Addiction Neuroscience

Genetic factors play a significant role in the risk for development of alcohol use disorder (AUD). Using 3-bottle choice intermittent access ethanol (IEA), we have employed the Diversity Outbred (DO) mouse panel as a model of alcohol use disorder in a genetically diverse population. Through use of gene expression network analysis techniques, in combination with expression quantitative trait loci (eQTL) mapping, we have completed an extensive analysis of the influence of genetic background on gene expression changes in the prefrontal cortex (PFC). This approach revealed that, in DO mice, genes whose expression was significantly disrupted by intermittent ethanol in the PFC also tended to be those whose expression correlated to intake. This finding is in contrast to previous studies of both mice and nonhuman primates. Importantly, these analyses identified genes involved in myelination in the PFC as significantly disrupted by IEA, correlated to ethanol intake, and having significant eQTLs. Genes that code for canonical components of the myelin sheath, such as Mbp, also emerged as key drivers of the gene expression response to intermittent ethanol drinking. Several regulators of myelination were also key drivers of gene expression, and had significant QTLs, indicating that genetic background may play an important role in regulation of brain myelination. These findings underscore the importance of disruption of normal myelination in the PFC in response to prolonged ethanol exposure, that genetic variation plays an important role in this response, and that this interaction between genetics and myelin disruption in the presence of ethanol may underlie previously observed behavioral changes under intermittent access ethanol drinking such as escalation of consumption.

Compulsive-like alcohol drinking (CLAD), where intake persists despite adverse consequences, is often a core facet of alcohol use disorder. Recent work sheds light on underlying mechanisms, but much remains unknown about CLAD etiology. Previously, we showed that projections from anterior insula (aINS), a central mediator of emotion, motivation, and interoception, promote CLAD in rodents, and heavy human drinkers exhibit similar insula-circuit recruitment under compulsion-like conditions. However, global aINS inhibition also reduces alcohol-only drinking (AOD), and one major obstacle is the lack of information on aINS firing patterns that could promote different aspects of intake. Here, we recorded single-unit activity in right aINS from 15 rats during AOD or CLAD (10mg/L or 60mg/L quinine in alcohol). Neurons with a sustained-increase or sustained-decrease phenotype (SIP, SDP) showed no firing differences across drinking conditions. In contrast, aINS neurons with a phenotype of strong firing increase at initiation of responding (IRP) showed significantly greater activity across the rest of licking during CLAD versus AOD, concurring with our previous behavioral findings suggesting quick evaluation and response strategy adjustment under CLAD. There were also no condition-related differences in firing-phenotype abundance. Further, total responding only correlated with abundance of SDP cells, but SDP firing returned to baseline during pauses in licking, while IRP and SIP sustained responding through pauses in licking. Thus, only aINS cells with a particular strong firing at licking onset showd greater sustained responding under compulsion-like conditions, while other cells likely promoted drinking more generally, providing critical new information about how aINS activity could promote alcohol consumption under different drinking conditions.

Investigation of rodent drinking behavior has provided insight into drivers of thirst, circadian rhythms, anhedonia, and drug and ethanol consumption. Traditional methods of recording fluid intake involve weighing bottles, which is cumbersome and lacks temporal resolution. Several open-source devices have been designed to improve drink monitoring, particularly for two-bottle choice tasks. However, recent designs are limited by the use of infrared photobeam sensors and incompatibility with prolonged undisturbed use in ventilated home cages. Beam-break sensors lack accuracy for bout microstructure analysis and are prone to damage from rodents. Thus, we designed LIQ HD (Lick Instance Quantifier Home cage Device) with the goal of utilizing capacitive sensors to increase accuracy and analyze lick microstructure, building a device compatible with ventilated home cages, increasing scale with prolonged undisturbed recordings, and creating a design that is easy to build and use with an intuitive touchscreen graphical user interface. The system tracks two-bottle choice licking behavior in up to 18 rodent cages, or 36 single bottles, on a minute-to-minute timescale controlled by a single Arduino microcontroller. The data are logged to a single SD card, allowing for efficient downstream analysis. With sucrose, quinine, and ethanol two-bottle choice tasks, we validated that LIQ HD has superior accuracy compared to photobeam sensors. The system measures preference over time and changes in bout microstructure, with undisturbed recordings lasting up to 7 days. All designs and software are open-source to allow other researchers to build upon the system and adapt LIQ HD to their animal home cages. Significance StatementTwo-bottle choice drinking tasks are traditionally performed by periodically weighing bottles, which is cumbersome and lacks temporal resolution. Several open-source tools have been developed to improve drink monitoring in various settings. However, no open-source devices have been designed specifically to investigate temporally precise two-bottle choice drinking behavior and bout microstructure during prolonged undisturbed tasks in mouse ventilated home cages at a large scale. Our design, LIQ HD (Lick Instance Quantifier Home cage Device), is a home cage compatible system that utilizes capacitive sensors for highly accurate lick detection during two-bottle choice tasks in up to 18 cages driven by a single Arduino microcontroller. The system is low-cost, easy to build, and controlled via touchscreen with an intuitive graphical user interface.

Growing parity in Alcohol Use Disorder (AUD) diagnoses in men and women necessitates consideration of sex as a biological variable. In humans and rodents, the nucleus accumbens core (NAcc) regulates alcohol binge drinking, a risk factor for developing AUD. We labeled NAcc inputs with a viral retrograde tracer and quantified whole-brain c-Fos to determine the regions and NAcc inputs differentially engaged in male and female mice during binge-like ethanol drinking. We found that binge-like ethanol drinking females had 129 brain areas with greater c-Fos than males. Moreover, ethanol engaged more NAcc inputs in binge-like ethanol drinking females (as compared with males), including GABAergic and glutamatergic inputs. Relative to water controls, ethanol increased network modularity and decreased connectivity in both sexes and did so more dramatically in males. These results demonstrate that early-stage binge-like ethanol drinking engages brain regions and NAcc-inputs and alters network dynamics in a sex-specific manner. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=86 SRC="FIGDIR/small/608144v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@c47435org.highwire.dtl.DTLVardef@1a97d69org.highwire.dtl.DTLVardef@68b2cborg.highwire.dtl.DTLVardef@1b2453a_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical Summary:C_FLOATNO Binge-like ethanol drinking engages more regions and NAcc inputs in female relative to male mice.Left: Comparison of regions with both greater c-Fos expression and c-Fos+GFP colocalization in female relative to male ethanol drinking mice. Right: NAcc inputs engaged by binge-like ethanol drinking compared to water drinking mice, sex collapsed. Thalamic (TH) regions include left parasubthalamic nucleus, left anteromedial nucleus of the thalamus, left central medial nucleus of the thalamus, left medial group of the dorsal thalamus, left subparafascicular nucleus, left peripeduncular nucleus, and right paraventricular nucleus of the thalamus. EW, Edinger-Westphal nucleus; GU, gustatory areas. Bottom Middle: NAcc inputs with greater engagement in male than female ethanol drinking mice (left and right main olfactory bulbs (MOB). Bottom Right: NAcc inputs with greater engagement in female than male ethanol drinking mice. Amygdala (AMY) regions include left anterior amygdalar area and left intercalated amygdalar area. Hippocampal (HPF) regions include right dentate gyrus, right Field CA1, right Field CA2, and right Field CA3. Hypothalamic (HY) regions include left and right lateral hypothalamic area, left and right periventricular hypothalamic nucleus, preoptic part, right dorsomedial nucleus of the hypothalamus, right posterior hypothalamic nucleus, and right ventromedial hypothalamic nucleus. Midbrain (MB) regions include left and right midbrain reticular nucleus, retrorubral area, left and right superior colliculus, motor related, left nucleus of the brachium of the inferior colliculus, left nucleus of the posterior commissure, left olivary pretectal nucleus, left posterior pretectal nucleus, left superior colliculus, sensory related, and right substantia nigra, reticular parts. Pontine (P) regions include left superior central nucleus raphe, left supratrigeminal nucleus, right nucleus raphe pontis, right pontine reticular nucleus, and right superior olivary complex. Thalamic (TH) regions include left and right lateral dorsal nucleus of the thalamus, right dorsal part of the lateral geniculate complex, right lateral posterior nucleus of the thalamus, and right parasubthalamic nucleus. CB, Cerebellum; MA, magnocellular nucleus; SSp-m, primary somatosensory cortex, mouth; Created with BioRender.com. See Table S18 for additional information. C_FIG

Problem alcohol drinking is a substantial social and economic burden. Studies show that the misuse of alcohol is increasing in women, and that women can face higher consequences from alcohol exposure, but females have historically been understudied. Thus, there is considerable interest in understanding potential sex-different and -similar cognitive/emotional strategies, and underlying mechanisms, for alcohol responding, which would inform more effective, personalized treatments. Here, we used large cohorts of adult Wistar rats (28 females, 30 males) to provide robust assessment of potential sex differences in responding for alcohol-only and under compulsion-like drinking with moderate or higher challenge (since intake despite negative consequences can be a major obstacle to human treatment). Females had similar total licking but higher intake for all drinking conditions. However, females had significantly longer bouts under alcohol-only and moderate challenge, but not higher challenge. Further, under higher challenge, females retained several aspects of responding not seen in males, including more efficient lick volume and earlier onset of longer bouts. In addition, females overall licked slightly faster, but licking speed averaged within-bout showed no sex differences, and female intake level under alcohol-only and moderate challenge was unlinked from licking speed (unlike males, where slower licking predicted lower intake). We interpret these differences as greater persistence-like responding but not vigor per se in females, and with different strategies under lower versus higher challenge. Finally, drinking levels did not differ across the estrous cycle, although ovariectomy reduced alcohol-only and moderate-challenge intake. Together, while many aspects were sex-similar, suggesting some common drinking mechanisms, there was clear evidence for (perhaps more nuanced) sex-different alcohol strategies, which might make an outsized contribution to excessive drinking since women can have more drinking problems. Thus, our studies provide important context for future work examining sex differences in pathological drinking mechanisms.

Alcohol use disorder (AUD) is a chronic behavioral disease with greater than 50% of its risk due to complex genetic contributions. Existing pharmacological and behavioral treatments for AUD are minimally effective and underutilized. Animal model behavioral genetics and human genome-wide association studies have begun to identify individual genes contributing to the progressive compulsive consumption of ethanol that occurs with AUD, promising possible new therapeutic targets. Our laboratory has previously identified Gsk3b as a central member in a network of ethanol-responsive genes in mouse prefrontal cortex, which altered ethanol consumption with genetic manipulation and was also significantly associated with risk for alcohol dependence in human genome-wide association studies. Here we perform detailed brain RNA sequencing transcriptomic studies to characterize a highly specific and clinically available GSK3B pharmacological inhibitor, tideglusib, as a possible therapeutic for clinical trials on treatment of AUD. A model of chronic intermittent ethanol consumption was used to study gene expression changes in prefrontal cortex and nucleus accumbens in the presence or absence of tideglusib treatment. Multivariate analysis of differentially expressed genes showed that tideglusib largely reversed ethanol- induced expression changes for two prominent clusters of genes in both prefrontal cortex and nucleus accumbens. Bioinformatic analysis showed these genes to have prominent roles in neuronal functioning and synaptic activity. Additionally, mouse brain differential gene expression data was analyzed together with human protein-protein interaction and genome-wide association studies on AUD to derive networks responding to tideglusib and relevant to human genetic risk for alcohol dependence. These studies identified discrete networks significantly enriched with genes provisionally associated with AUD, and provide key information on central hubs of such networks. Together these studies document tideglusib as a major modulator of chronic ethanol consumption-evoked brain gene expression signatures, and identify possible new targets for therapeutic modulation of AUD.

Continued drug-taking despite adverse consequences is hypothesized to be an insidious behavioral hallmark of drug addiction. Although most preclinical research has focused on drug self-administration in the presence of positive punishment, another source of potential adverse consequences is behavioral allocation away from negative reinforcers (i.e., escape/avoid electric shock) and towards drug reinforcers. The goals of the present study were to establish a discrete-trial cocaine-vs-negative reinforcer choice procedure in male and female rats and determine sensitivity of choice behavior to environmental and pharmacological manipulations. Rats could make up to nine discrete choices between an intravenous cocaine infusion (0.32 - 1.8 mg/kg/inf) under a fixed-ratio (FR) 3 schedule and a negative reinforcer (escape or avoidance of electric shock, 0.1 - 0.7 mA) under an FR1 schedule. The negative reinforcer was consistently chosen over all cocaine doses. Lowering shock magnitude decreased negative reinforcer trials, increased omitted trials, and failed to promote behavioral reallocation towards cocaine. Increasing the negative reinforcement response requirement between sessions only increased omitted trials. Introduction of 12-hr extended access cocaine self-administration sessions across two weeks resulted in high daily cocaine intakes but failed to significantly increase cocaine choice. Acute diazepam pretreatment also did not impact choice behavior up to doses that produced behavioral depression. Overall, the lack of behavioral allocation between cocaine infusions and a negative reinforcer suggests these two reinforcers may be economic independents. Additionally, the failure of extended cocaine access to increase cocaine choice highlights the importance of alternative reinforcers and environmental context in preclinical models of drug addiction.

The medial and orbitofrontal regions of prefrontal cortex (PFC) have been implicated in guiding optimal behavior and updating the economic value of rewards that result from choice behaviors. Both regions mature through adolescence into early adulthood and are thus vulnerable to exposure to neurotoxins, such as alcohol, during this critical developmental window. We sought to examine how voluntary alcohol consumption during adolescence would alter long-term PFC function and subsequent decision-making behavior in adulthood. Male and female rats were given adolescent intermittent ethanol (AIE) exposure to provide voluntary access to alcohol during the period of PFC maturation. In adulthood, we assessed the long-term effects on decision-making behavior using a risk task in adulthood, while concurrently recording neural activity in orbitofrontal cortex (OFC) and medial prefrontal cortex (mPFC). While control animals preferences for risky rewards increased with the likelihood of their delivery, AIE animals showed an overall reduction in their preferences for the risky option with higher levels of alcohol consumption, suggesting reduced discriminability of uncertain rewards and a shift away from the potential for reward omission. During task performance, neurons in mPFC and OFC responded to events (lever press, reward delivery). In mPFC, neurons with phasic increases at the time of lever press showed a reversal from larger elevations for risky presses in control animals to larger elevations for certain presses as prior alcohol consumption increased. Neurons in mPFC generally showed less discrimination of reward outcome with increased alcohol consumption as well. In OFC, responses to lever press were largely unaffected by AIE exposure. However, encoding of reward size in OFC showed differential effects in males and females. With higher alcohol consumption in males, OFC neurons showed largest excursions from baseline activity in response to largest reward, and smallest excursions for reward omission. This discrimination was reduced as prior alcohol consumption increased. In females, neurons with increased reward-activity, showed an overall higher level of activity due to stronger responses to certain rewards that were selected more frequently. Collectively the results show diminished capacity of PFC to encode decision-related elements to guide adaptive behavior and further clarify the lasting impact of adolescent alcohol use on neural function and behavior, even in the absence of continued use.

Delay discounting refers to the behavioral tendency to devalue rewards as a function of their delay in receipt. Heightened delay discounting has been associated with substance use disorders, as well as multiple co-occurring psychopathologies. Genetic studies in humans and animal models have established that delay discounting is a heritable trait, but only a few specific genes have been associated with delay discounting. Here, we aimed to identify novel genetic loci associated with delay discounting through a genome-wide association study (GWAS) using Heterogenous Stock rats, a genetically diverse outbred population derived from eight inbred founder strains. We assessed delay discounting in 650 male and female rats using an adjusting amount procedure in which rats chose between smaller immediate sucrose rewards or a larger reward at variable delays. Preference switch points were calculated for each rat and both exponential and hyperbolic functions were fitted to these indifference points. Area under the curve (AUC) and the discounting parameter k of both functions were used as delay discounting measures. GWAS for AUC, exponential k, and indifference points for a short delay identified significant loci on chromosomes 20 and 14. The gene Slc35f1, which encodes a member of the solute carrier family of nucleoside sugar transporters, was the only gene within the chromosome 20 locus. That locus also contained an eQTL for Slc35f1, suggesting that heritable differences in the expression of that gene might be responsible for the association with behavior. The gene Adgrl3, which encodes a member of the latrophilin family of G-protein coupled receptors, was the only gene within the chromosome 14 locus. These findings implicate novel genes in delay discounting and highlight the need for further exploration.

Alcohol use disorder (AUD) is a chronic, relapsing condition and a major public health problem. However, few medications are approved to treat AUD, and those available show limited efficacy. Drug repurposing is a cost-effective strategy to identify novel therapeutic uses for existing medications. Here, we describe a pipeline that integrates genetic and electronic health record (EHR) data to identify and evaluate drugs to be repurposed for treating AUD. Our approach comprises 1) alcohol-associated gene identification and biological network generation; 2) mapping drugs to target proteins; 3) filtering promising repurposing candidates; and 4) an exemplar pharmacoepidemiologic analysis of the effect of an identified drug (i.e., baclofen) on alcohol consumption. Linking loci to genes from a genome-wide association study (GWAS) of problematic alcohol use identified 94 genes, which we expanded to 327 alcohol-related genes through network-based analyses. Across these analyses, 52 genes were linked to 195 FDA-approved drugs, including four already approved or used off-label to treat AUD. After filtering for safety, relevance, and data availability, 26 candidate drugs, including baclofen, were selected for further evaluation. An evaluation of the real-world effectiveness of baclofen using national EHR data from the United States Department of Veterans Affairs provided evidence that baclofen-exposed patients reduced alcohol consumption more than propensity-score-matched unexposed patients. This approach, which aligns genomic findings with real-world clinical data, provides an efficient method for identifying promising drug repurposing candidates and prioritizing those that merit evaluation in randomized trials to ultimately advance pharmacotherapies for AUD.

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 M 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.

The development of drug addiction is characterized by molecular changes in brain reward regions that lead to the transition from recreational to compulsive drug use. These neurobiological processes in brain reward regions, such as the nucleus accumbens (NAc), are orchestrated in large part by transcriptional regulation. Our group recently identified the transcription factor E2F3a as a novel regulator of cocaines rewarding effects and gene expression regulation in the NAc of male mice. Despite this progress, no information is available about the role of E2F3a in regulating cocaine reward at the sex- and cell-specific levels. Here, we used male and female mice expressing Cre-recombinase in either D1- or D2-type medium spiny neurons (MSNs) combined with viral-mediated gene transfer to bidirectionally control levels of E2F3a in a cell-type-specific manner in the NAc during conditioned place preference (CPP) to cocaine. Our findings show that selective overexpression of E2F3a in D1-MSNs increased cocaine CPP in both male and female mice, whereas opposite effects were observed under knockdown conditions. In contrast, equivalent E2F3a manipulations in D2-MSNs had no significant effects. To further explore the role of E2F3a in sophisticated operant and motivated behaviors, we performed viral manipulations of all NAc neurons in combination with cocaine self-administration and behavioral economics procedures in rats and demonstrated that E2F3a regulates sensitivity aspects of cocaine seeking and taking. These results confirm E2F3a as a central substrate of cocaine reward and demonstrate that this effect is mediated in D1-MSNs, thereby providing increased knowledge of cocaine action at the transcriptional level.

Polysubstance use is prevalent in the population but remains understudied in preclinical models. Alcohol and opioid polysubstance use is associated with negative outcomes, worse treatment prognosis, and higher overdose risk; but underlying mechanisms are still being uncovered. Examining factors that motivate use of one substance over another in different contexts in preclinical models will better our understanding of polysubstance use and improve translational value. Here we assessed baseline anxiety-like and locomotive behavior and then measured voluntary consumption of multiple doses of alcohol and fentanyl in group housed male and female mice using our novel Socially Integrated Polysubstance (SIP) system. Fifty-six male (n=32) and female (n=24) adult mice were housed in groups of 4 for one week with continuous access to food, water, two doses of ethanol (5% and 10%) and two doses of fentanyl (5 ug/ml and 20 ug/ml). Our analyses revealed sex differences across multiple domains - female mice consumed more liquid in the dark cycle, had higher activity, a higher preference for both ethanol and fentanyl over water, and their fentanyl preference increased over the seven days. Furthermore, both male and female mice displayed polysubstance consumption patterns, with female mice displaying more prolonged polysubstance use across days in the SIP chambers. We then used machine-learning techniques to reveal underlying relationships between baseline behavioral phenotypes and subsequent polysubstance consumption patterns, where anxiety- and risk-taking-like behavioral phenotypes mapped onto discrete patterns of polysubstance use, preference, and escalation. By simulating more translationally relevant substance use and improving our understanding of the motivations for different patterns of consumption, this study contributes to the developing preclinical literature on polysubstance use with the goal of facilitating better treatment outcomes and novel therapeutic strategies.

Substance craving and maladaptive choices are intertwined across addictive disorders. However, the computational mechanisms connecting craving and decision-making remain elusive. Here, we tested a hypothesis that momentary craving and value-based decision-making influence each other during substance-related reinforcement learning. We measured momentary craving as two groups of human participants (alcohol drinkers and cannabis users; total n=132) performed a reinforcement learning task in which they received group-specific addictive cue or monetary rewards. Using computational modeling, we found that, across both groups, momentary craving biased learning rate related to substance-associated prediction errors (RPEs), but not monetary RPEs. Additionally, expected values and RPEs jointly influenced elicited craving across reward types and participant groups. Alcohol and cannabis users also differed in the extent to which their craving and decision-making influenced each other, suggesting important computational divergence between the two groups. Finally, regressions incorporating model-derived parameters best predicted substance use severity in the alcohol, but not cannabis group, supporting the utility of using these model-based parameters in making clinical predictions for selective substance groups. Together, these findings provide a computational mechanism for the interaction between substance craving and maladaptive choices that is generalizable across addictive domains.

While many adults consume alcohol, yet only some individuals are at a risk to develop alcohol use disorder (AUD). Variability in the risk for alcohol abuse is multifactorial and includes differences in behavioral and neuronal traits. The lateral habenula (LHb) has been shown to mediate aversive state-related behavioral responses. Interestingly, in both humans and rodents, depression-like symptoms are associated with high LHb activity. Additionally, there is a high co-morbidity between major depressive disorder and AUD. However, LHb lesions in rodents increase ethanol intake over time. Thus, we wanted to determine how baseline LHb activity correlates with ethanol intake over days. Specifically, we wanted to test whether individual variation in baseline LHb activity in ethanol-naive rats is related to home-cage ethanol drinking patterns. Hence, in this study, we determined the correlation between individual variability in baseline LHb neural activity, the negative-affective state-related ultrasonic vocalizations (USVs; 22-28 kHz), and the extent of ethanol intake over days. We first surgically implanted a unilateral 16-wire electrode array in the LHb of adult male Long Evans rats (n=11). Following recovery from surgery, rats were placed in sound-insulated chambers for two hours, where they were free to explore while we simultaneously recorded neuronal signals from their LHb and the USVs emitted by them. Next, these rats underwent an intermittent access to ethanol (IAE) paradigm, where they received 20% ethanol for 24 hours on alternate days (Monday-Wednesday-Friday) and ad-libitum water in their home cages for four weeks. The change in ethanol intake over days differed between rats, with some rats escalating their ethanol intake in the four weeks, while other rats showing no meaningful change in ethanol intake over days as compared to the first session. We found a significant negative correlation between average baseline LHb firing rates in rats and the changes in ethanol intake in the first week of IAE. Specifically, rats with higher baseline LHb firing rats, unlike rats with lower baseline firing rates, did not escalate their ethanol intake from the first session to the second and fourth ethanol sessions of the IAE paradigm. We also found a moderate positive correlation between the number of 22-28 kHz USVs and the average LHb firing rates of these rats. These results indicate that higher baseline LHb neuronal activity in normal adult ethanol naive rats is associated with decreased motivation to seek and consume ethanol during the early stages of ethanol consumption.

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 C57BL/6 mice were determined from the first 9 sessions of 2-hour 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) chronic alcohol drinking promoted behavioral engagement with alcohol, especially for individuals with less initial engagement.

Free-choice paradigms such as two-bottle choice (2BC) are commonly used to characterize ethanol consumption and preference of rodent models used to study alcohol use disorder (AUD). However, these assays are limited by low temporal resolution that misses finer patterns of drinking behavior, including circadian drinking patterns that are known to vary with age and sex and are affected in AUD pathogenesis. Modern, cost-effective tools are becoming widely available that could elucidate these patterns, including open-source, Arduino-based home-cage sipper devices. We hypothesized that adaptation of these home-cage sipper devices would uncover distinct age- and sex-related differences in temporal drinking patterns. To test this hypothesis, we used the sipper devices in a continuous 2BC paradigm using water and ethanol (10%; v/v) for 14 days to measure drinking patterns of male and female adolescent (3-week), young adult (6-week), and mature adult (18-week) C57BL/6J mice. Daily grams of fluid consumption were manually recorded at the beginning of the dark cycle, while home-cage sipper devices continuously recorded the number of sips. Consistent with prior studies, females consumed more ethanol than males, and adolescent mice consumed the most out of any age group. Correlation analyses of manually recorded fluid consumption versus home-cage sipper activity revealed a statistically significant prediction of fluid consumption across all experimental groups. Sipper activity was able to capture subtle circadian differences between experimental groups, as well as distinct individual variation in drinking behavior among animals. Blood ethanol concentrations were significantly correlated with sipper data, suggesting that home-cage sipper devices can accurately determine individual timing of ethanol consumption. Overall, our studies show that augmenting the 2BC drinking paradigm with automated home-cage sipper devices can accurately measure ethanol consumption across sexes and age groups, revealing individual differences and temporal patterns of ethanol drinking behavior. Future studies utilizing these home-cage sipper devices will further dissect circadian patterns for age and sex relevant to the pathogenesis of AUD, as well as underlying molecular mechanisms for patterns in ethanol consumption. HighlightsO_LIFemale mice consume more ethanol than males in a continuous access paradigm C_LIO_LIAdolescent male and female mice consume more ethanol than young or mature adult mice C_LIO_LIAutomated home-cage sipper devices accurately measure ethanol consumption C_LIO_LIDevices reveal sex- and age-dependent differences in circadian drinking patterns C_LIO_LIDevices reveal distinct individual variation in circadian drinking patterns C_LI

Alcohol use disorder (AUD) is characterized by the prioritization of alcohol over healthier non-alcohol rewards, posing significant challenges for addiction treatment. Understanding the neural mechanisms driving this maladaptive preference is crucial for effective intervention. We previously showed that rats will choose alcohol over social reward in a discrete-choice task. Here, we used fiber photometry to investigate how anterior insula cortex (aIC) activity relates to choice and employed Linear Ballistic Accumulator (LBA) modelling to dissect the underlying decision processes. Male and female rats, transfected with calcium indicator jGCaMP7f in aIC, were trained to lever-press for either social reward or alcohol (20% ethanol) in alternating sessions, followed by discrete-choice sessions, and then punishment of alcohol choices. Rats developed a preference for alcohol over social reward, which was reversed when alcohol choices were punished. Model output successfully described this behaviour with the model-derived decision bias tracking preference across all phases. Photometry recordings showed that, as alcohol preference emerged, increased aIC activity during the cue period preceding alcohol choices (relative to social choices) was significantly correlated with decision bias towards alcohol. During punishment, aIC activity bias was no longer related to decision bias, despite the preference shift. These results demonstrate that aIC activity is linked to alcohol reward and choice and suggest that aIC contributes to alcohol preference by encoding a bias in the evidence accumulation process. This highlights a specific role of aIC in the cognitive mechanisms of alcohol-seeking, and its potential as a target for therapeutic interventions. SignificanceUnderstanding the neural basis of prioritizing alcohol over natural rewards is critical for combating alcohol use disorder. This study investigates how anterior insula cortex (aIC) activity in rats relates to choices between alcohol and social reward. Using fiber photometry and cognitive modelling, we found that aIC activity is not only consistently higher for alcohol-related actions but also, during the decision period prior to choice. Differential activity for alcohol versus social choices significantly correlates with a model-derived "decision bias", the speed of evidence accumulation, favouring alcohol, once preference is established. This provides novel mechanistic insight, suggesting aIC contributes to alcohol preference by encoding a bias in the decision-making process, highlighting its role in alcohol seeking and as a potential therapeutic target.

Alcohol use disorder (AUD) is characterized by loss of control in limiting alcohol intake. This may involve intermittent periods of abstinence followed by alcohol seeking and, consequently, relapse. However, little is understood of the molecular mechanisms underlying the impact of alcohol deprivation on behavior. Using a new Drosophila melanogaster repeated intermittent alcohol exposure model, we sought to identify how ethanol deprivation alters spontaneous behavior, determine the associated neural structures, and reveal correlated changes in brain gene expression. We found that repeated intermittent ethanol-odor exposures followed by ethanol-deprivation dynamically induces behaviors associated with a negative affect state. Although behavioral states broadly mapped to many brain regions, persistent changes in social behaviors mapped to the mushroom body and surrounding neuropil. This occurred concurrently with changes in expression of genes associated with sensory responses, neural plasticity, and immunity. Like social behaviors, immune response genes were upregulated following three-day repeated intermittent ethanol-odor exposures and persisted with one or two days of ethanol-deprivation, suggesting an enduring change in molecular function. Our study provides a framework for identifying how ethanol deprivation alters behavior with correlated underlying circuit and molecular changes.

The gut-brain axis is a bi-directional communication system through which microbial communities in the gut interact with the nervous system, perhaps influencing neuropsychiatric disorders such as drug abuse. This study used behavioral data and biological samples from the Cocaine Biobank to test the hypothesis that the gut microbiota can predict and reflect susceptibility to cocaine reinforcement. Adult male heterogenous rats were catheterized and allowed to self-administer cocaine in short-access sessions (2 hr/day, 10 days, 0.5 mg/kg per intravenous infusion), followed by progressive ratio (PR) tests, long-access sessions (6 hr/day, 14 days), and alternating blocks of PR, long-access, and footshock testing. Fecal samples were collected at three time points and bacterial 16s rRNA genes were sequenced to profile the microbiota. As expected, cocaine-related behavior varied among subjects, such that a quartile split identified low and high responders on each measure, as well as an overall addiction index. Although beta diversity in the microbiota at baseline and after short access did not predict membership in high or low addiction quartiles, linear discriminant analysis (LDA) identified taxa that were more robustly represented in low or high responders. Beta diversity after long access was different among quartiles, as were several specific taxa. Investigation of baseline differences revealed that high relative abundance of Akkermansia muciniphila predicted future low response rates, whereas Ruminococcaceae predicted high response. This study is the first to report that microbiota variability reflects levels of cocaine intake and that microbial profiles might facilitate diagnosis and identify risk factors predictive of drug vulnerability. Significance StatementMicrobial organisms inhabiting the gut of animals appear to influence organismal function through various signaling pathways, ultimately affecting behavior and disease vulnerability. This experiment investigates links between gut bacteria and vulnerability to addiction-related behaviors in adult male rats. Not only did gut bacterial profiles change as a result of cocaine intake but also gut bacterial profiles before any exposure to cocaine predicted which animals would be high or low addiction-prone individuals. These results suggest that microbial profiles might facilitate diagnosis and identify risk factors predictive of drug addiction.