Absence of effects of intermittent access to alcohol on negative affective and anxiety-like behaviors in male and female C57BL/6J mice

The impact of abstinence from chronic alcohol consumption on the mouse striatal proteome: sex and subregion-specific differences

Alcohol misuse is the third leading preventable cause of death in the world. The World Health Organization currently estimates that 1 in 20 deaths are directly alcohol related. One of the ways in which consuming excessive levels of alcohol can both directly and indirectly affect human mortality and morbidity, is through chronic inflammation. Recently, studies have suggested a link between increased alcohol use and the incidence of neuroinflammatory-related diseases. However, the mechanism in which alcohol potentially influences neuroinflammatory processes is still being uncovered. We implemented an unbiased proteomics exploration of alcohol-induced changes in the striatum, with a specific emphasis on proteins related to inflammation. The striatum is a brain region that is critically involved with the progression of alcohol use disorder. Using mass spectrometry following voluntary alcohol self-administration in mice, we show that distinct protein abundances and signaling pathways in different subregions of the striatum are disrupted by chronic exposure to alcohol compared to water drinking control mice. Further, in mice that were allowed to experience abstinence from alcohol compared to mice that were non-abstinent, the overall proteome and signaling pathways showed additional differences, suggesting that the responses evoked by chronic alcohol exposure are dependent on alcohol use history. To our surprise we did not find that chronic alcohol drinking or abstinence altered protein abundance or pathways associated with inflammation, but rather affected proteins and pathways associated with neurodegeneration and metabolic, cellular organization, protein translation, and molecular transport processes. These outcomes suggest that in this drinking model, alcohol-induced neuroinflammation in the striatum is not a primary outcome controlling altered neurobehavioral function, but these changes are rather mediated by altered striatal neuronal structure and cellular health.

Home cage voluntary alcohol consumption increases binge drinking without affecting abstinence-related depressive-like behaviors or operant responding in crossed high alcohol-preferring mice (cHAPs)

Chronic alcohol consumption can lead to tolerance and escalation of drinking in humans and animals, but mechanisms underlying these changes are not fully characterized. Preclinical models can delineate which mechanisms are involved. The chronic intermittent ethanol exposure (CIE) procedure uses forced exposure to vaporized alcohol that elicits withdrawal and increased responding for alcohol in operant tasks in C57BL/6J inbred mice. Chronic two-bottle choice (2BC) drinking in the same strain elicits abstinent-related depression-like behavior, suggestive of allostatic changes. Selected lines such as crossed High Alcohol Preferring (cHAP) mice voluntarily drink to blood alcohol concentrations comparable to those attained in CIE and could be used to assess how alcohol affects these same endpoints without the confounds of involuntary vapor inhalation. In three experiments, we assess how 2BC drinking in cHAP mice affects abstinence-related depressive- and anxiety-like behavior, operant responding for alcohol, and binge consumption using drinking-in-the-dark (DID). We hypothesized that cHAPs with home-cage drinking experience would exhibit more depressive behavior after abstinence, increased responding for alcohol in the operant box, and increased DID intake. Of these, a drinking history increased DID intake in female cHAPs only and increased sucrose preference and intake following abstinence, but had no effects on operant responding or NSFT latency and FST immobility following forced abstinence. These results are consistent with recent findings using slice electrophysiology showing tolerance to alcohol's actions on the dorsolateral striatum following 2BC drinking in female, but not male cHAP mice. Overall, these data suggest that cHAPs may require procedures allowing rapid intoxication, such as DID, to demonstrate changes in alcohol's rewarding effects.

Network States in the Basolateral Amygdala Predicts Voluntary Alcohol Consumption

Although most adults in the United States will drink alcohol in their life, only about 6% will go on to develop an alcohol use disorder (AUD). While a great deal of work has furthered our understanding of the cycle of addiction, it remains unclear why certain people transition to disordered drinking. Altered activity in regions implicated in AUDs, like the basolateral amygdala (BLA), has been suggested to play a role in the pathophysiology of AUDs, but how these networks contribute to alcohol misuse remains unclear. Our recent work demonstrated that alcohol can modulate BLA network states and that GABAergic parvalbumin (PV) interneurons are crucial modulators of network activity in the BLA. Further, our lab has demonstrated that δ subunit-containing GABA A receptors, which are modulated by alcohol, are highly expressed on PV interneurons in the BLA. These receptors on PV interneurons have also been shown to influence alcohol intake in a voluntary binge drinking paradigm and anxiety-like behavior in withdrawal. Therefore, we hypothesized that alcohol may impact BLA network states via δ subunit-containing GABA A receptors on PV interneurons to impact the extent of alcohol use. To test this hypothesis, we measured the impact of acute alcohol exposure on oscillatory states in the basolateral amygdala and then assessed the relationship to the extent of voluntary ethanol consumption in the Intermittent Access, Drinking-in-the-Dark-Multiple Scheduled Access, and Chronic Intermittent Ethanol exposure paradigms. Remarkably, we demonstrate that the average alcohol intake negatively correlates with δ subunit-containing GABA A receptor expression on PV interneurons and gamma power in the BLA after the first exposure to alcohol. These data implicate δ subunit-containing GABA A receptor expression on PV interneurons in the BLA in voluntary alcohol intake and suggest that BLA network states may serve as a useful biomarker for those at risk for alcohol misuse.

Significance Statement

Oscillatory states in the BLA have been demonstrated to drive behavioral states involved in emotional processing, including negative valence processing. Given that negative emotional states/hyperkatifeia contribute to the cycle of AUDs, our previous work demonstrating the ability of alcohol to modulate BLA network states and thereby behavioral states suggests that this mechanism may influence alcohol intake. Here we demonstrate a relationship between the ability of alcohol to modulate oscillations in the BLA and future alcohol intake such that the extent to which alcohol influences BLA network states predict the extent of future voluntary alcohol intake. These findings suggest that individual variability in the sensitivity of the BLA network to alcohol influences voluntary alcohol consumption.

Association between RMTg Neuropeptide Genes and Negative Effect during Alcohol Withdrawal in Mice

Alcohol use disorders (AUDs) frequently co-occur with negative mood disorders, such as anxiety and depression, exacerbating relapse through dopaminergic dysfunction. Stress-related neuropeptides play a crucial role in AUD pathophysiology by modulating dopamine (DA) function. The rostromedial tegmental nucleus (RMTg), which inhibits midbrain dopamine neurons and signals aversion, has been shown to increase ethanol consumption and negative emotional states during abstinence. Despite some stress-related neuropeptides acting through the RMTg to affect addiction behaviors, their specific roles in alcohol-induced contexts remain underexplored. This study utilized an intermittent voluntary drinking model in mice to induce negative effect behavior 24 h into ethanol (EtOH) abstinence (post-EtOH). It examined changes in pro-stress (Pnoc, Oxt, Npy) and anti-stress (Crf, Pomc, Avp, Orx, Pdyn) neuropeptide-coding genes and analyzed their correlations with aversive behaviors. We observed that adult male C57BL/6J mice displayed evident anxiety, anhedonia, and depression-like symptoms at 24 h post-EtOH. The laser-capture microdissection technique, coupled with or without retrograde tracing, was used to harvest total ventral tegmental area (VTA)-projecting neurons or the intact RMTg area. The findings revealed that post-EtOH consistently reduced Pnoc and Orx levels while elevating Crf levels in these neuronal populations. Notably, RMTg Pnoc and Npy levels counteracted ethanol consumption and depression severity, while Crf levels were indicative of the mice's anxiety levels. Together, these results underscore the potential role of stress-related neuropeptides in the RMTg in regulating the negative emotions related to AUDs, offering novel insights for future research.

Animal Models of Excessive Alcohol Consumption in Rodents

The development of animal models that demonstrate excessive levels of alcohol consumption has played an important role in advancing our knowledge about neurobiological underpinnings and environmental circumstances that engender such maladaptive behavior. The use of these preclinical models has also provided valuable opportunities for discovering new and novel therapeutic targets that may be useful in the treatment of alcohol use disorder (AUD). While no single model can fully capture the complexities of AUD, the goal is to develop animal models that closely approximate characteristics of heavy alcohol drinking in humans to enhance their translational value and utility. A variety of experimental approaches have been employed to produce the desired phenotype of interest-robust and reliable excessive levels of alcohol drinking. Here we provide an updated review of five animal models that are commonly used. The models entail procedural manipulations of scheduled access to alcohol (time of day, duration, frequency), periods of time when access to alcohol is withheld, and history of alcohol exposure. Specially, the models involve (a) scheduled access to alcohol, (b) scheduled periods of alcohol deprivation, (c) scheduled intermittent access to alcohol, (d) scheduled-induced polydipsia, and (e) chronic alcohol (dependence) and withdrawal experience. Each of the animal models possesses unique experimental features that engender excessive levels of alcohol consumption. Both advantages and disadvantages of each model are described along with discussion of future work to be considered in developing more optimal models. Ultimately, the validity and utility of these models will lie in their ability to aid in the discovery of new and novel potential therapeutic targets as well as serve as a platform to evaluate treatment strategies that effectively reduce excessive levels of alcohol consumption associated with AUD.

Sex differences in binge alcohol drinking and the behavioral consequences of protracted abstinence in C57BL/6J mice

BACKGROUND

Binge alcohol drinking is a risk factor linked to numerous disease states including alcohol use disorder (AUD). While men binge drink more alcohol than women, this demographic gap is quickly shrinking, and preclinical studies demonstrate that females consistently consume more alcohol than males. Further, women are at increased risk for the co-expression of AUD with neuropsychiatric diseases such as anxiety and mood disorders. However, little is understood about chronic voluntary alcohol drinking and its long-term effects on behavior. Here, we sought to characterize sex differences in chronic binge drinking and the effects of protracted alcohol abstinence on anxiety- and affective-related behaviors in males and females.

METHODS

We assessed binge alcohol drinking patterns in male and female C57BL/6J mice using a modified Drinking in the Dark (DID) paradigm in which mice received home cage access to one bottle of 10% or 20% alcohol (EtOH) or water for 2 h per day on Days 1-3 and to two bottles (EtOH/H2O + H2O) for 24 h on Day 4 for 8 weekly cycles. Mice were then tested for the effects of protracted abstinence on avoidance, affective, and compulsive behaviors.

RESULTS

Female mice consumed more alcohol than males consistently across cycles of DID and at 2, 4, and 24-h timepoints within the day, with a more robust sex difference for 20% than 10% EtOH. Females also consumed more water than males, an effect that emerged at the later time points; this water consumption bias diminished when alcohol was available. Further, while increased alcohol consumption was correlated with decreased water consumption in males, there was no relationship between these two measures in females. Alcohol preference was higher in 10% vs. 20% EtOH for both sexes. During protracted abstinence following chronic binge drinking, mice displayed decreased avoidance behavior (elevated plus maze, open field, novelty suppressed feeding) and increased compulsive behavior (marble burying) that was especially robust in females. There was no effect of alcohol history on stress coping and negative affective behaviors (sucrose preference, forced swim test, tail suspension) in either sex.

CONCLUSION

Female mice engaged in higher volume binge drinking than their male counterparts. Although females also consumed more water than males, their higher alcohol consumption was not driven by increased total fluid intake. Further, the effects of protracted abstinence following chronic binge drinking was driven by behavioral disinhibition that was more pronounced in females. Given the reciprocal relationship between risk-taking and alcohol use in neuropsychiatric disease states, these results have implications for sex-dependent alcohol drinking patterns and their long-term negative neuropsychiatric/physiological health outcomes in humans.

Aversion-associated drug and alcohol seeking in females

Compulsive drug intake is characterized by the continuation of use regardless of negative consequences. This is modeled preclinically using procedures where a negative stimulus is delivered contingently with consumption of the reinforcer. In humans, women and men exhibit different drug taking behavior as it pertains to overall use, withdrawal symptoms, and rate of dependence. In substance use research, females have often been excluded from many studies due to concerns that circulating sex hormones may affect drug seeking behavior. However, the more recent inclusion of females in preclinical studies has identified interesting sex differences in aversion-resistant intake of drugs and alcohol. This review will serve to summarize key findings in aversion-related intake of alcohol, psychostimulants, and opioids in females by examining studies that have included female subjects. Further discussion will examine the effect of intake model, neuroanatomical pathways, and sex hormones in the expression of aversion-resistant drug and alcohol consumption.

Sex differences in binge alcohol drinking and the behavioral consequences of protracted abstinence in C57BL/6J mice

Background

Binge alcohol drinking is a risk factor linked to numerous disease states including alcohol use disorder (AUD). While men binge drink more alcohol than women, this demographic gap is quickly shrinking, and preclinical studies demonstrate that females consistently consume more alcohol than males. Further, women are at increased risk for the co-expression of AUD with neuropsychiatric diseases such as anxiety and mood disorders. However, little is understood about chronic voluntary alcohol drinking and its long-term effects on behavior. Here, we sought to characterize sex differences in chronic binge drinking and the effects of protracted alcohol abstinence on anxiety- and affective-related behaviors in males and females.

Methods

We assessed binge alcohol drinking patterns in male and female C57BL/6J mice using a modified Drinking in the Dark (DID) paradigm in which mice received home cage access to one bottle of 10% or 20% alcohol (EtOH) or water for 2 hrs per day on Days 1-3 and to two bottles (EtOH/H2O + H2O) for 24 hrs on Day 4 for eight weekly cycles. Mice were then tested for the effects of protracted abstinence on avoidance, affective, and compulsive behaviors.

Results

Female mice consumed more alcohol than males consistently across cycles of DID and at 2, 4, and 24-hr timepoints within the day, with a more robust sex difference for 20% than 10% EtOH. Females also consumed more water than males, an effect that emerged at the later time points; this water consumption bias diminished when alcohol was available. Further, while increased alcohol consumption was correlated with decreased water consumption in males, there was no relationship between these two measures in females. Alcohol preference was higher in 10% vs. 20% EtOH for both sexes. During protracted abstinence following chronic binge drinking, mice displayed decreased avoidance behavior (elevated plus maze, open field, novelty suppressed feeding) and increased compulsive behavior (marble burying) that was especially robust in females. There was no effect of alcohol history on stress coping and negative affective behaviors (sucrose preference, forced swim test, tail suspension) in either sex.

Conclusion

Female mice engaged in higher volume binge drinking than their male counterparts. Although females also consumed more water than males, their higher alcohol consumption was not driven by increased total fluid intake. Further, the effects of protracted abstinence following chronic binge drinking was driven by behavioral disinhibition that was more pronounced in females. Given the reciprocal relationship between risk-taking and alcohol use in neuropsychiatric disease states, these results have implications for sex-dependent alcohol drinking patterns and their long-term negative neuropsychiatric/physiological health outcomes in humans.

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.

Alcohol Exposure Induces Depressive and Anxiety-like Behaviors via Activating Ferroptosis in Mice

Alcohol use disorder (AUD) is a global public health problem and is frequently comorbid with mental disorders, including anxiety and depression. Ferroptosis is an iron-dependent cell death, which is involved in the pathological process of various diseases such as neurodegenerative diseases, but the role of ferroptosis in the mediation of AUD and its induced mental disorders is unclear. In this study, we aimed to investigate whether ferroptosis was involved in alcohol-induced depressive and anxiety-like behaviors in mice. Following an 8-week period of intermittent alcohol exposure, the alcohol group showed noticeable depressive and anxiety-like behaviors. In addition, nissl staining revealed that alcohol exposure induced neuron damage in the hippocampus (Hip) and prefrontal cortex (PFC) of mice. The levels of synapse-related proteins were significantly reduced in the alcohol group. Iron staining demonstrated that alcohol increased the number of iron-positive staining cells. The protein expression of the transferrin receptor (TFRC) was increased, and the expression of glutathione peroxidase 4 (GPX4) was decreased, respectively, in the alcohol group. Furthermore, the ferroptosis inhibitor ferrostatin-1 significantly prevented alcohol-induced neuron damage and enhanced the expression of N-methyl-d-aspartic acid (NMDA) receptor 2B (NR2B), α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor 1 (GluA1) and GPX4 in vitro. These results indicated that alcohol exposure could induce depressive and anxiety-like behaviors, and that this effect may occur via activating ferroptosis.

Chronic alcohol consumption alters home-cage behaviors and responses to ethologically relevant predator tasks in mice

BACKGROUND

Alcohol withdrawal is a key component of severe alcohol use disorder. Animal models of alcohol withdrawal tend to focus on traditional anxiety/stress tests. While these have been essential to advancing our understanding of the biology of alcohol withdrawal, abrupt cessation of drinking following heavy alcohol consumption can also trigger withdrawal-related affective states that impact responses to a variety of life events and stressors. To this end, we show that behaviors in a variety of tasks that differ in task demand and intensity are altered during withdrawal in male and female mice after voluntary alcohol access.

METHODS

Male and female miceunderwent six weeks of intermittent two-bottle choice alcohol exposure followed by behavioral tests. The tests included-Home cage: low-stress baseline environment to measure spontaneous natural behaviors; Open field: anxiety-inducing bright novel environment; Looming disc: arena with a protective hut where mice are exposed to a series of discs that mimic an overhead advancing predator, and Robogator-simulated predator task: forced foraging behavioral choice in the presence of an advancing robot predator that "attacks" when mice are near a food pellet in a large open arena.

RESULTS

A history of alcohol exposure impacted behaviors in these tasks in a sex-dependent manner. In the home cage, alcohol induced reductions in digging and heightened stress coping through an increase in grooming time. In males, increased rearing yielded greater vigilance/exploration in a familiar environment. The open-field test revealed an anxiety phenotype in both male and female mice exposed to alcohol. Male mice showed no behavioral alterations to the looming disc task, while females exposed to alcohol showed greater escape responses than water controls, indicative of active stress-response behaviors. In males, the Robogator task revealed a hesitant/avoidant phenotype in alcohol-exposed mice under greater task demands.

CONCLUSIONS

Few drugs show robust evidence of efficacy in clinical trials for alcohol withdrawal. Understanding how withdrawal alters a variety of behaviors in both males and females that are linked to stress coping can increase our understanding of alcohol misuse and aid in developing better medications for treating individuals with AUD.

Sex differences in stress-induced alcohol intake: a review of preclinical studies focused on amygdala and inflammatory pathways

Clinical studies suggest that women are more likely than men to relapse to alcohol drinking in response to stress; however, the mechanisms underlying this sex difference are not well understood. A number of preclinical behavioral models have been used to study stress-induced alcohol intake. Here, we review paradigms used to study effects of stress on alcohol intake in rodents, focusing on findings relevant to sex differences. To date, studies of sex differences in stress-induced alcohol drinking have been somewhat limited; however, there is evidence that amygdala-centered circuits contribute to effects of stress on alcohol seeking. In addition, we present an overview of inflammatory pathways leading to microglial activation that may contribute to alcohol-dependent behaviors. We propose that sex differences in neuronal function and inflammatory signaling in circuits centered on the amygdala are involved in sex-dependent effects on stress-induced alcohol seeking and suggest that this is an important area for future studies.

Assessing negative affect in mice during abstinence from alcohol drinking: Limitations and future challenges

Alcohol use disorder (AUD) is frequently comorbid with mood disorders, and these co-occurring neuropsychiatric disorders contribute to the development and maintenance of alcohol dependence and relapse. In preclinical models, mice chronically exposed to alcohol display anxiety-like and depressive-like behaviors during acute withdrawal and protracted abstinence. However, in total, results from studies using voluntary alcohol-drinking paradigms show variable behavioral outcomes in assays measuring negative affective behaviors. Thus, the main objective of this review is to summarize the literature on the variability of negative affective behaviors in mice after chronic alcohol exposure. We compare the behavioral phenotypes that emerge during abstinence across different exposure models, including models of alcohol and stress interactions. The complicated outcomes from these studies highlight the difficulties of assessing negative affective behaviors in mouse models designed for the study of AUD. We discuss new behavioral assays, comprehensive platforms, and unbiased machine-learning algorithms as promising approaches to better understand the interaction between alcohol and negative affect in mice. New data-driven approaches in the understanding of mouse behavior hold promise for improving the identification of mechanisms, cell subtypes, and neurocircuits that mediate negative affect. In turn, improving our understanding of the neurobehavioral basis of alcohol-associated negative affect will provide a platform to test hypotheses in mouse models that aim to improve the development of more effective strategies for treating individuals with AUD and co-occurring mood disorders.

Behavioral characterization of withdrawal following chronic voluntary ethanol consumption via intermittent two-bottle choice points to different susceptibility categories

BACKGROUND

Alcohol is among the most commonly abused drugs worldwide. Cessation of chronic alcohol consumption can result in the appearance of withdrawal symptoms that commonly promote relapse in individuals with alcohol use disorder (AUD). Thus, preclinical models of voluntary alcohol consumption, in which animals manifest spontaneous signs of withdrawal after alcohol cessation, can be useful for studying AUD and its treatment. The intermittent two-bottle choice paradigm (I2BC) has been used extensively to examine alcohol intake in rodents. However, previous studies have reported conflicting observations regarding its potential to result in the spontaneous manifestation of withdrawal upon alcohol cessation.

METHODS

We employed a battery of behavioral tests to examine the emergence of affective and physical signs of withdrawal in female and male mice exposed to alcohol in the I2BC for 10 weeks. Specifically, mice of both sexes undergoing 24-h withdrawal from the I2BC were tested for physical signs of withdrawal, anxiety-like behavior in the open field arena (OFA) and elevated plus maze (EPM), and anxiety/compulsive-like behavior in the marble burying test (MBT). The main outcomes from these tests were combined into a behavioral severity score to describe the overall behavioral phenotype.

RESULTS

Both female and male mice undergoing withdrawal from the I2BC displayed elevated physical signs of withdrawal and anxiety-associated behavior in the EPM and MBT. Analysis of the overall behavioral severity score revealed more severe phenotypes in female and male mice undergoing withdrawal from the I2BC than controls. Additionally, stratification of the mice based on severity scores demonstrated a differential distribution of severities between the exposure groups.

CONCLUSIONS

We confirmed that a significant fraction of mice chronically exposed to alcohol in the I2BC display spontaneous withdrawal. In addition, we showed that computing a severity score from a combination of behavioral metrics can be useful in preclinical research to model evaluation tools used in patients with AUD.

Sex differences in affective states and association with voluntary ethanol intake in Sprague-Dawley rats

Alcohol use disorders (AUDs) are a major problem across the USA. While AUD remains a complex human condition, it is difficult to isolate the directionality of anxiety and ethanol (EtOH) drinking from outside influences. The present study sought to investigate the relationship between affective states and EtOH intake using male and female Sprague-Dawley rats. Using complementary tests of anxiety- and depressive-like behavior, we found sex- and test-specific differences in basal affective behavior such that females displayed enhanced anxiety-like behavior in the splash test and males displayed enhanced anxiety-like behavior in the novelty-suppressed feeding test. Although, there were no sex differences in EtOH intake and no correlation between baseline anxiety-like behavior and subsequent EtOH intake, we did find that depressive-like behavior predicted future EtOH intake in female rats only. In addition, we observed an increase in depressive-like behavior is male rats in both the water and EtOH drinking groups (compared to baseline levels). Furthermore, post-drinking anxiety-like behavior, but not depressive-like behavior predicted subsequent EtOH intake in female rats. Lastly, we found a history of EtOH intake decreased pain thresholds in male and female rats, but increased anxiety-like and depressive-like behavior was associated with decreased thermal sensitivity only in EtOH-drinking males. Together, these experiments provide important information on the complex interaction between negative affect and EtOH intake and how these two contexts reciprocally do, or do not, influence each other in a sex-specific manner.

Relationship between voluntary ethanol drinking and approach-avoidance biases in the face of motivational conflict: novel sex-dependent associations in rats

RATIONALE

Aberrant approach-avoidance conflict processing may contribute to compulsive seeking that characterizes addiction. Exploration of the relationship between drugs of abuse and approach-avoidance behavior remains limited, especially with ethanol.

OBJECTIVES

To investigate the effects of voluntary ethanol consumption on approach-avoidance conflict behavior and to examine the potential approach/avoidance bias to predict drinking in male and female rats.

METHODS

Long-Evans rats consumed ethanol for 5 weeks under the intermittent access two-bottle choice (IA2BC) paradigm. Approach-avoidance tendencies were assessed before and after IA2BC drinking using a previously established cued approach-avoidance conflict maze task and the elevated plus maze (EPM).

RESULTS

Female rats displayed higher consumption of and preference for ethanol than males. In the conflict task, males showed greater approach bias towards cues predicting conflict than females. In females only, a median split and regression analysis of cued-conflict preference scores revealed that the more conflict-avoidant group displayed higher intake and preference for ethanol in the first few weeks of drinking. In both sexes, ethanol drinking did not affect cued-conflict preference, but ethanol exposure led to increased time spent in the central hub in the males only. Finally, anxiety levels in EPM predicted subsequent onset of ethanol drinking in males only.

CONCLUSIONS

Our results highlight sex and individual differences in both drinking and approach-avoidance bias in the face of cued conflict and further suggest that cued-conflict preference should be examined as a potential predictor of ethanol drinking. Ethanol exposure may also affect the timing of decision-making in the face of conflict.