Effects of naltrexone, duloxetine, and a corticotropin-releasing factor type 1 receptor antagonist on binge-like alcohol drinking in rats

Glucagon-like peptide-1 receptor agonists, but not dipeptidyl peptidase-4 inhibitors, reduce alcohol intake

BACKGROUNDDespite growing preclinical evidence that glucagon-like peptide1 receptor agonists (GLP-1RAs) could be repurposed to treat alcohol use disorder (AUD), clinical evidence is scarce. Additionally, the potential impact of dipeptidyl peptidase-4 inhibitors (DPP-4Is) on alcohol intake is largely unknown.METHODSWe conducted a large cohort study using 2008-2023 electronic health records data from the U.S. Department of Veterans Affairs. Changes in Alcohol Use Disorders Identification Test-Consumption (AUDIT-C) scores were compared between propensity-score-matched GLP-1RA recipients, DPP-4I recipients, and unexposed comparators. We further tested the effects of 2 DPP-4Is, linagliptin and omarigliptin, on binge-like alcohol drinking in mice and operant oral alcohol self administration in alcohol-dependent rats, models previously used to show a significant effect of the GLP-1RA semaglutide in reducing alcohol intake.RESULTSGLP-1RA recipients reported a greater reduction in AUDIT-C scores than unexposed individuals (difference-in-difference [DiD]: 0.09 [95% CI: 0.03, 0.14], P = 0.0025) and DPP-4I recipients (DiD: 0.11 [95% CI: 0.05,0.17], P = 0.0002). Reductions in drinking were more pronounced among individuals with baseline AUD (GLP-1RA versus unexposed: 0.51 [95% CI: 0.29,0.72], P < 0.0001; GLP-1RA versus DPP-4I: 0.65 [95% CI: 0.43,0.88], P < 0.0001) and baseline hazardous drinking (GLP-1RA versus unexposed: 1.38 [95% CI: 1.07,1.69], P < 0.0001; GLP-1RA versus DPP-4I: 1.00 [95% CI: 0.68,1.33], P < 0.0001). There were no differences between DPP-4I recipients and unexposed individuals. The latter results were confirmed via a reverse translational approach. Specifically, neither linagliptin nor omarigliptin reduced alcohol drinking in mice or rats. The rodent experiments also confirmed target engagemhent, as both DPP-4Is reduced blood glucose levels.CONCLUSIONConvergent findings across humans, mice, and rats indicated that GLP-1RAs, but not DPP-4Is, reduce alcohol consumption and may be efficacious in treating AUD.FUNDINGThis work was supported by the National Institutes of Health Intramural Research Program (ZIA DA000635, ZIA DA000644, ZIA DA000602), National Institute on Alcohol Abuse and Alcoholism extramural funding (R01 AA030041, P01 AA029545, U01 AA026224, U24 AA020794, U01 AA020790, U10 AA013566), the U.S. Department of Veterans Affairs (I01BX004820), and an Alkermes Pathways Research Award.

Kappa-opioid receptor antagonism in the nucleus accumbens shell distinguishes escalated alcohol consumption and negative affective-like behavior from physiological withdrawal in alcohol-dependence

Alcohol use disorder (AUD) is a chronic relapsing disease that is deleterious at individual, familial, and societal levels. Although AUD is one of the highest preventable causes of death in the USA, therapies for the treatment of AUD are not sufficient given the heterogeneity of the disorder and the limited number of approved medications. To provide better pharmacological strategies, it is important to understand the neurological underpinnings of AUD. Evidence implicates the endogenous dynorphin (DYN)/κ-opioid receptor (KOR) system recruitment in dysphoric and negative emotional states in AUD to promote maladaptive behavioral regulation. The nucleus accumbens shell (AcbSh), mediating motivational and emotional processes that is a component of the mesolimbic dopamine system and the extended amygdala, is an important site related to alcohol's reinforcing actions (both positive and negative) and neuroadaptations in the AcbSh DYN/KOR system have been documented to induce maladaptive symptoms in AUD. We have previously shown that in other nodes of the extended amygdala, site-specific KOR antagonism can distinguish different symptoms of alcohol dependence and withdrawal. In the current study, we examined the role of the KOR signaling in the AcbSh of male Wistar rats in operant alcohol self-administration, measures of negative affective-like behavior, and physiological symptoms during acute alcohol withdrawal in alcohol-dependence. To induce alcohol dependence, rats were exposed to chronic intermittent ethanol vapor for 14 h/day for three months, during which stable escalation of alcohol self-administration was achieved and pharmacological AcbSh KOR antagonism ensued. The results showed that AcbSh KOR antagonism significantly reduced escalated alcohol intake and negative affective-like states but did not alter somatic symptoms of withdrawal. Understanding the relative contribution of these different drivers is important to understand and inform therapeutic efficacy approaches in alcohol dependence and further emphasis the importance of the KOR/DYN system as a target for AUD therapeutics.

The CRF/Urocortin systems as therapeutic targets for alcohol use disorders

Development and maintenance of alcohol use disorders have been proposed to recruit critical mechanisms involving Corticotropin Releasing Factor and Urocortins (CRF/Ucns). The CRF/Ucns system is comprised of a family of peptides (CRF, Ucn 1, Ucn 2, Ucn 3) which act upon two receptor subtypes, CRFR1 and CRFR2, each with different affinity profiles to the endogenous peptides and differential brain distribution. Activity of CRF/Ucn system is further modulated by CRF binding protein (CRF-BP), which regulates availability of CRF and Ucns to exert their actions. Extensive evidence in preclinical models support the involvement of CRF/Ucn targets in escalated alcohol drinking, as well as point to changes in CRF/Ucn brain function as a result of chronic alcohol exposure and/or withdrawal. It highlights the role of CRF and CRFR1-mediated signaling in conditions of excessive alcohol taking and seeking, including during various stages of withdrawal and relapse to alcohol. Besides its role in the hypothalamic-pituitary-adrenal (HPA) axis, the importance of extra-hypothalamic CRF pathways, especially in the extended amygdala, in the neurobiology of alcohol abuse and dependence is emphasized. Emerging roles for other targets of the CRF/Ucn system, such as CRF2 receptors, CRF-BP and Ucns in escalated alcohol drinking is also discussed. Finally, the limited translational value of CRF/Ucn interventions in stress-related and alcohol use disorders is discussed. So far, CRFR1 antagonists have shown little or no efficacy in human clinical trials, although a range of unexplored conditions and possibilities remain to be explored.

Intermittent-access operant alcohol self-administration promotes binge-like drinking and drinking despite negative consequences in male and female heterogeneous stock rats

The study of Alcohol Use Disorders (AUD) in preclinical models is hampered by difficulty in training rodents to voluntarily consume high levels of alcohol. The intermittency of alcohol access/exposure is well known to modulate alcohol consumption (e.g., alcohol deprivation effect, intermittent-access two-bottle-choice) and recently, intermittent access operant self-administration procedures have been used to produce more intense and binge-like self-administration of intravenous psychostimulant and opioid drugs. In the present study, we sought to systematically manipulate the intermittency of operant self-administered alcohol access to determine the feasibility of promoting more intensified, binge-like alcohol consumption. To this end, 24 male and 23 female NIH Heterogeneous Stock rats were trained to self-administer 10% w/v ethanol, before being split into three different-access groups. Short Access (ShA) rats continued receiving 30-min training sessions, Long Access (LgA) rats received 16-h sessions, and Intermittent Access (IntA) rats received 16-h sessions, wherein the hourly alcohol-access periods were shortened over sessions, down to 2 min. IntA rats demonstrated an increasingly binge-like pattern of alcohol drinking in response to restriction of alcohol access, while ShA and LgA rats maintained stable intake. All groups were tested on orthogonal measures of alcohol-seeking and quinine-punished alcohol drinking. The IntA rats displayed the most punishment-resistant drinking. In a separate experiment, we replicated our main finding, that intermittent access promotes a more binge-like pattern of alcohol self-administration using 8 male and 8 female Wistar rats. In conclusion, intermittent access to self-administered alcohol promotes more intensified self-administration. This approach may be useful in developing preclinical models of binge-like alcohol consumption in AUD.

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.

The glucagon-like peptide-1 (GLP-1) analogue semaglutide reduces alcohol drinking and modulates central GABA neurotransmission

Growing evidence indicates that the glucagon-like peptide-1 (GLP-1) system is involved in the neurobiology of addictive behaviors, and GLP-1 analogues may be used for the treatment of alcohol use disorder (AUD). Here, we examined the effects of semaglutide, a long-acting GLP-1 analogue, on biobehavioral correlates of alcohol use in rodents. A drinking-in-the-dark procedure was used to test the effects of semaglutide on binge-like drinking in male and female mice. We also tested the effects of semaglutide on binge-like and dependence-induced alcohol drinking in male and female rats, as well as acute effects of semaglutide on spontaneous inhibitory postsynaptic currents (sIPSCs) from central amygdala (CeA) and infralimbic cortex (ILC) neurons. Semaglutide dose-dependently reduced binge-like alcohol drinking in mice; a similar effect was observed on the intake of other caloric/noncaloric solutions. Semaglutide also reduced binge-like and dependence-induced alcohol drinking in rats. Semaglutide increased sIPSC frequency in CeA and ILC neurons from alcohol-naive rats, suggesting enhanced GABA release, but had no overall effect on GABA transmission in alcohol-dependent rats. In conclusion, the GLP-1 analogue semaglutide decreased alcohol intake across different drinking models and species and modulated central GABA neurotransmission, providing support for clinical testing of semaglutide as a potentially novel pharmacotherapy for AUD.

Impact of adolescent intermittent ethanol exposure in male and female rats on social drinking and neuropeptide gene expression

BACKGROUND

Alcohol use during adolescence can alter maturational changes that occur in brain regions associated with social and emotional responding. Our previous studies have shown that adult male, but not female rats demonstrate social anxiety-like alterations and enhanced sensitivity to ethanol-induced social facilitation following adolescent intermittent ethanol exposure (AIE). These consequences of AIE may influence adult social drinking in a sex-specific manner.

METHODS

To test the effects of AIE on social drinking, male and female Sprague-Dawley rats exposed to water or ethanol (0 or 4 g/kg, intragastrically, every other day, between postnatal day [P] 25 and 45) were tested as adults (P72-83) in a social drinking paradigm (30-minute access to a 10% ethanol solution in supersac or supersac alone in groups of three same-sex littermates across two 4-day cycles separated by 4 days off). Social behavior was assessed during the last drinking session, along with assessment of oxytocin (OXT), oxytocin receptor (OXTR), vasopressin (AVP), and vasopressin receptors 1a and 1b (AVPR1a, AVPR1b) in the hypothalamus and lateral septum.

RESULTS

Males exposed to AIE consumed more ethanol than water-exposed controls during the second drinking cycle, whereas AIE did not affect supersac intake in males. AIE-exposed females consumed less ethanol and more supersac than water-exposed controls. Water-exposed females drinking ethanol showed more social investigation and significantly higher hypothalamic OXTR, AVP, and AVPR1b gene expression than their counterparts ingesting supersac and AIE females drinking ethanol. In males, hypothalamic AVPR1b gene expression was affected by drinking solution, with significantly higher expression evident in males drinking ethanol than those consuming supersac.

CONCLUSIONS

Collectively, these findings provide new evidence regarding sex-specific effects of AIE on social drinking and suggest that the hypothalamic OXT and AVP systems are implicated in the effects of ingested ethanol on social behavior in a sex- and adolescent-exposure-dependent manner.

Compulsive Alcohol Seeking and Relapse: Central Role of Conditioning Factors Associated with Alleviation of Withdrawal States by Alcohol

Background and Purpose

Learned associations between environmental stimuli and drugs of abuse represent a major factor in the chronically relapsing nature of drug addiction. In drug dependent subjects these associations must be presumed to include associations linked to reversal of adverse withdrawal states by drug use—“withdrawal‐associated learning” (WDL). However, their significance in drug seeking has received little experimental scrutiny.

Experimental Approach

Using alcohol as a drug of abuse, the behavioural consequences of WDL were investigated in animal models of relapse and compulsive drug seeking by comparing the effects of WD L‐associated stimuli versus stimuli associated with alcohol without WDL experience in nondependent and post‐dependent rats. Brain sites activated by exposure to the respective stimuli were identified by c‐fos immunohistochemistry.

Key Results

(1) WDL‐associated stimuli elicited significant alcohol seeking. In rats with WDL experience, stimuli associated with alcohol in the nondependent state no longer elicited robust alcohol seeking. (2) Responding elicited by WDL‐associated stimuli, but not stimuli conditioned to alcohol in the nondependent state, was resistant to footshock punishment and increased response effort requirements for presentation of WDL‐related stimuli. (3) Stimuli conditioned to alcohol in rats with a dependence but not WDL history did not sustain punished responding or tolerance of increased effort. (4) The central nucleus of the amygdala was identified as a site selectively responsive to WDL stimulus exposure.

Conclusion and Implications

Environmental stimuli associated with reversal of adverse withdrawal states by alcohol elicit compulsive‐like alcohol seeking and establish WDL as a major, not well‐recognized factor, in relapse vulnerability.

From binge eating to binge drinking: A new and robust paradigm for assessing binge ethanol self-administration in male rats

Animal models of alcohol (ethanol) self-administration are crucial to dissect the neurobiological mechanisms underlying alcohol dependence, yet only a few of these induce pharmacologically relevant levels of alcohol consumption and rarely the alcohol self-administration co-occurs with other addictive behaviours. The present study aims to validate a novel model of voluntary ethanol consumption in male Wistar rats, in which ethanol access follows a binge eating experience. Over 10 sessions, Wistar rats were exposed to binge or control eating (i.e., the ingestion of 11.66 and 0.97 kcal/3 min, respectively, derived from a highly palatable food), immediately followed by two-bottle choice intake tests (2%, 6%, 10% or 14% w/w ethanol vs. water). Rats exposed to binge eating drank significantly more 6% or 10% (w/w) ethanol than control peers, reaching up to 6.3 g_EtOH /kg. Rats stimulated with 2%, 6%, 10% or 14% ethanol after binge eating, but not those given those ethanol concentrations after control eating, exhibited significant within-group increases in ethanol drinking. This ethanol consumption was not altered by quinine adulteration (up to 0.1 g/L), and it was blocked by naltrexone (10 mg/kg), administered immediately before binge eating. Blood ethanol levels significantly correlated with ethanol consumption; and the more ethanol consumed, the greater the distance travelled in an open field test conducted after the two-bottle choice test. Altogether, this self-administration model seems a valid and robust alternative with remarkable potential for research on different stages of the alcohol addiction and, particularly, to assess interactions between alcohol consumption and others addictive-like behaviours.

An Overview of Glycine Transporter Subtype 1 Inhibitors Under Preclinical and Clinical Evaluation for the Treatment of Alcohol Abuse

Abstract:

Being a historical issue that withstands multiple societal control measures, alcohol abuse remains a major healthcare problem. Despite worldwide efforts to limit consumption and educate people about its effects, consumption rates remain unchanged. Alcohol abuse arises from chronic alcohol exposure-caused permanent synaptic plasticity changes in the brain. These manifest in life-threatening withdrawal symptoms and drive relapse even after detoxification and treatment. Since ethanol has multiple targets in the human brain, it warrants a multiapproach therapy; here we introduce the potential therapeutic effects of glycine transporter subtype 1 inhibitors. We have listed the various glycine transporter 1 inhibitors used in studies of alcoholism and how they influenced glycine release from rat hippocampus was demonstrated in a preliminary study. Glycine transporters modulate both glutamatergic and glycinergic pathways: (i) glutamatergic neurotransmission plays an important role in the development of chronic changes in alcoholism as daily alcohol administration was shown to increase N-methyl-D-aspartic acid receptor activity long-term, and (ii) ethanol has access to the dopaminergic reward system via glycine receptors, being an allosteric modulator of glycine receptors. This manuscript summarises the progress and development of glycine transporter 1 inhibitors, characterizing them by their mode of action, adverse effects, and discusses their clinical applicability. Furthermore, we highlight the progress in the latest clinical trials, outline currently applied treatment methods, and offer suggestions for implementing glycine transporter 1 inhibitors into the long-term treatment of alcohol abuse.

FACTORS CONTRIBUTING TO THE ESCALATION OF ALCOHOL CONSUMPTION

Understanding factors that contribute to the escalation of alcohol consumption is key to understanding how an individual transitions from non/social drinking to AUD and to providing better treatment. In this review, we discuss how the way ethanol is consumed as well as individual and environmental factors contribute to the escalation of ethanol consumption from intermittent low levels to consistently high levels. Moreover, we discuss how these factors are modelled in animals. It is clear a vast array of complex, interacting factors influence changes in alcohol consumption. Some of these factors act early in the acquisition of ethanol consumption and initial escalation, while others contribute to escalation of ethanol consumption at a later stage and are involved in the development of alcohol dependence. There is considerable need for more studies examining escalation associated with the formation of dependence and other hallmark features of AUD, especially studies examining mechanisms, as it is of considerable relevance to understanding and treating AUD.

Gut microbiome and metabolome in a non-human primate model of chronic excessive alcohol drinking

A relationship between the gut microbiome and alcohol use disorder has been suggested. Excessive alcohol use produces changes in the fecal microbiome and metabolome in both rodents and humans. Yet, these changes can be observed only in a subgroup of the studied populations, and reversal does not always occur after abstinence. We aimed to analyze fecal microbial composition and function in a translationally relevant baboon model of chronic heavy drinking that also meets binge criteria (drinking too much, too fast, and too often), i.e., alcohol ~1 g/kg and blood alcohol levels (BALs) ≥ 0.08 g/dL in a 2-hour period, daily, for years. We compared three groups of male baboons (Papio anubis): L = Long-term alcohol drinking group (12.1 years); S = Short-term alcohol drinking group (2.7 years); and C = Control group, drinking a non-alcoholic reinforcer (Tang®) (8.2 years). Fecal collection took place during 3 days of Drinking (D), followed by a short period (3 days) of Abstinence (A). Fecal microbial alpha- and beta-diversity were significantly lower in L vs. S and C (p's < 0.05). Members of the commensal families Lachnospiraceae and Prevotellaceae showed a relative decrease, whereas the opportunistic pathogen Streptococcus genus showed a relative increase in L vs. S and C (p's < 0.05). Microbiota-related metabolites of aromatic amino acids, tricarboxylic acid cycle, and pentose increased in L vs. S and C (FDR-corrected p < 0.01), with the latter two suggesting high energy metabolism and enhanced glycolysis in the gut lumen in response to alcohol. Consistent with the long-term alcohol exposure, mucosal damage and oxidative stress markers (N-acetylated amino acids, 2-hydroxybutyrate, and metabolites of the methionine cycle) increased in L vs. S and C (FDR-corrected p < 0.01). Overall, S showed few differences vs. C, possibly due to the long-term, chronic alcohol exposure needed to alter the normal gut microbiota. In the three groups, the fecal microbiome barely differed between conditions D and A, whereas the metabolome shifted in the transition from condition D to A. In conclusion, changes in the fecal microbiome and metabolome occur after significant long-term excessive drinking and are only partially affected by acute forced abstinence from alcohol. These results provide novel information on the relationship between the fecal microbiome and metabolome in a controlled experimental setting and using a unique non-human primate model of chronic excessive alcohol drinking.

Mixtures of Sweeteners and Maltodextrin Enhance Flavor and Intake of Alcohol in Adolescent Rats

Sweet flavorants enhance palatability and intake of alcohol in adolescent humans. We asked whether sweet flavorants have similar effects in adolescent rats. The inherent flavor of ethanol in adolescent rats is thought to consist of an aversive odor, bitter/sweet taste, and burning sensation. In Experiment 1, we compared ingestive responses of adolescent rats to 10% ethanol solutions with or without added flavorants using brief-access lick tests. We used 4 flavorants, which contained mixtures of saccharin and sucrose or saccharin, sucrose, and maltodextrin. The rats approached (and initiated licking from) the flavored ethanol solutions more quickly than they did unflavored ethanol, indicating that the flavorants attenuated the aversive odor of ethanol. The rats also licked at higher rates for the flavored than unflavored ethanol solutions, indicating that the flavorants increased the naso-oral acceptability of ethanol. In Experiment 2, we offered rats chow, water, and a flavored or unflavored ethanol solution every other day for 8 days. The rats consistently consumed substantially more of the flavored ethanol solutions than unflavored ethanol across the 8 days. When we switched the rats from the flavored to unflavored ethanol for 3 days, daily intake of ethanol plummeted. We conclude that sweet and sweet/maltodextrin flavorants promote high daily intake of ethanol in adolescent rats (i.e., 6-10 g/kg) and that they do so in large part by improving the naso-oral sensory attributes of ethanol.

Sigma receptor-induced heavy drinking in rats: Modulation by the opioid receptor system

Alcohol use disorder (AUD) is a major cause of morbidity and mortality worldwide, for which new efficacious treatments are necessary. The opioid receptor system is a mediator of the rewarding effects of alcohol; in particular, while activation of μ opioid receptors enhances ethanol intake in rodents, opioid-receptor antagonists, such as naloxone and naltrexone, reduce its pleasurable and reinforcing effects, thereby decreasing alcohol. Sigma receptors (Sig-Rs) have been proposed as modulators of the effects of alcohol and, therefore, as a potential new pharmacological target for AUD. Somewhat analogously to μ opioid ligands, SigR agonists increase, while SigR antagonists decrease alcohol intake in animal models of excessive alcohol drinking. However, a potential cross-talk between these two receptor systems in relation to alcohol consumption has so far not been investigated. Here, we addressed this question pharmacologically, by testing the effects of either activating or inhibiting opioid receptors on the heavy alcohol drinking induced by chronic stimulation of SigR in alcohol-preferring rats. We found that the opioid receptor agonist morphine, which per se increases ethanol intake, at a sub-threshold dose reduces the binge-like drinking induced by the repeated treatment with the SigR agonist 1,3-di-o-tolylguanidine (DTG); conversely, the opioid receptor antagonist naltrexone, which per se reduces ethanol intake, at a sub-threshold dose potentiates the DTG-induced binge-like drinking. Our data show a cross-talk between the opioid and SigR systems relevant to the modulation of alcohol drinking, which provides important insights into the neurobiology of AUD and may lead to the development of novel therapies, either standalone or in combination.

Alcohol and Pain: A Translational Review of Preclinical and Clinical Findings to Inform Future Treatment Strategies

Alcohol use disorder (AUD) and chronic pain are enduring and devastating conditions that share an intersecting epidemiology and neurobiology. Chronic alcohol use itself can produce a characteristic painful neuropathy, while the regular analgesic use of alcohol in the context of nociceptive sensitization and heightened affective pain sensitivity may promote negative reinforcement mechanisms that underlie AUD maintenance and progression. The goal of this review was to provide a broad translational framework that communicates research findings spanning preclinical and clinical studies, including a review of genetic, molecular, behavioral, and social mechanisms that facilitate interactions between persistent pain and alcohol use. We also consider recent evidence that will shape future investigations into novel treatment mechanisms for pain in individuals suffering from AUD.

Excitatory/inhibitory balance across ontogeny contributes to age-specific behavioral outcomes of ethanol-like challenge in conditioned taste aversion

Adolescent-typical sensitivities to ethanol (EtOH) are characterized in part by reduced sensitivity to EtOH's aversive effects. Rodent studies have shown that adolescents are less sensitive than adults to aversive properties of EtOH in a conditioned taste aversion (CTA) paradigm. To the extent that EtOH exerts antagonist-like actions upon glutamate receptors and/or agonist-like actions upon γ-aminobutyric acid (GABA) receptors, age differences in excitatory/inhibitory balance may regulate age-specific EtOH sensitivities, such as attenuated sensitivity of adolescents to EtOH aversion. In our experiments, adolescent and adult Sprague-Dawley rats were tested for CTA following challenge with one of the following pharmacological agents: glutamatergic AMPA1 receptor antagonist NBQX, glutamatergic N-methyl-d-aspartate NR2B receptor antagonist ifenprodil, and extrasynaptic GABAA receptor agonist THIP to determine whether these induced age-specific aversive sensitivities like those seen with EtOH. NBQX administration did not induce CTA. The highest dose of extrasynaptic GABAA agonist THIP induced CTA in adolescents but not adults, an opposite ontogenetic profile as seen following EtOH. Ifenprodil exerted an age-specific pattern of CTA similar to that seen with EtOH in males, with adolescents being insensitive to ifenprodil's aversive effects relative to adults. Thus, only antagonism of NR2B receptors in male rats mimicked age-specific sensitivities to the aversive effects of EtOH.

Prenatal ethanol exposure attenuates sensitivity to the aversive effects of ethanol in adolescence and increases adult preference for a 5% ethanol solution in males, but not females

The present set of experiments investigated the effects of a moderate dose of ethanol (2 g/kg; 20% v/v intragastrically) during late gestation (G17-20 [gestational day]) on ethanol-induced conditioned taste aversion (CTA) in adolescence, and on ethanol consumption during adolescence and early adulthood. In experiment 1, male and female Sprague-Dawley rats were given 30-min access to a sweetened "supersaccharin" (SS) solution or sodium chloride (NaCl), followed by an intraperitoneal injection of 20% ethanol (0, 1, 1.25, or 1.5 g/kg) for three conditioning/test sessions. Among animals conditioned with SS, prenatally ethanol-exposed males exhibited attenuated ethanol-induced CTA relative to males prenatally gavaged with water or non-manipulated, whereas prenatal treatment had no effect on CTA in females. Among animals conditioned with NaCl, there were no exposure group differences in males, with modest evidence for attenuated CTA in prenatally ethanol-exposed females. In experiment 2, the effects of prenatal ethanol exposure on ethanol consumption in adolescents (P35 ± 1 day [postnatal day]) and adults (P56-60) were explored. At the beginning of the dark cycle, pair-housed rats were given three bottles containing 0, 5, and 10% ethanol for 18 h every other day (i.e., Monday, Wednesday, Friday) for 3 weeks. Relative to water controls, adult males prenatally exposed to ethanol showed greater preference and more intake (g/kg) of 5% ethanol, while showing lower intake of 10% ethanol. These intake and preference differences were not evident in adolescent males. Among females at both ages, ethanol-exposed animals showed lower preference and intake (g/kg) of 5% ethanol than their water-exposed controls. Thus, moderate ethanol exposure during late gestation produced a largely male-specific attenuation in the aversive effects of ethanol during adolescence that could contribute to later increases in preference and intake of a 5% ethanol solution, although this emergent effect was not evident in adolescence (or in females), but only manifested in adulthood.

Fos activation patterns related to acute ethanol and conditioned taste aversion in adolescent and adult rats

Studies in rats have revealed marked age differences in sensitivity to the aversive properties of ethanol, with a developmental insensitivity to ethanol aversion that is most pronounced during pre- and early adolescence, declining thereafter to reach the enhanced aversive sensitivity of adults. The adolescent brain undergoes significant transitions throughout adolescence, including in regions linked with drug reward and aversion; however, it is unknown how ontogenetic changes within this reward/aversion circuitry contribute to developmental differences in aversive sensitivity. The current study examined early adolescent (postnatal day [P]28-30) and adult (P72-74) Sprague-Dawley male rats for conditioned taste aversion (CTA) after doses of 0, 1.0, or 2.5 g/kg ethanol, and patterns of neuronal activation in response to ethanol using Fos-like immunohistochemistry (Fos+) to uncover regions where age differences in activation are associated with ethanol aversion. An adolescent-specific ethanol-induced increase in Fos+ staining was seen within the nucleus accumbens shell and core. An age difference was also noted within the Edinger-Westphal nucleus (EW) following administration of the lower dose of ethanol, with 1 g/kg ethanol producing CTA in adults but not in adolescents and inducing a greater EW Fos response in adults than adolescents. Regression analysis revealed that greater numbers of Fos+ neurons within the EW and insula (Ins) were related to lower consumption of the conditioned stimulus (CS) on test day (reflecting greater CTA). Some regionally specific age differences in Fos+ were noted under baseline conditions, with adolescents displaying fewer Fos+ neurons than adults within the prelimbic (PrL) cortex, but more than adults in the bed nucleus of the stria terminalis (BNST). In the BNST (but not PrL), ethanol-induced increases in Fos-immunoreactivity (IR) were evident at both ages. Increased ethanol-induced activity within critical appetitive brain regions (NAc core and shell) supports a role for greater reward-related activation during adolescence, possibly along with attenuated responsiveness to ethanol in EW and Ins in the age-typical resistance of adolescents to the aversive properties of ethanol.

Ghrelin receptor deletion reduces binge-like alcohol drinking in rats

Ghrelin is a gastric hormone that has been implicated in the neurobiology of alcohol drinking. We have recently developed a ghrelin receptor (growth hormone secretagogue receptor; GHSR) knockout (KO) rat model, which exhibits reduced food consumption and body weight. In addition, recent preliminary work suggests that the gut-microbiome, which appears to interact with the ghrelin system, may modulate alcohol drinking. In the present study, we investigated the effects of GHSR deletion on alcohol consumption utilising GHSR KO and wild-type (WT) rats in three separate alcohol consumption paradigms: (i) operant self-administration (30-minute sessions); (ii) drinking in the dark (DID) (4-hour sessions); and (iii) intermittent access (24-hour sessions). These paradigms model varying degrees of alcohol consumption. Furthermore, we aimed to investigate the gut-microbiome composition of GHSR KO and WT rats before and after alcohol exposure. We found that the GHSR KO rats self-administered significantly less alcohol compared to WT rats in the operant paradigm, and consumed less alcohol than WT in the initial stages of the DID paradigm. No genotype differences were found in the intermittent access test. In addition, we found a significant decrease in gut-microbial diversity after alcohol exposure in both genotypes. Thus, the present results indicate that the ghrelin system may be involved in drinking patterns that result in presumably increased alcohol exposure levels. Furthermore, GHSR may constitute a potential pharmacological target for the reduction of binge-alcohol consumption. The potential functional role of the gut-microbiome in alcohol drinking, as well as interaction with the ghrelin system, is an interesting topic for further investigation.

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

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

Duloxetine by Modulating the Akt/GSK3 Signaling Pathways Has Neuroprotective Effects against Methamphetamine-Induced Neurodegeneration and Cognition Impairment in Rats

BACKGROUND

The neuroprotective effects of duloxetine, as an antidepressant agent, and the neurodegenerative effects of methamphetamine have been shown in previous studies. Nonetheless, their exact neurochemical and behavioral effects are still unclear. In the current study, we sought to clarify the molecular mechanisms involved in the protective effects of duloxetine against methamphetamine-induced neurodegeneration.

METHODS

Forty adult male rats were divided randomly into 5 groups. Group 1 was the negative control and received normal saline, Group 2 was the positive control and received methamphetamine, and Groups 3, 4, and 5 were concurrently treated with methamphetamine (10 mg/kg) and duloxetine (5, 10, and 15 mg/kg, respectively). All the treatments were continued for 21 days. Between days 17 and 21, the Morris Water Maze (MWM) was used to assess learning and memory in the treated groups. On day 22, the hippocampus was isolated from each rat and oxidative, antioxidant, and inflammatory factors were measured. Additionally, the expression levels of the total and phosphorylated forms of the Akt and GSK3 proteins were evaluated via the ELISA method.

RESULTS

Duloxetine in all the administered doses ameliorated the effects of the methamphetamine-induced cognition impairment in the MWM. The chronic abuse of methamphetamine increased malondialdehyde, tumor necrosis factor-α, and interleukin-1β, while it decreased superoxide dismutase, glutathione peroxidase, and glutathione reductase activities. Duloxetine not only prevented these malicious effects of methamphetamine but also activated the expression of Akt (both forms) and inhibited the expression of GSK3 (both forms) in the methamphetamine-treated rats.

CONCLUSION

We conclude that the Akt/GSK3 signaling pathways might have a critical role in the protective effects of duloxetine against methamphetamine-induced neurodegeneration and cognition impairment.

Possible Role of Cyclic AMP Response Element Binding/Brain-Derived Neurotrophic Factor Signaling Pathway in Mediating the Pharmacological Effects of Duloxetine against Methamphetamine Use-Induced Cognitive Impairment and Withdrawal-Induced Anxiety and Depression in Rats

BACKGROUND

Duloxetine is used for treating depression and anxiety. The current study evaluated the effects of duloxetine against methamphetamine withdrawal-induced anxiety, depression, and motor disturbances and methamphetamine use-induced cognitive impairments.

MATERIALS AND METHODS

Ninety-six adult male rats were used for two independent experiments. Each experiment consisted of Groups 1 and 2 which received normal saline (0.2 ml/rat) and methamphetamine (10 mg/kg) respectively, Groups 3, 4, and 5 received both methamphetamine and duloxetine at doses of 5, 10, and 15 mg/kg, respectively. Groups 6, 7, and 8 received 5, 10, and 15 mg/kg of duloxetine, respectively. All administrations were performed for 21 days. In experiment 1, elevated plus maze (EPM), open-field test (OFT), forced swim test (FST), and tail suspension test (TST) were used to examine anxiety and depression in animals during withdrawal period. In experiment 2, Morris water maze (MWM) test was used to assess the effect of methamphetamine use followed by duloxetine treatment, on learning and memory. In the experiments, the expression of cyclic AMP response element binding (CREB) and brain-derived neurotrophic factor (BDNF) proteins were evaluated using enzyme-linked immunosorbent assay.

RESULTS

In the first experiment, duloxetine at all doses attenuated methamphetamine withdrawal induced-depression, anxiety, and motor disturbances in FST, OFT, EPM, and TST. In the second experiment, duloxetine at all doses attenuated methamphetamine use-induced cognitive impairment in MWM. In both experiments, duloxetine activated cAMP, CREB, and BDNF proteins' expression in methamphetamine-treated rats.

CONCLUSIONS

Duloxetine can protect the brain against methamphetamine withdrawal-induced mood and motor disturbances and can also inhibit methamphetamine-induced cognitive impairment, possibly via cAMP/CREB/BDNF signaling pathway.

Ethanol and Naltrexone Have Distinct Effects on the Lateral Nano-organization of Mu and Kappa Opioid Receptors in the Plasma Membrane

The complex spatiotemporal organization of proteins and lipids in the plasma membrane is an important determinant of receptor function. Certain substances, such as ethanol, can penetrate into the hydrophobic regions of the plasma membrane. By altering protein-lipid and protein-protein interactions, these substances can modify the dynamic lateral organization and the function of plasma membrane receptors. To assess changes in plasma membrane receptor organization, we used photoactivated localization microscopy (PALM). This single molecule localization microscopy technique was employed to quantitatively characterize the effects of pharmacologically relevant concentrations of ethanol and naltrexone (an opioid receptor antagonist and medication used to treat alcohol use disorders) on the lateral nano-organization of mu and kappa opioid receptors (MOR and KOR, respectively). Ethanol affected the lateral organization of MOR and KOR similarly: It reduced the size and occupancy of opioid receptor nanodomains and increased the fraction of opioid receptors residing outside of nanodomains. In contrast, naltrexone affected MOR and KOR lateral organization differently. It significantly increased KOR surface density, nanodomain size, and the occupancy of KOR nanodomains. However, naltrexone marginally affected these parameters for MOR. Pretreatment with naltrexone largely protected against ethanol-induced changes in MOR and KOR lateral organization. Based on these data, we propose a putative mechanism of naltrexone action that operates in addition to its canonical antagonistic effect on MOR- and KOR-mediated signaling.

Exploring Sex Differences in the Attenuation of Ethanol Drinking by Naltrexone in Dependent Rats During Early and Protracted Abstinence

BACKGROUND

Despite considerable efforts, few drugs are available for the treatment of alcohol (ethanol [EtOH]) use disorder (AUD). EtOH directly or indirectly modulates several aspects of the central nervous system, including neurotransmitter/neuromodulator systems. Relapse vulnerability is a challenge for the treatment of EtOH addiction. EtOH withdrawal symptoms create motivational states that lead to compulsive EtOH drinking and relapse even after long periods of abstinence. Among the therapeutics to treat AUD, naltrexone (NTX) is a pharmacological treatment for relapse. The present study evaluated the effect of NTX on EtOH drinking in male and female EtOH-dependent rats during abstinence.

METHODS

Wistar rats (males and females) were first trained to orally self-administer 10% EtOH. Half of the rats were then made dependent by chronic intermittent EtOH (CIE) vapor exposure, and the other half were exposed to air. Using this model, rats exhibit somatic and motivational signs of withdrawal. At the end of EtOH vapor (or air) exposure, the rats were tested for the effects of NTX (10 mg/kg, oral) on EtOH self-administration at 3 abstinence time points: acute abstinence (A-Abst, 8 hours), late abstinence (L-Abst, 2 weeks), and protracted abstinence (P-Abst, 6 weeks).

RESULTS

NTX decreased EtOH intake in nondependent rats, regardless of sex and abstinence time point. In postdependent rats, NTX decreased EtOH intake only at a delayed abstinence time point (P-Abst) in males, whereas it similarly reduced EtOH drinking in females at all abstinence time points.

CONCLUSIONS

The therapeutic efficacy of NTX depends on the time of intervention during abstinence and is different between males and females. The data further suggest that EtOH dependence causes different neuroadaptations in male and female rats, reflected by differential effects of NTX. The results underscore the significance of considering the duration of EtOH abstinence and sex as a biological variable as important factors when developing pharmacotherapies for AUD.

Postnatal Exposure to Ethanol Increases Its Oral Acceptability to Adolescent Rats

The aversive flavor of ethanol limits intake by many consumers. We asked whether intermittent consumption of ethanol increases its oral acceptability, using rats as a model system. We focused on adolescent rats because they (like their human counterparts) have a higher risk for alcohol overconsumption than do adult rats following experience with the drug. We measured the impact of ethanol exposure on 1) the oral acceptability of ethanol and surrogates for its bitter (quinine) and sweet (sucrose) flavor components in brief-access lick tests and 2) responses of the glossopharyngeal (GL) taste nerve to oral stimulation with the same chemical stimuli. During the exposure period, the experimental rats had access to chow, water and 10% ethanol every other day for 16 days; the control rats had access to chow and water over the same time period. The experimental rats consumed 7-14 g/day of 10% ethanol across the exposure period. This ethanol consumption significantly increased the oral acceptability of 3%, 6% and 10% ethanol, but had no impact on the oral acceptability of quinine, sucrose or NaCl. The ethanol exposure also diminished responses of the GL nerve to oral stimulation with ethanol, but not quinine, sucrose or NaCl. Taken together, these findings indicate that ethanol consumption increases the oral acceptability of ethanol in adolescent rats and that this increased oral acceptability is mediated, at least in part, by an exposure-induced reduction in responsiveness of the peripheral taste system to ethanol per se, rather than its bitter and sweet flavor components.

Ethanol Reinforcement Elicits Novel Response Inhibition Behavior in a Rat Model of Ethanol Dependence

Lower impulse control is a known risk factor for drug abuse vulnerability. Chronic experience with illicit drugs is suggested to enhance impulsivity and thereby perpetuate addiction. However, the nature of this relationship (directionality, causality) with regard to alcohol use disorder is unclear. The present study tested the hypothesis that higher impulsivity is observed during chronic intermittent ethanol vapor inhalation (CIE; a model of ethanol dependence) and subsequent abstinence from CIE in adult Wistar rats. Impulsivity was tested using a differential reinforcement of low rates 15 s (DRL15) schedule using either nondrug reward (palatable modified sucrose pellets) or sweetened ethanol. A decrease in the efficiency of earning reinforcers (expressed as % reinforcers/responses) is indicative of a decrease in response inhibition or an increase in impulsivity. The efficiency of reinforcement and amount of reinforcers earned were unaltered in CIE and control animals when the reinforcer was sucrose. When the reinforcer was sweetened ethanol, the efficiency of reinforcement increased in CIE rats compared with controls only during protracted abstinence. Responding for sweetened ethanol under a progressive-ratio schedule was more rapid in CIE rats during protracted abstinence. Contrary to the initial hypothesis, impulsivity did not increase in rats with a history of CIE; instead, it decreased when ethanol was used as the reinforcer. Furthermore, although the efficiency of ethanol reinforcement did not differ between CIE and control animals during CIE, CIE rats escalated the amount of sweetened ethanol consumed, suggesting that behavioral adaptations that are induced by CIE in rats that are tested under a DRL15 schedule appear to be targeted toward the maximization of ethanol intake and thus may contribute to escalation and relapse.

Medications for alcohol use disorders: An overview

Patients who suffer from alcohol use disorders (AUDs) usually go through various socio-behavioral and pathophysiological changes that take place in the brain and other organs. Recently, consumption of unhealthy food and excess alcohol along with a sedentary lifestyle has become a norm in both developed and developing countries. Despite the beneficial effects of moderate alcohol consumption, chronic and/or excessive alcohol intake is reported to negatively affect the brain, liver and other organs, resulting in cell death, organ damage/failure and death. The most effective therapy for alcoholism and alcohol related comorbidities is alcohol abstinence, however, chronic alcoholic patients cannot stop drinking alcohol. Therefore, targeted therapies are urgently needed to treat such populations. Patients who suffer from alcoholism and/or alcohol abuse experience harmful effects and changes that occur in the brain and other organs. Upon stopping alcohol consumption, alcoholic patients experience acute withdrawal symptoms followed by a protracted abstinence syndrome resulting in the risk of relapse to heavy drinking. For the past few decades, several drugs have been available for the treatment of AUDs. These drugs include medications to reduce or stop severe alcohol withdrawal symptoms during alcohol detoxification as well as recovery medications to reduce alcohol craving and support abstinence. However, there is no drug that completely antagonizes the adverse effects of excessive amounts of alcohol. This review summarizes the drugs which are available and approved by the FDA and their mechanisms of action as well as the medications that are under various phases of preclinical and clinical trials. In addition, the repurposing of the FDA approved drugs, such as anticonvulsants, antipsychotics, antidepressants and other medications, to prevent alcoholism and treat AUDs and their potential target mechanisms are summarized.

Naltrexone alters alcohol self-administration behaviors and hypothalamic-pituitary-adrenal axis activity in a sex-dependent manner in rats

BACKGROUND

The mu-opioid antagonist, naltrexone (NTX), is a FDA-approved treatment for alcohol use disorder (AUD); however, the data on whether it differentially affects males vs. females are mixed. NTX increases hypothalamic-pituitary-adrenal (HPA) axis activity that associates with subjective responses to alcohol and craving in individuals with AUD. The present study tested for sex differences in the ability of NTX to decrease appetitive and consummatory behaviors in rats in operant alcohol self-administration. Because the opioid system and HPA axis are sexually dimorphic, we examined NTX's effect on adrenocorticotropic hormone (ACTH) and corticosterone (CORT) levels.

METHODS

Male and female Sprague-Dawley rats (n's = 6-8) were trained to lever press for alcohol (10% v/v) under a fixed-ratio 2 schedule of reinforcement. NTX doses (0, 0.1-10 mg/kg) were assessed in tests conducted under a progressive ratio schedule of reinforcement. Separate groups of alcohol and water drinking rats (n's = 8) were used to assess NTX's (10 mg/kg) effects on HPA axis hormones.

RESULTS

NTX decreased consummatory behaviors for alcohol in a dose-related manner, but not appetitive behaviors in males. In females, NTX decreased appetitive behaviors for alcohol in a dose-dependent manner, but only decreased consummatory behaviors at the highest (10 mg/kg) NTX dose. NTX increased ACTH levels in alcohol drinking females in diestrus, but not in other groups. However, NTX increased CORT levels for longer durations in alcohol drinking males relative to alcohol drinking females in diestrus.

CONCLUSIONS

Our findings suggest that NTX selectively reduces consummatory behaviors for alcohol in males and appetitive behaviors in females, while also showing differential sex effects on HPA hormones.

A Novel and Selective Nociceptin Receptor (NOP) Agonist (1-(1-((cis)-4-isopropylcyclohexyl)piperidin-4-yl)-1H-indol-2-yl)methanol (AT-312) Decreases Acquisition of Ethanol-Induced Conditioned Place Preference in Mice

BACKGROUND

Nociceptin/orphanin FQ, the endogenous peptide agonist for the opioid receptor-like receptor (also known as NOP or the nociceptin receptor), has been shown to block the acquisition and expression of ethanol (EtOH)-induced conditioned place preference (CPP). Here, we report the characterization of a novel small-molecule NOP ligand AT-312 (1-(1-((cis)-4-isopropylcyclohexyl)piperidin-4-yl)-1H-indol-2-yl)methanol) in receptor binding and GTPγS functional assays in vitro. We then investigated the effect of AT-312 on the rewarding action of EtOH in mice using the CPP paradigm. Further, using mice lacking the NOP receptor and their wild-type controls, we also examined the involvement of NOP in the effect of AT-312. Motivational effects of AT-312 alone were also assessed in the CPP paradigm.

METHODS

Female mice lacking NOP and/or their wild-type controls received conditioning in the presence or absence of the NOP agonist [AT-312 (1, 3, and 10 mg/kg) or the control NOP agonist SCH221510 (10 mg/kg)] followed by saline/EtOH for 3 consecutive days (twice daily) and tested for CPP in a drug-free state on the next day.

RESULTS

Our in vitro data showed that AT-312 is a high-affinity, selective NOP full agonist with 17-fold selectivity over the mu opioid receptor and >200-fold selectivity over the kappa opioid receptor. The results of our in vivo studies showed that AT-312 reduced EtOH CPP at the lowest dose (1 mg/kg) tested but completely abolished EtOH CPP at higher doses (3 or 10 mg/kg) compared to their vehicle-treated control group. AT-312 (3 mg/kg) did not alter EtOH-induced CPP in mice lacking NOP, confirming that AT-312 reduced EtOH CPP through its action at the NOP receptor. AT-312 (3 mg/kg) did not induce reward or aversion when administered alone, showing that the novel small-molecule NOP agonist shows efficacy in blocking EtOH-induced CPP via the NOP receptor.

CONCLUSIONS

Together, these data suggest that small-molecule NOP agonists have the potential to reduce alcohol reward and may be promising as medications to treat alcohol addiction.

Medications development for the treatment of alcohol use disorder: insights into the predictive value of animal and human laboratory models

Development of effective treatments for alcohol use disorder (AUD) represents an important public health goal. This review provides a summary of completed preclinical and clinical studies testing pharmacotherapies for the treatment of AUD. We discuss opportunities for improving the translation from preclinical findings to clinical trial outcomes, focusing on the validity and predictive value of animal and human laboratory models of AUD. Specifically, while preclinical studies of medications development have offered important insights into the neurobiology of the disorder and alcohol's molecular targets, limitations include the lack of standardized methods and streamlined processes whereby animal studies can readily inform human studies. Behavioral pharmacology studies provide a less expensive and valuable opportunity to assess the feasibility of a pharmacotherapy prior to initiating larger scale clinical trials by providing insights into the mechanism of the drug, which can then inform recruitment, analyses, and assessments. Summary tables are provided to illustrate the wide range of preclinical, human laboratory, and clinical studies of medications development for alcoholism. Taken together, this review highlights the challenges associated with animal paradigms, human laboratory studies, and clinical trials with the overarching goal of advancing treatment development and highlighting opportunities to bridge the gap between preclinical and clinical research.

Don't stress about CRF: assessing the translational failures of CRF1antagonists

BACKGROUND

Dr. Athina Markou sought treatments for a common neural substrate shared by depression and drug dependence. Antagonists of corticotropin-releasing factor (CRF) receptors, a target of interest to her, have not reached the clinic despite strong preclinical rationale and sustained translational efforts.

METHODS

We explore potential causes for the failure of CRF1 antagonists and review recent findings concerning CRF-CRF1 systems in psychopathology.

RESULTS

Potential causes for negative outcomes include (1) poor safety and efficacy of initial drug candidates due to bad pharmacokinetic and physicochemical properties, (2) specificity problems with preclinical screens, (3) the acute nature of screens vs. late-presenting patients, (4) positive preclinical results limited to certain models and conditions with dynamic CRF-CRF1 activation not homologous to tested patients, (5) repeated CRF1 activation-induced plasticity that reduces the importance of ongoing CRF1 agonist stimulation, and (6) therapeutic silencing which may need to address CRF2 receptor or CRF-binding protein molecules, constitutive CRF1 activity, or molecules that influence agonist-independent activity or to target structural regions other than the allosteric site bound by all drug candidates. We describe potential markers of activation towards individualized treatment, human genetic, and functional data that still implicate CRF1 systems in emotional disturbance, sex differences, and suggestive clinical findings for CRF1 antagonists in food craving and CRF-driven HPA-axis overactivation.

CONCLUSION

The therapeutic scope of selective CRF1 antagonists now appears narrower than had been hoped. Yet, much remains to be learned about CRF's role in the neurobiology of dysphoria and addiction and the potential for novel anti-CRF therapies therein.

Neurobiology of comorbid post-traumatic stress disorder and alcohol-use disorder

Post-traumatic stress disorder (PTSD) and alcohol-use disorder (AUD) are highly comorbid in humans. Although we have some understanding of the structural and functional brain changes that define each of these disorders, and how those changes contribute to the behavioral symptoms that define them, little is known about the neurobiology of comorbid PTSD and AUD, which may be due in part to a scarcity of adequate animal models for examining this research question. The goal of this review is to summarize the current state-of-the-science on comorbid PTSD and AUD. We summarize epidemiological data documenting the prevalence of this comorbidity, review what is known about the potential neurobiological basis for the frequent co-occurrence of PTSD and AUD and discuss successes and failures of past and current treatment strategies. We also review animal models that aim to examine comorbid PTSD and AUD, highlighting where the models parallel the human condition, and we discuss the strengths and weaknesses of each model. We conclude by discussing key gaps in our knowledge and strategies for addressing them: in particular, we (1) highlight the need for better animal models of the comorbid condition and better clinical trial design, (2) emphasize the need for examination of subpopulation effects and individual differences and (3) urge cross-talk between basic and clinical researchers that is reflected in collaborative work with forward and reverse translational impact.

An Update on CRF Mechanisms Underlying Alcohol Use Disorders and Dependence

Alcohol is the most commonly used and abused substance worldwide. The emergence of alcohol use disorders, and alcohol dependence in particular, is accompanied by functional changes in brain reward and stress systems, which contribute to escalated alcohol drinking and seeking. Corticotropin-releasing factor (CRF) systems have been critically implied in the transition toward problematic alcohol drinking and alcohol dependence. This review will discuss how dysregulation of CRF function contributes to the vulnerability for escalated alcohol drinking and other consequences of alcohol consumption, based on preclinical evidence. CRF signaling, mostly via CRF1 receptors, seems to be particularly important in conditions of excessive alcohol taking and seeking, including during early and protracted withdrawal, relapse, as well as during withdrawal-induced anxiety and escalated aggression promoted by alcohol. Modulation of CRF1 function seems to exert a less prominent role over low to moderate alcohol intake, or to species-typical behaviors. While CRF mechanisms in the hypothalamic-pituitary-adrenal axis have some contribution to the neurobiology of alcohol abuse and dependence, a pivotal role for extra-hypothalamic CRF pathways, particularly in the extended amygdala, is well characterized. More recent studies further suggest a direct modulation of brain reward function by CRF signaling in the ventral tegmental area, nucleus accumbens, and the prefrontal cortex, among other structures. This review will further discuss a putative role for other components of the CRF system that contribute for the overall balance of CRF function in reward and stress pathways, including CRF2 receptors, CRF-binding protein, and urocortins, a family of CRF-related peptides.

Ethanol intake under social circumstances or alone in sprague-dawley rats: impact of age, sex, social activity, and social anxiety-like behavior

BACKGROUND

In human adolescents, heavy drinking is often predicted by high sociability in males and high social anxiety in females. This study assessed the impact of baseline levels of social activity and social anxiety-like behavior in group-housed adolescent and adult male and female Sprague-Dawley rats on ethanol (EtOH) intake when drinking alone or in a social group.

METHODS

Social activity and anxiety-like behavior initially were assessed in a modified social interaction test, followed by 6 drinking sessions that occurred every other day in animals given ad libitum food and water. Sessions consisted of 30-minute access to 10% EtOH in a "supersac" (3% sucrose + 0.1% saccharin) solution given alone as well as in groups of 5 same-sex littermates, with order of the alternating session types counterbalanced across animals.

RESULTS

Adolescent males and adults of both sexes overall consumed more EtOH under social than alone circumstances, whereas adolescent females ingested more EtOH when alone. Highly socially active adolescent males demonstrated elevated levels of EtOH intake relative to their low and medium socially active counterparts when drinking in groups, but not when tested alone. Adolescent females with high levels of social anxiety-like behavior demonstrated the highest EtOH intake under social, but not alone circumstances. Among adults, baseline levels of social anxiety-like behavior did not contribute to individual differences in EtOH intake in either sex.

CONCLUSIONS

The results clearly demonstrate that in adolescent rats, but not their adult counterparts, responsiveness to a social peer predicts EtOH intake in a social setting-circumstances under which drinking typically occurs in human adolescents. High levels of social activity in males and high levels of social anxiety-like behavior in females were associated with elevated social drinking, suggesting that males ingest EtOH for its socially enhancing properties, whereas females ingest EtOH for its socially anxiolytic effects.

Chronic intermittent ethanol exposure during adolescence: Effects on stress-induced social alterations and social drinking in adulthood

We previously observed lasting and sex-specific detrimental consequences of early adolescent intermittent ethanol exposure (AIE), with male, but not female, rats showing social anxiety-like alterations when tested as adults. The present study used Sprague Dawley rats to assess whether social alterations induced by AIE (3.5g/kg, intragastrically, every other day, between postnatal days [P] 25-45) are further exacerbated by stressors later in life. Another aim was to determine whether AIE alone or in combination with stress influenced intake of a sweetened ethanol solution (Experiment 1) or a sweetened solution ("supersac") alone (Experiment 2) under social circumstances. Animals were exposed to restraint on P66-P70 (90min/day) or left nonstressed, with corticosterone (CORT) levels assessed on day 1 and day 5 in Experiment 2. Social anxiety-like behavior emerged after AIE in non-stressed males, but not females, whereas stress-induced social anxiety was evident only in water-exposed males and females. Adult-typical habituation of the CORT response to repeated restraint was not evident in adult animals after AIE, a lack of habituation reminiscent of that normally evident in adolescents. Neither AIE nor stress affected ethanol intake under social circumstances, although AIE and restraint independently increased adolescent-typical play fighting in males during social drinking. Among males, the combination of AIE and restraint suppressed "supersac" intake; this index of depression-like behavior was not seen in females. The results provide experimental evidence associating adolescent alcohol exposure, later stress, anxiety, and depression, with young adolescent males being particularly vulnerable to long-lasting adverse effects of repeated ethanol. This article is part of a Special Issue entitled SI: Adolescent plasticity.

The ontogeny of ethanol aversion

Recent work has suggested separate developmental periods within the broader framework of adolescence, with data suggesting distinct alterations and vulnerabilities within these intervals. While previous research has suggested reduced sensitivity to the aversive effects of alcohol in adolescence relative to adults, a more detailed ontogeny of this effect has yet to be conducted. The adolescent brain undergoes significant transitions throughout adolescence, including in regions linked with drug reward and aversion. The current study aimed to determine the ontogeny of ethanol aversion by utilizing a conditioned taste aversion procedure at six different ages to test the hypothesis that the transitions into, through, and out of adolescence are associated with ontogenetic alterations in sensitivity to the aversive properties of ethanol. Non-deprived animals given Boost® as the conditioned stimulus (CS) were used in Experiment 1, whereas Experiment 2 used water-restricted animals provided with a saccharin/sucrose solution as the CS. In both experiments, an attenuated sensitivity to the aversive properties of ethanol was evident in adolescents compared to adults, although more age differences were apparent in water deprived animals than when a highly palatable CS was given to ad libitum animals. Overall, the data suggest an attenuated sensitivity to the aversive properties of ethanol that is most pronounced during pre- and early adolescence, declining thereafter to reach the enhanced aversive sensitivity of adults.

Adolescent social isolation increases anxiety-like behavior and ethanol intake and impairs fear extinction in adulthood: Possible role of disrupted noradrenergic signaling

Alcohol use disorder, anxiety disorders, and post-traumatic stress disorder (PTSD) are highly comorbid, and exposure to chronic stress during adolescence may increase the incidence of these conditions in adulthood. Efforts to identify the common stress-related mechanisms driving these disorders have been hampered, in part, by a lack of reliable preclinical models that replicate their comorbid symptomatology. Prior work by us, and others, has shown that adolescent social isolation increases anxiety-like behaviors and voluntary ethanol consumption in adult male Long-Evans rats. Here we examined whether social isolation also produces deficiencies in extinction of conditioned fear, a hallmark symptom of PTSD. Additionally, as disrupted noradrenergic signaling may contribute to alcoholism, we examined the effect of anxiolytic medications that target noradrenergic signaling on ethanol intake following adolescent social isolation. Our results confirm and extend previous findings that adolescent social isolation increases anxiety-like behavior and enhances ethanol intake and preference in adulthood. Additionally, social isolation is associated with a significant deficit in the extinction of conditioned fear and a marked increase in the ability of noradrenergic therapeutics to decrease ethanol intake. These results suggest that adolescent social isolation not only leads to persistent increases in anxiety-like behaviors and ethanol consumption, but also disrupts fear extinction, and as such may be a useful preclinical model of stress-related psychopathology. Our data also suggest that disrupted noradrenergic signaling may contribute to escalated ethanol drinking following social isolation, thus further highlighting the potential utility of noradrenergic therapeutics in treating the deleterious behavioral sequelae associated with early life stress.

Ethanol reduces evoked dopamine release and slows clearance in the rat medial prefrontal cortex

BACKGROUND

Ethanol (EtOH) intoxication affects cognitive performance, contributing to attentional deficits and poor decision making, which may occur via actions in the medial prefrontal cortex (mPFC). mPFC function is modulated by the catecholamines dopamine and norepinephrine. In this study, we examine the acute effects of EtOH on electrically evoked dopamine release and clearance in the mPFC of anesthetized rats naïve to alcohol or chronically exposed to alcohol during adolescence.

METHODS

Dopamine release and clearance was evoked by electrical stimulation of the ventral tegmental area (VTA) and measured in the mPFC of anesthetized rats with fast-scan cyclic voltammetry. In Experiments 1 and 2, effects of a high dose of EtOH (4 g/kg, intraperitoneally) on dopamine neurotransmission in the mPFC of EtOH-naïve rats and rats given EtOH exposure during adolescence were investigated. Effects of cumulative dosing of EtOH (0.5 to 4 g/kg) on the dopamine release and clearance were investigated in Experiment 3. Experiment 4 studied effects of EtOH locally applied to the VTA on the dopamine neurotransmission in the mPFC of EtOH-naïve rats.

RESULTS

A high dose of EtOH decreased evoked dopamine release within 10 minutes of administration in EtOH-naïve rats. When tested via cumulative dosing from 0.5 to 4 g/kg, both 2 and 4 g/kg EtOH inhibited evoked dopamine release in the mPFC of EtOH-naïve rats, while 4 g/kg EtOH also slowed dopamine clearance. A similar effect on electrically evoked dopamine release in the mPFC was observed after infusion of EtOH into the VTA. Interestingly, intermittent EtOH exposure during adolescence had no effect on observed changes in mPFC dopamine release and clearance induced by acute EtOH administration.

CONCLUSIONS

Taken together, these data describe EtOH-induced reductions in the dynamics of VTA-evoked mPFC dopamine release and clearance, with the VTA contributing to the attenuation of evoked mPFC dopamine release induced by EtOH.

Reduction of ethanol intake by corticotropin-releasing factor receptor-1 antagonist in "heavy-drinking" mice in a free-choice paradigm

RATIONALE

We hypothesized that the corticotropin-releasing factor (CRF) system is hyperresponsive in animals with high ethanol intake, which exhibits a reduction of ethanol intake when administered with a CRF1 receptor antagonist.

METHODS

Outbred Swiss mice were subjected to a long-term, three-bottle, free-choice paradigm (5 and 10 % [v/v] ethanol and water) that consisted of four phases: acquisition (AC; 10 weeks), withdrawal (W; 2 weeks), reexposure (RE; 2 weeks), and quinine-adulteration (AD; 2 weeks). Based on individual ethanol intake, the mice were classified into three groups: A group, preference for ethanol and persistently high consumption during AD phase; B group, preference for ethanol and a reduction of ethanol intake in the AD phase; and C group; preference for water during all phases. A control group only had access to water. CRF1 receptor messenger RNA (mRNA) levels in the amygdala and the effect of the CRF1 receptor antagonist CP-154,526 on ethanol and water intake in the subgroups were studied.

RESULTS

CRF1 transcript levels were higher in the B group than in the control group. The highest dose of CP-154,526 reduced ethanol intake and preference, with no changes in water consumption, in the A group compared with vehicle. The B group exhibited a reduction of both ethanol and water intake, with no changes in preference. The C group exhibited no changes in response to the CRF1 antagonist.

CONCLUSIONS

CRF1 receptors appear to be involved in ethanol consumption in mice with high ethanol consumption, and CRF system-mediated neuroadaptations depend on drinking profiles.

Effects of Withania somnifera on oral ethanol self-administration in rats

Recent evidence has shown that Withania somnifera Dunal (Ashwagandha or Indian ginseng), a herbal remedy used in traditional medicine, impairs morphine-elicited place conditioning. Here, we investigated the effect of W. somnifera roots extract (WSE) on motivation for drinking ethanol using operant self-administration paradigms. Wistar rats were trained to self-administer ethanol (10%) by nose-poking. The effects of WSE (25-75 mg/kg) were evaluated on acquisition and maintenance, on ethanol breakpoint under a progressive-ratio schedule of reinforcement and on the deprivation effect and reinstatement of seeking behaviours. Moreover, on the basis of the recent suggestion of an involvement of GABAB receptors in WSE central effects, we studied the interaction between WSE and GABAB ligands. The effect of WSE on saccharin (0.05%) oral self-administration was also tested. The results show that WSE reduced the acquisition, maintenance and breakpoint of ethanol self-administration. WSE also reduced the deprivation effect, reinstatement of ethanol-seeking behaviours and saccharin reinforcement. Furthermore, the GABAB receptor antagonist, phaclofen, counteracted the ability of WSE to impair the maintenance of ethanol self-administration. These findings show that WSE, by an action that may involve GABAB receptors, impairs motivation for drinking ethanol and suggest that further investigations should be performed to determine whether W. somnifera may represent a new approach for the management of alcohol abuse.

Consequences of repeated ethanol exposure during early or late adolescence on conditioned taste aversions in rats

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Adolescent Intermittent Ethanol (AIE) resulted in attenuated CTA in adulthood.

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AIE in late adolescence resulted in greater CTA attenuation 2 days post-exposure.

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All AIE animals were equally insensitive when tested 3 weeks post-exposure.

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No metabolic tolerance was noted following AIE.

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AIE results in a decreased sensitivity to aversive effects of ethanol in adulthood.

Alcohol use is prevalent during adolescence, yet little is known about possible long-lasting consequences. Recent evidence suggests that adolescents are less sensitive than adults to ethanol's aversive effects, an insensitivity that may be retained into adulthood after repeated adolescent ethanol exposure. This study assessed whether intermittent ethanol exposure during early or late adolescence (early-AIE or late-AIE, respectively) would affect ethanol conditioned taste aversions 2 days (CTA1) and >3 weeks (CTA2) post-exposure using supersaccharin and saline as conditioning stimuli (CS), respectively. Pair-housed male Sprague-Dawley rats received 4 g/kg i.g. ethanol (25%) or water every 48 h from postnatal day (P) 25–45 (early AIE) or P45-65 (late AIE), or were left non-manipulated (NM). During conditioning, 30 min home cage access to the CS was followed by 0, 1, 1.5, 2 or 2.5 g/kg ethanol i.p., with testing 2 days later. Attenuated CTA relative to controls was seen among early and late AIE animals at both CTA1 and CTA2, an effect particularly pronounced at CTA1 after late AIE. Thus, adolescent exposure to ethanol was found to induce an insensitivity to ethanol CTA seen soon after exposure and lasting into adulthood, and evident with ethanol exposures not only early but also later in adolescence.

Preclinical evidence implicating corticotropin-releasing factor signaling in ethanol consumption and neuroadaptation

The results of many studies support the influence of the corticotropin-releasing factor (CRF) system on ethanol (EtOH) consumption and EtOH-induced neuroadaptations that are critical in the addiction process. This review summarizes the preclinical data in this area after first providing an overview of the components of the CRF system. This complex system involves hypothalamic and extra-hypothalamic mechanisms that play a role in the central and peripheral consequences of stressors, including EtOH and other drugs of abuse. In addition, several endogenous ligands and targets make up this system and show differences in their involvement in EtOH drinking and in the effects of chronic or repeated EtOH treatment. In general, genetic and pharmacological approaches paint a consistent picture of the importance of CRF signaling via type 1 CRF receptors (CRF(1)) in EtOH-induced neuroadaptations that result in higher levels of intake, encourage alcohol seeking during abstinence and alter EtOH sensitivity. Furthermore, genetic findings in rodents, non-human primates and humans have provided some evidence of associations of genetic polymorphisms in CRF-related genes with EtOH drinking, although additional data are needed. These results suggest that CRF(1) antagonists have potential as pharmacotherapeutics for alcohol use disorders. However, given the broad and important role of these receptors in adaptation to environmental and other challenges, full antagonist effects may be too profound and consideration should be given to treatments with modulatory effects.

Sex differences in sensitivity to the social consequences of acute ethanol and social drinking during adolescence

In human adolescents, sociable males frequently drink to enhance positive emotional states, whereas anxious females often drink to avoid negative affective states. This study used a rat model of adolescence to provide information regarding possible sex differences in contributors to social drinking. The effects of ethanol (0, 0.5, and 0.75g/kg) on play fighting and social preference were assessed on P30, P32, and P34 using a within-subject design. Then animals were tested in a social drinking paradigm (P37-P40), with this testing revealing high drinkers and low drinkers. Sex differences in sensitivity to ethanol emerged among high and low drinkers. High socially drinking males, but not females, when tested prior to drinking sessions, showed significant increases in play fighting at both doses. In low drinking males, play fighting was increased by 0.5g/kg ethanol, whereas the higher dose of 0.75g/kg produced significant decreases in play fighting. High drinking females initially showed low levels of social preference than high drinking males and low drinking females and were extremely sensitive to ethanol-induced enhancement of this social measure. Low social drinkers, both males and females, were more sensitive to the suppressing effects of ethanol on social preference following 0.75g/kg ethanol. These findings indicate that during adolescence enhanced sensitivity to the facilitating effects of ethanol on play fighting is associated with heavy drinking among males, whereas low social preference together with high sensitivity to ethanol-induced enhancement of social preference is related to high social drinking in females.

Investigational therapies for the pharmacological treatment of alcoholism

Introduction: Alcohol dependence is one of the most important psychiatric disorders leading to enormous harm in individuals and indeed within society. Yet, although alcohol dependence is a disease of significant importance, the availability of efficacious pharmacological treatment is still limited. Areas covered: The current review focuses on neurobiological pathways that are the rationale for recent preclinical and clinical studies testing novel compounds that could be used as treatments for alcohol dependence. These neurobiological mechanisms include the: glutamatergic, dopaminergic and GABA mediated pathways as well as neuroendocrine systems. There is also an interest in the approaches for influencing chromatin structure. Expert opinion: There are several compounds in Phase I and Phase II clinical studies that have produced potentially useful results for the treating alcoholism. Further evaluation is still necessary, and the implementation of Phase III studies will help to elucidate the usefulness of these compounds. It is important that personalized approaches (e.g., pharmacogenomics) are investigated in these later studies, as the efficacy of different compounds may vary substantially between subgroups of patients.

Alcohol, stress hormones, and the prefrontal cortex: a proposed pathway to the dark side of addiction

Chronic exposure to alcohol produces changes in the prefrontal cortex that are thought to contribute to the development and maintenance of alcoholism. A large body of literature suggests that stress hormones play a critical role in this process. Here we review the bi-directional relationship between alcohol and stress hormones, and discuss how alcohol acutely stimulates the release of glucocorticoids and induces enduring modifications to neuroendocrine stress circuits during the transition from non-dependent drinking to alcohol dependence. We propose a pathway by which alcohol and stress hormones elicit neuroadaptive changes in prefrontal circuitry that could contribute functionally to a dampened neuroendocrine state and the increased propensity to relapse-a spiraling trajectory that could eventually lead to dependence.

Chronic treatment with prazosin or duloxetine lessens concurrent anxiety-like behavior and alcohol intake: evidence of disrupted noradrenergic signaling in anxiety-related alcohol use

BACKGROUND

Alcohol use disorders have been linked to increased anxiety, and enhanced central noradrenergic signaling may partly explain this relationship. Pharmacological interventions believed to reduce the excitatory effects of norepinephrine have proven effective in attenuating ethanol intake in alcoholics as well as in rodent models of ethanol dependence. However, most preclinical investigations into the effectiveness of these drugs in decreasing ethanol intake have been limited to acute observations, and none have concurrently assessed their anxiolytic effects. The purpose of these studies was to examine the long-term effectiveness of pharmacological interventions presumed to decrease norepinephrine signaling on concomitant ethanol self-administration and anxiety-like behavior in adult rats with relatively high levels of antecedent anxiety-like behavior.

METHODS

Adult male Long-Evans rats self-administered ethanol on an intermittent access schedule for eight to ten weeks prior to being implanted with osmotic minipumps containing either an a1-adrenoreceptor antagonist (prazosin, 1.5 mg/kg/day), a β1/2-adrenoreceptor antagonist (propranolol, 2.5 mg/kg/day), a serotonin/norepinephrine reuptake inhibitor (duloxetine, 1.5 mg/kg/day) or vehicle (10% dimethyl sulfoxide). These drugs were continuously delivered across four weeks, during which animals continued to have intermittent access to ethanol. Anxiety-like behavior was assessed on the elevated plus maze before treatment and again near the end of the drug delivery period.

RESULTS

Our results indicate that chronic treatment with a low dose of prazosin or duloxetine significantly decreases ethanol self-administration (P < 0.05). Furthermore, this decrease in drinking is accompanied by significant reductions in the expression of anxiety-like behavior (P < 0.05).

CONCLUSIONS

These findings suggest that chronic treatment with putative inhibitors of central noradrenergic signaling may attenuate ethanol intake via a reduction in anxiety-like behavior.

Potent inhibition of alcohol self-administration in alcohol-preferring rats by a κ-opioid receptor antagonist

A substituted aryl amide derivative of 6-naltrexamine--17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-[(4'-trimethylfluoro)benzamido]morphinan-hydrochloride--(compound 5), previously shown to be a potent κ-opioid receptor antagonist, was used to characterize the physicochemical properties and efficacy to decrease alcohol self-administration in alcohol-preferring rats (P-rats) and binge-like P-rats. Previous studies showed that compounds closely related to compound 5 possessed favorable properties regarding penetration of the blood-brain barrier. Pharmacokinetic studies showed that compound 5 had acceptable bioavailability. In contrast to other κ-receptor antagonists, in particular norbinaltorphimine, compound 5 showed favorable drug-like properties. Based on these findings, further studies were done. Safety studies showed that compound 5 was not hepatotoxic at doses 200-fold greater than an efficacious dose. The effects of compound 5 or naltrexone on the hepatotoxicity of thiobenzamide were investigated. In contrast to naltrexone, which exacerbated thiobenzamide-mediated hepatotoxicity, compound 5 was observed to be hepatoprotective. Based on the physicochemical properties of compound 5, the compound was examined in rat animal models of alcohol self-administration. The inhibition of ethanol self-administration by compound 5 in alcohol-dependent and alcohol-nondependent P-rats trained to self-administer a 10% (w/v) ethanol solution, using operant techniques, showed very potent efficacy (i.e., estimated ED50 values of 4-5 μg/kg). In a binge-like P-rat animal model, inhibition of alcohol self-administration by compound 5 had an estimated ED50 value of 8 μg/kg. The results suggest that compound 5 is a potent drug-like κ-opioid receptor antagonist of utility in alcohol cessation medications development.

Neurotransmitters in alcoholism: A review of neurobiological and genetic studies

Recent advances in the study of alcoholism have thrown light on the involvement of various neurotransmitters in the phenomenon of alcohol addiction. Various neurotransmitters have been implicated in alcohol addiction due to their imbalance in the brain, which could be either due to their excess activity or inhibition. This review paper aims to consolidate and to summarize some of the recent papers which have been published in this regard. The review paper will give an overview of the neurobiology of alcohol addiction, followed by detailed reviews of some of the recent papers published in the context of the genetics of alcohol addiction. Furthermore, the author hopes that the present text will be found useful to novices and experts alike in the field of neurotransmitters in alcoholism.

"Drinking in the dark" (DID) procedures: a model of binge-like ethanol drinking in non-dependent mice

This review provides an overview of an animal model of binge-like ethanol drinking that has come to be called "drinking in the dark" (DID), a procedure that promotes high levels of ethanol drinking and pharmacologically relevant blood ethanol concentrations (BECs) in ethanol-preferring strains of mice. Originally described by Rhodes, Best, Belknap, Finn, and Crabbe (2005), the most common variation of the DID procedure, using singly housed mice, involves replacing the water bottle with a bottle containing 20% ethanol for 2-4 h, beginning 3 h into the dark cycle. Using this procedure, high ethanol drinking strains of mice (e.g., C57BL/6J) typically consume enough ethanol to achieve BECs greater than 100 mg/dL and to exhibit behavioral evidence of intoxication. This limited access procedure takes advantage of the time in the animal's dark cycle in which the levels of ingestive behaviors are high, yet high ethanol intake does not appear to stem from caloric need. Mice have the choice of drinking or avoiding the ethanol solution, eliminating the stressful conditions that are inherent in other models of binge-like ethanol exposure in which ethanol is administered by the experimenter, and in some cases, potentially painful. The DID procedure is a high throughput approach that does not require extensive training or the inclusion of sweet compounds to motivate high levels of ethanol intake. The high throughput nature of the DID procedure makes it useful for rapid screening of pharmacological targets that are protective against binge-like drinking and for identifying strains of mice that exhibit binge-like drinking behavior. Additionally, the simplicity of DID procedures allows for easy integration into other paradigms, such as prenatal ethanol exposure and adolescent ethanol drinking. It is suggested that the DID model is a useful tool for studying the neurobiology and genetics underlying binge-like ethanol drinking, and may be useful for studying the transition to ethanol dependence.