Recent Perspectives on Sex Differences in Compulsion-Like and Binge Alcohol Drinking

Cholinergic mu-opioid receptor deletion alters reward preference and aversion-resistance

The endogenous opioid system has been implicated in alcohol consumption and preference in both humans and animals. The mu opioid receptor (MOR) is expressed on multiple cells in the striatum, however little is known about the contributions of specific MOR populations to alcohol drinking behaviors. The current study used mice with a genetic deletion of MOR in cholinergic cells (ChAT-Cre/Oprm1fl/fl) to examine the role of MORs expressed in cholinergic interneurons (CINs) in home cage self-administration paradigms. Male and female ChAT-Cre/Oprm1fl/fl mice were generated and heterozygous Cre+ (knockout) and Cre- (control) mice were tested for alcohol consumption in two drinking paradigms: limited access "Drinking in the Dark" and intermittent access. Quinine was added to the drinking bottles in the DID experiment to test aversion-resistant, "compulsive" drinking. Nicotine and sucrose drinking were also assessed so comparisons could be made with other rewarding substances. Cholinergic MOR deletion did not influence consumption or preference for ethanol (EtOH) in either drinking task. Differences were observed in aversion-resistance in males with Cre + mice tolerating lower concentrations of quinine than Cre-. In contrast to EtOH, preference for nicotine was reduced following cholinergic MOR deletion while sucrose consumption and preference was increased in Cre+ (vs. Cre-) females. Locomotor activity was also greater in females following the deletion. These results suggest that cholinergic MORs participate in preference for rewarding substances. Further, while they are not required for consumption of alcohol alone, cholinergic MORs may influence the tendency to drink despite negative consequences.

Sex- and estrous-related response patterns for alcohol depend critically on the level of compulsion-like challenge

Alcohol use disorder is a substantial social and economic burden. During the last years, the number of women with drinking problems has been increasing, and one main concern is that they are particularly more vulnerable to negative consequences of alcohol. However, little is known about female-specific response patterns for alcohol, and potential underlying differences in brain mechanisms, including for compulsion-like alcohol drinking (when intake persists despite adverse consequences). We used lickometry to assess behavioral microstructure in adult Wistar male and female rats (n = 28-30) during alcohol-only drinking or moderate- or higher-challenge alcohol compulsion (10 or 60 mg/l quinine in alcohol, respectively). Estrous stages were determined and related to drinking levels and patterns of responding to alcohol, as was ovariectomy. Our findings showed that females (where we didn't determine estrus stage) had similar total licks in a session as males, but significantly longer licking bouts under alcohol-only and moderate-challenge, suggesting greater persistence. Further, greater intake under alcohol-only and moderate-challenge was related to faster licking in males, while female consumption was not related to licking speed. Thus, females could have increased persistence without greater vigor, unlike males. However, under higher-challenge, faster licking did predict higher intake in females, similar to males. To better understand female higher-challenge responding, we examined drinking in relation to phases of the estrous cycle. Higher-challenge had longer bouts only in late diestrus. In addition, ovariectomy led to longer bouts only under higher-challenge, suggesting that conditions with reduced hormone levels could increase female persistence for alcohol under higher-challenge. However, ovariectomy also reduced alcohol-only and moderate-challenge drinking but did not reduce bout length. Thus, intake level and response strategy could be regulated somewhat differently by ovarian hormones. Finally, moderate-challenge licking speed was less variable during early diestrus, and we previously showed more stereotyped responding specifically under moderate-challenge in males. By combining behavioral microstructure and sex- and estrus-related changes in drinking patterns, our results suggest that females have greater persistence for alcohol under lower-challenge drinking, while late diestrus and ovariectomy unmasked greater persistence under higher-challenge. Together, our novel insights could help develop more effective and personalized treatments for problematic alcohol use.

Global trends and differences in the burden of alcohol use disorders attributable to childhood sexual abuse by sex, age, and socio-demographic index: Findings from the Global Burden of Disease Study 2019

BACKGROUND

Childhood sexual abuse (CSA) is a severe global problem associated with alcohol use disorder (AUD). Previous studies have confirmed this relationship; however, there is a lack of research on the disease burden of AUD attributable to CSA.

OBJECTIVE

To analyze global spatiotemporal trends and differences in the disease burden of AUD attributable to CSA and its relationship with age, sex, and the sociodemographic index (SDI).

PARTICIPANTS AND SETTING

Data from the Global Burden of Disease 2019 Public Database.

METHODS

Summary exposure value (SEV) was used to evaluate CSA. Disability-adjusted life year (DALY), years lived with disability (YLD), years of life lost (YLL), and their annual rates of change were used to evaluate disease burden. Cluster analysis based on Ward's method was used to examine the global burden associated with age, sex, and SDI. A 95 % uncertainty intervals (UI), excluding 0, was considered statistically significant.

RESULTS

In 2019, 1.63 million (95 % UI 0.23-3.90 million) DALYs of AUD were caused by CSA and the age-standardized rates (ASRs) of DALY was 19.77 (95 % UI 2.78-47.46) globally. Annual rates of change in DALY of people over 65 years of age increased from 1990 to 2019 in all regions except the High-middle SDI regions. The ASRs of DALY of females in High SDI regions, were always at a much higher level than other SDI regions, and showed an upward trend from 1990 to 2019 (DALY 1990: 20.38 [95 % UI 2.87-47.77], 2019: 23.61 [95 % UI 3.55-54.94]).

CONCLUSIONS

Substantial geographical differences were observed in the burden of AUD attributable to CSA. The level of CSA exposure was inconsistent with the related burden of AUD in different regions according to the sociodemographic index. The burden of disease increased in the elderly population and in females in high sociodemographic index regions.

Understanding sex differences and the translational value of models of persistent substance use despite negative consequences

Persistent substance use despite negative consequences is a key facet of substance use disorder. The last decade has seen the preclinical field adopt the use of punishment to model adverse consequences associated with substance use. This has largely involved the pairing of drug use with either electric foot shock or quinine, a bitter tastant. Whilst at face value, these punishers may model aspects of the physical and psychological consequences of substance use, such models are yet to assist the development of approved medications for treatment. This review discusses progress made with animal models of punishment to understand the behavioral consequences of persistent substance use despite negative consequences. We highlight the importance of examining sex differences, especially when the behavioral response to punishment changes following drug exposure. Finally, we critique the translational value these models provide for the substance use disorder field.

Greater inhibition of female rat binge alcohol intake by adrenergic receptor blockers using a novel Two-Shot rat binge drinking model

Binge drinking (BD) contributes strongly to the harms of alcohol use disorder. Most rodent models do not result in binge-level blood alcohol concentrations (BACs), and to better understand individual and sex differences in neurobiological mechanisms related to BD, the use of outbred rat strains would be valuable. Here, we developed a novel BD model where after 3+ months of intermittent access to 20% alcohol Wistar rats drank, twice a week, with two 5-minute intake (what we called Two-shot) separated by a 10-minute break. Our findings showed during Two-Shot that most animals reached ≥ 80mg% BAC levels (when briefly food-restricted). However, when increasing alcohol concentrations from 20% to 30%, 40%, or 50%, rats titrated to similar intake levels, suggesting rapid sensing of alcohol effects even when front-loading. Two-Shot drinking was reduced in both sexes by naltrexone (1mg/kg), validating intake suppression by a clinical therapeutic agent. Further, both propranolol (β adrenergic receptor antagonist) and prazosin (α1 adrenergic receptor antagonist) reduced female but not male BD at the lower dose. Thus, our results provide a novel model for BD in outbred rats and suggest that female binging is more sensitive to adrenergic modulation than males, perhaps providing a novel sex-related therapy.

A novel mouse home cage lickometer system reveals sex- and housing-based influences on alcohol drinking

Alcohol use disorder (AUD) is a significant global health issue. Despite historically higher rates among men, AUD prevalence and negative alcohol-related outcomes in women are rising. Loneliness in humans has been associated with increased alcohol use, and traditional rodent drinking models involve single housing, presenting challenges for studying social enrichment. We developed LIQ PARTI (Lick Instance Quantifier with Poly-Animal RFID Tracking Integration), an open-source tool to examine home cage continuous access two-bottle choice drinking behavior in a group-housed setting, investigating the influence of sex and social isolation on ethanol consumption and bout microstructure in C57Bl/6J mice. LIQ PARTI, based on our previously developed single-housed LIQ HD system, accurately tracks drinking behavior using capacitive-based sensors and RFID technology. Group-housed female mice exhibited higher ethanol preference than males, while males displayed a unique undulating pattern of ethanol preference linked to cage changes, suggesting a potential stress-related response. Chronic ethanol intake distinctly altered bout microstructure between male and female mice, highlighting sex and social environmental influences on drinking behavior. Social isolation with the LIQ HD system amplified fluid intake and ethanol preference in both sexes, accompanied by sex- and fluid-dependent changes in bout microstructure. However, these effects largely reversed upon resocialization, indicating the plasticity of these behaviors in response to social context. Utilizing a novel group-housed home cage lickometer device, our findings illustrate the critical interplay of sex and housing conditions in voluntary alcohol drinking behaviors in C57Bl/6J mice, facilitating nuanced insights into the potential contributions to AUD etiology.

Encoding and context-dependent control of reward consumption within the central nucleus of the amygdala

Dysregulation of the central amygdala is thought to underlie aberrant choice in alcohol use disorder, but the role of central amygdala neural activity during reward choice and consumption is unclear. We recorded central amygdala neurons in male rats as they consumed alcohol or sucrose. We observed activity changes at the time of reward approach, as well as lick-entrained activity during ongoing consumption of both rewards. In choice scenarios where rats could drink sucrose, alcohol, or quinine-adulterated alcohol with or without central amygdala optogenetic stimulation, rats drank more of stimulation-paired options when the two bottles contained identical options. Given a choice among different options, central amygdala stimulation usually enhanced consumption of stimulation-paired rewards. However, optogenetic stimulation during consumption of the less-preferred option, alcohol, was unable to enhance alcohol intake while sucrose was available. These findings indicate that the central amygdala contributes to refining motivated pursuit toward the preferred available option.

Cholinergic mu-opioid receptor deletion alters reward preference and aversion-resistance

Heavy alcohol use and binge drinking are important contributors to alcohol use disorder (AUD). The endogenous opioid system has been implicated in alcohol consumption and preference in both humans and animals. The mu opioid receptor (MOR) is expressed on multiple cells in the striatum, however little is known about the contributions of specific MOR populations to alcohol drinking behaviors. The current study used mice with a genetic deletion of MOR in cholinergic cells (ChAT-Cre/Oprm1fl/fl) to examine the role of MORs expressed in cholinergic interneurons (CINs) in home cage self-administration paradigms. Male and female ChAT-Cre/Oprm1fl/fl mice were generated and heterozygous Cre+ (knockout) and Cre- (control) mice were tested for alcohol and nicotine consumption. In Experiment 1, binge-like and quinine-resistant drinking was tested using 15% ethanol (EtOH) in a two-bottle, limited-access Drinking in the Dark paradigm. Experiment 2 involved a six-week intermittent access paradigm in which mice received 20% EtOH, nicotine, and then a combination of the two drugs. Experiment 3 assessed locomotor activity, sucrose preference, and quinine sensitivity. Deleting MORs in cholinergic cells did not alter consumption of EtOH in Experiment 1 or 2. In Experiment 1, the MOR deletion resulted in greater consumption of quinine-adulterated EtOH in male Cre+ mice (vs. Cre-). In Experiment 2, Cre+ mice demonstrated a significantly lower preference for nicotine but did not differ from Cre- mice in nicotine or nicotine + EtOH consumption. Overall fluid consumption was also heightened in the Cre+ mice. In Experiment 3, Cre+ females were found to have greater locomotor activity and preference for sucrose vs. Cre- mice. These data suggest that cholinergic MORs are not required for EtOH, drinking behaviors but may contribute to aversion resistant EtOH drinking in a sex-dependent manner.

Inhibition of the Sodium-Calcium Exchanger Reverse Mode Activity Reduces Alcohol Consumption in Rats

Excessive and uncontrolled consumption of alcohol can cause alcohol use disorder (AUD), but its pharmacological mechanisms are not fully understood. Inhibiting the reverse mode activity of the sodium-calcium exchanger (NCX) can reduce the risk of alcohol withdrawal seizures, suggesting that NCX could play a role in controlling alcohol consumption. Here, we investigated how two potent inhibitors of NCX reverse mode activity, SN-6 (NCX1) and KB-R7943 (NCX3), affect voluntary alcohol consumption in adult male and female rats using the intermittent alcohol access two-bottle choice paradigm. Initially, animals were trained to drink 7.5% ethanol and water for four weeks before administering SN-6 and KB-R7934. Afterward, their alcohol intake, preference, and water intake were recorded 2 and 24 h after exposure to water and 7.5% ethanol. SN-6 significantly reduced alcohol consumption by 48% in male and 36% in female rats without affecting their water intake. Additionally, SN-6 significantly reduced alcohol preference in females by 27%. However, KB-R7943 reduced alcohol consumption by 42% in female rats and did not affect alcohol preference or water intake. These findings suggest that alcohol exposure increased NCX reverse activity, and targeting NCX1 could be an effective strategy for reducing alcohol consumption in subjects susceptible to withdrawal seizures.

Sexual dimorphism in the gut microbiota and sexual dimorphism in chronic diseases: Association or causation?

Understanding the sexual dimorphism in diseases is essential to investigate the pathogenesis of some chronic diseases (e.g., autoimmune diseases, etc). The gut microbiota has been found to show a notable impact on the pathology of several chronic diseases in recent years. Intriguingly, the composition of the gut microbiota varies between sexes. Here, we reviewed 'facts and fiction' regarding sexual dimorphism in chronic diseases and sexual dimorphism in the gut microbiota respectively. The association and causative relationship between them aiming to elucidate the pathological mechanisms of sexual dimorphism in chronic diseases were further explored. The development of gender-special food products based on the sexual dimorphism in the gut microbiota were recommended, which would be beneficial to facilitating the personalized treatment.

A paradigm for ethanol consumption in head-fixed mice during prefrontal cortical two-photon calcium imaging

The prefrontal cortex (PFC) is a hub for cognitive behaviors and is a key target for neuroadaptations in alcohol use disorders. Recent advances in genetically encoded sensors and functional microscopy allow multimodal in vivo PFC activity recordings at subcellular and cellular scales. While these methods could enable a deeper understanding of the relationship between alcohol and PFC function/dysfunction, they typically require animals to be head-fixed. Here, we present a method in mice for binge-like ethanol consumption during head-fixation. Male and female mice were first acclimated to ethanol by providing home cage access to 20% ethanol (v/v) for 4 or 8 days. After home cage drinking, mice consumed ethanol from a lick spout during head-fixation. We used two-photon calcium imaging during the head-fixed drinking paradigm to record from a large population of PFC neurons (>1000) to explore how acute ethanol affects their activity. Drinking exerted temporally heterogeneous effects on PFC activity at single neuron and population levels. Intoxication modulated the tonic activity of some neurons while others showed phasic responses around ethanol receipt. Population level activity did not show tonic or phasic modulation but tracked ethanol consumption over the minute-timescale. Network level interactions assessed through between-neuron pairwise correlations were largely resilient to intoxication at the population level while neurons with increased tonic activity showed higher synchrony by the end of the drinking period. By establishing a method for binge-like drinking in head-fixed mice, we lay the groundwork for leveraging advanced microscopy technologies to study alcohol-induced neuroadaptations in PFC and other brain circuits. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".

Bed Nucleus of the Stria Terminalis (BNST) neurons containing the serotonin 5HT2c receptor modulate operant alcohol self-administration behavior in mice

The serotonin 5HT2c receptor has been widely implicated in the pathophysiology of alcohol use disorder (AUD), particularly alcohol seeking and the affective consequences of chronic alcohol consumption. However, little is known about the brain sites in which 5HT2c exerts its effects on specific alcohol-related behaviors, especially in females. Here, we investigated the effects of site-specific manipulation of the 5HT2c receptor system in the BNST on operant alcohol self-administration behaviors in adult mice of both sexes, including the acquisition and maintenance of fixed-ratio responding, motivation for alcohol (progressive ratio), and quinine-adulterated responding for alcohol on a fixed-ratio schedule (punished alcohol seeking). Knockdown of 5HT2c in the BNST did not affect the acquisition or maintenance of operant alcohol self-administration, nor did it affect progressive ratio responding for alcohol. This manipulation had only a subtle effect on responding for quinine alcohol selectively in females. On the other hand, chemogenetic inhibition of BNST 5HT2c-containing neurons (BNST5HT2c) increased operant alcohol self-administration behavior in both sexes on day 2, but not day 9, of testing. It also increased operant responding for 1000 μM quinine-adulterated alcohol selectively in males. Importantly, chemogenetic inhibition of BNST5HT2c did not alter operant sucrose responding or motivation for sucrose in either sex. We then performed cell-type specific anterograde tracing, which revealed that BNST5HT2c project to similar regions in males and females, many of which have been previously implicated in AUD. We next used chemogenetics and quantification of the immediate early gene cFos to characterize the functional influence of BNST5HT2c inhibition on vlPAG activity. We show that chemogenetic inhibition of BNST5HT2c reduces vlPAG cFos in both sexes, but that this reduction is more robust in males. Together these findings suggest that BNST5HT2c neurons, and to a small extent the BNST 5HT2c receptor, serve to promote aversive responses to alcohol consumption, potentially through sex-dependent disinhibition of vlPAG neurons.

Subjective stress and any drinking during alcohol treatment: Disentangling within and between person autoregressive effects

Alcohol use has been shown to increase stress, and there is some evidence that stress predicts subsequent alcohol use during treatment for alcohol use disorder (AUD), particularly among females who are more likely to report coping-motivated drinking. Gaining a better understanding of the processes by which stress and alcohol use are linked during treatment could potentially inform AUD treatment planning. The current study aimed to characterize the association between stress and drinking during the course of AUD treatment and whether there were sex differences in these associations. Secondary data analyses of the COMBINE study (N = 1375; 69% male, 76.3% non-Hispanic and white, average age of 44.4 years) were conducted to examine self-reported perceived stress and alcohol consumption across 16 weeks of treatment for AUD using a Bayesian random-intercept cross-lagged panel model. There was stronger evidence for any alcohol use predicting greater than typical stress in subsequent weeks and less strong evidence for stress increasing the subsequent probability of alcohol use, particularly among males. For females, greater stress predicted subsequent drinking earlier in the treatment period, and a lower probability of subsequent drinking in the last week of treatment. Interventions might specifically focus on targeting reductions in stress following drinking occasions.

Neural Activity in the Anterior Insula at Drinking Onset and Licking Relates to Compulsion-Like Alcohol Consumption

Much remains unknown about the etiology of compulsion-like alcohol drinking, where consumption persists despite adverse consequences. The role of the anterior insula (AIC) in emotion, motivation, and interoception makes this brain region a likely candidate to drive challenge-resistant behavior, including compulsive drinking. Indeed, subcortical projections from the AIC promote compulsion-like intake in rats and are recruited in heavy-drinking humans during compulsion for alcohol, highlighting the importance of and need for more information about AIC activity patterns that support aversion-resistant responding. Single-unit activity was recorded in the AIC from 15 male rats during alcohol-only and compulsion-like consumption. We found three sustained firing phenotypes, sustained-increase, sustained-decrease, and drinking-onset cells, as well as several firing patterns synchronized with licking. While many AIC neurons had session-long activity changes, only neurons with firing increases at drinking onset had greater activity under compulsion-like conditions. Further, only cells with persistent firing increases maintained activity during pauses in licking, suggesting roles in maintaining drive for alcohol during breaks. AIC firing was not elevated during saccharin drinking, similar to lack of effect of AIC inhibition on sweet fluid intake in many studies. In addition, we observed subsecond changes in AIC neural activity tightly entrained to licking. One lick-synched firing pattern (determined for all licks in a session) predicted compulsion-like drinking, while a separate lick-associated pattern correlated with greater consumption across alcohol intake conditions. Collectively, these data provide a more integrated model for the role of AIC firing in compulsion-like drinking, with important relevance for how the AIC promotes sustained motivated responding more generally.

Influence of Inherited Seizure Susceptibility on Intermittent Voluntary Alcohol Consumption and Alcohol Withdrawal Seizures in Genetically Epilepsy-Prone Rats (GEPR-3s)

BACKGROUND

The link between epilepsy and alcohol consumption is complex, with conflicting reports. To enhance our understanding of this link, we conducted a study to determine how inherited seizure susceptibility affects voluntary alcohol consumption and influences alcohol withdrawal seizures in male and female genetically epilepsy-prone rats (GEPR-3s) compared to Sprague Dawley (SD) rats.

METHODS

In the first experiment, animals were given access to two bottles simultaneously, one containing water and the other 7.5%, 15%, or 30% (v/v) alcohol three times a week for each dose after acclimation to drinking water. In a second experiment, animals were tested for acoustically evoked alcohol seizures 24 h after the last session of voluntary alcohol consumption.

RESULTS

Analysis revealed that GEPR-3s (males and females) had lower alcohol intake and preference than SD rats, particularly at lower alcohol concentrations. However, female GEPR-3s consumed more alcohol and had a higher alcohol preference than males. Furthermore, withdrawal from voluntary alcohol consumption facilitated the onset and duration of seizures in GEPR-3s.

CONCLUSIONS

Our study suggests that genetic seizure susceptibility in GEPR-3s is negatively associated with alcohol consumption. However, withdrawal from low to moderate amounts of alcohol intake can promote epileptogenesis in the epileptic GEPR-3s.

Adolescent social isolation increases binge-like alcohol drinking in male but not female high-alcohol-preferring mice

AIMS

This study examined how adolescent social isolation affects adult binge-like alcohol drinking and stress-axis function, via basal levels of circulating corticosterone (CORT), in male and female mice with a genetic predisposition toward high alcohol preference (HAP).

METHODS

Male and female HAP2 mice were randomly assigned to a group-housed or social isolation (ISO) group. Social isolation began at postnatal Days 40-42 and lasted for 21 days prior to assessment of binge-like alcohol drinking using a 4-day drinking-in-the-dark (DID) procedure. Blood samples to assess basal CORT were taken 6 days after social isolation ended and 24 h before DID started, and again 60 h after DID ended, during the light portion of the light cycle.

RESULTS

Adolescent social isolation increased adult binge-like alcohol drinking in male but not female mice. All groups showed significantly lower CORT after DID compared to before DID. Pearson bivariate correlation coefficients between the first 2 h of grams-per-kilogram alcohol intake on Day 4 and CORT levels indicated a significant positive correlation in ISO males only after DID and negative correlations in ISO females before and after DID.

CONCLUSIONS

These findings demonstrate that adolescent social isolation increased binge-like alcohol drinking in male but not female adult HAP2 mice. Stress-axis adaptations in male HAP2 mice may be associated with the social-isolation-induced increase in binge-like alcohol drinking.

Rapid nongenomic estrogen signaling controls alcohol drinking behavior

The sex steroid hormone estrogen is a key modulator of numerous physiological processes and adaptive behaviors, but it may also be co-opted to drive maladaptive behaviors. While many behavioral roles for estrogen signaling have been shown to occur through canonical genomic signaling mechanisms via nuclear receptors, estrogen can also act in a neurotransmitter-like fashion at membrane-associated estrogen receptors to rapidly regulate neuronal function. Early alcohol drinking confers greater risk for alcohol use disorder in women than men, and binge alcohol drinking is correlated with high circulating estrogen but a causal role for estrogen in alcohol drinking has not been established. Here, we demonstrate that gonadally intact female mice consume more alcohol and display an anxiolytic phenotype when they have elevated levels of ovarian-derived estrogen across the estrous cycle. We found that rapid, nongenomic estrogen signaling at membrane-associated estrogen receptor alpha in the bed nucleus of the stria terminalis (BNST) is necessary and sufficient for the pro-alcohol drinking effects of ovarian estrogen signaling, regardless of the transcriptional program of a high ovarian estrogen state. We further show that a population of corticotropin-releasing factor (CRF) BNST neurons (BNSTCRF) is a critical mediator of these effects, as high estrogen rapidly enhances synaptic excitation of BNSTCRF neurons and promotes their role in driving binge alcohol drinking. These findings show a causal role for endogenous, ovarian-derived estrogen in hormonal modulation of risky alcohol consumption and provide the first demonstration of a purely rapid, nongenomic signaling mechanism of ovarian estrogen in the brain controlling behavior in gonadally intact females.

Sex, executive function, and prospective memory regulate the chain-mediation pathway of alcohol use and impulsivity

Objective

Evidence from previous studies indicates that impulsive behaviors are closely linked to alcohol use and misuse and that female drinkers are more impulsive than male drinkers. However, studies investigating the psychological mechanisms of alcohol use and impulsivity based on sex differences are relatively limited.

Methods

This cross-sectional study comprised 713 residents from 16 cities in Anhui Province, China. Each subject was evaluated for self-reporting measures using several questionnaires, including the general information questionnaire, the Alcohol Use Disorders Identification Test (AUDIT), the Prospective and Retrospective Memory Questionnaire (PRM), the Behavior Rating Inventory of Executive Function-Adult Version (BRIEF-A), and the Barratt Impulsiveness Scale-11 (BIS-11).

Results

Executive function and prospective memory may serve as intermediary links between alcohol use and impulsivity. Although the female alcohol usage level was significantly lower than that of males, the female drinkers had more severe executive dysfunction, prospective memory impairment, and impulsivity than male drinkers. Sex moderated the relationship between alcohol use and impulsivity. Furthermore, the indirect effect of executive function, and prospective memory between AUDIT and BIS was more significant in males than in females.

Conclusion

Alcohol consumption may be associated with impulsivity formation through executive dysfunction and PM impairment, implying that impulsivity in those with AUD or at risk for AUD might be treated by improving EF and PM. Alcohol use may cause more severe executive dysfunction, PM impairment, and impulsive behavior in females than in males, and impulsive behavior in women with AUD was more likely to be due to the direct effects of alcohol consumption, while impulsive behavior in men with AUD was more likely to be due to the indirect effects of executive dysfunction and PM impairment. These findings provide both clinical and theoretical foundations for addressing issues related to alcohol use.

Engagement for Alcohol Escalates in the 5-Choice Serial Reaction Time Task After Intermittent Access

Uncontrollable binge drinking is becoming an increasingly prevalent issue in our society. This is a factor that plays a role in the development of alcohol use disorder (AUD). AUD impacts 15 million Americans annually, with approximately 88,000 dying from alcohol related deaths. There are several aspects of AUD that encourage a strong dependence on alcohol. Impulsivity, motivation, and attention are the primary behavioral facets we contribute to AUD. Many past studies have used the 5-Choice Serial Reaction Time Task (5-Choice) to analyze these types of behaviors using sugar as the reward. We have recently published a study where alcohol was used as a reward in the 5-Choice. 48 mice were trained to respond for alcohol in the 5-Choice, and the analyses for these animals were originally categorized by their alcohol preference and consumption. Upon looking at the data, we became more interested in a new way to classify these mice into groups. High engaged (HE) and low engaged (LE) mice were classified based on their number of correct responses in the last five late-stage sessions. During early-stage training, mice began to separate themselves into two groups based on their interaction with the task. The high-engaged (HE) mice were much more engaged with the task by having a high number of trials and correct responses, as well as a much lower percentage of omissions. The low engaged (LE) mice were not as engaged, this was apparent because of their lower number of trials and correct responses. They also had a much higher percentage of omissions in comparison to HE mice. LE mice presented no significant changes in late-stage training, while HE mice began responding and engaging more. These mice went through a period of intermittent access (IA), where they were allowed to drink alcohol in their cage for 3 weeks. After intermittent access, LE mice increased their responding which suggests an increase in motivation for alcohol as a reward. Engagement analysis presents two clearly different groups, one being motivated to work for alcohol and the other not wanting to work for this reward. These two distinct phenotypes in the 5-Choice could be used to model alcohol motivated behavior, which could help us further understand AUD.

Removal of the ovaries suppresses ethanol drinking and promotes aversion-resistance in C57BL/6J female mice

RATIONALE

Female rodents consume more ethanol (EtOH) than males and exhibit greater aversion-resistant drinking in some paradigms. Ovarian hormones promote EtOH drinking but the contribution of ovarian hormones to aversion-resistant drinking has not been assessed.

OBJECTIVES

We aimed to investigate the role of ovarian hormones to aversion-resistant drinking in female mice in a drinking in the dark (DID) task.

METHODS

Female C57BL/6 J mice first underwent an ovariectomy (OVX, n = 16) or sham (SHAM, n = 16) surgery. Four weeks following surgery, mice underwent a DID paradigm where they were given access to water and 15% EtOH 3 h into the dark cycle for up to 4 h across 15 drinking sessions. To assess frontloading behavior, bottles were weighed at 30 min, 2 h, and 4 h. Aversion-resistance was tested by adding escalating concentrations of quinine (0, 100, 250, and 500 µM) to the 15% EtOH bottle on sessions 16 - 19.

RESULTS

Removal of the ovaries reduced EtOH consumption in OVX subjects. When assessing aversion-resistant EtOH drinking, mice with ovarian hormones (SHAM) reduced consumption of 250 and 500 µM quinine in EtOH, while OVX subjects exhibited aversion-resistance at all quinine concentrations. OVX mice had greater frontloading for quinine + EtOH at higher concentrations of quinine.

CONCLUSIONS

These results indicate that circulating ovarian hormones may be protective against the development of aversion-resistant EtOH drinking and call for further investigation of the role of ovarian hormones in models of addictive behavior.

Bed Nucleus of the Stria Terminalis (BNST) neurons containing the serotonin 5HT2c receptor modulate operant alcohol self-administration behavior in mice

The serotonin 5HT2c receptor has been widely implicated in the pathophysiology of alcohol use disorder (AUD), particularly alcohol seeking and the affective consequences of chronic alcohol consumption. However, little is known about the brain sites in which 5HT2c exerts its effects on specific alcohol-related behaviors, especially in females. Here, we investigated the effects of site-specific manipulation of the 5HT2c receptor system in the BNST on operant alcohol self-administration behaviors in adult mice of both sexes, including the acquisition and maintenance of fixed-ratio responding, motivation for alcohol (progressive ratio), and quinine-adulterated responding for alcohol on a fixed-ratio schedule (punished alcohol seeking). Knockdown of 5HT2c in the BNST did not affect the acquisition or maintenance of operant alcohol self-administration, nor did it affect progressive ratio responding for alcohol. This manipulation had only a subtle effect on responding for quinine alcohol selectively in females. On the other hand, chemogenetic inhibition of BNST 5HT2c-containing neurons (BNST5HT2c) increased operant alcohol self-administration behavior in both sexes on day 2, but not day 9, of testing. It also increased operant responding for 1000 μM quinine-adulterated alcohol selectively in males. Importantly, chemogenetic inhibition of BNST5HT2c did not alter operant sucrose responding or motivation for sucrose in either sex. We then performed cell-type specific anterograde tracing, which revealed that BNST5HT2c project to similar regions in males and females, many of which have been previously implicated in AUD. We next used chemogenetics and quantification of the immediate early gene cFos to characterize the functional influence of BNST5HT2c inhibition on vlPAG activity. We show that chemogenetic inhibition of BNST5HT2c reduces vlPAG cFos in both sexes, but that this reduction is more robust in males. Together these findings suggest that BNST5HT2c neurons, and to a small extent the BNST 5HT2c receptor, serve to promote aversive responses to alcohol consumption, potentially through sex-dependent disinhibition of vlPAG neurons.

Using lickometry to infer differential contributions of salience network regions during compulsion-like alcohol drinking

Alcohol use disorder extracts substantial personal, social and clinical costs, and continued intake despite negative consequences (compulsion-like consumption) can contribute strongly. Here we discuss lickometry, a simple method where lick times are determined across a session, while analysis across many aspects of licking can offer important insights into underlying psychological and action strategies, including their brain mechanisms. We first describe studies implicating anterior insula (AIC) and dorsal medial prefrontal cortex (dMPF) in compulsion-like responding for alcohol, then review work suggesting that AIC/ventral frontal cortex versus dMPF regulate different aspects of behavior (oral control and overall response strategy, versus moment-to-moment action organization). We then detail our lickometer work comparing alcohol-only drinking (AOD) and compulsion-like drinking under moderate- or higher-challenge (ModChD or HiChD, using quinine-alcohol). Many studies have suggested utilization of one of two main strategies, with higher motivation indicated by more bouts, and greater palatability suggested by longer, faster bouts. Instead, ModChD shows decreased variability in many lick measures, which is unexpected but consistent with the suggested importance of automaticity for addiction. Also surprising is that HiChD retains several behavior changes seen with ModChD, reduced tongue variability and earlier bout start, even though intake is otherwise disrupted. Since AIC-related measures are retained under both moderate- and higher-challenge, we propose a novel hypothesis that AIC sustains overall commitment regardless of challenge level, while disordered licking during HiChD mirrors the effects of dMPF inhibition. Thus, while AIC provides overall drive despite challenge, the ability to act is ultimately determined within the dMPF.

The role of beta- and alpha-adrenergic receptors on alcohol drinking

Alcohol Use Disorders (AUD) is characterized by compulsion-like alcohol drinking (CLAD), where intake despite negative consequences can be a major clinical obstacle. With few treatment options available for AUD, there is a significant need for novel therapies. The noradrenergic system is an important hub for regulating stress responses and maladaptive drives for alcohol. Studies have shown that drugs targeting α1 adrenenergic receptors (ARs) may represent a pharmacological treatment for pathological drinking. However, the involvement of β ARs for treating human drinking has received scant investigation, and thus we sought to provide pre-clinical validation for possible AR utility for CLAD by analyzing whether β AR antagonists propranolol (β1/2), betaxolol (β1), and ICI, 118,551 (β2) impacted CLAD and alcohol-only drinking (AOD) in male Wistar rats. We found that the highest dose of propranolol tested systemically (10 mg/kg) reduced alcohol drinking, while 5 mg/kg propranolol reduced drinking with a trend to impact CLAD more than AOD, and with no effects of 2.5 mg/kg. Betaxolol (2.5 mg/kg) also decreased drinking, while ICI 118.551 had no effects. Also, while AR compounds might have utility for AUD, they can also lead to undesirable side effects. Here, a combination of ineffective doses of propranolol and prazosin reduced both CLAD and AOD. Finally, we investigated the effect of propranolol and betaxolol in two brain areas related to pathological drinking, the anterior insula (aINS) and medial prefrontal cortex (mPFC). Surprisingly, propranolol (1-10 μg) in aINS or mPFC did not affect CLAD or AOD. Together, our findings provide new pharmacological insights into noradrenergic regulation of alcohol consumption, which may inform AUD therapy.

A paradigm for ethanol consumption in head-fixed mice during prefrontal cortical two-photon calcium imaging

The prefrontal cortex (PFC) is a hub for higher-level cognitive behaviors and is a key target for neuroadaptations in alcohol use disorders. Preclinical models of ethanol consumption are instrumental for understanding how acute and repeated drinking affects PFC structure and function. Recent advances in genetically encoded sensors of neuronal activity and neuromodulator release combined with functional microscopy (multiphoton and one-photon widefield imaging) allow multimodal in-vivo PFC recordings at subcellular and cellular scales. While these methods could enable a deeper understanding of the relationship between alcohol and PFC function/dysfunction, they require animals to be head-fixed. Here, we present a method in mice for binge-like ethanol consumption during head-fixation. Male and female mice were first acclimated to ethanol by providing home cage access to 20% ethanol (v/v) for 4 or 8 days. After home cage drinking, mice consumed ethanol from a lick spout during head-fixation. We used two-photon calcium imaging during the head-fixed drinking paradigm to record from a large population of PFC neurons (>1000) to explore how acute ethanol affects their activity. Drinking modulated activity rates in a subset of neurons on slow (minutes) and fast (seconds) time scales but the majority of neurons were unaffected. Moreover, ethanol intake did not significantly affect network level interactions in the PFC as assessed through inter-neuronal pairwise correlations. By establishing a method for binge-like drinking in head-fixed mice, we lay the groundwork for leveraging advanced microscopy technologies to study alcohol-induced neuroadaptations in PFC and other brain circuits.

Encoding and context-dependent control of reward consumption within the central nucleus of the amygdala

The ability to evaluate and select a preferred option among a variety of available offers is an essential aspect of goal-directed behavior. Dysregulation of this valuation process is characteristic of alcohol use disorder, with the central amygdala being implicated in persistent alcohol pursuit. However, the mechanism by which the central amygdala encodes and promotes the motivation to seek and consume alcohol remains unclear. We recorded single-unit activity in male Long-Evans rats as they consumed 10% ethanol or 14.2% sucrose. We observed significant activity at the time of approach to alcohol or sucrose, as well as lick-entrained activity during the ongoing consumption of both alcohol and sucrose. We then evaluated the ability of central amygdala optogenetic manipulation time-locked to consumption to alter ongoing intake of alcohol or sucrose, a preferred non-drug reward. In closed two-choice scenarios where rats could drink only sucrose, alcohol, or quinine-adulterated alcohol with or without central amygdala stimulation, rats drank more of stimulation-paired options. Microstructural analysis of licking patterns suggests these effects were mediated by changes in motivation, not palatability. Given a choice among different options, central amygdala stimulation enhanced consumption if the stimulation was associated with the preferred reward while closed-loop inhibition only decreased consumption if the options were equally valued. However, optogenetic stimulation during consumption of the less-preferred option, alcohol, was unable to enhance overall alcohol intake while sucrose was available. Collectively, these findings indicate that the central amygdala processes the motivational value of available offers to promote pursuit of the most preferred available option.

Sex- and Gender-Specific Drug Abuse Dynamics: The Need for Tailored Therapeutic Approaches

Sex and gender have been gaining ever greater attention due to their associated risks, dynamics, patterns and protective factors underlying substance abuse and addiction. Such differentiations and the clarification of complexities thereof take on even greater relevance in light of drug abuse scope worldwide. According to the 2022 World Drug Report released by the United Nations Office on Drugs and Crime (UNODC), in 2020 an estimated 284 million people worldwide aged 15-64 had used a drug within the last 12 months. The authors have set out to shed a light on determinants and contributing factors of drug abuse based on sex and gender and outline policy and medicolegal remarks aimed at delineating sex- and gender-based approaches towards drug abuse therapeutic interventions that are both therapeutically and ethically/legally viable and grounded in an evidence-based set of standards. Neurobiological data suggest that estrogen may facilitate drug taking by interacting with reward- and stress-related systems. In animal research, the administration of estrogen increases drug taking and facilitates the acquisition, escalation, and reinstatement of cocaine-seeking behavior. From a medicolegal perspective, it is of utmost importance to take into account the whole picture constituting each patient profile, which certainly includes gender factors and contributors, when outlining a therapeutic approach. Failure to do so could lead to negligence-based malpractice allegations, in light of the scientific findings representing best practices with which clinicians need to comply when caring for SUD patients.

Greater resistance to footshock punishment in female C57BL/6J mice responding for ethanol

BACKGROUND

One characteristic of alcohol use disorder is compulsive drinking or drinking despite negative consequences. When quinine is used to model such aversion-resistant drinking, female rodents typically are more resistant to punishment than males. Using an operant response task where C57BL/6J responded for ethanol mixed with quinine, we previously demonstrated that female mice tolerate higher concentrations of quinine in ethanol than males. Here, we aimed to determine whether this female vulnerability to aversion-resistant drinking behavior is similarly observed with footshock punishment.

METHODS

Male and female C57BL/6J mice were trained to respond for 10% ethanol in an operant task on a fixed-ratio three schedule. After consistent responding, mice were tested in a punishment session using either a 0.25 mA or 0.35 milliamp (mA) footshock. To assess footshock sensitivity, a subset of mice underwent a flinch, jump, and vocalize test in which behavioral responses to increasing amplitudes of footshock (0.05 to 0.95 mA) were assessed. In a separate cohort of mice, males and females were trained to respond for 2.5% sucrose and responses were punished using a 0.25 mA footshock.

RESULTS

Males and females continued to respond for 10% ethanol when paired with a 0.25 mA footshock. Females alone continued to respond for ethanol when a 0.35 mA footshock was delivered. Both males and females reduced responding for 2.5% sucrose when punished with a 0.25 mA footshock. Footshock sensitivity in the flinch, jump, and vocalize test did not differ by sex.

CONCLUSIONS

Females continue to respond for 10% ethanol despite a 0.35 mA footshock, and this behavior is not due to differences in footshock sensitivity between males and females. These results show that female C57BL/6J mice are generally more resistant to punishment in an operant self-administration paradigm. The findings add to the literature characterizing aversion-resistant alcohol-drinking behaviors in females.

Structured tracking of alcohol reinforcement (STAR) for basic and translational alcohol research

There is inherent tension between methodologies developed to address basic research questions in model species and those intended for preclinical to clinical translation: basic investigations require flexibility of experimental design as hypotheses are rapidly tested and revised, whereas preclinical models emphasize standardized protocols and specific outcome measures. This dichotomy is particularly relevant in alcohol research, which spans a diverse range of basic sciences in addition to intensive efforts towards understanding the pathophysiology of alcohol use disorder (AUD). To advance these goals there is a great need for approaches that facilitate synergy across basic and translational areas of nonhuman alcohol research. In male and female mice, we establish a modular alcohol reinforcement paradigm: Structured Tracking of Alcohol Reinforcement (STAR). STAR provides a robust platform for quantitative assessment of AUD-relevant behavioral domains within a flexible framework that allows direct crosstalk between translational and mechanistically oriented studies. To achieve cross-study integration, despite disparate task parameters, a straightforward multivariate phenotyping analysis is used to classify subjects based on propensity for heightened alcohol consumption and insensitivity to punishment. Combining STAR with extant preclinical alcohol models, we delineate longitudinal phenotype dynamics and reveal putative neuro-biomarkers of heightened alcohol use vulnerability via neurochemical profiling of cortical and brainstem tissues. Together, STAR allows quantification of time-resolved biobehavioral processes essential for basic research questions simultaneous with longitudinal phenotyping of clinically relevant outcomes, thereby providing a framework to facilitate cohesion and translation in alcohol research.

Subcortical serotonin 5HT2c receptor-containing neurons sex-specifically regulate binge-like alcohol consumption, social, and arousal behaviors in mice

Binge alcohol consumption induces discrete social and arousal disturbances in human populations that promote increased drinking and accelerate the progression of Alcohol Use Disorder. Here, we show in a mouse model that binge alcohol consumption disrupts social recognition in females and potentiates sensorimotor arousal in males. These negative behavioral outcomes were associated with sex-specific adaptations in serotonergic signaling systems within the lateral habenula (LHb) and the bed nucleus of the stria terminalis (BNST), particularly those related to the receptor 5HT2c. While both BNST and LHb neurons expressing this receptor display potentiated activation following binge alcohol consumption, the primary causal mechanism underlying the effects of alcohol on social and arousal behaviors appears to be excessive activation of LHb5HT2c neurons. These findings may have valuable implications for the development of sex-specific treatments for mood and alcohol use disorders targeting the brain's serotonin system.

Animal models of compulsion alcohol drinking: Why we love quinine-resistant intake and what we learned from it

Alcohol Use Disorder (AUD) ranks among the most prevalent mental disorders, extracting ~$250 billion/year in the US alone and producing myriad medical and social harms. Also, the number of deaths related to problem drinking has been increasing dramatically. Compulsive alcohol drinking, characterized by intake that persists despite negative consequences, can be particularly important and a major obstacle to treatment. With the number of people suffering from AUD increasing during the past years, there is a critical need to understand the neurobiology related to compulsive drives for alcohol, as well as the development of novel AUD pharmacological therapies. Here we discuss rodent compulsion-like alcohol drinking (CLAD) models, focusing on the two most widely used adverse stimuli to model rodent compulsion-like responding, quinine adulteration of alcohol and footshook-resistant alcohol intake. For both cases, the goal is to uncover behavior patterns and brain circuits that underlie drive for alcohol even in the face of negative consequences. We discuss caveats, benefits, and potential brain mechanisms, of models for consequence-resistant responding for alcohol more generally, and especially highlight some advantages of quinine-resistance over footshook-resistance. Further, since this review contributes to a Special issue focused on Molecular Aspects of Compulsive Drug Use, we discuss our new findings showing how the noradrenergic system is related to CLAD responding. In particular, we comment on the importance of α1 and β adrenergic receptors (ARs) as potential targets for treating AUD.

Sex chromosome and gonadal hormone contributions to binge-like and aversion-resistant ethanol drinking behaviors in Four Core Genotypes mice

Introduction

While substantial research has focused on the contribution of sex hormones to driving elevated levels of alcohol drinking in female rodents, fewer studies have investigated how genetic influences may underlie sex differences in this behavior.

Methods

We used the Four Core Genotypes (FCG) mouse model to explore the contribution of sex chromosome complement (XX/XY) and gonad type [ovaries (Sry-)/testes (Sry+)] to ethanol (EtOH) consumption and quinine-resistant drinking across two voluntary self-administration tasks: limited access consumption in the home cage and an operant response task.

Results

For limited access drinking in the dark, XY/Sry + (vs. XX/Sry +) mice consumed more 15% EtOH across sessions while preference for 15% EtOH vs. water was higher in XY vs. XX mice regardless of gonad type. XY chromosomes promoted quinine-resistant drinking in mice with ovaries (Sry-) and the estrous cycle did not affect the results. In the operant response task, responding for EtOH was concentration dependent in all genotypes except XX/Sry + mice, which maintained consistent response levels across all concentrations (5-20%) of EtOH. When increasing concentrations of quinine (100-500 μM) were added to the solution, FCG mice were insensitive to quinine-punished EtOH responding, regardless of sex chromosome complement. Sry + mice were further found to be insensitive to quinine when presented in water. Importantly, these effects were not influenced by sensitivity to EtOH's sedative effect, as no differences were observed in the time to lose the righting reflex or the time to regain the righting reflex between genotypes. Additionally, no differences in EtOH concentration in the blood were observed between any of the genotypes once the righting reflex was regained.

Discussion

These results provide evidence that sex chromosome complement regulates EtOH consumption, preference, and aversion resistance and add to a growing body of literature suggesting that chromosomal sex may be an important contributor to alcohol drinking behaviors. Examination of sex-specific genetic differences may uncover promising new therapeutic targets for high-risk drinking.

Sexually dimorphic role for insular perineuronal nets in aversion-resistant alcohol consumption

Compulsive alcohol drinking is a key symptom of alcohol use disorder (AUD) that is particularly resistant to treatment. An understanding of the biological factors that underly compulsive drinking will allow for the development of new therapeutic targets for AUD. One animal model of compulsive alcohol drinking involves the addition of bitter-tasting quinine to an ethanol solution and measuring the willingness of the animal to consume ethanol despite the aversive taste. Previous studies have demonstrated that this type of aversion-resistant drinking is modulated in the insular cortex of male mice by specialized condensed extracellular matrix known as perineuronal nets (PNNs), which form a lattice-like structure around parvalbumin-expressing neurons in the cortex. Several laboratories have shown that female mice exhibit higher levels of aversion-resistant ethanol intake, but the role of PNNs in females in this behavior has not been examined. Here we compared PNNs in the insula of male and female mice and determined if disrupting PNNs in female mice would alter aversion-resistant ethanol intake. PNNs were visualized in the insula by fluorescent labeling with Wisteria floribunda agglutinin (WFA) and disrupted in the insula by microinjecting chondroitinase ABC, an enzyme that digests the chondroitin sulfate glycosaminoglycan component of PNNs. Mice were tested for aversion-resistant ethanol consumption by the addition of sequentially increasing concentrations of quinine to the ethanol in a two-bottle choice drinking in the dark procedure. PNN staining intensity was higher in the insula of female compared to male mice, suggesting that PNNs in females might contribute to elevated aversion-resistant drinking. However, disruption of PNNs had limited effect on aversion-resistant drinking in females. In addition, activation of the insula during aversion-resistant drinking, as measured by c-fos immunohistochemistry, was lower in female mice than in males. Taken together, these results suggest that neural mechanisms underlying aversion-resistant ethanol consumption differ in males and females.

Sex differences in neuronal activation during aversion-resistant alcohol consumption

BACKGROUND

One of the DSM-5 criteria for Alcohol Use Disorder is continued alcohol consumption despite negative consequences. This has been modeled in mice using adulteration of alcohol solution with the bitter tastant quinine. Mice that continue to consume alcohol despite this adulteration are considered aversion resistant. The limited number of studies dissecting the underlying neuronal mechanisms of aversion-resistant drinking behaviors used only male subjects. We have previously shown that female mice are more resistant to quinine adulteration of alcohol than males. Our aim here is to identify potential sex differences in neuronal activation that may underlie this behavior.

METHODS

Male and female C57BL/6J mice were allowed continuous access to 20% alcohol in a two-bottle choice procedure. To test aversion-resistance, the alcohol was adulterated with increasing concentrations (0.03, 0.1, and 0.2 mM) of quinine hydrochloride. After consumption rates were calculated, brains were extracted to examine neuronal activation using Fos immunohistochemistry.

RESULTS

We found that female mice suppressed their intake to a lesser extent than males when the alcohol solution was adulterated with quinine. Our Fos staining revealed three regions of interest that exhibit a sex difference during quinine-adulterated alcohol drinking: the ventromedial prefrontal cortex (vmPFC), the posterior insular cortex (PIC), and the ventral tegmental area (VTA). Both the vmPFC and the PIC exhibited higher neuronal activation in males during quinine-adulterated alcohol consumption. However, females showed higher Fos activation in the VTA during quinine-adulterated alcohol consumption.

CONCLUSIONS

Females more readily exhibit aversion-resistant alcohol intake than their male counterparts and exhibit some differences in neuronal activation patterns. We conclude that there are sex differences in neurocircuitry that may underlie compulsive drinking behaviors.

Sexually Dimorphic Role for Insular Perineuronal Nets in Aversion-Resistant Ethanol Consumption

Compulsive alcohol drinking is a key symptom of alcohol use disorder (AUD) that is particularly resistant to treatment. An understanding of the biological factors that underly compulsive drinking will allow for the development of new therapeutic targets for AUD. One animal model of compulsive alcohol drinking involves the addition of bitter-tasting quinine to an ethanol solution and measuring the willingness of the animal to consume ethanol despite the aversive taste. Previous studies have demonstrated that this type of aversion-resistant drinking is modulated in the insular cortex of male mice by specialized condensed extracellular matrix known as perineuronal nets (PNNs), which form a lattice-like structure around parvalbumin-expressing neurons in the cortex. Several laboratories have shown that female mice exhibit higher levels of aversion-resistant ethanol intake but the role of PNNs in females in this behavior has not been examined. Here we compared PNNs in the insula of male and female mice and determined if disrupting PNNs in female mice would alter aversion-resistant ethanol intake. PNNs were visualized in the insula by fluorescent labeling with Wisteria floribunda agglutinin (WFA) and disrupted in the insula by microinjecting chondroitinase ABC, an enzyme that digests the chondroitin sulfate glycosaminoglycan component of PNNs. Mice were tested for aversion-resistant ethanol consumption by the addition of sequentially increasing concentrations of quinine to the ethanol in a two-bottle choice drinking in the dark procedure. PNN staining intensity was higher in the insula of female compared to male mice, suggesting that PNNs in females might contribute to elevated aversion-resistant drinking. However, disruption of PNNs had limited effect on aversion-resistant drinking in females. In addition, activation of the insula during aversion-resistant drinking, as measured by c-fos immunohistochemistry, was lower in female mice than in males. Taken together, these results suggest that neural mechanisms underlying aversion-resistant ethanol consumption differ in males and females.

Sex, but not early life stress, effects on two-bottle choice alcohol drinking behaviors in mice

In humans, early life stress (ELS) is associated with an increased risk for developing both alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD). We have previously used an infant footshock model to explore this shared predisposition. Infant footshock produces stress-enhanced fear learning (SEFL) in rats and mice and increases aversion-resistant alcohol drinking in rats. The goal of the current study was to extend this model of comorbid PTSD and AUD to male and female C57BL/6J mice. Acute ELS was induced using 15 foot-shocks on postnatal day 17. In adulthood, after PND 90, ethanol drinking behavior was tested in one of three two-bottle choice drinking paradigms: continuous access, limited access drinking in the dark, or intermittent access. In continuous access, mice were given 24 h access to 5% or 10% ethanol and water. Each ethanol concentration was provided for five consecutive drinking sessions. In limited access drinking in the dark, mice were given 2 h of access to 15% ethanol and water across 15 sessions. Ethanol was provided 3 h into the dark cycle to maximize task engagement when mice are most active. In intermittent access, mice were presented with 20% ethanol and water Monday, Wednesday, and Friday, for four consecutive weeks. In a fifth week of intermittent access drinking, increasing concentrations of quinine (10 mg/L, 100 mg/L, and 200 mg/L) were added to the ethanol to test aversion-resistant drinking. Our results indicate that infant footshock does not influence adult ethanol consumption in mice. Infant footshock did not affect ethanol-only consumption or preference in any of the three drinking paradigms. Further, and in contrast to our previous results in rats, infant footshock did not appear to influence consumption of quinine-adulterated ethanol. The biological sex of the mice did affect ethanol-only consumption in all three drinking paradigms, with females consuming more ethanol than males. Preference for ethanol vs. water was higher in females only under continuous access conditions. Our results suggest that infant footshock alone may not be sufficient to increase drinking levels in mice. We hypothesize that infant footshock may require a secondary, adolescent stress exposure to influence ethanol drinking behavior. Further research is needed to create a valid model of PTSD-AUD comorbidity in male and female mice.

Drinking history dependent functionality of the dorsolateral striatum on gating alcohol and quinine-adulterated alcohol front-loading and binge drinking

After an extended alcohol-drinking history, alcohol use can transition from controlled to compulsive, causing deleterious consequences. Alcohol use can be segregated into two distinct behaviors, alcohol seeking and alcohol taking. Expression of habitual and compulsive alcohol seeking depends on the dorsolateral striatum (DLS), a brain region thought to engage after extended alcohol access. However, it is unknown whether the DLS is also involved in compulsive-like alcohol taking. The purpose of this experiment was to identify whether the DLS gates compulsive-like binge alcohol drinking. To ask this question, we gave adult male and female C57BL/6J mice a binge-like alcohol-drinking history, which we have previously demonstrated to produce compulsive-like alcohol drinking (Bauer, McVey, & Boehm, 2021), or a water-drinking history. We then tested the involvement of the DLS on gating binge-like alcohol drinking and compulsive-like quinine-adulterated alcohol drinking via intra-DLS AMPA receptor antagonism. We hypothesized that pharmacological lesioning of the DLS would reduce compulsive-like quinine-adulterated alcohol (QuA) drinking, but not non-adulterated alcohol drinking, in male and female C57BL/6J mice. Three important findings were made. First, compulsive-like alcohol drinking is significantly blunted in cannulated mice. Because of this, we conclude that we were not able to adequately assess the effect of intra-DLS lesioning on compulsive-like alcohol drinking. Second, we found that the DLS gates binge-like alcohol drinking initially, which replicates findings in our previous work (Bauer, McVey, Germano, Zhang, & Boehm, 2022). However, following an extended alcohol history, the DLS no longer drives this behavior. Finally, alcohol and QuA front-loading is DLS-dependent in alcohol-history mice. Intra-DLS NBQX altered these drinking behaviors without altering ambulatory locomotor activity. These data demonstrate the necessity of the DLS in binge-like alcohol drinking before, but not following, an extended binge-like alcohol-drinking history and in alcohol front-loading in alcohol-history mice.

Crossed high alcohol preferring mice exhibit aversion-resistant responding for alcohol with quinine but not footshock punishment

A symptom of alcohol use disorder (AUD) is compulsive drinking, or drinking that persists despite negative consequences. In mice, aversion-resistant models are used to model compulsive-like drinking by pairing the response for alcohol with a footshock or by adding quinine, a bitter tastant, to the alcohol solution. crossed High Alcohol Preferring (cHAP) mice, a selectively bred line of mice that consumes pharmacologically relevant levels of alcohol, demonstrate a high level of aversion-resistance to quinine-adulterated alcohol. The current study investigated quinine-resistant and footshock-resistant responding for 10% ethanol in male and female cHAP mice with vs. without a history of alcohol exposure. cHAP mice were first trained to respond for 10% ethanol in an operant-response task. Next, mice were exposed to water or 10% ethanol for twelve 24-h sessions using a two-bottle choice procedure. Footshock-resistant ethanol responding was then tested in the operant chamber by pairing a footshock (0.35 mA) with the nose-poke response during one session. Quinine-resistant responding for alcohol was tested over five sessions (500-2500 μM quinine). Finally, footshock sensitivity was assessed using a flinch, jump, vocalize test. Alcohol exposure history did not influence responses for 10% ethanol or either measure of aversion-resistance. Further, cHAP mice were sensitive to footshock punishment but continued to respond for alcohol at all quinine concentrations. No sex differences were observed in any measure of alcohol responding, but female cHAP mice were less sensitive to footshock than males. These results replicate and extend the previous demonstration of a robust, innate resistance to quinine aversion in cHAP mice and further suggest that this tendency is not observed when footshock is used to punish drinking.

Adaptation of the 5-choice serial reaction time task to measure engagement and motivation for alcohol in mice

Alcohol use disorder (AUD) is related to excessive binge alcohol consumption, and there is considerable interest in associated factors that promote intake. AUD has many behavioral facets that enhance inflexibility toward alcohol consumption, including impulsivity, motivation, and attention. Thus, it is important to understand how these factors might promote responding for alcohol and can change after protracted alcohol intake. Previous studies have explored such behavioral factors using responding for sugar in the 5-Choice Serial Reaction Time Task (5-CSRTT), which allows careful separation of impulsivity, attention, and motivation. Importantly, our studies uniquely focus on using alcohol as the reward throughout training and testing sessions, which is critical for beginning to answer central questions relating to behavioral engagement for alcohol. Alcohol preference and consumption in male C57BL/6 mice were determined from the first 9 sessions of 2-h alcohol drinking which were interspersed among 5-CSRTT training. Interestingly, alcohol preference but not consumption level significantly predicted 5-CSRTT responding for alcohol. In contrast, responding for strawberry milk was not related to alcohol preference. Moreover, high-preference (HP) mice made more correct alcohol-directed responses than low-preference (LP) during the first half of each session and had more longer reward latencies in the second half, with no differences when performing for strawberry milk, suggesting that HP motivation for alcohol may reflect “front-loading.” Mice were then exposed to an Intermittent Access to alcohol paradigm and retested in 5-CSRTT. While both HP and LP mice increased 5-CSRTT responding for alcohol, but not strawberry milk, LP performance rose to HP levels, with a greater change in correct and premature responding in LP versus HP. Overall, this study provides three significant findings: (1) alcohol was a suitable reward in the 5-CSRTT, allowing dissection of impulsivity, attention, and motivation in relation to alcohol drinking, (2) alcohol preference was a more sensitive indicator of mouse 5-CSRTT performance than consumption, and (3) intermittent alcohol drinking promoted behavioral engagement with alcohol, especially for individuals with less initial engagement.

Mutation of the α5 nicotinic acetylcholine receptor subunit increases ethanol and nicotine consumption in adolescence and impacts adult drug consumption

Alcohol and nicotine are commonly used during adolescence, establishing long-lasting neuroplastic alterations that influence subsequent drug use and abuse. Drinking- and smoking-related traits have been extensively associated with variation in CHRNA5 - the gene that encodes the α5 subunit of neuronal nicotinic acetylcholine receptors (nAChRs). The single nucleotide polymorphism (SNP) rs16969968 in CHRNA5 encodes an amino acid substitution (D398N) that alters the function and pharmacokinetics of α5-containing nAChR. When expressed in rodents, this variant results in increased ethanol and nicotine operant self-administration. How disruption of α5-containing nAChRs influences adolescent ethanol and nicotine intake, and how it modulates interactions between these drugs has not been previously explored. In the present study, we examined volitional ethanol and nicotine consumption in adolescent mice (post-natal day 30-43) of both sexes with mutated (SNP) or lacking (KO) the α5 nAChR subunit. The effect of adolescent alcohol or nicotine exposure on home cage consumption of the opposite drug in adulthood and its modulation by Chrna5 mutation and sex were examined. During adolescence, we found that α5 nAChR disruption increases nicotine intake in mice of both sexes, but the effect on alcohol intake was only observed in females. The sex-specific increase in alcohol consumption in α5 SNP and KO was replicated in adulthood. The effect of adolescent alcohol or nicotine exposure on subsequent intake of the opposite drug in adulthood is modulated by sex and Chrna5 mutation. These observations suggest sex differences in the genetic architecture of alcohol dependence, and modulators of alcohol and nicotine interactions.

Gonadal hormones and sex chromosome complement differentially contribute to ethanol intake, preference, and relapse-like behaviour in four core genotypes mice

Alcohol use and high-risk alcohol drinking behaviours among women are rapidly rising. In rodent models, females typically consume more ethanol (EtOH) than males. Here, we used the four core genotypes (FCG) mouse model to investigate the influence of gonadal hormones and sex chromosome complement on EtOH drinking behaviours. FCG mice were given access to escalating concentrations of EtOH in a two-bottle, 24-h continuous access drinking paradigm to assess consumption and preference. Relapse-like behaviour was measured by assessing escalated intake following repeated cycles of deprivation and re-exposure. Twenty-four-hour EtOH consumption was greater in mice with ovaries (Sry-), relative to those with testes, and in mice with the XX chromosome complement, relative to those with XY sex chromosomes. EtOH preference was higher in XX versus XY mice. For both consumption and preference, the influences of the Sry gene and sex chromosomes were concentration dependent. Escalated intake following repeated cycles of deprivation and re-exposure emerged only in XX mice (vs. XY). Mice with ovaries (Sry- FCG mice and C57BL/6J females) were also found to consume more water than mice with testes. These results demonstrate that aspects of EtOH drinking behaviour may be independently regulated by sex hormones and chromosomes and inform our understanding of the neurobiological mechanisms which contribute to EtOH dependence in male and female mice. Future investigation of the contribution of sex chromosomes to EtOH drinking behaviours is warranted. We used the FCG mouse model to investigate the influence of gonadal hormones and sex chromosome complement on EtOH drinking behaviours, including the alcohol deprivation effect. Escalated intake following repeated cycles of deprivation and re-exposure emerged only in XX mice (vs. XY). These results demonstrate that aspects of EtOH drinking behaviour may be independently regulated by sex hormones and chromosomes.

Modeling Aversion Resistant Alcohol Intake in Indiana Alcohol-Preferring (P) Rats

With the substantial social and medical burden of addiction, there is considerable interest in understanding risk factors that increase the development of addiction. A key feature of alcohol use disorder (AUD) is compulsive alcohol (EtOH) drinking, where EtOH drinking becomes “inflexible” after chronic intake, and animals, such as humans with AUD, continue drinking despite aversive consequences. Further, since there is a heritable component to AUD risk, some work has focused on genetically-selected, EtOH-preferring rodents, which could help uncover critical mechanisms driving pathological intake. In this regard, aversion-resistant drinking (ARD) takes >1 month to develop in outbred Wistar rats (and perhaps Sardinian-P EtOH-preferring rats). However, ARD has received limited study in Indiana P-rats, which were selected for high EtOH preference and exhibit factors that could parallel human AUD (including front-loading and impulsivity). Here, we show that P-rats rapidly developed compulsion-like responses for EtOH; 0.4 g/L quinine in EtOH significantly reduced female and male intake on the first day of exposure but had no effect after one week of EtOH drinking (15% EtOH, 24 h free-choice paradigm). Further, after 4−5 weeks of EtOH drinking, males but not females showed resistance to even higher quinine (0.5 g/L). Thus, P-rats rapidly developed ARD for EtOH, but only males developed even stronger ARD with further intake. Finally, rats strongly reduced intake of quinine-adulterated water after 1 or 5 weeks of EtOH drinking, suggesting no changes in basic quinine sensitivity. Thus, modeling ARD in P-rats may provide insight into mechanisms underlying genetic predispositions for compulsive drinking and lead to new treatments for AUDs.

Sex differences and the lack of effects of chemogenetic manipulation of pro-opiomelanocortin (POMC) neurons on alcohol consumption in male and female mice

The endogenous opioid system has been implicated in the rewarding and reinforcing effects of alcohol. Pro-opiomelanocortin (POMC) neurons located within the arcuate nucleus of the hypothalamus (ArcN) secrete multiple peptides associated with alcohol consumption, including β-endorphin (β-END), α-melanocyte stimulating hormone (α-MSH), and adrenocorticotropic hormone (ACTH). In this study, we utilized chemogenetics to bidirectionally modulate ArcN POMC neurons to determine their role in alcohol and saccharin consumption and regional levels of POMC-derived peptides. Male and female POMC-cre mice were infused with viral vectors designed for cre-dependent expression of either excitatory and inhibitory DREADDs or a control vector into the ArcN. Following recovery, animals were allowed to consume alcohol or saccharin using the drinking-in-the-dark (DID) paradigm of binge-like intake for 4 consecutive days. Prior to the final test session, animals were injected with clozapine-N-oxide (2.5 mg/kg, i.p.) for DREADD activation. Following the last DID session, animals were euthanized and the ArcN, VTA, amygdala and NAc were dissected and assessed for POMC peptide expression utilizing western blotting. We found that female mice consumed more alcohol than males during DID sessions 2-4, and that chemogenetic activation had no effect on alcohol or saccharin consumption in either sex. We found that β-END expression within the ArcN positively correlated with alcohol consumption. Given the molecular and functional heterogeneity of ArcN POMC neurons, future studies are needed to assess the effects of modulation of specific subpopulations of these neurons within the ArcN on consumption of rewarding substances such as alcohol and saccharin.

Alcohol Consumption and Risk of Atrial Fibrillation: A Dose-Response Meta-Analysis of Prospective Studies

Background

This study aimed to investigate the dose-response association between alcohol consumption and atrial fibrillation (AF) risk.

Methods

PubMed, Embase, Cochrane Library, and Web of Science were systematically searched using keywords related to alcohol and AF from the establishment of databases up to 1 March 2021. Prospective studies examining the impact of alcohol on the risk of AF with hazard ratios (HRs) were included. Restricted cubic spline regression was performed to quantify the dose-response relationship between alcohol consumption and AF risk.

Results

Thirteen eligible studies were included in the meta-analysis, with a total of 645,826 participants and 23,079 cases of AF. When compared with non-/seldom-drinkers, the pooled adjusted HRs of AF were 1.30 (95% confidence interval [CI]: 1.20–1.41) and 1.00 (95% CI: 0.96–1.05) for high and low alcohol consumption, respectively. Moderate alcohol intake significantly increased the risk of AF in males (HR, 1.21; 95% CI: 1.10–1.33) but not in females (HR, 1.02; 95% CI: 0.91–1.14). The cubic spline regression analysis illustrated that the risk of AF significantly increased with daily alcohol intake in a Non-linear manner (R² = 0.64, P = 5.785 × 10⁻¹²).

Conclusion

This study revealed a Non-linearly positive association between alcohol intake and the risk of AF. Low alcohol intake was not associated with the development of AF, whereas moderate alcohol intake significantly increased the risk of AF in males but not in females. Our meta-analysis highlighted that alcohol consumption should be restricted to a low level to reduce the risk of AF.

Prenatal opioid exposure reprograms the behavioural response to future alcohol reward

As the opioid crisis has continued to grow, so has the number of infants exposed to opioids during the prenatal period. A growing concern is that prenatal exposure to opioids may induce persistent neurological changes that increase the propensity for future addictions. Although alcohol represents the most likely addictive substance that the growing population of prenatal opioid exposed will encounter as they mature, no studies to date have examined the effect of prenatal opioid exposure on future sensitivity to alcohol reward. Using a recently developed mouse model of prenatal methadone exposure (PME), we investigated the rewarding properties of alcohol and alcohol consumption in male and female adolescent PME and prenatal saline exposed (PSE) control animals. Conditioned place preference to alcohol was disrupted in PME offspring in a sex-dependent manner with PME males exhibiting resistance to the rewarding properties of alcohol. Repeated injections of alcohol revealed enhanced sensitivity to the locomotor-stimulating effects of alcohol specific to PME females. PME males consumed significantly more alcohol over 4 weeks of alcohol access relative to PSE males and exhibited increased resistance to quinine-adulterated alcohol. Further, a novel machine learning model was developed to employ measured differences in alcohol consumption and drinking microstructure to reliably predict prenatal exposure. These findings indicate that PME alters the sensitivity to alcohol reward in adolescent mice in a sex-specific manner and suggests prenatal opioid exposure may induce persistent effects on reward neurocircuitry that can reprogram offspring behavioural response to alcohol later in life.

Orbitofrontal cortex subregion inhibition during binge-like and aversion-resistant alcohol drinking

Two important contributors to alcohol-related problems and alcohol use disorder (AUD) are binge- and compulsive-like drinking. The orbitofrontal cortex (OFC), a brain region implicated in outcome valuation and behavioral flexibility, is functionally altered by alcohol exposure. Data from animal models also suggest that both the medial (mOFC) and lateral (lOFC) subregions of the OFC regulate alcohol-related behaviors. The current study was designed to examine the contributions of mOFC and lOFC using a model of binge-like and aversion-resistant ethanol drinking in C57BL/6J male and female mice. The inhibitory Designer Receptor Exclusively Activated by Designer Drugs (DREADD) hM4Di were used to inhibit neurons in either the mOFC or the lOFC in mice drinking 15% ethanol in a two-bottle, limited-access, modified drinking in the dark paradigm. The effects of chemogenetic inhibition on consumption of quinine-adulterated ethanol, water, and water + quinine were also assessed. Inhibiting the mOFC did not alter consumption of ethanol or aversion-resistant drinking of ethanol + quinine. In contrast, inhibition of neurons in the lOFC increased consumption, but not preference, of ethanol alone. mOFC and lOFC inhibition did not alter water or quinine-adulterated water intake, indicating the effects shown here are specific to ethanol drinking. These data support the role of the lOFC in regulating alcohol consumption but fail to find a similar role for mOFC.

Influx of kynurenine into the brain is involved in the reduction of ethanol consumption induced by Ro 61-8048 after chronic intermittent ethanol in mice

BACKGROUND AND PURPOSE

The kynurenine pathway has been proposed as a new target for modulating drug abuse. We previously demonstrated that inhibition of kynurenine 3-monooxygenase (KMO) using Ro 61-8048 reduces ethanol consumption in a binge drinking model. Here we investigate the effect of the kynurenine pathway modulation in ethanol -dependent mice.

EXPERIMENTAL APPROACH

Adult male and female mice were subjected to the Chronic Intermittent Ethanol (CIE) paradigm. On the last day of CIE, mice were treated with Ro 61-8048, Ro 61-8048 + PNU-120596, a positive allosteric modulator of α7nAChR, and Ro 61-8048 + L-leucine or probenecid, which block the influx or efflux of kynurenine from the brain, respectively. Ethanol, water consumption and preference were measured and kynurenine levels in plasma and limbic forebrain were determined.

KEY RESULTS

Ro 61-8048 decreases consumption and preference for ethanol in both sexes exposed to the CIE model, an effect that is prevented by PNU-120596. The Ro 61-8048-induced decrease in ethanol consumption depends on the influx of kynurenine into the brain.

CONCLUSION AND IMPLICATIONS

Inhibition of KMO reduces ethanol consumption and preference in both male and female mice subjected to CIE model by a mechanism involving α7nAChR. Moreover, the effect which is mediated centrally depends on the influx of peripheral kynurenine to the brain and can be prolonged by blocking the efflux of kynurenine from the brain. Here, for the first time we demonstrate that the modulation of the kynurenine pathway is a valid strategy for the treatment of ethanol dependence in both sexes.