Long-term ethanol effects on acute stress responses: modulation by dynorphin

The arousal effect of An-Gong-Niu-Huang-Wan on alcoholic-induced coma rats: A research based on EEG

ETHNOPHARMACOLOGICAL RELEVANCE

Acute alcohol intoxication is one of the leading causes of coma. A well-regarded Chinese herbal formula, known as An-Gong-Niu-Huang-Wan (AGNHW), has garnered recognition for its efficacy in treating various brain disorders associated with impaired consciousness, including acute alcohol-induced coma. Despite its clinical effectiveness, the scientific community lacks comprehensive research on the mechanistic aspects of AGNHW's impact on the electroencephalogram (EEG) patterns observed during alcohol-induced coma. Gaining a deeper understanding of AGNHW's mechanism of action in relation to EEG characteristics would hold immense importance, serving as a solid foundation for further advancing its clinical therapeutic application.

AIM OF THE STUDY

The study sought to investigate the impact of AGNHW on EEG activity and sleep EEG patterns in rats with alcoholic-induced coma.

MATERIALS AND METHODS

A rat model of alcohol-induced coma was used to examine the effects of AGNHW on EEG patterns. Male Sprague-Dawley rats were intraperitoneally injected with 32% ethanol to induce a coma, followed by treatment with AGNHW. Wireless electrodes were implanted in the cortex of the rats to obtain EEG signals. Our analysis focused on evaluating alterations in the Rat Coma Scale (RCS), as well as assessing changes in the frequency and distribution of EEG patterns, sleep rhythms, and body temperature subsequent to AGNHW treatment.

RESULTS

The study found a significant increase in the δ-band power ratio, as well as a decrease in RCS scores and β-band power ratio after modeling. AGNHW treatment significantly reduced the δ-band power ratio and increased the β-band power ratio compared to naloxone, suggesting its superior arousal effects. The results also revealed a decrease in the time proportion of WAKE and REM EEG patterns after modeling, accompanied by a significant increase in the time proportion of NREM EEG patterns. Both naloxone and AGNHW effectively counteracted the disordered sleep EEG patterns. Additionally, AGNHW was more effective than naloxone in improving hypothermia caused by acute alcohol poisoning in rats.

CONCLUSION

Our study provides evidence for the arousal effects of AGNHW in alcohol-induced coma rats. It also suggests a potential role for AGNHW in regulating post-comatose sleep rhythm disorders.

JZL184 increases anxiety-like behavior and does not reduce alcohol consumption in female rats after repeated mild traumatic brain injury

Alcohol use disorder (AUD) is highly comorbid with traumatic brain injury (TBI). Previously, using a lateral fluid percussion model (LFP) (an open model of head injury) to generate a single mild to moderate traumatic brain injury (TBI), we showed that TBI produces escalation in alcohol drinking, that alcohol exposure negatively impacts TBI outcomes, and that the endocannabinoid degradation inhibitor (JZL184) confers significant protection from behavioral and neuropathological outcomes in male rodents. In the present study, we used a weight drop model (a closed model of head injury) to produce a repeated mild TBI (rmTBI, 3 TBIs, spaced by 24 hours) to examine the sex-specific effects on alcohol consumption and anxiety-like behavior in rats, and whether systemic treatment with JZL184 would reverse TBI effects on those behaviors in both sexes. In two separate studies, adult male and female Wistar rats were subjected to rmTBI or sham using the weight drop model. Physiological measures of injury severity were collected from all animals. Animals in both studies were allowed to consume alcohol using an intermittent 2-bottle choice procedure (12 pre-TBI sessions and 12 post-TBI sessions). Neurological severity and neurobehavioral scores (NSS and NBS, respectively) were tested 24 hours after the final injury. Anxiety-like behavior was tested at 37-38 days post-injury in Study 1, and 6-8 days post-injury in Study 2. Our results show that females exhibited reduced respiratory rates relative to males with no significant differences between Sham and rmTBI, no effect of rmTBI or sex on righting reflex, and increased neurological deficits in rmTBI groups in both studies. In Study 1, rmTBI increased alcohol consumption in female but not male rats. Male rats consistently exhibited higher levels of anxiety-like behavior than females. rmTBI did not affect anxiety-like behavior 37-38 days post-injury. In Study 2, rmTBI once again increased alcohol consumption in female but not male rats, and repeated systemic treatment with JZL184 did not affect alcohol consumption. Also in Study 2, rmTBI increased anxiety-like behavior in males but not females and repeated systemic treatment with JZL184 produced an unexpected increase in anxiety-like behavior 6-8 days post-injury. In summary, rmTBI increased alcohol consumption in female rats, systemic JZL184 treatment did not alter alcohol consumption, and both rmTBI and sub-chronic systemic JZL184 treatment increased anxiety-like behavior 6-8 days post-injury in males but not females, highlighting robust sex differences in rmTBI effects.

Dynorphin/kappa opioid receptor system regulation on amygdaloid circuitry: Implications for neuropsychiatric disorders

Amygdaloid circuits are involved in a variety of emotional and motivation-related behaviors and are impacted by stress. The amygdala expresses several neuromodulatory systems, including opioid peptides and their receptors. The Dynorphin (Dyn)/kappa opioid receptor (KOR) system has been implicated in the processing of emotional and stress-related information and is expressed in brain areas involved in stress and motivation. Dysregulation of the Dyn/KOR system has also been implicated in various neuropsychiatric disorders. However, there is limited information about the role of the Dyn/KOR system in regulating amygdala circuitry. Here, we review the literature on the (1) basic anatomy of the amygdala, (2) functional regulation of synaptic transmission by the Dyn/KOR system, (3) anatomical architecture and function of the Dyn/KOR system in the amygdala, (4) regulation of amygdala-dependent behaviors by the Dyn/KOR system, and (5) future directions for the field. Future work investigating how the Dyn/KOR system shapes a wide range of amygdala-related behaviors will be required to increase our understanding of underlying circuitry modulation by the Dyn/KOR system. We anticipate that continued focus on the amygdala Dyn/KOR system will also elucidate novel ways to target the Dyn/KOR system to treat neuropsychiatric disorders.

mTORC1 pathway is involved in the kappa opioid receptor activation-induced increase in excessive alcohol drinking in mice

KOP-r agonist U50,488H produces strong aversion and anxiety/depression-like behaviors that enhance alcohol intake and promote alcohol seeking and relapse-like drinking in rodents. Mammalian target of rapamycin complex 1 (mTORC1) pathway in mouse striatum is highly involved in excessive alcohol intake and seeking, and in the U50,488H-induced conditioned place aversion. Therefore, we hypothesized that KOP-r activation increases alcohol consumption through the mTORC1 activation. This study focuses on: (1) how chronic excessive alcohol drinking (4-day drinking-in-the-dark paradigm followed by 3-week chronic intermittent access drinking paradigm [two-bottle choice, 24-h access every other day]) affected nuclear transcript levels of the mTORC1 pathway genes in mouse nucleus accumbens shell (NAcs), using transcriptome-wide RNA sequencing analysis; and (2) whether selective mTORC1 inhibitor rapamycin could alter excessive alcohol drinking and prevent U50,488H-promoted alcohol intake. Thirteen nuclear transcripts of mTORC1 pathway genes showed significant up-regulation in the NAcs, with two genes down-regulated, after excessive alcohol drinking, suggesting the mTORC1 pathway was profoundly disrupted. Single administration of rapamycin decreased alcohol drinking in a dose-dependent manner. U50,488H increased alcohol drinking, and pretreatment with rapamycin, at a dose lower than effective doses, blocked the U50,488H-promoted alcohol intake in a dose-dependent manner, indicating a mTORC1-mediated mechanism. Our results provide supportive and direct evidence relevant to the transcriptional profiling of the critical mTORC1 genes in mouse NAc shell: with functional and pharmacological effects of rapamycin, altered nuclear transcripts in the mTORC1 signaling pathway after excessive alcohol drinking may contribute to increased alcohol intake triggered by KOP-r activation.

Dynorphin and its role in alcohol use disorder

The dynorphin / kappa opioid receptor (KOR) system has been implicated in many aspects that influence neuropsychiatric disorders. Namely, this system modulates neural circuits that primarily regulate reward seeking, motivation processing, stress responsivity, and pain sensitivity, thus affecting the development of substance and alcohol use disorder (AUD). The effects of this system are often bidirectional and depend on projection targets. To date, a majority of the studies focusing on this system have examined the KOR function using agonists and antagonists. Indeed, there are studies that have examined prodynorphin and dynorphin levels by measuring mRNA and tissue content levels; however, static levels of the neuropeptide and its precursor do not explain complete and online function of the peptide as would be explained by measuring dynorphin transmission in real time. New and exciting methods using optogenetics, chemogenetics, genetic sensors, fast scan cyclic voltammetry are now being developed to detect various neuropeptides with a focus on opioid peptides, including dynorphin. In this review we discuss studies that examine dynorphin projections in areas involved in AUD, its functional involvement in AUD and vulnerability to develop AUD at various ages. Moreover, we discuss dynorphin's role in promoting AUD by dysregulation motivation circuits and how advancements in opioid peptide detection will further our understanding.

GPCR and Alcohol-Related Behaviors in Genetically Modified Mice

G protein-coupled receptors (GPCRs) constitute the largest class of cell surface signaling receptors and regulate major neurobiological processes. Accordingly, GPCRs represent primary targets for the treatment of brain disorders. Several human genetic polymorphisms affecting GPCRs have been associated to different components of alcohol use disorder (AUD). Moreover, GPCRs have been reported to contribute to several features of alcohol-related behaviors in animal models. Besides traditional pharmacological tools, genetic-based approaches mostly aimed at deleting GPCR genes provided substantial information on how key GPCRs drive alcohol-related behaviors. In this review, we summarize the alcohol phenotypes that ensue from genetic manipulation, in particular gene deletion, of key GPCRs in rodents. We focused on GPCRs that belong to fundamental neuronal systems that have been shown as potential targets for the development of AUD treatment. Data are reviewed with particular emphasis on alcohol reward, seeking, and consumption which are behaviors that capture essential aspects of AUD. Literature survey indicates that in most cases, there is still a gap in defining the intracellular transducers and the functional crosstalk of GPCRs as well as the neuronal populations in which their signaling regulates alcohol actions. Further, the implication of only a few orphan GPCRs has been so far investigated in animal models. Combining advanced pharmacological technologies with more specific genetically modified animals and behavioral preclinical models is likely necessary to deepen our understanding in how GPCR signaling contributes to AUD and for drug discovery.

Combination of Clinically Utilized Kappa-Opioid Receptor Agonist Nalfurafine With Low-Dose Naltrexone Reduces Excessive Alcohol Drinking in Male and Female Mice

BACKGROUND

Nalfurafine is the first clinically approved kappa-opioid receptor (KOP-r) agonist as an antipruritus drug with few side effects in humans (e.g., sedation, depression, and dysphoria). No study, however, has been done using nalfurafine on alcohol drinking in rodents or humans.

METHODS

We investigated whether nalfurafine alone or in combination with mu-opioid receptor (MOP-r) antagonist naltrexone changed excessive alcohol drinking in male and female C57BL/6J (B6) mice subjected to a chronic intermittent-access drinking paradigm (2-bottle choice, 24-hour access every other day) for 3 weeks. Neuronal proopiomelanocortin enhancer (nPE) knockout mice with brain-specific deficiency of beta-endorphin (endogenous ligand of MOP-r) were used as a genetic control for the naltrexone effects.

RESULTS

Single administration of nalfurafine decreased alcohol intake and preference in both male and female B6 mice in a dose-dependent manner. Pretreatment with nor-BNI (a selective KOP-r antagonist) blocked the nalfurafine effect on alcohol drinking, indicating a KOP-r-mediated mechanism. Pharmacological effects of a 5-dosing nalfurafine regimen were further evaluated: The repeated nalfurafine administrations decreased alcohol consumption without showing any blunted effects, suggesting nalfurafine did not develop a tolerance after the multidosing regimen tested. Nalfurafine did not produce any sedation (spontaneous locomotor activity), anhedonia-like (sucrose preference test), anxiety-like (elevated plus maze test), or dysphoria-like (conditioned place aversion test) behaviors, suggesting that nalfurafine had few side effects. Investigating synergistic effects between low-dose naltrexone and nalfurafine, we found that single combinations of nalfurafine and naltrexone, at doses lower than individual effective dose, profoundly decreased excessive alcohol intake in both sexes. The effect of nalfurafine on decreasing alcohol consumption was confirmed in nPE-/- mice, suggesting independent mechanisms by which nalfurafine and naltrexone reduced alcohol drinking.

CONCLUSION

The clinically utilized KOP-r agonist nalfurafine in combination with low-dose naltrexone has potential in alcoholism treatment.

Dynorphin-kappa opioid receptor activity in the central amygdala modulates binge-like alcohol drinking in mice

Although previous research has demonstrated a role for kappa opioid receptor-mediated signaling in escalated alcohol consumption associated with dependence and stress exposure, involvement of the dynorphin/kappa opioid receptor (DYN/KOR) system in binge-like drinking has not been fully explored. Here we used pharmacological and chemogenetic approaches to examine the influence of DYN/KOR signaling on alcohol consumption in the drinking-in-the-dark (DID) model of binge-like drinking. Systemic administration of the KOR agonist U50,488 increased binge-like drinking (Experiment 1) while, conversely, systemic administration of the KOR antagonist nor-BNI reduced drinking in the DID model (Experiment 2). These effects of systemic KOR manipulation were selective for alcohol as neither drug influenced consumption of sucrose in the DID paradigm (Experiment 3). In Experiment 4, administration of the long-acting KOR antagonist nor-BNI into the central nucleus of the amygdala (CeA) decreased alcohol intake. Next, targeted "silencing" of DYN+ neurons in the CeA was accomplished using a chemogenetic strategy. Cre-dependent viral expression in DYN+ neurons was confirmed in CeA of Pdyn-IRES-Cre mice and functionality of an inhibitory (hM4Di) DREADD was validated (Experiment 5). Activating the inhibitory DREADD by CNO injection reduced binge-like alcohol drinking, but CNO injection did not alter alcohol intake in mice that were treated with control virus (Experiment 6). Collectively, these results demonstrate that DYN/KOR signaling in the CeA contributes to excessive alcohol consumption in a binge-drinking model.

Sex differences in stress-related alcohol use

Rates of alcohol use disorder (AUD) have increased in women by 84% over the past ten years relative to a 35% increase in men. This substantive increase in female drinking is alarming given that women experience greater alcohol-related health consequences compared to men. Stress is strongly associated with all phases of alcohol addiction, including drinking initiation, maintenance, and relapse for both women and men, but plays an especially critical role for women. The purpose of the present narrative review is to highlight what is known about sex differences in the relationship between stress and drinking. The critical role stress reactivity and negative affect play in initiating and maintaining alcohol use in women is addressed, and the available evidence for sex differences in drinking for negative reinforcement as it relates to brain stress systems is presented. This review discusses the critical structures and neurotransmitters that may underlie sex differences in stress-related alcohol use (e.g., prefrontal cortex, amygdala, norepinephrine, corticotropin releasing factor, and dynorphin), the involvement of sex and stress in alcohol-induced neurodegeneration, and the role of ovarian hormones in stress-related drinking. Finally, the potential avenues for the development of sex-appropriate pharmacological and behavioral treatments for AUD are identified. Overall, women are generally more likely to drink to regulate negative affect and stress reactivity. Sex differences in the onset and maintenance of alcohol use begin to develop during adolescence, coinciding with exposure to early life stress. These factors continue to affect alcohol use into adulthood, when reduced responsivity to stress, increased affect-related psychiatric comorbidities and alcohol-induced neurodegeneration contribute to chronic and problematic alcohol use, particularly for women. However, current research is limited regarding the examination of sex in the initiation and maintenance of alcohol use. Probing brain stress systems and associated brain regions is an important future direction for developing sex-appropriate treatments to address the role of stress in AUD.

Age as a factor in stress and alcohol interactions: A critical role for the kappa opioid system

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

Preclinical evaluation of the kappa-opioid receptor antagonist CERC-501 as a candidate therapeutic for alcohol use disorders

Prior work suggests a role of kappa-opioid signaling in the control of alcohol drinking, in particular when drinking is escalated due to alcohol-induced long-term neuroadaptations. Here, we examined the small molecule selective kappa antagonist CERC-501 in rat models of alcohol-related behaviors, with the objective to evaluate its potential as a candidate therapeutic for alcohol use disorders. We first tested the effect of CERC-501 on acute alcohol withdrawal-induced anxiety-like behavior. CERC-501 was then tested on basal as well as escalated alcohol self-administration induced by 20% alcohol intermittent access. Finally, we determined the effects of CERC-501 on relapse to alcohol seeking triggered by both stress and alcohol-associated cues. Control experiments were performed to confirm the specificity of CERC-501 effects on alcohol-related behaviors. CERC-501 reversed anxiety-like behavior induced by alcohol withdrawal. It did not affect basal alcohol self-administration but did dose-dependently suppress self-administration that had escalated following long-term intermittent access to alcohol. CERC-501 blocked relapse to alcohol seeking induced by stress, but not when relapse-like behavior was triggered by alcohol-associated cues. The effects of CERC-501 were observed in the absence of sedative side effects and were not due to effects on alcohol metabolism. Thus, in a broad battery of preclinical alcohol models, CERC-501 has an activity profile characteristic of anti-stress compounds. Combined with its demonstrated preclinical and clinical safety profile, these data support clinical development of CERC-501 for alcohol use disorders, in particular for patients with negatively reinforced, stress-driven alcohol seeking and use.

Sex Specific Alterations in α4*Nicotinic Receptor Expression in the Nucleus Accumbens

Background: The mechanisms leading from traumatic stress to social, emotional and cognitive impairment and the development of mental illnesses are still undetermined and consequently there remains a critical need to develop therapies for preventing the adverse consequences of traumatic stress. Research indicates nicotinic acetylcholine receptors containing α4 subunits (α4*nAChRs) are both impacted by stress and capable of modulating the stress response. In this study, we investigated whether varenicline, a partial α4β2*nAChR agonist which reduces nicotine, alcohol and sucrose consumption, can reduce stress, a driving factor in substance use disorders. We also examined the effect of stress on nucleus accumbens (NAc) α4*nAChR expression. Methods: Transgenic mice with fluorescent tags attached to α4*nAChRs were administered varenicline and/or yohimbine (a pharmacological stressor) and plasma corticosterone and NAc α4*nAChR expression were measured. A separated group of mice were exposed to maternal separation (MS) during post-natal day (P) 2–14, then restraint stressed (30 min) at six weeks of age. Body weight, anxiety-like behaviours (elevated plus maze), plasma corticosterone and NAc α4*nAChR levels were measured. Results: Varenicline attenuated yohimbine-induced plasma corticosterone increases with no effect on NAc α4*nAChR expression. MS reduced unrestrained plasma corticosterone levels in both sexes. In females, MS increased body weight and NAc α4*nAChR expression, whereas, in males, MS and restraint caused a greater change in anxiety-like behaviours and plasma corticosterone levels. Restraint altered NAc α4*nAChR expression in both male and female MS mice. Conclusions: The effects of stress on NAc α4*nAChR are sex-dependent. While varenicline attenuated acute stress-induced rises in corticosterone levels, future studies are required to determine whether varenicline is effective for relieving the effects of stress.

Dynorphin/Kappa Opioid Receptor Signaling in Preclinical Models of Alcohol, Drug, and Food Addiction

The dynorphin/kappa opioid receptor (KOR) system is implicated in the "dark side" of addiction, in which stress exacerbates maladaptive responses to drug and alcohol exposure. For example, acute stress and acute ethanol exposure result in an elevation in dynorphin, the KOR endogenous ligand. Activation of KORs results in modulation of several neurotransmitters; however, this chapter will focus on its regulatory effects on dopamine in mesolimbic areas. Specifically, KOR activation has an inhibitory effect on dopamine release, thereby influencing reward processing. Repeated stimulation of KORs, for example, via chronic drug and/or stress exposure, results in increased function of the dynorphin/KOR system. This augmentation in KOR function shifts the homeostatic balance in favor of an overall reduction in dopamine signaling via either by reducing dopamine release or by increasing dopamine transporter function. This chapter examines the effects of chronic ethanol exposure on KOR function and the downstream effects on dopamine transmission. Additionally, the impact of chronic cocaine exposure and its effects on KOR function will be explored. Further, KORs may also be involved in driving excessive consumption of food, contributing to the risk of developing obesity. While some studies have shown that KOR agonists reduce drug intake, other studies have shown that antagonists reduce addiction-like behaviors, demonstrating therapeutic potential. For example, KOR inhibition reduces ethanol intake in dependent animals, motivation to self-administer cocaine in chronic stress-exposed animals, and food consumption in obese animals. This chapter will delve into the mechanisms by which modulation of the dynorphin/KOR system may be therapeutic.

Role of the Dynorphin/Kappa Opioid Receptor System in the Motivational Effects of Ethanol

Evidence has demonstrated that dynorphin (DYN) and the kappa opioid receptor (KOR) system contribute to various psychiatric disorders, including anxiety, depression, and addiction. More recently, this endogenous opioid system has received increased attention as a potential therapeutic target for treating alcohol use disorders. In this review, we provide an overview and synthesis of preclinical studies examining the influence of alcohol (ethanol [EtOH]) exposure on DYN/KOR expression and function, as well as studies examining the effects of DYN/KOR manipulation on EtOH's rewarding and aversive properties. We then describe work that has characterized effects of KOR activation and blockade on EtOH self-administration and EtOH dependence/withdrawal-related behaviors. Finally, we address how the DYN/KOR system may contribute to stress-EtOH interactions. Despite an apparent role for the DYN/KOR system in motivational effects of EtOH, support comes from relatively few studies. Nevertheless, review of this literature reveals several common themes: (i) rodent strains genetically predisposed to consume more EtOH generally appear to have reduced DYN/KOR tone in brain reward circuitry; (ii) acute and chronic EtOH exposure typically up-regulate the DYN/KOR system; (iii) KOR antagonists reduce behavioral indices of negative affect associated with stress and chronic EtOH exposure/withdrawal; and (iv) KOR antagonists are effective in reducing EtOH consumption, but are often more efficacious under conditions that engender high levels of consumption, such as dependence or stress exposure. These results support the contention that the DYN/KOR system plays a significant role in contributing to dependence- and stress-induced elevation in EtOH consumption. Overall, more comprehensive analyses (on both behavioral and mechanistic levels) are needed to provide additional insight into how the DYN/KOR system is engaged and adapts to influence the motivation effects of EtOH. This information will be critical for the development of new pharmacological agents targeting KORs as promising novel therapeutics for alcohol use disorders and comorbid affective disorders.

Synergistic blockade of alcohol escalation drinking in mice by a combination of novel kappa opioid receptor agonist Mesyl Salvinorin B and naltrexone

Mesyl Salvinorin B (MSB) is a potent selective kappa opioid receptor (KOP-r) agonist that has potential for development as an anti-psychostimulant agent with fewer side-effects (e.g., sedation, depression and dysphoria) than classic KOP-r agonists. However, no such study has been done on alcohol. We investigated whether MSB alone or in combination with naltrexone (mu-opioid receptor antagonist) altered voluntary alcohol drinking in both male and female mice. Mice, subjected to 3weeks of chronic escalation drinking (CED) in a two-bottle choice paradigm with 24-h access every other day, developed rapid escalation of alcohol intake and high preference. We found that single, acute administration of MSB dose-dependently reduced alcohol intake and preference in mice after 3-week CED. The effect was specific to alcohol, as shown by the lack of any effect of MSB on sucrose or saccharin intake. We also used the drinking-in-the-dark (DID) model with limited access (4h/day) to evaluate the pharmacological effect of MSB after 3weeks of DID. However, MSB had no effect on alcohol drinking after 3-week DID. Upon investigation of potential synergistic effects between naltrexone and MSB, we found that acute administration of a combination of MSB and naltrexone reduced alcohol intake profoundly after 3-week CED at doses lower than those individual effective doses. Repeated administrations of this combination showed less tolerance development than repeated MSB alone. Our study suggests that the novel KOP-r agonist MSB both alone and in combination with naltrexone shows potential in alcoholism treatment models.

Stress-Induced Enhancement of Ethanol Intake in C57BL/6J Mice with a History of Chronic Ethanol Exposure: Involvement of Kappa Opioid Receptors

Our laboratory has previously demonstrated that daily forced swim stress (FSS) prior to ethanol drinking sessions facilitates enhanced ethanol consumption in mice with a history of chronic intermittent ethanol (CIE) vapor exposure without altering ethanol intake in air-exposed controls. Because both stress and chronic ethanol exposure have been shown to activate the dynorphin/kappa opioid receptor (KOR) system, the present study was designed to explore a potential role for KORs in modulating stress effects on ethanol consumption in the CIE model of dependence and relapse drinking. After stable baseline ethanol intake was established in adult male C57BL/6J mice, subjects received chronic intermittent exposure (16 h/day × 4 days/week) to ethanol vapor (CIE group) or air (CTL group). Weekly cycles of inhalation exposure were alternated with 5-day limited access drinking tests (1 h access to 15% ethanol). Experiment 1 compared effects of daily FSS and KOR activation on ethanol consumption. CIE and CTL mice were either exposed to FSS (10 min), the KOR agonist U50,488 (5 mg/kg), or a vehicle injection (non-stressed condition) prior to each daily drinking session during test weeks. FSS selectively increased drinking in CIE mice. U50,488 mimicked this effect in CIE mice, but also increased drinking in CTL mice. Experiment 2 assessed effects of KOR blockade on stress-induced drinking in CIE and CTL mice. Stressed and non-stressed mice were administered the short-acting KOR antagonist LY2444296 (0 or 5 mg/kg) 30 min prior to each drinking session during test weeks. FSS selectively increased ethanol consumption in CIE mice, an effect that was abolished by LY2444296 pretreatment. In Experiment 3, CIE and CTL mice were administered one of four doses of U50,488 (0, 1.25, 2.5, 5.0 mg/kg) 1 h prior to each daily drinking test (in lieu of FSS). All doses of U50,488 increased ethanol consumption in both CIE and CTL mice. The U50,488-induced increase in drinking was blocked by LY2444296. Our results demonstrate that the KOR system contributes to the stress enhancement of ethanol intake in mice with a history of chronic ethanol exposure.

Genes and Alcohol Consumption: Studies with Mutant Mice

In this chapter, we review the effects of global null mutant and overexpressing transgenic mouse lines on voluntary self-administration of alcohol. We examine approximately 200 publications pertaining to the effects of 155 mouse genes on alcohol consumption in different drinking models. The targeted genes vary in function and include neurotransmitter, ion channel, neuroimmune, and neuropeptide signaling systems. The alcohol self-administration models include operant conditioning, two- and four-bottle choice continuous and intermittent access, drinking in the dark limited access, chronic intermittent ethanol, and scheduled high alcohol consumption tests. Comparisons of different drinking models using the same mutant mice are potentially the most informative, and we will highlight those examples. More mutants have been tested for continuous two-bottle choice consumption than any other test; of the 137 mouse genes examined using this model, 97 (72%) altered drinking in at least one sex. Overall, the effects of genetic manipulations on alcohol drinking often depend on the sex of the mice, alcohol concentration and time of access, genetic background, as well as the drinking test.

Quantification of alcohol drinking patterns in mice

The use of mice in alcohol research provides an excellent model system for a better understanding of the genetics and neurobiology of alcohol addiction. Almost 60 years ago, alcohol researchers began to test strains of mice for alcohol preference and intake. In particular, various voluntary alcohol drinking paradigms in the home cage were developed. In mouse models of voluntary oral alcohol consumption, animals have concurrent access to water and either one or several concentrated alcohol solutions in their home cages. Although these models have high face validity, many experimental conditions require a more precise monitoring of alcohol consumption in mice in order to capture the role of specific strains or genes, or any other manipulation on alcohol drinking behavior. Therefore, we have developed a fully automated, highly precise monitoring system for alcohol drinking in mice in the home cage. This system is now commercially available. We show that this drinkometer system allows for detecting differences in drinking behavior (i) in transgenic mice, (ii) following alcohol deprivation, and (iii) following stress applications that are usually not detected by classical home-cage drinking paradigms. In conclusion, our drinkometer system allows disturbance-free and high resolution monitoring of alcohol drinking behavior. In particular, micro-drinking and circadian drinking patterns can be monitored in genetically modified and inbred strains of mice after environmental and pharmacological manipulation, and therefore this system represents an improvement in measuring behavioral features that are of relevance for the development of alcohol use disorders.

Kappa opioid receptor signaling in the brain: Circuitry and implications for treatment

Kappa opioid receptors (KORs) in the central nervous system have been known to be important regulators of a variety of psychiatry illnesses, including anxiety and addiction, but their precise involvement in these disorders is complex and has yet to be fully elucidated. Here, we briefly review the pharmacology of KORs in the brain, including KOR's involvement in anxiety, depression, and drug addiction. We also review the known neuronal circuitry impacted by KOR signaling, and interactions with corticotrophin-releasing factor (CRF), another key peptide in anxiety-related illnesses, as well as the role of glucocorticoids. We suggest that KORs are a promising therapeutic target for a host of neuropsychiatric conditions.

Alcohol-induced changes in opioid peptide levels in adolescent rats are dependent on housing conditions

Background

Endogenous opioids are implicated in the mechanism of action of alcohol and alcohol affects opioids in a number of brain areas, although little is known about alcohol's effects on opioids in the adolescent brain. One concern, in particular when studying young animals, is that alcohol intake models often are based on single housing that may result in alcohol effects confounded by the lack of social interactions. The aim of this study was to investigate short- and long-term alcohol effects on opioids and the influence of housing conditions on these effects.

Methods

In the first part, opioid peptide levels were measured after one 24-hour session of single housing and 2-hour voluntary alcohol intake in adolescent and adult rats. In the second part, a model with a cage divider inserted during 2-hour drinking sessions was tested and the effects on opioids were examined after 6 weeks of adolescent voluntary intake in single-and pair-housed rats, respectively.

Results

The effects of single housing were age specific and affected Met-enkephalin-Arg⁶Phe⁷ (MEAP) in particular. In adolescent rats, it was difficult to distinguish between effects induced by alcohol and single housing, whereas alcohol-specific effects were seen in dynorphin B (DYNB), beta-endorphin (BEND), and MEAP levels in adults. Voluntary drinking affected several brain areas and the majority of alcohol-induced effects were not dependent on housing. However, alcohol effects on DYNB and BEND in the amygdala were dependent on housing. Housing alone affected MEAP in the cingulate cortex.

Conclusions

Age-specific housing- and alcohol-induced effects on opioids were found. In addition, prolonged voluntary alcohol intake under different housing conditions produced several alcohol-induced effects independent of housing. However, housing-dependent effects were found in areas implicated in stress, emotionality, and alcohol use disorder. Housing condition and age may therefore affect the reasons and underlying mechanisms for drinking and could potentially affect the outcome of a number of end points in research on alcohol intake.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Alcohol: a stimulant activating brain stress responsive systems with persistent neuroadaptation

Addictive diseases, including addiction to alcohol, opiates or cocaine, pose massive public health costs. Addictions are chronic relapsing brain diseases, caused by drug-induced direct effects and persistent neuroadaptations at the molecular, cellular and behavioral levels. These drug-type specific neuroadapations are mainly contributed by three factors: environment, including stress, the direct reinforcing effects of the drug on the CNS, and genetics. Results from animal models and basic clinical research (including human genetic study) have shown important interactions between the stress responsive systems and alcohol abuse. In this review we will discuss the involvement of the dysregulation of the stress responsive hypothalamic-pituitary-adrenal (HPA) axis in alcohol addiction (Section I). Addictions to specific drugs such as alcohol, psychostimulants and opiates (e.g., heroin) have some common direct or downstream effects on several brain stress-responsive systems, including vasopressin and its receptor system (Section II), POMC and mu opioid receptor system (Section III) and dynorphin and kappa opioid receptor systems (Section IV). Further understanding of these systems, through laboratory-based and translational studies, have the potential to optimize early interventions and to discover new treatment targets for the therapy of alcoholism. This article is part of the Special Issue entitled 'CNS Stimulants'.

15 years of genetic approaches in vivo for addiction research: Opioid receptor and peptide gene knockout in mouse models of drug abuse

The endogenous opioid system is expressed throughout the brain reinforcement circuitry, and plays a major role in reward processing, mood control and the development of addiction. This neuromodulator system is composed of three receptors, mu, delta and kappa, interacting with a family of opioid peptides derived from POMC (β-endorphin), preproenkephalin (pEnk) and preprodynorphin (pDyn) precursors. Knockout mice targeting each gene of the opioid system have been created almost two decades ago. Extending classical pharmacology, these mutant mice represent unique tools to tease apart the specific role of each opioid receptor and peptide in vivo, and a powerful approach to understand how the opioid system modulates behavioral effects of drugs of abuse. The present review summarizes these studies, with a focus on major drugs of abuse including morphine/heroin, cannabinoids, psychostimulants, nicotine or alcohol. Genetic data, altogether, set the mu receptor as the primary target for morphine and heroin. In addition, this receptor is essential to mediate rewarding properties of non-opioid drugs of abuse, with a demonstrated implication of β-endorphin for cocaine and nicotine. Delta receptor activity reduces levels of anxiety and depressive-like behaviors, and facilitates morphine-context association. pEnk is involved in these processes and delta/pEnk signaling likely regulates alcohol intake. The kappa receptor mainly interacts with pDyn peptides to limit drug reward, and mediate dysphoric effects of cannabinoids and nicotine. Kappa/dynorphin activity also increases sensitivity to cocaine reward under stressful conditions. The opioid system remains a prime candidate to develop successful therapies in addicted individuals, and understanding opioid-mediated processes at systems level, through emerging genetic and imaging technologies, represents the next challenging goal and a promising avenue in addiction research. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.

Effects of voluntary alcohol drinking on corticotropin-releasing factor and preprodynorphin mRNA levels in the central amygdala of Sardinian alcohol-preferring rats

The stress-response corticotropin-releasing factor (CRF) and dynorphin systems are critically involved in alcohol drinking and "anxiety"-related behaviors. Selectively bred Sardinian alcohol-preferring (sP) rats display high inherent "anxiety"-related behaviors, in comparison with their alcohol-nonpreferring counterpart (sNP rats). The present study was undertaken to investigate: (1) if there were genetically determined differences in basal gene expression levels of CRF, CRF-R1, preprodynorphin (ppDyn) and kappa opioid receptor (KOP-r) between sP and sNP rats; specifically, mRNA levels of the above genes were measured in the central amygdala (CeA), hypothalamus and other stress responsive and mesolimbic regions of alcohol-naive sP and sNP rats; and (2) if the above mRNA levels were altered by voluntary alcohol drinking in sP rats exposed to the standard, homecage 2-bottle "alcohol vs. water" choice regimen 24h/day for 17 days. Higher basal CRF mRNA levels were found only in CeA of alcohol-naive sP rats, compared with sNP rats; these levels were decreased after alcohol consumption. In contrast, ppDyn mRNA levels in CeA of sP rats were increased by alcohol consumption, but with no basal difference from sNP rats. Although higher basal ppDyn mRNA levels were found in hypothalamus of sP rats, compared with sNP rats, there was no alteration after alcohol drinking in sP rats. No difference for the above mRNA levels was observed in other regions, including nucleus accumbens shell or core, caudate-putamen, ventral tegmental area and medial/basolateral amygdala, between the two rat lines before or after alcohol consumption. Our results demonstrate the existence of genetically determined high basal CRF mRNA levels in CeA of sP rats. Alcohol consumption decreased CeA CRF mRNA levels with parallel increases in CeA ppDyn mRNA levels.