymmetry in ethanol's actions, and it was accompanied by behavioral changes in the offspring, including a significant increase in novelty-induced locomotor activity but not thigmotaxis measured at 6 dpf and also in voluntary consumption of 0.1% ethanol-gelatin at 12 dpf. Notably, these measures of ethanol intake and locomotor activity stimulated by preconception ethanol were strongly, positively correlated with the number of hcrt neurons. These findings demonstrate that preconception maternal ethanol consumption affects the brain and behavior of the offspring, producing effects similar to those caused by embryonic ethanol exposure, and they provide further evidence that the ethanol-induced increase in hcrt neurogenesis contributes to the behavioral disturbances caused by ethanol.

Chronic ketamine abuse is associated with orexin-A reduction and ACTH elevation

BACKGROUND

Ketamine has emerged as a major substance of abuse worldwide. Evidence suggests a role of orexin system in reward processing, withdrawal, and stress response. It also interacts with the stress mechanisms of hypothalamic-pituitary-adrenal (HPA) axis to regulate drug-taking behavior. The study aimed to explore the relevance of orexin and stress hormones to chronic ketamine abuse.

METHODS

We enrolled 67 ketamine-dependent (KD) patients and 64 controls. The levels of orexin-A, adrenocorticotropic hormone (ACTH), and cortisol were measured at baseline, 1 week, and 2 weeks after ketamine discontinuation. KD patients were assessed by Beck Depression Inventory, Beck Anxiety Inventory, and Visual Analogue Scale for ketamine craving at baseline.

RESULTS

Compared with the controls, KD patients had significantly lower orexin-A (0.65 ± 0.12 vs. 0.74 ± 0.10 ng/mL, p < 0.001) and increased ACTH (32.3 ± 16.3 vs. 22.3 ± 11.0 pg/mL, p = 0.008) levels at baseline, whereas cortisol levels were similar between two groups. Levels of the three markers did not correlate with ketamine use variables, craving, depression, or anxiety symptoms. The levels did not alter after 1 or 2 weeks of ketamine discontinuation. Notably, those with higher anxiety had lower orexin-A but increased cortisol levels than did those with lower anxiety.

CONCLUSIONS

This study showed that KD patients had persistent orexin-A reduction and stress hormone dysregulation in early abstinence. The anxious phenotype of KD might be associated with a lower orexin-A expression. These results point to a promising pathway to investigate the neurochemical mechanisms of ketamine addiction.

Suvorexant to treat alcohol use disorder and comorbid insomnia: Plan for a phase II trial

Alcohol use disorder (AUD) is a complex neuropsychiatric disease state in which currently approved pharmacotherapeutics are of relatively low effect at a population level. One reason for this may be that current pharmacotherapeutics focus on the reward pathway in relapse prevention, rather than addressing AUD from a holistic perspective. Importantly, one often overlooked symptom of AUD is sleep disruption. In recent years, an efficient, relatively low risk and economic strategy that has proven successful in other disorders is the repositioning or repurposing of drugs approved for the treatment of other indications. Suvorexant, a dual orexin receptor antagonist, has been licensed for the treatment of insomnia in the USA, Australia and Japan. The orexin system also plays a role in the emotional dysregulation that occurs during withdrawal from alcohol use and in alcohol-seeking behaviours. These two factors prompted the planning of a clinical trial into the use of suvorexant to treat insomnia in alcohol dependent individuals during and 24 weeks post-acute alcohol withdrawal. In this review we outline the comorbid nature of AUD and sleep disruptions. We then highlight the role of the orexin system in both sleep-wake regulation and AUD. Finally, we discuss our plan for a Phase II double blind placebo controlled trial examining the effectiveness of suvorexant for the treatment of comorbid insomnia and AUD.

Regulation of Brain DNA Methylation Factors and of the Orexinergic System by Cocaine and Food Self-Administration

Inhibitors of DNA methylation and orexin type-1 receptor antagonists modulate the neurobiological effects driving drugs of abuse and natural reinforcers by activating common brain structures of the mesolimbic reward system. In this study, we applied a self-administration paradigm to assess the involvement of factors regulating DNA methylation processes and satiety or appetite signals. These factors include Dnmts and Tets, miR-212/132, orexins, and orx-R1 genes. The study focused on dopamine projection areas such as the prefrontal cortex (PFCx) and caudate putamen (CPu) and in the hypothalamus (HP) that is interconnected with the reward system. Striking changes were observed in response to both reinforcers, but differed depending on contingent and non-contingent delivery. Expression also differed in the PFCx and the CPu. Cocaine and food induced opposite effects on Dnmt3a expression in both brain structures, whereas they repressed both miRs to a different extent, without affecting their primary transcript in the CPu. Unexpectedly, orexin mRNAs were found in the CPu, suggesting a transport from their transcription site in the HP. The orexin receptor1 gene was found to be induced by cocaine in the PFCx, consistent with a regulation by DNA methylation. Global levels of 5-methylcytosines in the PFCx were not significantly altered by cocaine, suggesting that it is rather their distribution that contributes to long-lasting behaviors. Together, our data demonstrate that DNA methylation regulating factors are differentially altered by cocaine and food. At the molecular level, they support the idea that neural circuits activated by both reinforcers do not completely overlap.

Building better strategies to develop new medications in Alcohol Use Disorder: Learning from past success and failure to shape a brighter future

Alcohol Use Disorder (AUD) is a chronic disease that develops over the years. The complexity of the neurobiological processes contributing to the emergence of AUD and the neuroadaptive changes occurring during disease progression make it difficult to improve treatments. On the other hand, this complexity offers researchers the possibility to explore new targets. Over years of intense research several molecules were tested in AUD; in most cases, despite promising preclinical data, the clinical efficacy appeared insufficient to justify futher development. A prototypical example is that of corticotropin releasing factor type 1 receptor (CRF1R) antagonists that showed significant effectiveness in animal models of AUD but were largely ineffective in humans. The present article attempts to analyze the most recent venues in the development of new medications in AUD with a focus on the most promising drug targets under current exploration. Moreover, we delineate the importance of using a more integrated translational framework approach to correlate preclinical findings and early clinical data to enhance the probability to validate biological targets of interest.

A sleeping giant: Suvorexant for the treatment of alcohol use disorder?

There are currently 3 FDA approved treatments for alcohol use disorder (AUD) in the USA, opioid receptor antagonists such as naltrexone, disulfiram and acamprosate. To date, these have been largely inadequate at preventing relapse at a population level and this may be because they only target certain aspects of AUD. Recently, suvorexant, a dual orexin receptor antagonist, has been FDA approved for the treatment of insomnia. Importantly, sleep disruptions occur during both acute and prolonged alcohol exposure and sleep deprivation is a potent factor promoting relapse to alcohol use. In this mini review article, we explore the therapeutic potential of suvorexant for the treatment of AUD. In particular, we highlight that in addition to altering the motivational properties of alcohol, suvorexant may also address key physiological components associated with alcohol withdrawal and abstinence, such as sleep disruptions, which should in turn help reduce or prevent relapse.

The hypocretin/orexin system as a target for excessive motivation in alcohol use disorders

The hypocretin/orexin (ORX) system has been repeatedly demonstrated to regulate motivation for drugs of abuse, including alcohol. In particular, ORX seems to be critically involved in highly motivated behaviors, as is observed in high-seeking individuals in a population, in the seeking of highly palatable substances, and in models of dependence. It seems logical that this system could be considered as a potential target for treatment for addiction, particularly alcohol addiction, as ORX pharmacological manipulations significantly reduce drinking. However, the ORX system also plays a role in a wide range of other behaviors, emotions, and physiological functions and is disrupted in a number of non-dependence-associated disorders. It is therefore important to consider how the ORX system might be optimally targeted for potential treatment for alcohol use disorders either in combination with or separate from its role in other functions or diseases. This review will focus on the role of ORX in alcohol-associated behaviors and whether and how this system could be targeted to treat alcohol use disorders while avoiding impacts on other ORX-relevant functions. A brief overview of the ORX system will be followed by a discussion of some of the factors that makes it particularly intriguing as a target for alcohol addiction treatment, a consideration of some potential challenges associated with targeting this system and, finally, some future directions to optimize new treatments.

Orexin A in men with heroin use disorder undergoing methadone maintenance treatment

Orexins have played a role in reward-seeking and addiction-related behavior. There are few reports in the literature on serum levels of orexins in patients with heroin use disorder (HUD) undergoing methadone maintenance treatment (MMT). The aim of this study was to investigate the serum levels of orexin A in HUD patients undergoing MMT. Fifty male HUD patients undergoing MMT and 25 healthy males were enrolled for this study. Serum orexin A were measured with assay kits. Using analysis of covariance (ANCOVA) with body mass index (BMI) adjustments, the serum levels of orexin A in HUD men undergoing MMT were found to be significantly higher than in healthy controls. In conclusion, our results suggest that MMT might increase orexin A levels in HUD patients.

Contribution of Dynorphin and Orexin Neuropeptide Systems to the Motivational Effects of Alcohol

Understanding the neural systems that drive alcohol motivation and are disrupted in alcohol use disorders is of critical importance in developing novel treatments. The dynorphin and orexin/hypocretin neuropeptide systems are particularly relevant with respect to alcohol use and misuse. Both systems are strongly associated with alcohol-seeking behaviors, particularly in cases of high levels of alcohol use as seen in dependence. Furthermore, both systems also play a role in stress and anxiety, indicating that disruption of these systems may underlie long-term homeostatic dysregulation seen in alcohol use disorders. These systems are also closely interrelated with one another - dynorphin/kappa opioid receptors and orexin/hypocretin receptors are found in similar regions and hypocretin/orexin neurons also express dynorphin - suggesting that these two systems may work together in the regulation of alcohol seeking and may be mutually disrupted in alcohol use disorders. This chapter reviews studies demonstrating a role for each of these systems in motivated behavior, with a focus on their roles in regulating alcohol-seeking and self-administration behaviors. Consideration is also given to evidence indicating that these neuropeptide systems may be viable targets for the development of potential treatments for alcohol use disorders.

Role of the orexin receptors within the nucleus accumbens in the drug priming-induced reinstatement of morphine seeking in the food deprived rats

Orexin plays a key role in mediating stress-induced drug relapse. However, the role of different types of orexinergic receptors that modulate stress-induced drug seeking remains unknown. The nucleus accumbens (NAc) has an important role in the reward system and receives orexinergic projections of the lateral hypothalamus. In addition, orexin interacts with other receptors that are involved in drug reinstatement. Therefore, in the present study, the role of orexin receptors in the NAc in morphine priming- induced reinstatement and the effect of food deprivation (FD) on drug reinstatement were examined. The extinguished morphine preference rats were tested for reinstatement following the 24-h FD condition after conditioning was induced. In the other groups, the animals were given intra-accumbal administration of SB334867 (01, 1 and 10 nM/0.5 μl DMSO) as an orexin-1 receptor antagonist and TCSOX229 (1, 5 and 25 nM/0.5 μl DMSO), as an orexin-2 receptor antagonist. The results showed that the blockade of two types of orexin receptors in the NAc remarkably attenuated the effect of FD on the drug reinstatement; however, they were more effective in FD condition. These findings indicate that the NAc is a brain area within which orexin has a fundamental role in the effect of stress on morphine-induced reinstatement and the effect of food deprivation- on the reinstatement of morphine.

The Role of Orexins/Hypocretins in Alcohol Use and Abuse

Addiction is a chronic relapsing disorder characterized by compulsive drug seeking and drug taking despite negative consequences. Alcohol abuse and addiction have major social and economic consequences and cause significant morbidity and mortality worldwide. Currently available therapeutics are inadequate, outlining the need for alternative treatments. Detailed knowledge of the neurocircuitry and brain chemistry responsible for aberrant behavior patterns should enable the development of novel pharmacotherapies to treat addiction. Therefore it is important to expand our knowledge and understanding of the neural pathways and mechanisms involved in alcohol seeking and abuse. The orexin (hypocretin) neuropeptide system is an attractive target, given the recent FDA and PMDA approval of suvorexant for the treatment of insomnia. Orexin is synthesized exclusively in neurons located in the lateral (LH), perifornical (PEF), and dorsal medial (DMH) hypothalamus. These neurons project widely throughout the neuraxis with regulatory roles in a wide range of behavioral and physiological responses, including sleep-wake cycle neuroendocrine regulation, anxiety, feeding behavior, and reward seeking. Here we summarize the literature to date, which have evaluated the interplay between alcohol and the orexin system.

The Role of Orexin Signaling in the Ventral Tegmental Area and Central Amygdala in Modulating Binge-Like Ethanol Drinking Behavior

BACKGROUND

Recent reports have demonstrated that binge-like ethanol (EtOH) drinking leads to an increase in hypothalamic orexin (OX) signaling and that suppressing this signaling via systemic administration of an orexin receptor (OXR) antagonist blocks this behavior; however, the specific OX pathways that modulate this behavior remain unknown. The goal of this study was to further elucidate the role of the OX system in binge-like EtOH drinking using behavioral, molecular, and pharmacological techniques.

METHODS

The drinking-in-the-dark (DID) paradigm was used to model binge-like drinking behavior in male C57BL/6J mice. Experiment 1 examined changes in the OX precursor, prepro-orexin, within the hypothalamus following multiple cycle EtOH or sucrose DID using polymerase chain reaction (PCR) analysis. In experiments 2a and 2b, we used site-directed infusion of an OXR antagonist to examine the individual contribution of each OXR subtype within the ventral tegmental area (VTA) and central nucleus of the amygdala (CeA), respectively, in binge-like EtOH or sucrose drinking.

RESULTS

Findings from our PCR study revealed that multiple cycles of binge-like EtOH drinking did not lead to changes in prepro-orexin mRNA as a function of binge-like EtOH drinking. However, data from site-directed pharmacology studies indicate that the orexin-1 receptor (OX1R) is the predominate receptor subtype within the VTA and CeA that regulates binge-like EtOH drinking. Interestingly, inhibition of OX1Rs did not affect binge-like sucrose intake, which suggests that these OX circuits are specific for EtOH consumption.

CONCLUSIONS

As a whole, these data suggest that the VTA and CeA are important regions in which OX regulates binge-like EtOH drinking behavior. Moreover, these findings identify OXR antagonists as a potential treatment option that may be used to ameliorate problematic drinking behavior while leaving responding to natural rewards relatively intact.

Review: DNA methylation and alcohol use disorders: Progress and challenges

BACKGROUND AND OBJECTIVES

Risk for alcohol use disorders (AUDs) is influenced by gene-environment interactions. Environmental factors can affect gene expression through epigenetic mechanisms such as DNA methylation. This review outlines the findings regarding the association of DNA methylation and AUDs.

METHODS

We searched PubMed (by April 2016) and identified 29 studies that examined the association of DNA methylation and AUDs. We also evaluated the methods used in these studies.

RESULTS

Two studies demonstrated elevated global (repetitive element) DNA methylation levels in AUD subjects. Fifteen candidate gene studies showed hypermethylation of promoter regions of six genes (AVP, DNMT3B, HERP, HTR3A, OPRM1, and SNCA) or hypomethylation of the GDAP1 promoter region in AUD subjects. Five genome-wide DNA methylation studies demonstrated widespread DNA methylation changes across the genome in AUD subjects. Six studies showed significant correlations of DNA methylation with gene expression in AUD subjects. Three studies revealed interactive effects of genetic variation and DNA methylation on susceptibility to AUDs. Most studies analyzed AUD-associated DNA methylation changes in the peripheral blood; a few studies examined DNA methylation changes in postmortem brains of AUD subjects.

DISCUSSION AND CONCLUSIONS

Chronic alcohol consumption may result in DNA methylation changes, leading to neuroadaptations that may underlie some of the mechanisms of AUD risk and persistence. Future studies are needed to confirm the few existing results, and then to elucidate whether DNA methylation changes are the cause or consequence of AUDs.

SCIENTIFIC SIGNIFICANCE

DNA methylation profiles may be used to assess AUD status or monitor AUD treatment response. (Am J Addict 2017;26:502-515).

Smoking, Alcohol, Drug Use, Abuse and Dependence in Narcolepsy and Idiopathic Hypersomnia: A Case-Control Study

STUDY OBJECTIVES

Basic experiments support the impact of hypocretin on hyperarousal and motivated state required for increasing drug craving. Our aim was to assess the frequencies of smoking, alcohol and drug use, abuse and dependence in narcolepsy type 1 (NT1, hypocretin-deficient), narcolepsy type 2 (NT2), idiopathic hypersomnia (IH) (non-hypocretin-deficient conditions), in comparison to controls. We hypothesized that NT1 patients would be less vulnerable to drug abuse and addiction compared to other hypersomniac patients and controls from general population.

METHODS

We performed a cross-sectional study in French reference centres for rare hypersomnia diseases and included 450 adult patients (median age 35 years; 41.3% men) with NT1 (n = 243), NT2 (n = 116), IH (n = 91), and 710 adult controls. All participants were evaluated for alcohol consumption, smoking habits, and substance (alcohol and illicit drug) abuse and dependence diagnosis during the past year using the Mini International Neuropsychiatric Interview.

RESULTS

An increased proportion of both tobacco and heavy tobacco smokers was found in NT1 compared to controls and other hypersomniacs, despite adjustments for potential confounders. We reported an increased regular and frequent alcohol drinking habit in NT1 versus controls but not compared to other hypersomniacs in adjusted models. In contrast, heavy drinkers were significantly reduced in NT1 versus controls but not compared to other hypersomniacs. The proportion of patients with excessive drug use (codeine, cocaine, and cannabis), substance dependence, or abuse was low in all subgroups, without significant differences between either hypersomnia disorder categories or compared with controls.

CONCLUSIONS

We first described a low frequency of illicit drug use, dependence, or abuse in patients with central hypersomnia, whether Hcrt-deficient or not, and whether drug-free or medicated, in the same range as in controls. Conversely, heavy drinkers were rare in NT1 compared to controls but not to other hypersomniacs, without any change in alcohol dependence or abuse frequency. Although disruption of hypocretin signaling in rodents reduces drug-seeking behaviors, our results do not support that hypocretin deficiency constitutes a protective factor against the development of drug addiction in humans.

Oxidoreductive homeostasis in alcohol-dependent male patients and the risk of alcohol drinking relapse in a 6-month follow-up

Disturbances in the central signaling of reactive oxygen species (ROS) in response to energy intake are recognized as taking part in appetitive and consummative phases of eating disorders. This study aimed to verify the hypothesis that blood oxidoreductive balance can also affect demand for energy substances, such as alcoholic beverages in alcohol-dependent individuals, as well as the severity of their alcohol dependence and risk of drinking relapse. The following values were determined in the blood of 54 alcohol-dependent male patients after alcohol withdrawal, again after 4 weeks and after 6 months: the aldehyde products of lipid peroxidation (malonyl dialdehyde [MDA] and 4-hydroxynonenal [4-HNE]), nitric oxide (NO) metabolites, total antioxidant status (TAS), the blood activities of glutathione peroxidase (GSHpx), superoxide dismutase (SOD), glutathione reductase (GSHred), blood glucose, and lipids. Alcoholics who relapsed during 6 months of observation (n = 31, 57%) compared with patients who maintained alcohol abstinence for 6 months (n = 23, 43%) differed only in relation to initial and final NO metabolite serum concentrations. The risk of alcohol drinking relapse was lower in patients with an above-median initial blood concentration of NO metabolites and TAS. The oxidative stress parameters correlated with alcohol-dependence severity markers. No significant correlations between the studied antioxidant balance parameters and markers of nutritional status, including blood glucose and lipids, were found. Although the results of our study have some limitations and require further investigation, they suggest the role of oxidoreductive balance in the pathomechanisms of alcohol dependence and drinking relapse. In addition, due to a lack of association found between blood oxidative stress parameters and BMI, blood glucose, and lipid concentrations, they show the presence of disturbances in systemic ROS signaling in response to energy availability in alcoholics after alcohol withdrawal.

Orexin in Patients with Alcohol Dependence Treated for Relapse Prevention: A Pilot Study

AIM

The aim of the study was to assess the blood concentration of orexin and its association with other clinical factors in patients with alcohol dependence.

METHODS

Thirty-two males hospitalized on an addiction treatment ward due to alcohol dependence and 23 healthy men as a control group were enrolled in the study. The measurement of orexin in the blood was made at the beginning of the treatment (after withdrawal symptoms had stopped) and again after 4 weeks of observation.

RESULTS

At the beginning of the observation, the alcohol-dependent patients had significantly greater orexin blood concentration than the control group. After 4 weeks of treatment for relapse prevention, the blood orexin level decreased significantly to a value similar to that in the control group. At the beginning of the study, more severely alcohol-dependent patients (Short Alcohol Dependence Data [SADD] score range: 20-45) had significantly greater orexin blood concentration than individuals with moderate addiction severity (SADD score range: 10-19). However, after 4 weeks of abstinence, the peptide blood concentration was similar in both groups of alcoholic patients.

CONCLUSIONS

Orexin or its receptor is a potential target for relapse prevention treatment, but further study with long-term observation is needed to verify the usefulness of blood orexin determination as a marker of alcohol relapse risk.

Current and Future Prospects for Epigenetic Biomarkers of Substance Use Disorders

Substance abuse has an enormous impact on economic and quality of life measures throughout the world. In more developed countries, overutilization of the most common forms of substances of abuse, alcohol and tobacco, is addressed primarily through prevention of substance use initiation and secondarily through the treatment of those with substance abuse or dependence. In general, these therapeutic approaches to substance abuse are deemed effective. However, there is a broad consensus that the development of additional tools to aid diagnosis, prioritize treatment selection and monitor treatment response could have substantial impact on the effectiveness of both substance use prevention and treatment. The recent demonstrations by a number of groups that substance use exposure is associated with robust changes in DNA methylation signatures of peripheral blood cells suggests the possibility that methylation assessments of blood or saliva could find broad clinical applications. In this article, we review recent progress in epigenetic approaches to substance use assessment with a particular emphasis on smoking (and alcohol) related applications. In addition, we highlight areas, such as the epigenetics of psychostimulant, opioid and cannabis abuse, which are markedly understudied and could benefit from intensified collaborative efforts to define epigenetic biomarkers of abuse and dependence.

Future pharmacological treatments for substance use disorders

Substance use disorders represent a serious public health and social issue worldwide. Recent advances in our understanding of the neurobiological basis of the addictive processes have led to the development of a growing number of pharmacological agents to treat addictions. Despite this progress, there are no approved pharmacological treatments for cocaine, methamphetamine and cannabis addiction. Moving treatment development to the next stage will require novel ways of approaching substance use disorders. One such novel approach is to target individual vulnerabilities, such as cognitive function, sex differences and psychiatric comorbidities. This review provides a summary of promising pharmacotherapies for alcohol, opiate, stimulant and nicotine addictions. Many medications that target positive and negative reinforcement of drugs, as well as individual vulnerabilities to addiction, are in different phases of development. Clinical trials testing the efficacy of these medications for substance use disorder are warranted.

The paraventricular nucleus of the thalamus is recruited by both natural rewards and drugs of abuse: recent evidence of a pivotal role for orexin/hypocretin signaling in this thalamic nucleus in drug-seeking behavior

A major challenge for the successful treatment of drug addiction is the long-lasting susceptibility to relapse and multiple processes that have been implicated in the compulsion to resume drug intake during abstinence. Recently, the orexin/hypocretin (Orx/Hcrt) system has been shown to play a role in drug-seeking behavior. The Orx/Hcrt system regulates a wide range of physiological processes, including feeding, energy metabolism, and arousal. It has also been shown to be recruited by drugs of abuse. Orx/Hcrt neurons are predominantly located in the lateral hypothalamus that projects to the paraventricular nucleus of the thalamus (PVT), a region that has been identified as a "way-station" that processes information and then modulates the mesolimbic reward and extrahypothalamic stress systems. Although not thought to be part of the "drug addiction circuitry", recent evidence indicates that the PVT is involved in the modulation of reward function in general and drug-directed behavior in particular. Evidence indicates a role for Orx/Hcrt transmission in the PVT in the modulation of reward function in general and drug-directed behavior in particular. One hypothesis is that following repeated drug exposure, the Orx/Hcrt system acquires a preferential role in mediating the effects of drugs vs. natural rewards. The present review discusses recent findings that suggest maladaptive recruitment of the PVT by drugs of abuse, specifically Orx/Hcrt-PVT neurotransmission.

The hypocretin system and psychiatric disorders

The hypocretin system is constituted by a small group of hypothalamic neurons with widespread connections within the entire central nervous system producing two neuropeptides involved in several key physiological functions such as the regulation of sleep and wakefulness, motor control, autonomic functions, metabolism, feeding behavior, and reward. Narcolepsy with cataplexy is a neurological disorder regarded as a disease model for the selective hypocretin system damage, and also shares several psychopatological traits and comorbidities with psychiatric disorders. We reviewed the available literature on the involvement of the hypocretin system in psychiatric nosography. Different evidences such as cerebrospinal hypocretin-1 levels, genetic polymorphisms of the neuropeptides or their receptors, response to treatments, clinical, experimental and functional data directly or indirectly linked the hypocretin system to schizophrenia, mood, anxiety and eating disorders, as well as to addiction. Future genetic and pharmacological studies will disentangle the hypocretin system role in the field of psychiatry.

Neurochemical mechanisms of alcohol withdrawal

Alcohol dependence encompasses a serious medical and societal problem that constitutes a major public health concern. A serious consequence of dependence is the emergence of symptoms associated with the alcohol withdrawal syndrome when drinking is abruptly terminated or substantially reduced. Clinical features of alcohol withdrawal include signs of central nervous system hyperexcitability, heightened autonomic nervous system activation, and a constellation of symptoms contributing to psychologic discomfort and negative affect. The development of alcohol dependence is a complex and dynamic process that ultimately reflects a maladaptive neurophysiologic state. Perturbations in a wide range of neurochemical systems, including glutamate, γ-aminobutyric acid, monoamines, a host of neuropeptide systems, and various ion channels produced by the chronic presence of alcohol ultimately compromise the functional integrity of the brain. These neuroadaptations not only underlie the emergence and expression of many alcohol withdrawal symptoms, but also contribute to enhanced relapse vulnerability as well as perpetuation of uncontrolled excessive drinking. This chapter highlights the hallmark features of the alcohol withdrawal syndrome, and describes neuroadaptations in a wide array of neurotransmitter and neuromodulator systems (amino acid and monoamine neurotransmitter, neuropeptide systems, and various ion channels) as they relate to the expression of various signs and symptoms of alcohol withdrawal, as well as their relationship to the significant clinical problem of relapse and uncontrolled dangerous drinking.

The hypocretins and the reward function: what have we learned so far?

A general consensus acknowledges that drug consumption (including alcohol, tobacco, and illicit drugs) constitutes the leading cause of preventable death worldwide. But the global burden of drug abuse extends the mortality statistics. Indeed, the comorbid long-term debilitating effects of the disease also significantly deteriorate the quality of life of individuals suffering from addiction disorders. Despite the large body of evidence delineating the cellular and molecular adaptations induced by chronic drug consumption, the brain mechanisms responsible for drug craving and relapse remain insufficiently understood, and even the most recent developments in the field have not brought significant improvement in the management of drug dependence. Though, recent preclinical evidence suggests that disrupting the hypocretin (orexin) system may serve as an anticraving medication therapy. Here, we discuss how the hypocretins, which orchestrate normal wakefulness, metabolic health and the execution of goal-oriented behaviors, may be compromised and contribute to elicit compulsive drug seeking. We propose an overview on the most recent studies demonstrating an important role for the hypocretin neuropeptide system in the regulation of drug reward and the prevention of drug relapse, and we question the relevance of disrupting the hypocretin system to alleviate symptoms of drug addiction.

Genome-wide DNA methylation analysis in alcohol dependence

Genetic, epigenetic, and environmental factors influence the development of alcohol dependence (AD). Recent studies have shown that DNA methylation markers in peripheral blood may serve as risk markers for AD. Yet a genome-wide epigenomic approach investigating the role of DNA methylation in AD has yet to be performed. We conducted a population-based, case-control study of genome-wide DNA methylation to determine if alterations in gene-specific methylation were associated with AD in a Chinese population. Using the Illumina Infinium Human Methylation27 BeadChip, we assessed gene-specific methylation in over 27 000 CpG sites from DNA isolated from lymphocytes in 63 male AD in-patients and 65 male healthy controls. Using a multi-factorial statistical model, we observed differential methylation between cases and controls at multiple CpG sites with the majority of the methylated CpG sites being hypomethylated. Analyses with the online gene set analysis toolkit WebGestalt revealed that the genes of interest were enriched in multiple biological processes involved in AD development. Gene Ontology function annotation showed that stress, immune response and signal transduction were highly associated with AD. Further analysis by the Kyoto Encyclopedia of Genes and Genomes revealed associations with multiple pathways involved in metabolism through cytochrome P450, cytokine-cytokine receptor interaction and calcium signaling. Associations with canonical pathways previously shown to be involved in AD were also observed, such as dehydrogenases 1A (ADH1A), ADH7, aldehyde dehydrogenases 3B2 (ALDH3B2) and cytochrome P450 2A13. We present evidence that alterations in DNA methylation may be associated with AD, which is consistent with epigenetic theory.

Epigenetic regulation of memory formation and maintenance

Understanding the cellular and molecular mechanisms underlying the formation and maintenance of memories is a central goal of the neuroscience community. It is well regarded that an organism's ability to lastingly adapt its behavior in response to a transient environmental stimulus relies on the central nervous system's capability for structural and functional plasticity. This plasticity is dependent on a well-regulated program of neurotransmitter release, post-synaptic receptor activation, intracellular signaling cascades, gene transcription, and subsequent protein synthesis. In the last decade, epigenetic markers like DNA methylation and post-translational modifications of histone tails have emerged as important regulators of the memory process. Their ability to regulate gene transcription dynamically in response to neuronal activation supports the consolidation of long-term memory. Furthermore, the persistent and self-propagating nature of these mechanisms, particularly DNA methylation, suggests a molecular mechanism for memory maintenance. In this review, we will examine the evidence that supports a role of epigenetic mechanisms in learning and memory. In doing so, we hope to emphasize (1) the widespread involvement of these mechanisms across different behavioral paradigms and distinct brain regions, (2) the temporal and genetic specificity of these mechanisms in response to upstream signaling cascades, and (3) the functional outcome these mechanisms may have on structural and functional plasticity. Finally, we consider the future directions of neuroepigenetic research as it relates to neuronal storage of information.

Orexin A expression and promoter methylation in patients with cannabis dependence in comparison to nicotine-dependent cigarette smokers and nonsmokers

BACKGROUND

The orexins (hypocretins) are neuropeptides with an origin in the lateral hypothalamus. They have been found to be crucial within the context of drug craving, withdrawal und relapse.

METHODS

Therefore, orexin A gene expression and promoter methylation in peripheral blood cells of 77 subjects [36 with tetrahydrocannabinol (THC) dependence, 20 nicotine-dependent cigarette smokers and 21 nonsmokers] were assessed by quantitative real-time PCR and methylation-specific digestion PCR.

RESULTS

There was a statistically significant difference in orexin A expression between the three groups [p = 0.000, F = 131.4, d.f. = 2, analysis of variance (ANOVA)]. Orexin A gene expression was statistically significantly correlated with the Satisfaction with Life Scale (r = -0.28, p = 0.018), a visual analogue scale of craving (r = 0.734, p = 0.000) and three subscales of the World Health Organization Alcohol, Smoking and Substance Involvement Screening Test, i.e. nicotine consumption (r = 0.388, p = 0.001), alcohol consumption (r = 0.354, p = 0.002) and cannabis consumption (r = 0.783, p = 0.000). The mean promoter methylation (as a percentage) was not statistically related to orexin gene expression. However, there was a statistically significant difference in promoter methylation with regard to body mass index in general (F = 2.37, d.f. = 54, p = 0.016, ANOVA).

CONCLUSIONS

Orexin might be a possible target in THC as well as nicotine dependence, taking into account the effect of THC on energy homeostasis in the circuit of reward and motivation and its impact on appetite and body weight.

CB1 and CB2 receptor expression and promoter methylation in patients with cannabis dependence

CB1 and CB2 receptors are influenced via exogenous and endogenous cannabinoids. To date, little is known regarding changes in receptor expression and methylation in THC (tetrahydrocannabinol) dependence. Therefore, the CB1 and CB2 receptor mRNA expression levels and promoter methylation status in the peripheral blood cells of 77 subjects (36 with THC dependence, 21 cigarette smokers and 20 nonsmokers) were assessed by quantitative real-time PCR and methylation-specific PCR. There was a significant difference in CB1 receptor expression levels between the three groups (ANOVA, p < 0.001, d.f. = 2, F = 71.3). The mean promoter methylation (%) was significantly negatively correlated with CB1 receptor mRNA expression levels (Spearman's rho: r = -0.37; p = 0.002). Using a mixed general linear model, it was demonstrated that the CB1 mRNA expression (as the dependent variable) was associated with the satisfaction with life scale (SWLS) (r = 0.101; T = 2.8; p = 0.007), craving (as measured with the VAS; r = -0.023; T = -2.3; p = 0.023) and the WHO-Assist Subscale for Cannabis consumption (r = -0.068; T = -2.4; p = 0.02). CB1 receptor expression levels and methylation status appear to be altered in subjects with THC dependence.

The role of orexins/hypocretins in alcohol use and abuse: an appetitive-reward relationship

Orexins (hypocretins) are neuropeptides synthesized in neurons located in the lateral (LH), perifornical, and dorsomedial (DMH) hypothalamus. These neurons innervate many regions in the brain and modulate multiple other neurotransmitter systems. As a result of these extensive projections and interactions orexins are involved in numerous functions, such as feeding behavior, neuroendocrine regulation, the sleep-wake cycle, and reward-seeking. This review will summarize the literature to date which has evaluated a role of orexins in the behavioral effects of alcohol, with a focus on understanding the importance of this peptide and its potential as a clinical therapeutic target for alcohol use disorders.

Prenatal ethanol exposure stimulates neurogenesis in hypothalamic and limbic peptide systems: possible mechanism for offspring ethanol overconsumption

Exposure to ethanol during the prenatal period contributes to increased alcohol consumption and preference in rodents and increased risk for alcoholism in humans. With studies in adult animals showing the orexigenic peptides, enkephalin (ENK), galanin (GAL) and orexin (OX), to stimulate ethanol consumption, the question addressed here is whether prenatal ethanol alters the development in utero of specific neurons that express these peptides. With reports describing suppressive effects of high doses of ethanol, we examined the offspring of dams gavaged from embryonic day 9 to parturition with a control solution or lower ethanol doses, 1 and 3g/kg/day, known to promote ethanol consumption in the offspring. To understand underlying mechanisms, measurements were taken in postnatal offspring of the expression of ENK in the hypothalamic paraventricular nucleus (PVN) and nucleus accumbens (NAc), GAL in the PVN, and OX in the perifornical lateral hypothalamus (PFLH) using real-time qPCR and in situ hybridization, and also of the cell proliferation marker, 5-bromo-2-deoxyuridine (BrdU), and its double-labeling with either neuronal nuclei (NeuN), a marker of mature neurons, or the peptides. On postnatal day 15 (P15), after two weeks without ethanol, the offspring showed increased expression of ENK in the PVN and NAc core but not shell, GAL in the PVN, and OX in the PFLH. In these same areas, prenatal ethanol compared to control increased the density at birth (P0) of neurons expressing these peptides and at P0 and P15 of neurons double-labeling BrdU and NeuN, indicating increased neurogenesis. These BrdU-positive neurons were found to express ENK, GAL and OX, indicating that prenatal ethanol promotes neurogenesis in these specific peptide systems. There were no changes in gliogenesis or apoptosis. This increase in neurogenesis and density of peptide-expressing neurons suggests the involvement of these hypothalamic and accumbal peptide systems in mediating the increased alcohol consumption observed in prenatal ethanol-exposed offspring.

The hypocretin/orexin system: implications for drug reward and relapse

Hypocretins (also known as orexins) are hypothalamic neuropeptides involved in the regulation of sleep/wake states and feeding behavior. Recent studies have also demonstrated an important role for the hypocretin/orexin system in the addictive properties of drugs of abuse, consistent with the reciprocal innervations between hypocretin neurons and brain areas involved in reward processing. This system participates in the primary reinforcing effects of opioids, nicotine, and alcohol. Hypocretins are also involved in the neurobiological mechanisms underlying relapse to drug-seeking behavior induced by drug-related environmental stimuli and stress, as mainly described in the case of psychostimulants. Based on these preclinical studies, the use of selective ligands targeting hypocretin receptors could represent a new therapeutical strategy for the treatment of substance abuse disorders. In this review, we discuss and update the current knowledge about the participation of the hypocretin system in drug addiction and the possible neurobiological mechanisms involved in these processes regulated by hypocretin transmission.

Multiple roles for orexin/hypocretin in addiction

Orexins/hypocretins are hypothalamic peptides involved in arousal and wakefulness, but also play a critical role in drug addiction and reward-related behaviors. Here, we review the roles played by orexins in a variety of animal models of drug addiction, emphasizing both commonalities and differences for orexin's involvement in seeking of the major classes of abused drugs, as well as food. One common theme that emerges is an involvement of orexins in drug seeking triggered by external stimuli (e.g., cues, contexts or stressors). We also discuss the functional neuronal circuits in which orexins are embedded, and how these circuits mediate addiction-related behaviors, with particular focus on the role of orexin and glutamate interactions within the ventral tegmental area. Finally, we attempt to contextualize the role of orexins in reward by discussing ways in which these peptides, expressed in only a few thousand neurons in the brain, can have such wide-ranging effects on behavior.