A key role for corticotropin-releasing factor in alcohol dependence

Corticotropin releasing hormone receptor 1 in the medial prefrontal cortex mediates aversion resistant alcohol intake

RATIONALE

Alcohol consumption despite negative consequences is a core symptom of Alcohol Use Disorder. In animal models, this is studied by pairing aversive stimuli with alcohol access, and continuation of drinking under these conditions is known as aversion resistance. Previously, we found that female mice are more aversion resistant than males. Corticotropin releasing hormone (Crh) and the Crh receptor 1 (Crhr1) regulate stress-induced reinstatement, alcohol dependence, and binge-like drinking. However, the role of the Crh system in aversion resistance has not been assessed.

OBJECTIVES

We aimed to identify sex differences in the Crh system during quinine-adulterated alcohol intake.

METHODS

We used two-bottle choice and adulterated the alcohol solution with quinine. Next, we measured Crh and Crhr1 levels in brain tissue using real-time polymerase chain reaction (RT-qPCR) and RNAscope in situ hybridization. We then infused a Crhr1 antagonist into the medial prefrontal cortex (mPFC) prior to quinine-alcohol intake.

RESULTS

After quinine-alcohol consumption, females exhibited increased mPFC Crhr1 mRNA levels as measured by RT-qPCR. This was confirmed with greater anatomical specificity using RNAscope, with females exhibiting an increased number of Crhr1 + cells in the dorsomedial PFC and the ventromedial PFC. mPFC Crhr1 antagonist treatment reduced quinine-alcohol consumption in females but did not impact consumption in males. Quinine-free alcohol intake was unaffected by Crhr1 antagonist treatment.

CONCLUSIONS

Our findings suggest that Crhr1 in mPFC plays a role in aversion resistant alcohol intake in females. Future experiments will examine the sources of Crh innervation to the mPFC and their distinct roles in alcohol seeking.

Behavioral and Amygdala Biochemical Damage Induced by Alternating Mild Stress and Ethanol Intoxication in Adolescent Rats: Reversal by Argan Oil Treatment?

Adolescence is a critical period when the effects of ethanol and stress exposure are particularly pronounced. Argan oil (AO), a natural vegetable oil known for its diverse pharmacological benefits, was investigated for its potential to mitigate addictive-like behaviors and brain damage induced by adolescent intermittent ethanol intoxication (IEI) and unpredictable mild stress (UMS). From P30 to P43, IEI rats received a daily ip ethanol (3 g/kg) on a two-day on/two-day off schedule. On alternate days, the rats were submitted to UMS protocol. Next, a two-bottle free access paradigm was performed over 10 weeks to assess intermittent 20% ethanol voluntary consumption. During the same period, the rats were gavaged daily with AO (15 mL/kg). Our results show that IEI/UMS significantly increased voluntary alcohol consumption (from 3.9 g/kg/24 h to 5.8 g/kg/24 h) and exacerbated withdrawal signs and relapse-like drinking in adulthood. Although AO treatment slightly reduced ethanol intake, it notably alleviated withdrawal signs during abstinence and relapse-like drinking in adulthood. AO's effects were associated with its modulation of the HPA axis (elevated serum corticosterone), restoration of amygdala oxidative balance, BDNF levels, and attenuation of neurodegeneration. These findings suggest that AO's neuroprotective properties could offer a potential therapeutic avenue for reducing ethanol/stress-induced brain damage and addiction. Further research is needed to explore its mechanisms and therapeutic potential in alcohol use disorders.

Good Practice Guideline for Preclinical Alcohol Research: The STRINGENCY Framework

Research in the field of preclinical alcohol research, but also science in general, has a problem: Many published scientific results cannot be repeated. As a result, findings from preclinical research often do not translate well to humans, causing increasing disappointment and calls for restructuring of preclinical research, that is, better reproducibility of preclinical research. However, the replication crisis is an inherent problem in biomedical research. Replication failures are not only due to small experimental variations but are often the result of poor methodology. In response to the replication crisis, numerous guidelines and recommendations have been proposed to promote transparency, rigor, and reproducibility in scientific research. What is missing today is a framework that integrates all the confusing information that results from all these guidelines and recommendations. Here we present STRINGENCY, an integrative approach to good practice guidelines for preclinical alcohol research, which can also apply to behavioral research in general and which aims to improve preclinical research to better prepare it for translation and minimize the "valley of death" in translational research. STRINGENCY includes systematic review and, when possible, meta-analysis prior to study design, sample size calculation, preregistration, multisite experiments, scientific data management (FAIR), reporting of data using ARRIVE, generalization of research data, and transparent publications that allow reporting of null results. We invite the scientific community to adopt STRINGENCY to improve the reliability and impact of preclinical alcohol research.

Mouse parasubthalamic Crh neurons drive alcohol drinking escalation and behavioral disinhibition

Corticotropin-releasing factor (CRF, encoded by Crh) signaling is thought to play a critical role in the development of excessive alcohol drinking and the emotional and physical pain associated with alcohol withdrawal. Here, we investigated the parasubthalamic nucleus (PSTN) as a potential source of CRF relevant to the control of alcohol consumption, affect, and nociception in mice. We identified PSTN Crh neurons as a neuronal subpopulation that exerts a potent and unique influence on behavior by promoting not only alcohol but also saccharin drinking, while PSTN neurons are otherwise known to suppress consummatory behaviors. Furthermore, PSTN Crh neurons are causally implicated in the escalation of alcohol and saccharin intake produced by chronic intermittent ethanol (CIE) vapor inhalation, a mouse model of alcohol use disorder. In contrast to our predictions, the ability of PSTN Crh neurons to increase alcohol drinking is not mediated by CRF1 signaling. Moreover, the pattern of behavioral disinhibition and reduced nociception driven by their activation does not support a role of negative reinforcement as a motivational basis for the concomitant increase in alcohol drinking. Finally, silencing Crh expression in the PSTN slowed down the escalation of alcohol intake in mice exposed to CIE and accelerated their recovery from withdrawal-induced mechanical hyperalgesia. Altogether, our results suggest that PSTN Crh neurons may represent an important node in the brain circuitry linking alcohol use disorder with sweet liking and novelty seeking.

JNK Signaling Positively Regulates Acute Ethanol Tolerance in C. elegans

Alcohol use disorder (AUD) is a chronic neurobehavioral condition characterized by a cycle of tolerance development, increased consumption, and reinstated craving and seeking behaviors during withdrawal. Understanding the intricate mechanisms of AUD necessitates reliable animal models reflecting its key features. Caenorhabditis elegans (C. elegans), with its conserved nervous system and genetic tractability, has emerged as a valuable model organism to study AUD. Here, we employ an ethanol vapor exposure model in Caenorhabditis elegans, recapitulating AUD features while maintaining high-throughput scalability. We demonstrate that ethanol vapor exposure induces intoxication-like behaviors, acute tolerance, and ethanol preference, akin to mammalian AUD traits. Leveraging this model, we elucidate the conserved role of c-jun N-terminal kinase (JNK) signaling in mediating acute ethanol tolerance. Mutants lacking JNK signaling components exhibit impaired tolerance development, highlighting JNK's positive regulation. Furthermore, we detect ethanol-induced JNK activation in C. elegans. Our findings underscore the utility of C. elegans with ethanol vapor exposure for studying AUD and offer novel insights into the molecular mechanisms underlying acute ethanol tolerance through JNK signaling.

Distinct roles of the left and right prelimbic cortices in the modulation of ethanol consumption in male mice under acute and chronic social defeat stress

RATIONALE

Chronic stress exposure disrupts the medial prefrontal cortex's (mPFC) ability to regulate impulses, leading to the loss of control over alcohol drinking in rodents, emphasizing the critical role of this forebrain area in regulating alcohol consumption. Moreover, chronic stress exposure causes lateralization of mPFC functions with volumetric and functional changes, resulting in hyperactivity in the right hemisphere and functional decrease in the left.

OBJECTIVES

This study investigated the inhibitory role of the left prelimbic cortex (LPrL) on ethanol consumption induced by chronic social defeat stress (SDS) in male mice and to examine if inactivation of the LPrL causes disinhibition of the right mPFC, leading to an increase in ethanol consumption. We also investigated the role of lateralization and neurochemical alterations in the mPFC related to ethanol consumption induced by chronic SDS. To this end, we examined the activation patterns of ΔFosB, VGLUT2, and GAD67 in the left and right mPFC.

RESULTS

Temporarily blocking the LPrL or right PrL (RPrL) cortices during acute SDS did not affect male mice's voluntary ethanol consumption in male mice. When each cortex was blocked in mice previously exposed to chronic SDS, ethanol consumption also remained unaffected. However, male mice with LPrL lesions during chronic SDS showed an increase in voluntary ethanol consumption, which was associated with enhanced ΔFosB/VGLUT2-positive neurons within the RPrL cortex.

CONCLUSIONS

The results suggest that the LPrL may play a role in inhibiting ethanol consumption induced by chronic SDS, while the RPrL may be involved in the disinhibition of ethanol consumption.

The effect of MK-801 on stress-ethanol cross-sensitization is dissociable from its effects on nNOS activity

Locomotor behavioral sensitization represents an animal model for understanding neuroadaptive processes related to repeated drug exposure. Repeated stress can elicit a cross-sensitization to the stimulant response of ethanol, which involves neuronal nitric oxide synthase (nNOS). Activation of N-methyl d-aspartate (NMDA) glutamate receptors triggers nNOS and the synthesis of nitric oxide (NO). In this study, we investigated the effects of blocking NMDA receptors using the NMDA receptor antagonist MK-801 on the cross-sensitization between restraint stress and ethanol. We also evaluated the nNOS activity in the prefrontal cortex (PFC) and hippocampus. Mice were pretreated with saline or MK-801 30 min before an injection of saline or stress exposure for 14 days. On the following day, they were challenged with either saline or 1.8 g/kg ethanol. Swiss male mice pretreated with 0.25 mg/kg MK-801 exhibited a sensitized response to ethanol. Moreover, MK-801 potentiated the cross-sensitization between stress and ethanol. However, MK-801 prevented the enhanced nNOS activity in stress-exposed groups (challenged with saline or ethanol) in the PFC; the antagonist also prevented the ethanol-induced increase in nNOS activity and reduced this enzyme activity in mice exposed to stress in the hippocampus. These data indicate that systemic treatment with the NMDA antagonist potentiated, rather than blocked, ethanol-induced behavioral sensitization and that this effect is dissociable from the capacity of NMDA antagonists to reduce ethanol/stress-induced NOS stimulation in the PFC and hippocampus.

Alcohol Dependence Modifies Brain Networks Activated During Withdrawal and Reaccess: A c-Fos-Based Analysis in Mice

BACKGROUND

High-level alcohol consumption causes neuroplastic changes in the brain that promote pathological drinking behavior. Some of these changes have been characterized in defined brain circuits and cell types, but unbiased approaches are needed to explore broader patterns of adaptations.

METHODS

We used whole-brain c-Fos mapping and network analysis to assess patterns of neuronal activity during alcohol withdrawal and following reaccess in a well-characterized model of alcohol dependence. Mice underwent 4 cycles of chronic intermittent ethanol to increase voluntary alcohol consumption, and a subset underwent forced swim stress to further escalate consumption. Brains were collected either 24 hours (withdrawal) or immediately following a 1-hour period of alcohol reaccess. c-fos counts were obtained for 110 brain regions using iDISCO and ClearMap. Then, we classified mice as high or low drinkers and used graph theory to identify changes in network properties associated with high-drinking behavior.

RESULTS

During withdrawal, chronic intermittent ethanol mice displayed widespread increased c-Fos expression relative to air-exposed mice, independent of forced swim stress. Reaccess drinking reversed this increase. Network modularity, a measure of segregation into communities, was increased in high-drinking mice after alcohol reaccess relative to withdrawal. The cortical amygdala showed increased cross-community coactivation during withdrawal in high-drinking mice, and cortical amygdala silencing in chronic intermittent ethanol mice reduced voluntary drinking.

CONCLUSIONS

Alcohol withdrawal in dependent mice causes changes in brain network organization that are attenuated by reaccess drinking. Olfactory brain regions, including the cortical amygdala, drive some of these changes and may play an important but underappreciated role in alcohol dependence.

Theoretical Frameworks and Mechanistic Aspects of Alcohol Addiction: Alcohol Addiction as a Reward Deficit/Stress Surfeit Disorder

Alcohol use disorder (AUD) can be defined by a compulsion to seek and take alcohol, the loss of control in limiting intake, and the emergence of a negative emotional state when access to alcohol is prevented. Alcohol use disorder impacts multiple motivational mechanisms and can be conceptualized as a disorder that includes a progression from impulsivity (positive reinforcement) to compulsivity (negative reinforcement). Compulsive drug seeking that is associated with AUD can be derived from multiple neuroadaptations, but the thesis argued herein is that a key component involves the construct of negative reinforcement. Negative reinforcement is defined as drug taking that alleviates a negative emotional state. The negative emotional state that drives such negative reinforcement is hypothesized to derive from the dysregulation of specific neurochemical elements that are involved in reward and stress within basal forebrain structures that involve the ventral striatum and extended amygdala, respectively. Specific neurochemical elements in these structures include decreases in reward neurotransmission (e.g., decreases in dopamine and opioid peptide function in the ventral striatum) and the recruitment of brain stress systems (e.g., corticotropin-releasing factor [CRF]) in the extended amygdala, which contributes to hyperkatifeia and greater alcohol intake that is associated with dependence. Glucocorticoids and mineralocorticoids may play a role in sensitizing the extended amygdala CRF system. Other components of brain stress systems in the extended amygdala that may contribute to the negative motivational state of withdrawal include norepinephrine in the bed nucleus of the stria terminalis, dynorphin in the nucleus accumbens, hypocretin and vasopressin in the central nucleus of the amygdala, and neuroimmune modulation. Decreases in the activity of neuropeptide Y, nociception, endocannabinoids, and oxytocin in the extended amygdala may also contribute to hyperkatifeia that is associated with alcohol withdrawal. Such dysregulation of emotional processing may also significantly contribute to pain that is associated with alcohol withdrawal and negative urgency (i.e., impulsivity that is associated with hyperkatifeia during hyperkatifeia). Thus, an overactive brain stress response system is hypothesized to be activated by acute excessive drug intake, to be sensitized during repeated withdrawal, to persist into protracted abstinence, and to contribute to the compulsivity of AUD. The combination of the loss of reward function and recruitment of brain stress systems provides a powerful neurochemical basis for a negative emotional state that is responsible for the negative reinforcement that at least partially drives the compulsivity of AUD.

Semaglutide reduces alcohol intake and relapse-like drinking in male and female rats

BACKGROUND

Glucagon-like peptide1 receptor (GLP-1R) agonists have been found to reduce alcohol drinking in rodents and overweight patients with alcohol use disorder (AUD). However, the probability of low semaglutide doses, an agonist with higher potency and affinity for GLP-1R, to attenuate alcohol-related responses in rodents and the underlying neuronal mechanisms is unknown.

METHODS

In the intermittent access model, we examined the ability of semaglutide to decrease alcohol intake and block relapse-like drinking, as well as imaging the binding of fluorescently marked semaglutide to nucleus accumbens (NAc) in both male and female rats. The suppressive effect of semaglutide on alcohol-induced locomotor stimulation and in vivo dopamine release in NAc was tested in male mice. We evaluated effect of semaglutide on the in vivo release of dopamine metabolites (DOPAC and HVA) and gene expression of enzymes metabolising dopamine (MAOA and COMT) in male mice.

FINDINGS

In male and female rats, acute and repeated semaglutide administration reduced alcohol intake and prevented relapse-like drinking. Moreover, fluorescently labelled semaglutide was detected in NAc of alcohol-drinking male and female rats. Further, semaglutide attenuated the ability of alcohol to cause hyperlocomotion and to elevate dopamine in NAc in male mice. As further shown in male mice, semaglutide enhanced DOPAC and HVA in NAc when alcohol was onboard and increased the gene expression of COMT and MAOA.

INTERPRETATION

Altogether, this indicates that semaglutide reduces alcohol drinking behaviours, possibly via a reduction in alcohol-induced reward and NAc dependent mechanisms. As semaglutide also decreased body weight of alcohol-drinking rats of both sexes, upcoming clinical studies should test the plausibility that semaglutide reduces alcohol intake and body weight in overweight AUD patients.

FUNDING

Swedish Research Council (2019-01676), LUA/ALF (723941) from the Sahlgrenska University Hospital and the Swedish brain foundation.

Stress-related neuropeptide systems as targets for treatment of alcohol addiction: A clinical perspective

Alcohol use is a major cause of disability and death globally. These negative consequences disproportionately affect people who develop alcohol addiction, a chronic relapsing condition characterized by increased motivation to use alcohol, choice of alcohol over healthy, natural rewards, and continued use despite negative consequences. Available pharmacotherapies for alcohol addiction are few, have effect sizes in need of improvement, and remain infrequently prescribed. Research aimed at developing novel therapeutics has in large part focused on attenuating pleasurable or "rewarding" properties of alcohol, but this targets processes that primarily play a role as initiation factors. As clinical alcohol addiction develops, long-term changes in brain function result in a shift of affective homeostasis, and rewarding alcohol effects become progressively reduced. Instead, increased stress sensitivity and negative affective states emerge in the absence of alcohol and create powerful incentives for relapse and continued use through negative reinforcement, or "relief." Based on research in animal models, several neuropeptide systems have been proposed to play an important role in this shift, suggesting that these systems could be targeted by novel medications. Two mechanisms in this category, antagonism at corticotropin-releasing factor type 1, and neurokinin 1/substance P receptors, have been subject to initial evaluation in humans. A third, kappa-opioid receptor antagonism, has been evaluated in nicotine addiction and could soon be tested for alcohol. This paper discusses findings with these mechanisms to date, and their prospects as future targets for novel medications.

Corticotropin-Releasing Factor receptor 1 (CRF1) antagonism in patients with alcohol use disorder and high anxiety levels: effect on neural response during Trier Social Stress Test video feedback

In preclinical models of alcohol use disorder, the corticotropin-releasing factor (CRF) receptor is upregulated, particularly in the extended amygdala. This upregulation is thought to play a role in stress-induced relapse to drinking by a mechanism that is independent of the hypothalamic-pituitary-adrenal axis. As part of a double-blind, placebo-controlled clinical study with pexacerfont, a selective, orally available, and brain-penetrant CRF1 receptor antagonist which has anti-anxiety effects in preclinical studies, we examined the effect of pexacerfont on the neural response to a social stress task adapted to fMRI. Subjects were 39 individuals (4 women) with high trait anxiety and moderate to severe alcohol use disorder randomized to receive pexacerfont or placebo. The task involved feedback of videoclips of an individual performing the Trier Social Stress Test. Pexacerfont had no effect on the neural response to self-observation under stress. The neural response to viewing oneself under stress vs an unknown other under stress activated prefrontal brain regions including insula, inferior frontal gyrus as well as medial, superior frontal gyri. These regions of activation overlap with those found in studies using similar paradigms. Potential applications of this task to probe neurocircuitry that is disrupted in addiction is discussed.

Age at onset of alcohol consumption and its association with alcohol misuse in adulthood

OBJECTIVE

This study aimed to explore the association between early age onset of alcohol consumption and alcohol misuse in adulthood.

METHODS

The study sample consisted of 16 829 individuals' (8349 males, 8435 females) survey responses obtained from the Korea National Health and Nutrition Examination Survey (KNHANES) from 2016 through 2019. Alcohol dependence was measured using the AUDIT-C (Alcohol Use Disorder Identification Test-Consumption), and the ages at which alcohol consumption began were grouped into four categories: under 16, 16 to 18, 19 to 23, and over 24. Multiple logistic regression was used to examine the association between current alcohol misuse and age at onset of alcohol consumption.

RESULTS

Compared to individuals who started drinking alcohol after the age of 24, those who began drinking alcohol before the age of 16 were more likely to score 8 or more on AUDIT-C questions (under 16: males, odds ratio [OR] 2.50, confidence interval [CI] 1.97-3.17; females, OR: 1.66, CI: 1.18-2.33). Similar to the main analysis, the earlier the onset of alcohol assumption starts, the more likely one is to develop alcohol misuse in adulthood according to subgroup analysis stratified by independent variables in both gender.

CONCLUSION

The lower the age at the onset of alcohol consumption, the higher the likelihood of alcohol misuse in adulthood. While both males and females showed the same trend in response to the AUDIT-C questions, males tended to have a stronger association between early onset alcohol consumption and alcohol misuse.

Epigenetic Dysregulation in Alcohol-Associated Behaviors: Preclinical and Clinical Evidence

Alcohol use disorder (AUD) is characterized by loss of control over intake and drinking despite harmful consequences. At a molecular level, AUD is associated with long-term neuroadaptations in key brain regions that are involved in reward processing and decision-making. Over the last decades, a great effort has been made to understand the neurobiological basis underlying AUD. Epigenetic mechanisms have emerged as an important mechanism in the regulation of long-term alcohol-induced gene expression changes. Here, we review the literature supporting a role for epigenetic processes in AUD. We particularly focused on the three most studied epigenetic mechanisms: DNA methylation, Histone modification and non-coding RNAs. Clinical studies indicate an association between AUD and DNA methylation both at the gene and global levels. Using behavioral paradigms that mimic some of the characteristics of AUD, preclinical studies demonstrate that changes in epigenetic mechanisms can functionally impact alcohol-associated behaviors. While many studies support a therapeutic potential for targeting epigenetic enzymes, more research is needed to fully understand their role in AUD. Identification of brain circuits underlying alcohol-associated behaviors has made major advances in recent years. However, there are very few studies that investigate how epigenetic mechanisms can affect these circuits or impact the neuronal ensembles that promote alcohol-associated behaviors. Studies that focus on the role of circuit-specific and cell-specific epigenetic changes for clinically relevant alcohol behaviors may provide new insights on the functional role of epigenetic processes in AUD.

Alcohol Withdrawal and the Associated Mood Disorders-A Review

Recreational use of alcohol is a social norm in many communities worldwide. Alcohol use in moderation brings pleasure and may protect the cardiovascular system. However, excessive alcohol consumption or alcohol abuse are detrimental to one's health. Three million deaths due to excessive alcohol consumption were reported by the World Health Organization. Emerging evidence also revealed the danger of moderate consumption, which includes the increased risk to cancer. Alcohol abuse and periods of withdrawal have been linked to depression and anxiety. Here, we present the effects of alcohol consumption (acute and chronic) on important brain structures-the frontal lobe, the temporal lobe, the limbic system, and the cerebellum. Apart from this, we also present the link between alcohol abuse and withdrawal and mood disorders in this review, thus drawing a link to oxidative stress. In addition, we also discuss the positive impacts of some pharmacotherapies used. Due to the ever-rising demands of life, the cycle between alcohol abuse, withdrawal, and mood disorders may be a never-ending cycle of destruction. Hence, through this review, we hope that we can emphasise the importance and urgency of managing this issue with the appropriate approaches.

Off-label and investigational drugs in the treatment of alcohol use disorder: A critical review

Compounds known to be successful in the treatment of alcohol use disorder include the aversive agent, Disulfiram, the glutamatergic NMDA receptor antagonist, Acamprosate, and the opioid receptor antagonists, Naltrexone and Nalmefene. Although all four are effective in maintaining abstinence or reduction of alcohol consumption, only a small percentage of patients receive pharmacological treatment. In addition, many other medications have been investigated for their therapeutic potential in the treatment of alcohol use disorder. In this review we summarize and compare Baclofen, Gabapentin, Topiramate, Ondansetron, Varenicline, Aripiprazole, Quetiapine, Clozapine, Antidepressants, Lithium, Neuropeptide Y, Neuropeptide S, Corticotropin-releasing factor antagonists, Oxytocin, PF-05190457, Memantine, Ifenprodil, Samidorphan, Ondelopran, ABT-436, SSR149415, Mifepristone, Ibudilast, Citicoline, Rimonabant, Surinabant, AM4113 and Gamma-hydroxybutyrate While some have shown promising results in the treatment of alcohol use disorder, others have disappointed and should be excluded from further investigation. Here we discuss the most promising results and highlight medications that deserve further preclinical or clinical study. Effective, patient-tailored treatment will require greater understanding provided by many more preclinical and clinical studies.

Association Between Brain Structure and Alcohol Use Behaviors in Adults: A Mendelian Randomization and Multiomics Study

Importance

Past studies have identified associations between brain macrostructure and alcohol use behaviors. However, identifying directional associations between these phenotypes is difficult due to the limitations of observational studies.

Objective

To use mendelian randomization (MR) to identify directional associations between brain structure and alcohol use and elucidate the transcriptomic and cellular underpinnings of identified associations.

Design, Setting, and Participants

The main source data comprised summary statistics from population-based and case-control genome-wide association studies (GWAS) of neuroimaging, behavioral, and clinical phenotypes (N = 763 874). Using these data, bidirectional and multivariable MR was performed analyzing associations between brain macrostructure and alcohol use. Downstream transcriptome-wide association studies (TWAS) and cell-type enrichment analyses investigated the biology underlying identified associations. The study approach was data driven and did not test any a priori hypotheses. Data were analyzed August 2021 to May 2022.

Main Outcomes and Measures

Brain structure phenotypes (global cortical thickness [GCT] and global cortical surface area [GCSA] in 33 709 individuals and left-right subcortical volumes in 19 629 individuals) and alcohol use behaviors (alcoholic drinks per week [DPW] in 537 349 individuals, binge drinking frequency in 143 685 individuals, and alcohol use disorder in 8845 individuals vs 20 657 control individuals [total of 29 502]).

Results

The main bidirectional MR analyses were performed in samples totaling 763 874 individuals, among whom more than 94% were of European ancestry, 52% to 54% were female, and the mean cohort ages were 40 to 63 years. Negative associations were identified between genetically predicted GCT and binge drinking (β, -2.52; 95% CI, -4.13 to -0.91) and DPW (β, -0.88; 95% CI, -1.37 to -0.40) at a false discovery rate (FDR) of 0.05. These associations remained significant in multivariable MR models that accounted for neuropsychiatric phenotypes, substance use, trauma, and neurodegeneration. TWAS of GCT and alcohol use behaviors identified 5 genes at the 17q21.31 locus oppositely associated with GCT and binge drinking or DPW (FDR = 0.05). Cell-type enrichment analyses implicated glutamatergic cortical neurons in alcohol use behaviors.

Conclusions and Relevance

The findings in this study show that the associations between GCT and alcohol use may reflect a predispositional influence of GCT and that 17q21.31 genes and glutamatergic cortical neurons may play a role in this association. While replication studies are needed, these findings should enhance the understanding of associations between brain structure and alcohol use.

Effects of moderate alcohol consumption on behavior and neural systems of Wistar rats

Chronic alcohol consumption affects various neurotransmitters, especially those implicated in the transitioning to alcohol use disorders (particularly dopaminergic and CRFergic systems). Few studies have investigated moderate alcohol consumption and its harmful consequences. The objective of this work was to analyze behavioral and neurochemical (dopaminergic and CRFergic systems) alterations during chronic moderate alcohol consumption. Twelve male Wistar rats were submitted to an intermittent alcohol ingestion protocol (alcohol group) for four weeks. The control group consisted of six rats. Open Field and Elevated Plus Maze tests were used for analysis of motor and anxiety-like behaviors. Immunohistochemistry analysis was performed in dopaminergic and CRFergic systems. Animals exposed to alcohol consumed moderate doses, chronic and intermittently. Behavioral tests detected fewer fecal boli in the alcohol exposed group, and immunohistochemical analysis indicated fewer dopamine-immunoreactive cells in the ventral tegmental area, and more CRF-immunoreactive cells in the anterior cingulate cortex and dorsolateral septum in this group. Thus we concluded that Wistar rats that consumed moderate doses of alcohol voluntarily and chronically showed a discreet anxiolytic effect in behavior, and a hypodopaminergic and hyperCRFergic neurochemical condition, which together are strong inducers of alcohol consumption predisposing to the development of alcohol use disorder (AUD).

Alcohol Dependence Induces CRF Sensitivity in Female Central Amygdala GABA Synapses

Alcohol use disorder (AUD) is a chronically relapsing disease characterized by loss of control in seeking and consuming alcohol (ethanol) driven by the recruitment of brain stress systems. However, AUD differs among the sexes: men are more likely to develop AUD, but women progress from casual to binge drinking and heavy alcohol use more quickly. The central amygdala (CeA) is a hub of stress and anxiety, with corticotropin-releasing factor (CRF)-CRF1 receptor and Gamma-Aminobutyric Acid (GABA)-ergic signaling dysregulation occurring in alcohol-dependent male rodents. However, we recently showed that GABAergic synapses in female rats are less sensitive to the acute effects of ethanol. Here, we used patch-clamp electrophysiology to examine the effects of alcohol dependence on the CRF modulation of rat CeA GABAergic transmission of both sexes. We found that GABAergic synapses of naïve female rats were unresponsive to CRF application compared to males, although alcohol dependence induced a similar CRF responsivity in both sexes. In situ hybridization revealed that females had fewer CeA neurons containing mRNA for the CRF1 receptor (Crhr1) than males, but in dependence, the percentage of Crhr1-expressing neurons in females increased, unlike in males. Overall, our data provide evidence for sexually dimorphic CeA CRF system effects on GABAergic synapses in dependence.

Neurobiology and Symptomatology of Post-Acute Alcohol Withdrawal: A Mixed-Studies Systematic Review

OBJECTIVE

This study aims to review the neurobiology and symptomatology of post-acute alcohol withdrawal syndrome (PAWS).

METHOD

We conducted a PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses)-guided systematic review of articles from two databases for English-language randomized and nonrandomized studies involving PAWS published between database inception and December 2020.

RESULTS

Twenty-seven studies met inclusion criteria. PAWS involves predominantly negative affect, which develops in early abstinence and can persist for 4-6 months or longer. Symptoms include anxiety, dysphoria, anhedonia, sleep disturbance, cognitive impairment, cravings, and irritability. PAWS symptoms appear to be risk factors for recurrent alcohol consumption. They have been associated with reported neurobiological differences in evoked potentials; measures of orexins, cortisol, serotonin, and pancreatic polypeptides; and neuroadaptation changes in the nucleus accumbens and the prefrontal cortex.

CONCLUSIONS

There is credible evidence to support the concept of PAWS based on this review's findings. There remains a need to develop and test specific criteria for PAWS. High-quality treatment studies involving agents addressing its neurobiological underpinnings are also recommended.

Neurobiology and Symptomatology of Post-Acute Alcohol Withdrawal: A Mixed-Studies Systematic Review

OBJECTIVE

This study aims to review the neurobiology and symptomatology of post-acute alcohol withdrawal syndrome (PAWS).

METHOD

We conducted a PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses)-guided systematic review of articles from two databases for English-language randomized and nonrandomized studies involving PAWS published between database inception and December 2020.

RESULTS

Twenty-seven studies met inclusion criteria. PAWS involves predominantly negative affect, which develops in early abstinence and can persist for 4-6 months or longer. Symptoms include anxiety, dysphoria, anhedonia, sleep disturbance, cognitive impairment, cravings, and irritability. PAWS symptoms appear to be risk factors for recurrent alcohol consumption. They have been associated with reported neurobiological differences in evoked potentials; measures of orexins, cortisol, serotonin, and pancreatic polypeptides; and neuroadaptation changes in the nucleus accumbens and the prefrontal cortex.

CONCLUSIONS

There is credible evidence to support the concept of PAWS based on this review's findings. There remains a need to develop and test specific criteria for PAWS. High-quality treatment studies involving agents addressing its neurobiological underpinnings are also recommended.

Ten Points to Improve Reproducibility and Translation of Animal Research

Findings from animal experiments are often difficult to transfer to humans. In this perspective article I discuss two questions. First, why are the results of animal experiments often so difficult to transfer to humans? And second, what can be done to improve translation from animal experiments to humans? Translation failures are often the result of poor methodology. It is not merely the fact that low statistical power of basic and preclinical studies undermine a "real effect," but the accuracy with which data from animal studies are collected and described, and the resulting robustness of the data is generally very low and often does not allow translation to a much more heterogeneous human condition. Equally important is the fact that the vast majority of publications in the biomedical field in the last few decades have reported positive findings and have thus generated a knowledge bias. Further contributions to reproducibility and translation failures are discussed in this paper, and 10 points of recommendation to improve reproducibility and translation are outlined. These recommendations are: (i) prior to planning an actual study, a systematic review or potential preclinical meta-analysis should be considered. (ii) An a priori power calculation should be carried out. (iii) The experimental study protocol should be pre-registered. (iv) The execution of the study should be in accordance with the most recent ARRIVE guidelines. (v) When planning the study, the generalizability of the data to be collected should also be considered (e.g., sex or age differences). (vi) "Method-hopping" should be avoided, meaning that it is not necessary to use the most advanced technology but rather to have the applied methodology under control. (vii) National or international networks should be considered to carry out multicenter preclinical studies or to obtain convergent evidence. (viii) Animal models that capture DSM-5 or ICD-11 criteria should be considered in the context of research on psychiatric disorders. (ix) Raw data of publication should be made publicly available and should be in accordance with the FAIR Guiding Principles for scientific data management. (x) Finally, negative findings should be published to counteract publication bias. The application of these 10 points of recommendation, especially for preclinical confirmatory studies but also to some degree for exploratory studies, will ultimately improve the reproducibility and translation of animal research.

Central amygdala corticotropin-releasing factor neurons promote hyponeophagia but do not control alcohol drinking in mice

Corticotropin-releasing factor (CRF) signaling in the central nucleus of the amygdala (CeA) plays a critical role in rodent models of excessive alcohol drinking. However, the source of CRF acting in the CeA during alcohol withdrawal remains to be identified. In the present study, we hypothesized that CeA CRF interneurons may represent a behaviorally relevant source of CRF to the CeA increasing motivation for alcohol via negative reinforcement. We first observed that Crh mRNA expression in the anterior part of the mouse CeA correlates positively with alcohol intake in C57BL/6J males with a history of chronic binge drinking followed by abstinence and increases upon exposure to chronic intermittent ethanol (CIE) vapor inhalation. We then found that chemogenetic activation of CeA CRF neurons in Crh-IRES-Cre mouse brain slices increases gamma-aminobutyric acid (GABA) release in the medial CeA, in part via CRF1 receptor activation. While chemogenetic stimulation exacerbated novelty-induced feeding suppression (NSF) in alcohol-naïve mice, thereby mimicking the effect of withdrawal from CIE, it had no effect on voluntary alcohol consumption, following either acute or chronic manipulation. Furthermore, chemogenetic inhibition of CeA CRF neurons did not affect alcohol consumption or NSF in chronic alcohol drinkers exposed to air or CIE. Altogether, these findings indicate that CeA CRF neurons produce local release of GABA and CRF and promote hyponeophagia in naïve mice, but do not drive alcohol intake escalation or negative affect in CIE-withdrawn mice. The latter result contrasts with previous findings in rats and demonstrates species specificity of CRF circuit engagement in alcohol dependence.

Pituitary adenylate cyclase-activating polypeptide type 1 receptor within the nucleus accumbens core mediates excessive alcohol drinking in alcohol-preferring rats

Alcohol use disorders (AUD) have a strong component of heritability; however, the neurobiological mechanisms mediating the propensity to consume excessive amounts of alcohol are still not well understood. Pituitary adenylate cyclase-activating polypeptide (PACAP), a highly conserved neuropeptide which exerts its effects mainly through the PAC1 receptor (PAC1R), has been suggested to be one of the mediators of the effects of drugs of abuse and alcohol. Here, we investigated the role of the PACAP/PAC1R system in excessive alcohol drinking in alcohol-preferring rats, an established animal model of AUD. Intracerebroventricular (i.c.v.) administration of the PAC1R antagonist PACAP(6-38) blocked excessive alcohol drinking and motivation to drink in Sardinian alcohol-preferring (Scr:sP) rats, without affecting water, saccharin, or sucrose intake. Notably, PACAP(6-38) did not affect ethanol responding in outbred Wistar rats. PACAP(6-38) also significantly reduced alcohol-seeking behavior under a second-order schedule of reinforcement. Using immunohistochemistry, a significant increase in the number of PAC1R positive cells was observed selectively in the nucleus accumbens (NAcc) Core of Scr:sP rats, compared to Wistar rats following alcohol drinking. Finally, excessive drinking in Scr:sP rats was suppressed by intra-NAcc Core, but not intra-NAcc Shell, PACAP(6-38), as well as by virally-mediated PAC1R knockdown in the NAcc Core. The present study shows that hyperactivity of the PACAP/PAC1R system specifically in the NAcc Core mediates excessive drinking of alcohol-preferring rats, and indicates that this system may represent a novel target for the treatment of AUD.

From a systems view to spotting a hidden island: A narrative review implicating insula function in alcoholism

Excessive use of alcohol promotes the development of alcohol addiction, but the understanding of how alcohol-induced brain alterations lead to addiction remains limited. To further this understanding, we adopted an unbiased discovery strategy based on the principles of systems medicine. We used functional magnetic resonance imaging data from patients and animal models of alcohol addiction-like behaviors, and developed mathematical models of the 'relapse-prone' network states to identify brain sites and functional networks that can be selectively targeted by therapeutic interventions. Our systems level, non-local, and largely unbiased analyses converged on a few well-defined brain regions, with the insula emerging as one of the most consistent finding across studies. In proof-of-concept experiments we were able to demonstrate that it is possible to guide network dynamics towards increased resilience in animals but an initial translation into a clinical trial targeting the insula failed. Here, in a narrative review, we summarize the key experiments, methodological developments and knowledge gained from this completed round of a discovery cycle moving from identification of 'relapse-prone' network states in humans and animals to target validation and intervention trial. Future concerted efforts are necessary to gain a deeper understanding of insula function a in a state-dependent, circuit-specific and cell population perspective, and to develop the means for insula-directed interventions, before therapeutic targeting of this structure may become possible.

At the heart of the interoception network: Influence of the parasubthalamic nucleus on autonomic functions and motivated behaviors

The parasubthalamic nucleus (PSTN), a small nucleus located on the lateral edge of the posterior hypothalamus, has emerged in recent years as a highly interconnected node within the network of brain regions sensing and regulating autonomic function and homeostatic needs. Furthermore, the strong integration of the PSTN with extended amygdala circuits makes it ideally positioned to serve as an interface between interoception and emotions. While PSTN neurons are mostly glutamatergic, some of them also express neuropeptides that have been associated with stress-related affective and motivational dysfunction, including substance P, corticotropin-releasing factor, and pituitary adenylate-cyclase activating polypeptide. PSTN neurons respond to food ingestion and anorectic signals, as well as to arousing and distressing stimuli. Functional manipulation of defined pathways demonstrated that the PSTN serves as a central hub in multiple physiologically relevant networks and is notably implicated in appetite suppression, conditioned taste aversion, place avoidance, impulsive action, and fear-induced thermoregulation. We also discuss the putative role of the PSTN in interoceptive dysfunction and negative urgency. This review aims to synthesize the burgeoning preclinical literature dedicated to the PSTN and to stimulate interest in further investigating its influence on physiology and behavior.

Neuropeptides and Behaviors: How Small Peptides Regulate Nervous System Function and Behavioral Outputs

One of the reasons that most multicellular animals survive and thrive is because of the adaptable and plastic nature of their nervous systems. For an organism to survive, it is essential for the animal to respond and adapt to environmental changes. This is achieved by sensing external cues and translating them into behaviors through changes in synaptic activity. The nervous system plays a crucial role in constantly evaluating environmental cues and allowing for behavioral plasticity in the organism. Multiple neurotransmitters and neuropeptides have been implicated as key players for integrating sensory information to produce the desired output. Because of its simple nervous system and well-established neuronal connectome, C. elegans acts as an excellent model to understand the mechanisms underlying behavioral plasticity. Here, we critically review how neuropeptides modulate a wide range of behaviors by allowing for changes in neuronal and synaptic signaling. This review will have a specific focus on feeding, mating, sleep, addiction, learning and locomotory behaviors in C. elegans. With a view to understand evolutionary relationships, we explore the functions and associated pathophysiology of C. elegans neuropeptides that are conserved across different phyla. Further, we discuss the mechanisms of neuropeptidergic signaling and how these signals are regulated in different behaviors. Finally, we attempt to provide insight into developing potential therapeutics for neuropeptide-related disorders.

Single-nucleus transcriptome analysis reveals cell-type-specific molecular signatures across reward circuitry in the human brain

Single-cell gene expression technologies are powerful tools to study cell types in the human brain, but efforts have largely focused on cortical brain regions. We therefore created a single-nucleus RNA-sequencing resource of 70,615 high-quality nuclei to generate a molecular taxonomy of cell types across five human brain regions that serve as key nodes of the human brain reward circuitry: nucleus accumbens, amygdala, subgenual anterior cingulate cortex, hippocampus, and dorsolateral prefrontal cortex. We first identified novel subpopulations of interneurons and medium spiny neurons (MSNs) in the nucleus accumbens and further characterized robust GABAergic inhibitory cell populations in the amygdala. Joint analyses across the 107 reported cell classes revealed cell-type substructure and unique patterns of transcriptomic dynamics. We identified discrete subpopulations of D1- and D2-expressing MSNs in the nucleus accumbens to which we mapped cell-type-specific enrichment for genetic risk associated with both psychiatric disease and addiction.

Research Needs for Inpatient Management of Severe Alcohol Withdrawal Syndrome: An Official American Thoracic Society Research Statement

Background: Severe alcohol withdrawal syndrome (SAWS) is highly morbid, costly, and common among hospitalized patients, yet minimal evidence exists to guide inpatient management. Research needs in this field are broad, spanning the translational science spectrum. Goals: This research statement aims to describe what is known about SAWS, identify knowledge gaps, and offer recommendations for research in each domain of the Institute of Medicine T0-T4 continuum to advance the care of hospitalized patients who experience SAWS. Methods: Clinicians and researchers with unique and complementary expertise in basic, clinical, and implementation research related to unhealthy alcohol consumption and alcohol withdrawal were invited to participate in a workshop at the American Thoracic Society 2019 International Conference. The committee was subdivided into four groups on the basis of interest and expertise: T0-T1 (basic science research with translation to humans), T2 (research translating to patients), T3 (research translating to clinical practice), and T4 (research translating to communities). A medical librarian conducted a pragmatic literature search to facilitate this work, and committee members reviewed and supplemented the resulting evidence, identifying key knowledge gaps. Results: The committee identified several investigative opportunities to advance the care of patients with SAWS in each domain of the translational science spectrum. Major themes included 1) the need to investigate non-γ-aminobutyric acid pathways for alcohol withdrawal syndrome treatment; 2) harnessing retrospective and electronic health record data to identify risk factors and create objective severity scoring systems, particularly for acutely ill patients with SAWS; 3) the need for more robust comparative-effectiveness data to identify optimal SAWS treatment strategies; and 4) recommendations to accelerate implementation of effective treatments into practice. Conclusions: The dearth of evidence supporting management decisions for hospitalized patients with SAWS, many of whom require critical care, represents both a call to action and an opportunity for the American Thoracic Society and larger scientific communities to improve care for a vulnerable patient population. This report highlights basic, clinical, and implementation research that diverse experts agree will have the greatest impact on improving care for hospitalized patients with SAWS.

Blockade of corticotropin-releasing factor receptor 1 in the central amygdala prevents cocaine-seeking behaviour induced by orexin-A administered to the posterior paraventricular nucleus of the thalamus in male rats

BACKGROUND

Orexin-A (OrxA) administration in the posterior paraventricular nucleus of the thalamus (pPVT) reinstates extinguished cocaine-seeking behaviour following extended access to the drug (a model of dependence). The pPVT receives and integrates information associated with emotionally salient events and sends excitatory inputs to brain regions involved in the expression of emotional states, such as those driving cocaine-seeking behaviour (i.e., the nucleus accumbens, the central nucleus of the amygdala [CeA], the basolateral amygdala, the bed nucleus of the stria terminalis [BNST] and the prefrontal cortex).

METHODS

We monitored the activation pattern of these regions (measured by Fos) during cocaine-seeking induced by OrxA administered to the pPVT. The BNST and CeA emerged as being selectively activated. To test whether the functionality of these regions was pivotal during OrxA-induced cocaine-seeking behaviour, we transiently inactivated these regions concomitantly with OrxA administration to the pPVT. We then tested the participation of corticotropin-releasing factor receptors (CRF1) in the CeA during OrxA-induced cocaine-seeking using the CRF1 antagonist CP154526.

RESULTS

We observed selective activation of the CeA and BNST during cocaine-seeking induced by OrxA administered to the pPVT, but only transient inactivation of the CeA prevented cocaine-seeking behaviour. Administration of CP154526 to the CeA prevented OrxAinduced cocaine-seeking behaviour.

LIMITATIONS

The use of only male rats could have been a limitation. Other limitations could have been the use of an indirect approach to test the hypothesis that administration of OrxA to the pPVT drives cocaine-seeking via CRF1 signalling in the CeA, and a lack of analysis of the participation of CeA subregions.

CONCLUSION

Cocaine-seeking behaviour induced by OrxA administered to the pPVT is driven by activation of the CeA via CRF1 signalling.

Lifetime heavy drinking years predict alcohol use disorder severity over and above current alcohol use

Background: Preclinical studies demonstrate that chronic and heavy alcohol use facilitates neuroadaptations that perpetuate addiction-like behaviors. In clinical studies, it is unclear whether the extent of heavy alcohol use over the lifetime contributes to alcohol use disorder (AUD) severity over and above current alcohol use patterns (i.e. last 30 days to 3-months). Such information may improve our understanding of the phenomenology of AUD.Objectives: The purpose of this study was to examine lifetime heavy drinking years in relation to a clinical assessment of AUD.Methods: Participants, who were non-treatment-seeking and engaged in heavy drinking (n = 140; 50% male), completed an interview-based assessment of lifetime regular and heavy drinking years along with a battery of measures indexing alcohol use and problems, drinking motives, and depression and anxiety symptomatology.Results: Lifetime heavy drinking years was positively associated with lifetime regular drinking years, current alcohol use, alcohol problems, tonic alcohol craving, drinking for the enhancing effects of alcohol, and drinking to cope (r's = .21-.58). Adjusting for lifetime regular drinking years and current alcohol use, lifetime heavy drinking years predicted higher scores on the Alcohol Use Disorder Identification Test (AUDIT; B = .382; SE = .123). A multivariate logistic regression found that lifetime heavy drinking years predicted greater odds of more severe AUD over and above current alcohol use (OR = 1.147).Conclusion: Our findings suggest that lifetime heavy drinking years are a clinically meaningful indicator of AUD severity that is not redundant with current alcohol use measures.

Similarities in alcohol and opioid withdrawal syndromes suggest common negative reinforcement mechanisms involving the interoceptive antireward pathway

Alcohol and opioids are two major contributors to so-called deaths of despair. Though the effects of these substances on mammalian systems are distinct, commonalities in their withdrawal syndromes suggest a shared pathophysiology. For example, both are characterized by marked autonomic dysregulation and are treated with alpha-2 agonists. Moreover, alcohol and opioids rapidly induce dependence motivated by withdrawal avoidance. Resemblances observed in withdrawal syndromes and abuse behavior may indicate common addiction mechanisms. We argue that neurovisceral feedback influences autonomic and emotional circuits generating antireward similarly for both substances. Amygdala is central to this hypothesis as it is principally responsible for negative emotion, prominent in addiction and motivated behavior, and processes autonomic inputs while generating autonomic outputs. The solitary nucleus (NTS) has strong bidirectional connections to the amygdala and receives interoceptive inputs communicating visceral states via vagal afferents. These visceral-emotional hubs are strongly influenced by the periphery including gut microbiota. We propose that gut dysbiosis contributes to alcohol and opioid withdrawal syndromes by contributing to peripheral and neuroinflammation that stimulates these antireward pathways and motivates substance dependence.

Neurobiology of alcohol seeking behavior

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

Pituitary adenylate cyclase-activating polypeptide (PACAP) modulates dependence-induced alcohol drinking and anxiety-like behavior in male rats

Alcohol use disorder (AUD) is a devastating illness defined by periods of heavy drinking and withdrawal, often leading to a chronic relapsing course. Initially, alcohol is consumed for its positive reinforcing effects, but later stages of AUD are characterized by drinking to alleviate withdrawal-induced negative emotional states. Brain stress response systems in the extended amygdala are recruited by excessive alcohol intake, sensitized by repeated withdrawal, and contribute to the development of addiction. In this study, we investigated one such brain stress response system, pituitary adenylate cyclase-activating polypeptide (PACAP), and its cognate receptor, PAC1R, in alcohol withdrawal-induced behaviors. During acute withdrawal, rats exposed to chronic intermittent ethanol vapor (ethanol-dependent) displayed a significant increase in PACAP levels in the bed nucleus of the stria terminalis (BNST), a brain area within the extended amygdala critically involved in both stress and withdrawal. No changes in PACAP levels were observed in the central nucleus of the amygdala. Site-specific microinfusion of the PAC1R antagonist PACAP(6-38) into the BNST dose-dependently blocked excessive alcohol intake in ethanol-dependent rats without affecting water intake overall or basal ethanol intake in control, nondependent rats. Intra-BNST PACAP(6-38) also reversed ethanol withdrawal-induced anxiety-like behavior in ethanol-dependent rats, but did not affect this measure in control rats. Our findings show that chronic intermittent exposure to ethanol recruits the PACAP/PAC1R system of the BNST and that these neuroadaptations mediate the heightened alcohol drinking and anxiety-like behavior observed during withdrawal, suggesting that this system represents a major brain stress element responsible for the negative reinforcement associated with the "dark side" of alcohol addiction.

Drug Addiction: Hyperkatifeia/Negative Reinforcement as a Framework for Medications Development

Compulsive drug seeking that is associated with addiction is hypothesized to follow a heuristic framework that involves three stages (binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation) and three domains of dysfunction (incentive salience/pathologic habits, negative emotional states, and executive function, respectively) via changes in the basal ganglia, extended amygdala/habenula, and frontal cortex, respectively. This review focuses on neurochemical/neurocircuitry dysregulations that contribute to hyperkatifeia, defined as a greater intensity of negative emotional/motivational signs and symptoms during withdrawal from drugs of abuse in the withdrawal/negative affect stage of the addiction cycle. Hyperkatifeia provides an additional source of motivation for compulsive drug seeking via negative reinforcement. Negative reinforcement reflects an increase in the probability of a response to remove an aversive stimulus or drug seeking to remove hyperkatifeia that is augmented by genetic/epigenetic vulnerability, environmental trauma, and psychiatric comorbidity. Neurobiological targets for hyperkatifeia in addiction involve neurocircuitry of the extended amygdala and its connections via within-system neuroadaptations in dopamine, enkephalin/endorphin opioid peptide, and γ-aminobutyric acid/glutamate systems and between-system neuroadaptations in prostress corticotropin-releasing factor, norepinephrine, glucocorticoid, dynorphin, hypocretin, and neuroimmune systems and antistress neuropeptide Y, nociceptin, endocannabinoid, and oxytocin systems. Such neurochemical/neurocircuitry dysregulations are hypothesized to mediate a negative hedonic set point that gradually gains allostatic load and shifts from a homeostatic hedonic state to an allostatic hedonic state. Based on preclinical studies and translational studies to date, medications and behavioral therapies that reset brain stress, antistress, and emotional pain systems and return them to homeostasis would be promising new targets for medication development. SIGNIFICANCE STATEMENT: The focus of this review is on neurochemical/neurocircuitry dysregulations that contribute to hyperkatifeia, defined as a greater intensity of negative emotional/motivational signs and symptoms during withdrawal from drugs of abuse in the withdrawal/negative affect stage of the drug addiction cycle and a driving force for negative reinforcement in addiction. Medications and behavioral therapies that reverse hyperkatifeia by resetting brain stress, antistress, and emotional pain systems and returning them to homeostasis would be promising new targets for medication development.

Genome-wide methylation in alcohol use disorder subjects: implications for an epigenetic regulation of the cortico-limbic glucocorticoid receptors (NR3C1)

Environmental factors, including substance abuse and stress, cause long-lasting changes in the regulation of gene expression in the brain via epigenetic mechanisms, such as DNA methylation. We examined genome-wide DNA methylation patterns in the prefrontal cortex (PFC, BA10) of 25 pairs of control and individuals with alcohol use disorder (AUD), using the Infinium^® MethylationEPIC BeadChip. We identified 5254 differentially methylated CpGs (p_nominal < 0.005). Bioinformatic analyses highlighted biological processes containing genes related to stress adaptation, including the glucocorticoid receptor (encoded by NR3C1). Considering that alcohol is a stressor, we focused our attention on differentially methylated regions of the NR3C1 gene and validated the differential methylation of several genes in the NR3C1 network. Chronic alcohol drinking results in a significant increased methylation of the NR3C1 exon variant 1_H, with a particular increase in the levels of 5-hydroxymethylcytosine over 5-methylcytosine. These changes in DNA methylation were associated with reduced NR3C1 mRNA and protein expression levels in PFC, as well as other cortico-limbic regions of AUD subjects when compared with controls. Furthermore, we show that the expression of several stress-responsive genes (e.g., CRF, POMC, and FKBP5) is altered in the PFC of AUD subjects. These stress-response genes were also changed in the hippocampus, a region that is highly susceptible to stress. These data suggest that alcohol-dependent aberrant DNA methylation of NR3C1 and consequent changes in other stress-related genes might be fundamental in the pathophysiology of AUD and lay the groundwork for treatments targeting the epigenetic mechanisms regulating NR3C1 in AUD.

CRF-5-HT interactions in the dorsal raphe nucleus and motivation for stress-induced opioid reinstatement

RATIONALE

The serotonin (5-hydroxytryptamine, 5-HT) system plays an important role in stress-related psychiatric disorders and substance abuse. Our previous data show that stressors can inhibit 5-HT neuronal activity and release by stimulating the release of the stress neurohormone corticotropin-releasing factor (CRF) within the serotonergic dorsal raphe nucleus (DRN). The inhibitory effects of CRF on 5-HT DRN neurons are indirect, mediated by CRF-R1 receptors located on GABAergic afferents.

OBJECTIVES

We tested the hypothesis that DRN CRF-R1 receptors contribute to stress-induced reinstatement of morphine-conditioned place preference (CPP). We also examined the role of this circuitry in stress-induced negative affective state with 22-kHz distress ultrasonic vocalizations (USVs), which are naturally emitted by rats in response to environmental challenges such as pain, stress, and drug withdrawal.

METHODS

First, we tested if activation of CRF-R1 receptors in the DRN with the CRF-R1-preferring agonist ovine CRF (oCRF) would reinstate morphine CPP and then if blockade of CRF-R1 receptors in the DRN with the CRF-R1 antagonist NBI 35965 would attenuate swim stress-induced reinstatement of morphine CPP. Second, we tested if intra-DRN pretreatment with NBI 35965 would attenuate foot shock stress-induced 22-kHz USVs.

RESULTS

Intra-DRN injection of oCRF reinstated morphine CPP, while intra-DRN injection of NBI 35965 attenuated swim stress-induced reinstatement. Moreover, intra-DRN pretreatment with NBI 35965 significantly reduced 22-kHz distress calls induced by foot shock.

CONCLUSIONS

These data provide evidence that stress-induced negative affective state is mediated by DRN CRF-R1 receptors and may contribute to reinstatement of morphine CPP.

Adolescent low-dose ethanol drinking in the dark increases ethanol intake later in life in C57BL/6J, but not DBA/2J mice

Alcohol is the most widely used and abused drug among youth in the United States. Youths aged 12-20 years old drink almost 11% of all alcohol consumed in the United States, and typically these young people are consuming alcohol in the form of binge drinking. Particularly concerning is that the risk of developing an alcohol use disorder over their lifetime increases the younger one begins to drink. Here we investigated the impact of ethanol drinking in early adolescence on adult ethanol intake using C57BL/6J and DBA/2J mice. We modeled low-dose drinking in adolescent mice using a modified Drinking in the Dark (DID) model where the total ethanol intake during adolescence was similar between the strains to specifically ask whether low-dose ethanol exposure in the high-alcohol preferring C57BL/6J strain will also lead to increased ethanol intake in adulthood. Our results show that low-dose ethanol drinking in early adolescence dramatically increases adult intake, but only in the alcohol-preferring C57BL/6J strain. Early adolescent ethanol exposure had no effect on ethanol intake in the alcohol-nonpreferring DBA/2J mice. These data add to the growing evidence that low-dose ethanol exposures, below the pharmacologically relevant dose, can also contribute to increased drinking in adulthood, but the effect may be influenced by genetic background.

Histone modifications, DNA methylation, and the epigenetic code of alcohol use disorder

Alcohol use disorder (AUD) is a leading cause of morbidity and mortality. Despite AUD's substantial contributions to lost economic productivity and quality of life, there are only a limited number of approved drugs for treatment of AUD in the United States. This chapter will update progress made on the epigenetic basis of AUD, with particular focus on histone post-translational modifications and DNA methylation and how these two epigenetic mechanisms interact to contribute to neuroadaptive processes leading to initiation, maintenance and progression of AUD pathophysiology. We will also evaluate epigenetic therapeutic strategies that have arisen from preclinical models of AUD and epigenetic biomarkers that have been discovered in human populations with AUD.

Improving translation of animal models of addiction and relapse by reverse translation

Critical features of human addiction are increasingly being incorporated into complementary animal models, including escalation of drug intake, punished drug seeking and taking, intermittent drug access, choice between drug and non-drug rewards, and assessment of individual differences based on criteria in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). Combined with new technologies, these models advanced our understanding of brain mechanisms of drug self-administration and relapse, but these mechanistic gains have not led to improvements in addiction treatment. This problem is not unique to addiction neuroscience, but it is an increasing source of disappointment and calls to regroup. Here we first summarize behavioural and neurobiological results from the animal models mentioned above. We then propose a reverse translational approach, whose goal is to develop models that mimic successful treatments: opioid agonist maintenance, contingency management and the community-reinforcement approach. These reverse-translated 'treatments' may provide an ecologically relevant platform from which to discover new circuits, test new medications and improve translation.

Epigenetic landscape of stress surfeit disorders: Key role for DNA methylation dynamics

Chronic exposure to stress throughout lifespan alters brain structure and function, inducing a maladaptive response to environmental stimuli, that can contribute to the development of a pathological phenotype. Studies have shown that hypothalamic-pituitary-adrenal (HPA) axis dysfunction is associated with various neuropsychiatric disorders, including major depressive, alcohol use and post-traumatic stress disorders. Downstream actors of the HPA axis, glucocorticoids are critical mediators of the stress response and exert their function through specific receptors, i.e., the glucocorticoid receptor (GR), highly expressed in stress/reward-integrative pathways. GRs are ligand-activated transcription factors that recruit epigenetic actors to regulate gene expression via DNA methylation, altering chromatin structure and thus shaping the response to stress. The dynamic interplay between stress response and epigenetic modifiers suggest DNA methylation plays a key role in the development of stress surfeit disorders.

A Distinct Neurophenotype of Fearful Face Processing in Alcohol Use Disorder With and Without Comorbid Anxiety

BACKGROUND

Individuals with alcohol use disorder (AUD) can present with comorbid anxiety symptoms and often have deficits in emotional processing. Previous research suggests brain response is altered during facial affect recognition tasks, especially in limbic areas, due to either AUD or anxiety symptomology; however, the impact of both AUD and clinically significant anxiety symptoms during these tasks has not yet been examined.

METHODS

In this study, we investigated neural activation differences during an emotional face-matching task. Participants (N = 232) underwent fMRI scanning, as part of a larger study. Three groups were investigated: individuals with diagnosed AUD and elevated anxiety traits (AUD + ANX, n = 90), individuals with diagnosed AUD but non-clinically significant levels of anxiety (AUD-ANX, n = 39), and healthy controls (HC, n = 103).

RESULTS

Our results illustrate distinct neurophenotypes of AUD, where individuals with comorbid anxiety symptomology have blunted emotional face processing while those with singular AUD are hyperresponsive.

CONCLUSIONS

This suggests AUD with anxiety symptomology may have a unique neurobiological underpinning, and treatment and intervention should be tailored to individual constellations of symptoms.

Understanding the neurobiological effects of drug abuse: Lessons from zebrafish models

Drug abuse and brain disorders related to drug comsumption are public health problems with harmful individual and social consequences. The identification of therapeutic targets and precise pharmacological treatments to these neuropsychiatric conditions associated with drug abuse are urgently needed. Understanding the link between neurobiological mechanisms and behavior is a key aspect of elucidating drug abuse-related targets. Due to various molecular, biochemical, pharmacological, and physiological features, the zebrafish (Danio rerio) has been considered a suitable vertebrate for modeling complex processes involved in drug abuse responses. In this review, we discuss how the zebrafish has been successfully used for modeling neurobehavioral phenotypes related to drug abuse and review the effects of opioids, cannabinoids, alcohol, nicotine, and psychedelic drugs on the central nervous system (CNS). Moreover, we summarize recent advances in zebrafish-based studies and outline potential advantages and limitations of the existing zebrafish models to explore the neurochemical bases of drug abuse and addiction. Finally, we discuss how the use of zebrafish models may present fruitful approaches to provide valuable clinically translatable data.

Drug instrumentalization

Psychoactive drugs with addiction potential are widely used by people of virtually all cultures in a non-addictive way. In order to understand this behaviour, its population penetrance, and its persistence, drug instrumentalization was suggested as a driving force for this consumption. Drug instrumentalization theory holds that psychoactive drugs are consumed in a very systematic way in order to make other, non-drug-related behaviours more efficient. Here, we review the evolutionary origin of this behaviour and its psychological mechanisms and explore the neurobiological and neuropharmacological mechanisms underlying them. Instrumentalization goals are discussed, for which an environmentally selective and mental state-dependent consumption of psychoactive drugs can be learned and maintained in a non-addictive way. A small percentage of people who regularly instrumentalize psychoactive drugs make a transition to addiction, which often starts with qualitative and quantitative changes in the instrumentalization goals. As such, addiction is proposed to develop from previously established long-term drug instrumentalization. Thus, preventing and treating drug addiction in an individualized medicine approach may essentially require understanding and supporting personal instrumentalization goals.

Chronic alcohol disrupts hypothalamic responses to stress by modifying CRF and NMDA receptor function

The chronic inability of alcoholics to effectively cope with relapse-inducing stressors has been linked to dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and corticotropin-releasing factor (CRF) signaling. However, the cellular mechanisms responsible for this dysregulation are yet to be identified. After exposure of male Sprague Dawley rats to chronic intermittent ethanol (CIE; 5-6 g/kg orally for 35 doses over 50 days) or water, followed by 40-60 days of protracted withdrawal, we investigated CIE effects on glutamatergic synaptic transmission, stress-induced plasticity, CRF- and ethanol-induced NMDAR inhibition using electrophysiological recordings in parvocellular neurosecretory cells (PNCs) of the paraventricular nucleus. We also assessed CIE effects on hypothalamic mRNA expression of CRF-related genes using real-time polymerase chain reaction, and on HPA axis function by measuring stress-induced increases in plasma adrenocorticotropic hormone, corticosterone, and self-grooming. In control rats, ethanol-mediated inhibition of NMDARs was prevented by CRF1 receptor (CRFR1) blockade with antalarmin, while CRF/CRFR1-mediated NMDAR blockade was prevented by intracellularly-applied inhibitor of phosphatases PP1/PP2A, okadaic acid, but not the selective striatal-enriched tyrosine protein phosphatase inhibitor, TC-2153. CIE exposure increased GluN2B subunit-dependent NMDAR function of PNCs. This was associated with the loss of both ethanol- and CRF-mediated NMDAR inhibition, and loss of stress-induced short-term potentiation of glutamatergic synaptic inputs, which could be reversed by intracellular blockade of NMDARs with MK801. CIE exposure also blunted the hormonal and self-grooming behavioral responses to repeated restraint stress. These findings suggest a cellular mechanism whereby chronic alcohol dysregulates the hormonal and behavioral responses to repetitive stressors by increasing NMDAR function and decreasing CRFR1 function.

Aberrant insular cortex connectivity in abstinent alcohol-dependent rats is reversed by dopamine D3 receptor blockade

A few studies have reported aberrant functional connectivity in alcoholic patients, but the specific neural circuits involved remain unknown. Moreover, it is unclear whether these alterations can be reversed upon treatment. Here, we used functional MRI to study resting state connectivity in rats following chronic intermittent exposure to ethanol. Further, we evaluated the effects of SB-277011-a, a selective dopamine D3 receptor antagonist, known to decrease ethanol consumption. Alcohol-dependent and control rats (N = 13/14 per group), 3 weeks into abstinence, were administered SB-277011-a or vehicle before fMRI sessions. Resting state connectivity networks were extracted by independent component analysis. A dual-regression analysis was performed using independent component maps as spatial regressors, and the effects of alcohol history and treatment on connectivity were assessed. A history of alcohol dependence caused widespread reduction of the internal coherence of components. Weaker correlation was also found between the insula cortex (IC) and cingulate cortices, key constituents of the salience network. Similarly, reduced connectivity was observed between a component comprising the anterior insular cortex, together with the caudate putamen (CPu-AntIns), and the posterior part of the IC. On the other hand, postdependent rats showed strengthened connectivity between salience and reward networks. In particular, higher connectivity was observed between insula and nucleus accumbens, between the ventral tegmental area and the cingulate cortex and between the VTA and CPu-AntIns. Interestingly, aberrant connectivity in postdependent rats was partially restored by acute administration of SB-277011-a, which, conversely, had no significant effects in naïve rats.

Chronic Ethanol Consumption Alters Glucocorticoid Receptor Isoform Expression in Stress Neurocircuits and Mesocorticolimbic Brain Regions of Alcohol-Preferring Rats

Evidence suggests the hypothalamic-pituitary-adrenal (HPA) axis is involved in Alcohol Use Disorders (AUDs), which might be mediated by an imbalance of glucocorticoid receptor (GR), GRα and GRβ, activity. GRβ antagonizes the GRα isoform to cause glucocorticoid (GC) resistance. In the present study, we aimed to investigate the effects of chronic continuous free-choice access to ethanol on GR isoform expression in subregions of the mesocorticolimbic reward circuit. Adult male alcohol-preferring (P) rats had concurrent access to 15% and 30% ethanol solutions, with ad lib access to lab chow and water, for six weeks. Quantitative Real-time PCR (RT-PCR) analysis showed that chronic ethanol consumption reduced GRα expression in the nucleus accumbens shell (NAcsh) and hippocampus, whereas ethanol drinking reduced GRβ in the nucleus accumbens core (NAcc), prefrontal cortex (PFC), and hippocampus. An inhibitor of GRα, microRNA-124-3p (miR124-3p) was significantly higher in the NAcsh, and GC-induced gene, GILZ, as a measure of GC-responsiveness, was significantly lower. These were not changed in the NAcc. Likewise, genes associated with HPA axis activity were not significantly changed by ethanol drinking [i.e., corticotrophin-releasing hormone (Crh), adrenocorticotrophic hormone (Acth), and proopiomelanocortin (Pomc)] in these brain regions. Serum corticosterone levels were not changed by ethanol drinking. These data indicate that the expression of GRα and GRβ isoforms are differentially affected by ethanol drinking despite HPA-associated peptides remaining unchanged, at least at the time of tissue harvesting. Moreover, the results suggest that GR changes may stem from ethanol-induced GC-resistance in the NAcsh. These findings confirm a role for stress in high ethanol drinking, with GRα and GRβ implicated as targets for the treatment of AUDs.

From Pleasure to Pain, and Back Again: The Intricate Relationship Between Alcohol and Nociception

AIMS

A close and bidirectional relationship between alcohol consumption and pain has been previously reported and discussed in influential reviews. The goal of the present narrative review is to provide an update on the developments in this field in order to guide future research objectives.

METHODS

We evaluated both epidemiological and neurobiological literature interrogating the relationship between alcohol use and pain for the presence of significant effects. We outlined studies on interactions between alcohol use and pain using both self-reports and objective experimental measures and discussed potential underlying mechanisms of these interactions.

RESULTS

Epidemiological, preclinical and clinical literature point to three major interactions between alcohol use and pain: (a) alcohol use leading to hyperalgesia, (b) alcohol use moderating pain and hyperalgesia and (c) chronic pain as a risk factor predisposing to alcohol relapse. Neurobiological studies using animal models to assess these interactions have transitioned from mostly involuntary modes of experimenter-controlled alcohol administration to self-administration procedures, and increasingly indicate that neuronal circuits implicated in both withdrawal and anticipation stages of alcohol use disorder also have a role in chronic pain. Mechanistically, alterations in GABA, glutamate, the corticotropin-releasing factor system, endogenous opioids and protein kinase C appear to play crucial roles in this maladaptive overlap.

CONCLUSIONS

Many of the principles explaining the interactions between alcohol and pain remain on a strong foundation, but continuing progress in modeling these interactions and underlying systems will provide a clearer basis for understanding, and ultimately treating, the damaging aspects of this interaction.

Differential sensitivity of alcohol drinking and partner preference to a CRFR1 antagonist in prairie voles and mice

Available pharmacotherapies to treat alcohol use disorder (AUD) show limited efficacy. Preclinical studies in mice and rats suggested that antagonists of the corticotropin releasing factor receptor 1 (CRFR1) could be more efficacious for such treatment. However, clinical trials with CRFR1 antagonists were not successful. While a number of potential explanations for this translational failure have been suggested, we hypothesized that the lack of success in clinical trials could be in part due to different neuroanatomical organization of the CRFR1 system in mice and rats versus humans. The CRF system in prairie voles (Microtus ochrogaster), a socially monogamous rodent species, also shows differences in organization from mice and rats. To test our hypothesis, we compared the efficacy of a potent CRFR1 antagonist, CP-376,395, to modulate alcohol drinking in male and female prairie voles versus male and female C57BL/6J mice using an almost identical 2-bottle choice drinking procedure. CP-376,375 (10 and 20 mg/kg, i.p.) significantly decreased alcohol intake (but not alcohol preference) in mice, but not prairie voles. Furthermore, administration of this antagonist (20 mg/kg, i.p.) prior to the partner preference test (PPT) decreased partner preference (PP) in male prairie voles. These findings support our hypothesis that the greater efficacy of CRFR1 antagonists to suppress alcohol consumption in mice and rats versus other mammalian species could be due to the differences in organization of the CRFR1 system between species. They further indicate that activity of the CRFR1 system is necessary for the formation of pair-bonds, but not consumption of high doses of alcohol. Overall, we suggest that testing potential pharmacotherapies should not rely only on studies in mice and rats.