Similar ethanol drinking in adolescent and adult C57BL/6J mice after chronic ethanol exposure and withdrawal

Neuroinflammatory responses and blood-brain barrier injury in chronic alcohol exposure: role of purinergic P2 × 7 Receptor signaling

Alcohol consumption leads to neuroinflammation and blood‒brain barrier (BBB) damage, resulting in neurological impairment. We previously demonstrated that ethanol-induced disruption of barrier function in human brain endothelial cells was associated with mitochondrial injury, increased ATP and extracellular vesicle (EV) release, and purinergic receptor P2 × 7R activation. Therefore, we aimed to evaluate the effect of P2 × 7R blockade on peripheral and neuro-inflammation in ethanol-exposed mice. In a chronic intermittent ethanol (CIE)-exposed mouse model, P2 × 7R was inhibited by two different methods: Brilliant Blue G (BBG) or gene knockout. We assessed blood ethanol concentration (BEC), brain microvessel gene expression by using RT2 PCR array, plasma P2 × 7R and P-gp, serum ATP, EV-ATP, number of EVs, and EV mtDNA copy numbers. An RT2 PCR array of brain microvessels revealed significant upregulation of proinflammatory genes involved in apoptosis, vasodilation, and platelet activation in CIE-exposed wild-type animals, which were decreased 15-50-fold in BBG-treated-CIE-exposed animals. Plasma P-gp levels and serum P2 × 7R shedding were significantly increased in CIE-exposed animals. Pharmacological or genetic suppression of P2 × 7R decreased receptor shedding to levels equivalent to those in control group. The increase in EV number and EV-ATP content in the CIE-exposed mice was significantly reduced by P2 × 7R inhibition. CIE mice showed augmented EV-mtDNA copy numbers which were reduced in EVs after P2 × 7R inhibition or receptor knockout. These observations suggested that P2 × 7R signaling plays a critical role in ethanol-induced brain injury. Increased extracellular ATP, EV-ATP, EV numbers, and EV-mtDNA copy numbers highlight a new mechanism of brain injury during alcohol exposure via P2 × 7R and biomarkers of such damage. In this study, for the first time, we report the in vivo involvement of P2 × 7R signaling in CIE-induced brain injury.

Neuroinflammatory Responses and Blood-Brain Barrier Injury in Chronic Alcohol Exposure: Role of Purinergic P2X7 Receptor Signaling

Alcohol consumption leads to neuroinflammation and blood-brain barrier (BBB) damage, resulting in neurological impairment. We previously demonstrated that ethanol-induced disruption of barrier function in human brain endothelial cells was associated with mitochondrial injury, increased ATP and extracellular vesicle (EV) release, and purinergic receptor P2X7R activation. Therefore, we aimed to evaluate the effect of P2X7r blockade on peripheral and neuro-inflammation in EtOH-exposed mice. In a chronic intermittent ethanol (CIE)-exposed mouse model, P2X7R was inhibited by two different methods: Brilliant Blue G (BBG) or gene knockout. We assessed blood ethanol concentration (BEC), plasma P2X7R and P-gp, number of extra-cellular vesicles (EV), serum ATP and EV-ATP levels. Brain microvessel gene expression and EV mtDNA copy numbers were measured by RT2 PCR array and digital PCR, respectively. A RT2 PCR array of brain microvessels revealed significant upregulation of proinflammatory genes involved in apoptosis, vasodilation, and platelet activation in CIE-exposed animals, which were decreased 15-50-fold in BBG-treated CIE-exposed animals. Plasma P-gp levels and serum P2X7R shedding were significantly increased in CIE-exposed animals. Pharmacological or genetic suppression of P2X7R decreased P2X7R shedding to levels equivalent to those in control group. The increase in EV number and EV-ATP content in the CIE-exposed mice was significantly reduced by P2X7R inhibition. CIE mice showed augmented EV-mtDNA copy numbers which were reduced in EVs after P2X7R inhibition or receptor knockout. These observations suggested that P2X7R signaling plays a critical role in ethanol-induced brain injury. Increased eATP, EV-ATP, EV numbers, and EV-mtDNA copy numbers highlight a new mechanism of brain injury during alcohol exposure via P2X7R and biomarkers of such damage. In this study, for the first time, we report the in vivo involvement of P2X7R signaling in CIE-induced brain injury.

Exposure to Running Wheels Prevents Ethanol Rewarding Effects: The Role of CREB and Deacetylases SIRT-1 and SIRT-2 in the Nucleus Accumbens and Prefrontal Cortex

Alcohol use disorder is one of the most prevalent addictions, strongly influenced by environmental factors. Voluntary physical activity (VPA) has proven to be intrinsically reinforcing and we hypothesized that, as a non-drug reinforcer, VPA could mitigate ethanol-induced rewarding effects. The transcriptional factor cAMP response element binding protein (CREB), and deacetylases isozymes sirtuins 1 and 2 (SIRT-1 and SIRT-2) have a complex interplay and both play a role in the rewarding effects of ethanol. To test whether the exposure of mice to running wheels inhibits the development of ethanol-induced conditioned place preference (CPP), mice were assigned into four groups: housed in home cages with locked ("Sedentary") or unlocked running wheels (VPA), and treated with saline or 1.8 g/kg ethanol during the conditioning phase. The groups were referred as Saline-Sedentary, Saline-VPA, Ethanol-Sedentary and Ethanol-VPA. The expression of CREB, SIRT-1 and SIRT-2 were evaluated in the prefrontal cortex (PFC) and nucleus accumbens (NAc). VPA prevented the development of ethanol-induced CPP. VPA, ethanol and the combination of both inhibited pCREB and pCREB/CREB ratio in the NAc, suggesting that both reward stimuli can share similar patterns of CREB activation. However, we have found that ethanol-induced increased CREB levels were prevented by VPA. Both VPA groups presented lower SIRT-1 levels in the NAc compared to the Sedentary groups. Thus, exposure to running wheels prevented ethanol-rewarding effects and ethanol-induced increases in CREB in the NAc. The molecular alterations underlying CPP prevention may be related to a lower expression of CREB in the NAc of Ethanol-VPA compared to the respective Sedentary group, given the positive correlation between CPP and CREB levels in the Ethanol-Sedentary group.

Adolescent intermittent ethanol exposure induces sex-dependent divergent changes in ethanol drinking and motor activity in adulthood in C57BL/6J mice

With alcohol readily accessible to adolescents, its consumption leads to many adverse effects, including impaired learning, attention, and behavior. Adolescents report higher rates of binge drinking compared to adults. They are also more prone to substance use disorder in adulthood due to physiological changes during the adolescent developmental period. We used C57BL/6J male and female mice to investigate the long-lasting impact of binge ethanol exposure during adolescence on voluntary ethanol intake and open field behavior during later adolescence (Experiment 1) and during emerging adulthood (Experiment 2). The present set of experiments were divided into four stages: (1) adolescent intermittent vapor inhalation exposure, (2) abstinence, (3) voluntary ethanol intake, and (4) open field behavioral testing. During adolescence, male and female mice were exposed to air or ethanol using intermittent vapor inhalation from postnatal day (PND) 28-42. Following this, mice underwent short-term abstinence from PND 43-49 (Experiment 1) or protracted abstinence from PND 43-69 (Experiment 2). Beginning on PND 50-76 or PND 70-97, mice were assessed for intermittent voluntary ethanol consumption using a two-bottle choice drinking procedure over 28 days. Male adolescent ethanol-exposed mice showed increased ethanol consumption following short-term abstinence and following protracted abstinence. In contrast, female mice showed no changes in ethanol consumption following short-term abstinence and decreased ethanol consumption following protracted abstinence. There were modest changes in open field behavior following voluntary ethanol consumption in both experiments. These data demonstrate a sexually divergent shift in ethanol consumption following binge ethanol exposure during adolescence and differences in open field behavior. These results highlight sex-dependent vulnerability to developing substance use disorders in adulthood.

Nicotinamide riboside alleviates alcohol-induced depression-like behaviours in C57BL/6J mice by altering the intestinal microbiota associated with microglial activation and BDNF expression

The gut microbiota play an important role in many central nervous system diseases through the gut microbiota-brain axis. Recent studies suggest that nicotinamide riboside (NR) has neuroprotective properties. However, it is unknown whether NR can prevent or protect against alcohol-induced depression. Furthermore, it is unclear whether its therapeutic action involves changes in the composition of the gut microbiome. Here, we investigated the effects of NR in the mouse model of alcohol-induced depression. Treatment with NR improved the alcohol-induced depressive behaviour in mice. In addition, NR decreased the number of activated microglia in the hippocampus, and it reduced the levels of pro-inflammatory (IL-1β, IL-6, and TNF-α) and anti-inflammatory (IL-10 and TGF-β) cytokines in the brain of mice with alcohol-induced depression. Furthermore, NR significantly upregulated BDNF and diminished the inhibition of the AKT/GSK3β/β-catenin signalling pathway in the hippocampus of these mice. 16S rRNA sequencing revealed that, compared with control and NR-treated mice, the gut microbiome richness and composition were significantly altered in the depressed mice. Spearman's correlation analysis showed that differential gut bacterial genera correlated with the levels of inflammation-related cytokines and BDNF in the brain. After faecal microbiota transplantation, cognitive behaviours, microglial activity, levels of cytokines and BDNF, and activation state of the AKT/GSK3β/β-catenin signalling pathway (which is downstream of the BDNF receptor, TrkB) in recipient mice were similar to those in donor mice. Collectively, our findings show that NR dietary supplementation protects against alcohol-induced depression-like behaviours, possibly by altering the composition of the gut microbiota.

Adolescent Ethanol Exposure: Anxiety-Like Behavioral Alterations, Ethanol Intake, and Sensitivity

Adolescence is a developmental period associated with rapid age-specific physiological, neural, and hormonal changes. Behaviorally, human adolescents are characterized by age-typical increases in novelty-seeking and risk-taking, including the frequent initiation of alcohol and drug use. Alcohol use typically begins during early adolescence, and older adolescents often report high levels of alcohol consumption, commonly referred to as high-intensity drinking. Early-onset and heavy drinking during adolescence are associated with an increased risk of developing alcohol use disorders later in life. Yet, long-term behavioral consequences of adolescent alcohol use that might contribute to excessive drinking in adulthood are still not well understood. Recent animal research, however, using different exposure regimens and routes of ethanol administration, has made substantial progress in identifying the consequences of adolescent ethanol exposure that last into adulthood. Alterations associated with adolescent ethanol exposure include increases in anxiety-like behavior, impulsivity, risk-taking, and ethanol intake, although the observed alterations differ as a function of exposure regimens and routes of ethanol administration. Rodent studies have also shown that adolescent ethanol exposure produces alterations in sensitivity to ethanol, with these alterations reminiscent of adolescent-typical ethanol responsiveness. The goal of this mini-review article is to summarize the current state of animal research, focusing on the long-term consequences related to adolescent ethanol exposure, with a special emphasis on the behavioral alterations and changes to ethanol sensitivity that can foster high levels of drinking in adulthood.

Neonatal alcohol exposure augments voluntary ethanol intake in the absence of potentiated anxiety-like behavior induced by chronic intermittent ethanol vapor exposure

Individuals fetally exposed to alcohol have a disproportionate risk for developing lifetime alcohol dependence, an association that may be confounded by the presence of comorbid conditions, such as anxiety. Anxiety is also observed following fetal alcohol exposure and is known to exacerbate ethanol consumption, highlighting the utility of animal models to assess this relationship. The present study evaluated the impact of third-trimester equivalent ethanol exposure on ethanol consumption and anxiety-like, marble burying behavior in adult, male C57BL/6 mice following exposure to chronic intermittent ethanol vapor, proposed to model dependence. Neonatal mice (P5-6, 2.5-3.0 g) were administered one injection of saline or ethanol (2.5 g/kg, subcutaneously [s.c.]). Pre-vapor marble burying and limited-access two-bottle choice ethanol intake (15% v/v, 2 h) were comparable in adults (8 weeks of age) across neonatal treatment groups. Five consecutive drinking sessions were repeated 72 h after each weekly ethanol vapor exposure procedure for a total of five vapor/drinking cycles. Consistent with prior research, an increase in voluntary ethanol drinking was observed in vapor-exposed, neonatal saline-treated mice throughout the study starting after the second vapor cycle compared to both air-exposed control groups. In neonatal ethanol-treated mice, this increase in ethanol intake and preference following vapor exposure was accelerated, being observed after the first vapor cycle, and observed at an augmented level compared to vapor-exposed, neonatal saline-treated mice and air controls for both neonatal conditions. Conversely, marble burying was enhanced equivalently in vapor-exposed mice from either neonatal treatment group relative to their respective air-exposed controls. These data recapitulate clinical observations of enhanced sensitivity for alcohol dependence following developmental alcohol exposure, which may reflect enhanced motivational drive rather than potentiated negative affect. The present model will facilitate the future exploration of mechanisms that underlie increased risk for alcohol use after early developmental exposure.

Chronic Ethanol During Adolescence Impacts Corticolimbic Dendritic Spines and Behavior

BACKGROUND

Risk for alcohol use disorders (AUDs) in adulthood is linked to alcohol drinking during adolescence, but understanding of the neural and behavioral consequences of alcohol exposure during adolescence remains incomplete. Here, we examined the neurobehavioral impact of adolescent chronic intermittent EtOH (CIE) vapor exposure in mice.

METHODS

C57BL/6J-background Thy1-EGFP mice were CIE-exposed during adolescence or adulthood and examined, as adults, for alterations in the density and morphology of dendritic spines in infralimbic (IL) cortex, prelimbic (PL) cortex, and basolateral amygdala (BLA). In parallel, adolescent- and adult-exposed C57BL/6J mice were tested as adults for 2-bottle EtOH drinking, sensitivity to EtOH intoxication (loss of righting reflex [LORR]), blood EtOH clearance, and measures of operant responding for food reward.

RESULTS

CIE during adolescence decreased IL neuronal spine density and increased the head width of relatively wide-head IL and BLA spines, whereas CIE decreased head width of relatively narrow-head BLA spines. Adolescents had higher EtOH consumption prior to CIE than adults, while CIE during adulthood, but not adolescence, increased EtOH consumption relative to pre-CIE baseline. CIE produced a tolerance-like decrease in LORR sensitivity to EtOH challenge, irrespective of the age at which mice received CIE exposure. Mice exposed to CIE during adolescence, but not adulthood, required more sessions than AIR controls to reliably respond for food reward on a fixed-ratio (FR) 1, but not subsequent FR3, reinforcement schedule. On a progressive ratio reinforcement schedule, break point responding was higher in the adolescent- than the adult-exposed mice, regardless of CIE. Finally, footshock punishment markedly suppressed responding for reward in all groups.

CONCLUSIONS

Exposure to CIE during adolescence altered dendritic spine density and morphology in IL and BLA neurons, in parallel with a limited set of behavioral alterations. Together, these data add to growing evidence that key corticolimbic circuits are vulnerable to the effects of alcohol during adolescence, with lasting, potentially detrimental, consequences for behavior.

Ethanol Sensitization during Adolescence or Adulthood Induces Different Patterns of Ethanol Consumption without Affecting Ethanol Metabolism

In previous study, we demonstrated that ethanol preexposure may increase ethanol consumption in both adolescent and adult mice, in a two-bottle choice model. We now questioned if ethanol exposure during adolescence results in changes of consumption pattern using a three-bottle choice procedure, considering drinking-in-the-dark and alcohol deprivation effect as strategies for ethanol consumption escalation. We also analyzed aldehyde dehydrogenase (ALDH) activity as a measurement of ethanol metabolism. Adolescent and adult Swiss mice were treated with saline (SAL) or 2.0 g/kg ethanol (EtOH) during 15 days (groups: Adolescent-SAL, Adolescent-EtOH, Adult-SAL and Adult-EtOH). Five days after the last injection, mice were exposed to the three-bottle choice protocol using sucrose fading procedure (4% + sucrose vs. 8%–15% ethanol + sucrose vs. water + sucrose) for 2 h during the dark phase. Sucrose was faded out from 8% to 0%. The protocol was composed of a 6-week acquisition period, followed by four withdrawals and reexposures. Both adolescent and adult mice exhibited ethanol behavioral sensitization, although the magnitude of sensitization in adolescents was lower than in adults. Adolescent-EtOH displayed an escalation of 4% ethanol consumption during acquisition that was not observed in Adult-EtOH. Moreover, Adult-EtOH consumed less 4% ethanol throughout all the experiment and less 15% ethanol in the last reexposure period than Adolescent-EtOH. ALDH activity varied with age, in which older mice showed higher ALDH than younger ones. Ethanol pretreatment or the pattern of consumption did not have influence on ALDH activity. Our data suggest that ethanol pretreatment during adolescence but not adulthood may influence the pattern of ethanol consumption toward an escalation in ethanol consumption at low dose, without exerting an impact on ALDH activity.

Sex differences in the behavioral sequelae of chronic ethanol exposure

Rates of alcohol use disorders (AUDs) differ between men and women, and there is also marked variation between sexes in the effects of acute and chronic alcohol. In parallel to observations in humans, prior studies in rodents have described male/female differences across a range of ethanol-related behaviors, including ethanol drinking. Nonetheless, there remain gaps in our knowledge of the role of sex in moderating the effects of ethanol, particularly in models of chronic ethanol exposure. The goal of the current study was to assess various behavioral sequelae of exposing female C57BL/6J mice to chronic intermittent ethanol (CIE) via ethanol vapors. Following four weeks of CIE exposure, adult male and female mice were compared for ethanol drinking in a two-bottle paradigm, for sensitivity to acute ethanol intoxication (via loss of righting reflex [LORR]) and for anxiety-like behaviors in the novelty-suppressed feeding and marble burying assays. Next, adult and adolescent females were tested on two different two-bottle drinking preparations (fixed or escalating ethanol concentration) after CIE. Results showed that males and females exhibited significantly blunted ethanol-induced LORR following CIE, whereas only males showed increased anxiety-like behavior after CIE. Increased ethanol drinking after CIE was also specific to males, but high baseline drinking in females may have occluded detection of a CIE-induced effect. The failure to observe elevated drinking in females in response to CIE was also seen in females exposed to CIE during adolescence, regardless of whether a fixed or escalating ethanol-concentration two-bottle procedure was employed. Collectively, these data add to the literature on sex differences in ethanol-related behaviors and provide a foundation for future studies examining how the neural consequences of CIE might differ between males and females.

Binge ethanol withdrawal: Effects on post-withdrawal ethanol intake, glutamate-glutamine cycle and monoamine tissue content in P rat model

Alcohol withdrawal syndrome (AWS) is a medical emergency situation which appears after abrupt cessation of ethanol intake. Decreased GABA-A function and increased glutamate function are known to exist in the AWS. However, the involvement of glutamate transporters in the context of AWS requires further investigation. In this study, we used a model of ethanol withdrawal involving abrupt cessation of binge ethanol administration (4 g/kg/gavage three times a day for three days) using male alcohol-preferring (P) rats. After 48 h of withdrawal, P rats were re-exposed to voluntary ethanol intake. The amount of ethanol consumed was measured during post-withdrawal phase. In addition, the expression of GLT-1, GLAST and xCT were determined in both medial prefrontal cortex (mPFC) and nucleus accumbens (NAc). We also measured glutamine synthetase (GS) activity, and the tissue content of glutamate, glutamine, dopamine and serotonin in both mPFC and NAc. We found that binge ethanol withdrawal escalated post-withdrawal ethanol intake, which was associated with downregulation of GLT-1 expression in both mPFC and NAc. The expression of GLAST and xCT were unchanged in the ethanol-withdrawal (EW) group compared to control group. Tissue content of glutamate was significantly lower in both mPFC and NAc, whereas tissue content of glutamine was higher in mPFC but unchanged in NAc in the EW group compared to control group. The GS activity was unchanged in both mPFC and NAc. The tissue content of DA was significantly lower in both mPFC and NAc, whereas tissue content of serotonin was unchanged in both mPFC and NAc. These findings provide important information of the critical role of GLT-1 in context of AWS.

Concomitant stress potentiates the preference for, and consumption of, ethanol induced by chronic pre-exposure to ethanol

Ethanol abuse is linked to several acute and chronic injuries that can lead to health problems. Ethanol addiction is one of the most severe diseases linked to the abuse of this drug. Symptoms of ethanol addiction include compulsive substance intake and withdrawal syndrome. Stress exposure has an important role in addictive behavior for many drugs of abuse (including ethanol), but the consequences of stress and ethanol in the organism when these factors are concomitant results in a complex interaction. We investigated the effects of concomitant, chronic administration of ethanol and stress exposure on the withdrawal and consumption of, as well as the preference for, ethanol in mice. Male Swiss mice (30-35 g, 8-10 per group) were exposed to an ethanol liquid diet as the only source of food for 15 days. In the final 5 days, they were exposed to forced swimming stress. Twelve hours after removal of the ethanol liquid diet, animals were evaluated for ethanol withdrawal by measuring anxiety-related behaviors and locomotor activity. Twenty-four hours after evaluation of ethanol withdrawal, they were evaluated for voluntary consumption of ethanol in a "three-bottle choice" paradigm. Mice exposed to chronic consumption of ethanol had decreased locomotor activity during withdrawal. Contrary to our expectations, a concomitant forced swimming stress did not aggravate ethanol withdrawal. Nevertheless, simultaneous ethanol administration and stress exposure increased voluntary consumption of ethanol, mainly solutions containing high concentrations of ethanol. These results showed that stressful situations during ethanol intake may aggravate specific addiction-related behaviors.

Effects of chronic ethanol exposure on neuronal function in the prefrontal cortex and extended amygdala

Chronic alcohol consumption and withdrawal leads to anxiety, escalated alcohol drinking behavior, and alcohol dependence. Alterations in the function of key structures within the cortico-limbic neural circuit have been implicated in underlying the negative behavioral consequences of chronic alcohol exposure in both humans and rodents. Here, we used chronic intermittent ethanol vapor exposure (CIE) in male C57BL/6J mice to evaluate the effects of chronic alcohol exposure and withdrawal on anxiety-like behavior and basal synaptic function and neuronal excitability in prefrontal cortical and extended amygdala brain regions. Forty-eight hours after four cycles of CIE, mice were either assayed in the marble burying test (MBT) or their brains were harvested and whole-cell electrophysiological recordings were performed in the prelimbic and infralimbic medial prefrontal cortex (PLC and ILC), the lateral and medial central nucleus of the amygdala (lCeA and mCeA), and the dorsal and ventral bed nucleus of the stria terminalis (dBNST and vBNST). Ethanol-exposed mice displayed increased anxiety in the MBT compared to air-exposed controls, and alterations in neuronal function were observed in all brain structures examined, including several distinct differences between subregions within each structure. Chronic ethanol exposure induced hyperexcitability of the ILC, as well as a shift toward excitation in synaptic drive and hyperexcitability of vBNST neurons; in contrast, there was a net inhibition of the CeA. This study reveals extensive effects of chronic ethanol exposure on the basal function of cortico-limbic brain regions, suggests that there may be complex interactions between these regions in the regulation of ethanol-dependent alterations in anxiety state, and highlights the need for future examination of projection-specific effects of ethanol in cortico-limbic circuitry.

Alcohol dependence and free-choice drinking in mice

Alcohol dependence continues to be an important health concern and animal models are critical to furthering our understanding of this complex disease. A hallmark feature of alcoholism is a significant increase in alcohol drinking over time. While several different animal models of excessive alcohol (ethanol) drinking exist for mice and rats, a growing number of laboratories are using a model that combines chronic ethanol exposure procedures with voluntary ethanol drinking with mice as experimental subjects. Primarily, these studies use a chronic intermittent ethanol (CIE) exposure pattern to render mice dependent and a 2-h limited access procedure to evaluate drinking behavior. Compared to non-dependent mice that also drink ethanol, the ethanol-dependent mice demonstrate significant increases in voluntary ethanol drinking. The increased drinking significantly elevates blood and brain ethanol concentrations compared to the non-dependent control mice. Studies report that the increased drinking by dependent mice is driven by neuroadaptations in glutamatergic and corticotropin-releasing factor signaling in different brain regions known to be involved in alcohol-related behaviors. The dysregulation of these systems parallels findings in human alcoholics and treatments that demonstrate efficacy in alcoholics can also reduce drinking in this model. Moreover, preclinical findings have informed the development of human clinical trials, further highlighting the translational potential of the model. As a result of these features, the CIE exposure and free-choice drinking model is becoming more widely used and promises to provide more insight into mechanisms of excessive drinking that may be important for developing treatments for human alcoholics. The salient features and possible future considerations for CIE exposure and free-choice drinking in mice are discussed.

The Effect of mGluR5 Antagonism During Binge Drinkingon Subsequent Ethanol Intake in C57BL/6J Mice: Sex- and Age-Induced Differences

BACKGROUND

Binge ethanol (EtOH) intake during adolescence leads to an array of behavioral and cognitive consequences including elevated intake of EtOH during adulthood, with female mice showing greater susceptibility than males. Administration of the metabotropic glutamate receptor 5 (mGluR5) antagonist 3-((2-Methyl-1,3-thiazol-4-yl)ethynyl)pyridine (MTEP) has been shown to reduce EtOH self-administration in adult male mice, but little is known about its effect on female and adolescent mice.

METHODS

MTEP (0, 10, 20 mg/kg, i.p.) was repeatedly administered to female and male, adult and adolescent C57BL/6J mice during binge sessions using the scheduled high alcohol consumption paradigm. Next, we assessed whether MTEP administration during binge altered the subsequent 24-hour EtOH intake following a period of abstinence. Finally, we investigated whether MTEP administration during binge followed by an abstinence period altered mRNA of glutamatergic genes within the nucleus accumbens of female mice.

RESULTS

MTEP significantly decreased binge EtOH intake in all mice, but only female mice exhibited altered subsequent 24-hour EtOH intake. Interestingly, the alteration in subsequent EtOH intake in female animals was age dependent, with adolescent exposure to MTEP during binge decreasing 24-hour intake and adult exposure to MTEP during binge increasing 24-hour intake. Finally, while there were no effects of MTEP pretreatment on the genes examined, there was a robust age effect found during analysis of mGluR1 (Grm1), mGluR5 (Grm5), the NR2A subunit of the NMDA receptor (Grin2a), phosphatidylinositol 3-kinase (Pik3r1), mammalian target of rapamycin (Mtor), and extracellular signal-regulated kinase (Mapk1) mRNA, with adolescent female animals having lower expression than their adult counterparts.

CONCLUSIONS

Collectively, the present findings add to existing evidence implicating the contribution of long-term effects of adolescent binge drinking to enhance alcohol abuse in adulthood, while suggesting that mGluR5 antagonism may not be the best pharmacotherapy to treat binge alcohol consumption in female and adolescent animals.