The neurobiology of binge-like ethanol drinking: evidence from rodent models

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

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

Changes in ethanol effects in knock-in mice expressing ethanol insensitive alpha1 and alpha2 glycine receptor subunits

AIMS

Glycine receptors (GlyRs) are potentiated by physiologically relevant concentrations of ethanol, and mutations in the intracellular loop of α1 and α2 subunits reduced the effect of the drug. Knock-in (KI) mice having these individual mutations revealed that α1 and α2 subunits played a role in ethanol-induced sedation and ethanol intake. In this study, we wanted to examine if the effects of stacking both mutations in a 2xKI mouse model (α1/α2) generated by a selective breeding strategy further impacted cellular and behavioral responses to ethanol.

MAIN METHODS

We used electrophysiological recordings to examine ethanol's effect on GlyRs and evaluated ethanol-induced neuronal activation using c-Fos immunoreactivity and the genetically encoded calcium indicator GCaMP6s in the nucleus accumbens (nAc). We also examined ethanol-induced behavior using open field, loss of the righting response, and drinking in the dark (DID) paradigm.

KEY FINDINGS

Ethanol did not potentiate GlyRs nor affect neuronal excitability in the nAc from 2xKI. Moreover, ethanol decreased the Ca2+ signal in WT mice, whereas there were no changes in the signal in 2xKI mice. Interestingly, there was an increase in c-Fos baseline in the 2xKI mice in the absence of ethanol. Behavioral assays showed that 2xKI mice recovered faster from a sedative dose of ethanol and had higher ethanol intake on the first test day of the DID test than WT mice. Interestingly, an open-field assay showed that 2xKI mice displayed less anxiety-like behavior than WT mice.

SIGNIFICANCE

The results indicate that α1 and α2 subunits are biologically relevant targets for regulating sedative effects and ethanol consumption.

Cholinergic Interneurons in the Accumbal Shell Region Regulate Binge Alcohol Self-Administration in Mice: An In Vivo Calcium Imaging Study

Recently, we and others have shown that manipulating the activity of cholinergic interneurons (CIN) present in the NAc can modulate binge alcohol consumption. The present study is designed to examine the relationship between binge alcohol consumption and the activity of the CIN in real time by using an in vivo microendoscopic technique. We hypothesized that mice exposed to Drinking in the Dark (DID)-a recognized mouse model for binge drinking-would exhibit increased activity in the accumbal shell region (NAcSh). To test this hypothesis, male mice expressing Cre-recombinase in the cholinergic neurons were exposed to binge alcohol consumption (alcohol group), employing the DID method, and utilized in vivo calcium imaging to observe CIN activity in real time during alcohol consumption. The control (sucrose) group was exposed to 10% (w/v) sucrose. As compared to sucrose, mice in the alcohol group displayed a significant increase in the frequency and amplitude of discharge activity, which was measured using calcium transients in the CIN present in the NAcSh. In summary, our findings suggest that the activity of CIN in the NAcSh plays a crucial role in alcohol self-administration. These results emphasize the potential significance of targeting CIN activity as a therapeutic approach for addressing AUD.

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

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

Basolateral amygdala neuropeptide Y system modulates binge ethanol consumption

Neuropeptide Y (NPY) signaling regulation of corticolimbic communication is known to modulate binge-like ethanol consumption in rodents. In this work we sought to assess the impact of intra-BLA NPY system modulation on binge-like ethanol intake and to assess the role of the NPY1R+ projection from the BLA to the mPFC in this behavior. We used "drinking-in-the-dark" (DID) procedures in C57BL6J mice to address these questions. First, the impact of intra-BLA administration of NPY on binge-like ethanol intake was assessed. Next, the impact of repeated cycles of DID intake on NPY1R expression in the BLA was assessed with use of immunohistochemistry (IHC). Finally, chemogenetic inhibition of BLA→mPFC NPY1R+ projections was assessed to determine if limbic communication with the mPFC was specifically involved in binge-like ethanol intake. Importantly, as both the BLA and NPY system are sexually dimorphic, both sexes were assessed in these studies. Intra-BLA NPY dose-dependently decreased binge-like ethanol intake in males only. Repeated DID reduced NPY1R expression in the BLA of both sexes. Silencing of BLA→mPFC NPY1R+ neurons significantly reduced binge-like ethanol intake in both sexes in a dose-dependent manner. We provide novel evidence that (1) intra-BLA NPY reduces binge-like ethanol intake in males; (2) binge-like ethanol intake reduces NPY1R levels in the BLA; and (3) chemogenetic inhibition of BLA→mPFC NPY1R+ neurons blunts binge-like drinking in male and female mice. These observations provide the first direct evidence that NPY signaling in the BLA, and specifically BLA communication with the mPFC, modulates binge-like ethanol consumption.

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

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

Chemogenetic inhibition of locus coeruleus to rostromedial tegmental nucleus noradrenergic pathway increases light cycle ethanol drinking in male and female mice and blunts ethanol-induced CTA

We recently showed that chemogenetic activation of the locus coeruleus (LC) to the rostromedial tegmental nucleus (RMTg) noradrenergic (NE) pathway significantly blunted binge-like ethanol drinking and induced aversive-like behaviors in mice. The aim of the present study is to determine if silencing this TH + LC → RMTg noradrenergic pathway promotes increased levels of binge-like ethanol intake and reduced ethanol-induced conditioned taste aversion (CTA). To this end, both male and female TH-ires-cre mice on a C57BL/6 J background were cannulated in the RMTg and injected in the LC with rAVV viruses that encode cre-dependent Gi-expressing designer receptor exclusively activated by designer drugs (DREADDs), or its control, to directly control the activity of NE neurons. Inhibition of the LC to RMTg pathway had no effect on the binge-ethanol drinking in a "drinking-in-the-dark" (DID) paradigm. However, when using this paradigm during the light cycle, silencing of this circuit significantly increased ethanol intake without altering sucrose drinking. Moreover, we found that inhibition of this circuit significantly attenuated an ethanol-induced CTA. In addition, when compared to control animals, pairing RMTg-directed Clozapine N-oxide (CNO) with an i.p. injection of 1.5 g/kg ethanol reduced c-Fos activation in the LC, and increased c-Fos expression in the ventral tegmental area (VTA) in Gi-expressing mice. Our data show that inhibition of the TH + LC to the RMTg pathway significantly increased ethanol drinking as well as attenuated ethanol-induced CTA, supporting the involvement of the LC to RMTg noradrenergic circuit as an important protective mechanism against excessive ethanol consumption.

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

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

Chronic alcohol metabolism results in DNA repair infidelity and cell cycle-induced senescence in neurons

Chronic binge-like drinking is a risk factor for age-related dementia, however, the lasting and irreversible effect of alcohol on the brain remains elusive. Transcriptomic changes in brain cortices revealed pro-ageing hallmarks upon chronic ethanol exposure and these changes predominantly occur in neurons. The changes are attributed to a prioritized ethyl alcohol oxidation in these cells via the NADPH-dependent cytochrome pathway. This hijacks the folate metabolism of the 1-carbon network which supports the pathway choice of DNA repair via the non-cell cycle-dependent mismatch repair networks. The lost-in-function of such results in the de-inactivation of the less preferred cell cycle-dependent homologous recombination (HR) repair, forcing these post-mitotic cells to re-engage in a cell cycle-like process. However, mature neurons are post-mitotic. Therefore, instead of successfully completing a full round of cell cycle which is necessary for the completion of HR-mediated repair; these cells are arrested at checkpoints. The resulting persistence of repair intermediates induces and promotes the nuclear accumulation of p21 and cyclin B-a trigger for permanent cell cycle exits and irreversible senescence response. Supplementation of bioactive 5-methyl tetrahydrofolate simultaneously at times with ethyl alcohol exposure supports the fidelity of the 1-carbon network and hence the activity of the mismatch repair. This prevents aberrant and irreversible cell cycle re-entry and senescence events of neurons. Together, our findings offer a direct connection between binge-drinking behaviour and its irreversible impact on the brain, which makes it a potential risk factor for dementia.

Chemogenetic inhibition of corticotropin-releasing factor neurons in the central amygdala alters binge-like ethanol consumption in male mice

Repetitive bouts of binge drinking can lead to neuroplastic events that alter ethanol's pharmacologic effects and perpetuate excessive consumption. The corticotropin-releasing factor (CRF) system is an example of ethanol-induced neuroadaptations that drive excessive ethanol consumption. Our laboratory has previously shown that CRF antagonist, when infused into the central amygdala (CeA), reduces binge-like ethanol consumption. The present study extends this research by assessing the effects of silencing CRF-producing neurons in CeA on binge-like ethanol drinking stemming from "Drinking in the Dark" (DID) procedures. CRF-ires-Cre mice underwent surgery to infuse Gi/o-coupled Designer Receptors Exclusively Activated by Designer Drugs (DREADD) virus or a control virus into either the CeA or basolateral amygdala (BLA). Gi/o-DREADD-induced CRF-neuronal inhibition in the CeA resulted in a 33% decrease in binge-like ethanol consumption. However, no effect on ethanol consumption was seen after DREADD manipulation in the BLA. Moreover, CeA CRF-neuronal inhibition had no effect on sucrose consumption. The effects of silencing CRF neurons in the CeA on ethanol consumption are not secondary to changes in motor function or anxiety-like behaviors as assessed in the open-field test (OFT). Finally, the DREADD construct's functional ability to inhibit CRF-neuronal activity was demonstrated by reduced ethanol-induced c-Fos following DREADD activation. Together, these data suggest that the CRF neurons in the CeA play an important role in binge ethanol consumption and that inhibition of the CRF-signaling pathway remains a viable target for manipulating binge-like ethanol consumption. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Targeting the Maladaptive Effects of Binge Drinking on Circadian Gene Expression

Previous studies (1) support a role of circadian genes in regulating alcohol intake, and (2) reveal that harmful alcohol use alters circadian rhythms. However, there is minimal knowledge of the effects of chronic alcohol processes on rhythmic circadian gene expression across brain regions important for circadian biology and alcohol intake. Therefore, the present study sought to test the effects of chronic binge-like drinking on diurnal circadian gene expression patterns in the master circadian pacemaker (SCN), the ventral tegmental area (VTA), and the nucleus accumbens (NAc) in High Drinking in the Dark-1 (HDID-1) mice, a unique genetic risk model for drinking to intoxication. Consistent with earlier findings, we found that 8 weeks of binge-like drinking reduced the amplitude of several core circadian clock genes in the NAc and SCN, but not the VTA. To better inform the use of circadian-relevant pharmacotherapies in reducing harmful drinking and ameliorating alcohol's effects on circadian gene expression, we tested whether the casein kinase-1 inhibitor, PF-67046, or the phosphodiesterase type-4 (an upstream regulator of circadian signalling) inhibitor, apremilast, would reduce binge-like intake and mitigate circadian gene suppression. PF-67046 did not reduce intake but did have circadian gene effects. In contrast, apremilast reduced drinking, but had no effect on circadian expression patterns.

Lateral habenula-projecting central amygdala circuits expressing GABA and NPY Y1 receptor modulate binge-like ethanol intake in mice

The central nucleus of the amygdala (CeA) is a critical brain region in the integration of emotional behaviors and is one of the major output areas of the amygdaloid complex. The CeA is composed of GABAergic interneurons and projection neurons which co-express a range of peptides including neuropeptide Y (NPY). Importantly, GABA and NPY signaling, via the NPY Y1 receptor (Y1R), in the CeA modulate binge-like ethanol intake in rodents and these systems undergo neuroplastic alterations following a history of ethanol consumption. Here we assessed the roles of GABAergic and Y1R+ circuits arising from the CeA and innervating the lateral habenula (LHb), a brain region that modulates the aversive properties of ethanol, in modulating binge-like ethanol intake in mice using "drinking in the dark" (DID) procedures. Using an anterograde cre-inducible reporter virus we established the CeA → LHb circuit in male and female vgat-ires-cre and NPY1r-cre mice. Next, we found that chemogenetic silencing of both the GABAergic or Y1R+ CeA → LHb circuit significantly blunted binge-like intake of a 20% ethanol solution but this same procedure failed to alter the consumption of a 3% sucrose solution. Finally, one, 4-day cycle of DID failed to alter basal or effects of ethanol or NPY on inhibitory transmission in Y1R+ CeA → LHb neurons. The present results suggest that blunting GABAergic tone in LHb-projecting CeA neurons may represent a new approach to preventing the development of AUDs. Drugs that target NPY Y1Rs are potential attractive targets.

Activation of the dorsal septum increases alcohol consumption in male C57BL/6J mice

Binge drinking is a common pattern of excessive alcohol consumption associated with Alcohol Use Disorder (AUD) and unraveling the neurocircuitry that promotes this type of drinking is critical to the development of novel therapeutic interventions. The septal region was once a focal point of alcohol research yet has seen limited study over the last decade in relation to binge drinking. Numerous studies point to involvement of the dorsal septum (dSep) in excessive drinking and withdrawal, but few studies have manipulated this region in the context of binge drinking behavior. The present experiments were primarily designed to determine the effect of chemogenetic manipulation of the dSep on binge-like alcohol drinking in male and female C57BL/6J mice. Mice received bilateral infusion of AAVs harboring hM4Di, hM3Dq, or mCherry into the dSep and subjects were challenged with systemic administration of clozapine-N-oxide (CNO) and vehicle in the context of binge-like alcohol consumption, locomotor activity, and sucrose drinking. CNO-mediated activation (hM3Dq) of the dSep resulted in increased binge-like alcohol consumption, locomotor activity, and sucrose intake in males. DSep activation promoted sucrose drinking in female mice, but alcohol intake and locomotor activity were unaffected. Conversely, silencing (hM4Di) of the dSep modestly decreased locomotor activity in males and did not influence alcohol or sucrose intake in either sex. These data support a role for the dSep in promoting binge-like drinking behavior in a sex-dependent fashion and suggests a broad role for the region in the modulation of general appetitive behaviors and locomotor activity.

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

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

Sleep, sleep homeostasis and arousal disturbances in alcoholism

The effects of alcohol on human sleep were first described almost 70 years ago. Since then, accumulating evidences suggest that alcohol intake at bed time immediately induces sleep [reduces the time to fall asleep (sleep onset latency), and consolidates and enhances the quality (delta power) and the quantity of sleep]. Such potent sleep promoting activity makes alcohol as one of the most commonly used "over the counter" sleep aid. However, the somnogenic effects, after alcohol intake, slowly wane off and often followed by sleep disruptions during the rest of the night. Repeated use of alcohol leads to the development of rapid tolerance resulting into an alcohol abuse. Moreover, chronic and excessive alcohol intake leads to the development of alcohol use disorder (AUD). Alcoholics, both during drinking periods and during abstinences, suffer from a multitude of sleep disruptions manifested by profound insomnia, excessive daytime sleepiness, and altered sleep architecture. Furthermore, subjective and objective indicators of sleep disturbances are predictors of relapse. Finally, within the USA, it is estimated that societal costs of alcohol-related sleep disorders exceed $18 billion. Thus, although alcohol associated sleep problems have significant economic and clinical consequences, very little is known about how and where alcohol acts to affect sleep. In this review, a conceptual framework and clinical research focused on understanding the relationship between alcohol and sleep is first described. In the next section, our new and exciting preclinical studies, to understand the cellular and molecular mechanism of how acute and chronic alcohol affects sleep, are described. In the end, based on observations from our recent findings and related literature, opportunities for the development of innovative strategies to prevent and treat AUD are proposed.

Activation of locus coeruleus to rostromedial tegmental nucleus (RMTg) noradrenergic pathway blunts binge-like ethanol drinking and induces aversive responses in mice

There is strong evidence that ethanol entails aversive effects that can act as a deterrent to overconsumption. We have found that in doses that support the development of a conditioned taste aversion ethanol increases the activity of tyrosine hydroxylase (TH) positive neurons in the locus coeruleus (LC), a primary source of norepinephrine (NE). Using cre-inducible AAV8-ChR2 viruses in TH-ires-cre mice we found that the LC provides NE projections that innervate the rostromedial tegmental nucleus (RMTg), a brain region that has been implicated in the aversive properties of drugs. Because the neurocircuitry underlying the aversive effects of ethanol is poorly understood, we characterized the role of the LC to RMTg circuit in modulating aversive unconditioned responses and binge-like ethanol intake. Here, both male and female TH-ires-cre mice were cannulated in the RMTg and injected in the LC with rAVV viruses that encode for a Gq-expressing designer receptor exclusively activated by designer drugs (DREADDs) virus, or its control virus, to directly control the activity of NE neurons. A Latin Square paradigm was used to analyze both 20% ethanol and 3% sucrose consumption using the "drinking-in-the-dark" (DID) paradigm. Chemogenetic activation of the LC to RMTg pathway significantly blunted the binge-ethanol drinking, with no effect on the sucrose consumption, increased the emission of mid-frequency vocalizations and induced malaise-like behaviors in mice. The present findings indicate an important involvement of the LC to RMTg pathway in reducing ethanol consumption, and characterize unconditioned aversive reactions induced by activation of this noradrenergic pathway.

Activation of hypothalamic oxytocin neurons reduces binge-like alcohol drinking through signaling at central oxytocin receptors

Preclinical and clinical evidence suggests that exogenous administration of oxytocin (OT) may hold promise as a therapeutic strategy for reducing heavy alcohol drinking. However, it remains unknown whether these effects are mediated by stimulation of endogenous sources of OT and signaling at oxytocin receptors (OTR) in brain or in the periphery. To address this question, we employed a targeted chemogenetic approach to examine whether selective activation of OT-containing neurons in the paraventricular nucleus of the hypothalamus (PVN) alters alcohol consumption in a binge-like drinking ("Drinking-in-the-Dark"; DID) model. Adult male Oxt-IRES-Cre mice received bilateral infusion of a Cre-dependent virus containing an excitatory DREADD (AAV8-hSyn-DIO-hM3Dq-mCherry) or control virus (AAV8-hSyn-DIO-mCherry) into the PVN. Chemogenetic activation of PVN^OT+ neurons following clozapine-N-oxide injection reduced binge-like alcohol drinking in a similar manner as systemic administration of the neuropeptide. Pretreatment with a brain-penetrant OTR antagonist (L-368,899) reversed this effect while systemic administration of a peripherally restricted OTR antagonist (Atosiban) did not alter reduced alcohol drinking following chemogenetic activation of PVN^OT+ neurons. Altogether, these data are the first to demonstrate that targeted activation of hypothalamic (endogenous) OT reduces alcohol consumption, providing further evidence that this neuropeptide plays a role in regulation of alcohol self-administration behavior. Further, results indicate that the ability OT to reduce alcohol drinking is mediated by signaling at OTR in the brain.

The serotonin 2C receptor agonist lorcaserin, alone and in combination with the opioid receptor antagonist naltrexone, attenuates binge-like ethanol drinking

The serotonin (5-HT) system has been implicated in the pathophysiology of alcohol (ethanol; EtOH) use disorders. Lorcaserin, a 5-HT_2C receptor agonist, attenuates drug self-administration in animal models. We investigated the effects of lorcaserin on EtOH intake using the drinking-in-the-dark (DID) procedure, an animal model of binge-like drinking. We compared the effects of lorcaserin to those of the Food and Drug Administration (FDA)-approved drug naltrexone and examined the effects of combining lorcaserin and naltrexone. To examine whether effects were specific for EtOH, we examined the effects of lorcaserin and naltrexone, administered alone and in combination, on saccharin intake. Adult male C57BL/6J mice received EtOH access (20% v/v) for 2 h in the home-cage during the first 3 days of the DID procedure, beginning 3 h into the dark cycle. On day 4, mice were injected with lorcaserin, naltrexone, or a combination of lorcaserin and naltrexone prior to a 4-h EtOH access. Intake was measured at 2 and 4 h. Lorcaserin reduced EtOH intake in a dose-dependent fashion over the 2- and 4-h measurement periods. Naltrexone also reduced EtOH intake when administered alone, with dose-dependent effects being more pronounced over 2 h rather than the full 4-h session. Combining lorcaserin and naltrexone reduced binge-like EtOH drinking to a greater extent than either drug alone. A similar pattern of results was obtained for saccharin intake. These results suggest that lorcaserin and naltrexone can have additive effects on binge-like EtOH drinking. They also support continued research into the therapeutic potential of lorcaserin for alcohol use disorders.

Lateral hypothalamus-projecting noradrenergic locus coeruleus pathway modulates binge-like ethanol drinking in male and female TH-ires-cre mice

A growing body of literature implicates noradrenergic (NE) signaling in the modulation of ethanol consumption. However, relatively few studies have detailed specific brain pathways that mediate NE-associated binge-like ethanol consumption. To begin to fill this gap in the literature, male and female C57BL6/J and TH-ires-cre mice underwent pharmacological and chemogenetic testing, respectively, in combination with "drinking in the dark" procedures to model binge-like consumption of ethanol or sucrose solutions. First, we showed that intraperitoneal administration of the NE reuptake inhibitor, reboxetine, blunted binge-like ethanol intake in C57BL6/J mice. Chemogenetic activation of locus coeruleus (LC) tyrosine hydroxylase (TH)-expressing neurons blunted binge-like ethanol intake regardless of sex. Chemogenetic activation of LC projections to the lateral hypothalamus (LH), a region implicated in ethanol consumption, blunted binge-like ethanol drinking without altering sucrose intake in ethanol-experienced or ethanol-naïve mice. In C57BL/6 J mice, LH-targeted microinfusion of an α1-adrenergic receptor (AR) agonist blunted binge-like ethanol intake across both sexes, while LH infusion of a β-AR agonist blunted binge-like ethanol intake in females exclusively. Finally, in mice with high baseline ethanol intake both an α1- AR agonist and an α-2 AR antagonist blunted binge-like ethanol intake. The present results provide novel evidence that increased NE tone in a circuit arising from the LC and projecting to the LH reduces binge-like ethanol drinking in mice, and may represent a novel approach to treating binge or heavy drinking prior to the development of dependence. This article is part of the special Issue on "Neurocircuitry Modulating Drug and Alcohol Abuse".

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

Alcohol use disorder remains a substantial social, health, and economic problem and problem drinking levels in women have been increasing in recent years. Understanding whether and how the underlying mechanisms that drive drinking vary by sex is critical and could provide novel, more targeted therapeutic treatments. Here, we examine recent results from our laboratories and others which we believe provide useful insights into similarities and differences in alcohol drinking patterns across the sexes. Findings for binge intake and aversion-resistant, compulsion-like alcohol drinking are considered, since both are likely significant contributors to alcohol problems in humans. We also describe studies regarding mechanisms that may underlie sex differences in maladaptive alcohol drinking, with some focus on the importance of nucleus accumbens (NAcb) core and shell regions, several receptor types (dopamine, orexin, AMPA-type glutamate), and possible contributions of sex hormones. Finally, we discuss how stressors such as early life stress and anxiety-like states may interact with sex differences to contribute to alcohol drinking. Together, these findings underscore the importance and critical relevance of studying female and male mechanisms for alcohol and co-morbid conditions to gain a true and clinically useful understanding of addiction and neuropsychiatric mechanisms and treatment.

Antisense-Induced Downregulation of Clock Genes in the Shell Region of the Nucleus Accumbens Reduces Binge Drinking in Mice

INTRODUCTIONS

Binge drinking is a deadly pattern of alcohol consumption. Evidence suggests that genetic variation in clock genes is strongly associated with alcohol misuse; however, the neuroanatomical basis for such a relationship is unknown. The shell region of the nucleus accumbens (NAcSh) is well known to play a role in binge drinking. Hence, we examined whether clock genes in the NAcSh regulate binge drinking.

METHODS

To address this question, 2 experiments were performed on male C57BL/6J mice. In the first experiment, mice exposed to alcohol or sucrose under the 4-day drinking-in-the-dark (DID) paradigm were euthanized at 2 different time points on day 4 [7 hours after light (pre-binge drinking) or dark (post-binge drinking) onset]. The brains were processed for RT-PCR to examine the expression of circadian clock genes (Clock, Per1, and Per2) in the NAcSh and suprachiasmatic nucleus (SCN). In the second experiment, mice were exposed to alcohol, sucrose, or water as described above. On day 4, 1 hour prior to the onset of alcohol exposure, mice were bilaterally infused with either a mixture of circadian clock gene antisense oligodeoxynucleotides (AS-ODNs; antisense group) or nonsense/random ODNs (R-ODNs; control group) through surgically implanted cannulas above the NAcSh. Alcohol/sucrose/water consumption was measured for 4 hours. Blood alcohol concentration was measured to confirm binge drinking. Microinfusion sites were histologically verified using cresyl violet staining.

RESULTS

As compared to sucrose, mice euthanized post-binge drinking (not pre-binge drinking) on day 4 displayed a greater expression of circadian genes in the NAcSh but not in the SCN. Knockdown of clock genes in the NAcSh caused a significantly lower volume of alcohol to be consumed on day 4 than in the control treatment. No differences were found in sucrose or water consumption.

CONCLUSIONS

Our results suggest that clock genes in the NAcSh play a crucial role in binge drinking.

The Influence of Moderate Physical Activity on Brain Monoaminergic Responses to Binge-Patterned Alcohol Ingestion in Female Mice

Monoamine neurotransmitter activity in brain reward, limbic, and motor areas play key roles in the motivation to misuse alcohol and can become modified by exercise in a manner that may affect alcohol craving. This study investigated the influence of daily moderate physical activity on monoamine-related neurochemical concentrations across the mouse brain in response to high volume ethanol ingestion. Adult female C57BL/6J mice were housed with or without 2.5 h of daily access to running wheels for 30 days. On the last 5 days, mice participated in the voluntary binge-like ethanol drinking procedure, “Drinking in the dark” (DID). Mice were sampled immediately following the final episode of DID. Monoamine-related neurochemical concentrations were measured across brain regions comprising reward, limbic, and motor circuits using ultra High-Performance Liquid Chromatography (UHPLC). The results suggest that physical activity status did not influence ethanol ingestion during DID. Moreover, daily running wheel access only mildly influenced alcohol-related norepinephrine concentrations in the hypothalamus and prefrontal cortex, as well as serotonin turnover in the hippocampus. However, access to alcohol during DID eliminated wheel running-related decreases of norepinephrine, serotonin, and 5-HIAA content in the hypothalamus, but also to a lesser extent for norepinephrine in the hippocampus and caudal cortical areas. Finally, alcohol access increased serotonin and dopamine-related neurochemical turnover in the striatum and brainstem areas, regardless of physical activity status. Together, these data provide a relatively thorough assessment of monoamine-related neurochemical levels across the brain in response to voluntary binge-patterned ethanol drinking, but also adds to a growing body of research questioning the utility of moderate physical activity as an intervention to curb alcohol abuse.

Childhood trauma and post-trauma environment affect fear memory and alcohol use differently in male and female mice

BACKGROUND

Childhood trauma is associated with the development of adult mental health and substance use disorders, with females generally being more at risk. Alcohol is commonly used for coping with trauma, and alcohol use disorder (AUD) affects ∼14.4 million adult Americans annually. Research investigating sex differences in the environmental modification of anxiety and alcohol use following childhood trauma will extend our understanding of the etiology of AUD. Here, we sought to model the interacting effects of a single-episode late childhood trauma with post-trauma environment on adult alcohol use using male and female mice.

METHODS

C57Bl6/J mice (d22) exposed to predator odor (TMT) or water were reared in standard environments (SE) or environmental enrichment (EE). Mice were assessed for adolescent anxiety and conditioned fear, and for adult alcohol use in a limited access, response non-contingent, alcohol exposure paradigm.

RESULTS

A single exposure to predator odor was an effective stressor, inducing long-term sex-dependent changes in conditioned fear and alcohol behaviors that interacted with post-trauma environment. Adolescent EE females showed more conditioned freezing to the trauma-associated context. Adult EE mice consumed less total alcohol than SE mice. However, alcohol use across time differed for males and females. Exposure to a childhood stressor increased alcohol use significantly in females, but not males. EE males, but not EE females, drank less than SE counterparts.

CONCLUSIONS

Findings from this model recapitulate greater vulnerability to childhood trauma in females and support sex differences in post-trauma development of conditioned fear and alcohol use that are modified by environment.

Distinct and Overlapping Patterns of Acute Ethanol-Induced C-Fos Activation in Two Inbred Replicate Lines of Mice Selected for Drinking to High Blood Ethanol Concentrations

The inbred high drinking in the dark (iHDID1 and iHDID2) strains are two replicate lines bred from the parent HS/Npt (HS) line for achieving binge levels of blood ethanol concentration (≥80 mg/dL BEC) in a four-hour period. In this work, we sought to evaluate differences in baseline and ethanol-induced c-Fos activation between the HS, iHDID1, and iHDID2 genetic lines in brain regions known to process the aversive properties of ethanol. Methods: Male and female HS, iHDID1, and iHDID2 mice underwent an IP saline 2 3 g/kg ethanol injection. Brain sections were then stained for c-Fos expression in the basolateral/central amygdala (BLA/CeA), bed nucleus of the stria terminals (BNST), A2, locus coeruleus (LC), parabrachial nucleus (PBN), lateral/medial habenula (LHb/MHb), paraventricular nucleus of the thalamus (PVT), periaqueductal gray (PAG), Edinger–Westphal nuclei (EW), and rostromedial tegmental nucleus (RMTg). Results: The iHDID1 and iHDID2 lines showed similar and distinct patterns of regional c-Fos; however, in no region did the two both significantly differ from the HS line together. Conclusions: Our findings lend further support to the hypothesis the iHDID1 and the iHDID2 lines arrive at a similar behavior phenotype through divergent genetic mechanisms.

Effects of naltrexone on alcohol, sucrose, and saccharin binge-like drinking in C57BL/6J mice: a study with a multiple bottle choice procedure

Chronic alcohol (ethyl alcohol, EtOH) binging has been associated with long-term neural adaptations that lead to the development of addiction. Many of the neurobiological features of EtOH abuse are shared with other forms of binging, like pathological feeding. The drinking-in-the-dark (DID) paradigm has been used extensively to study the neurobiology of EtOH binge-like drinking due to its ability to promote high intakes relevant to human behavior. DID can also generate high consumption of other tastants, but this procedure has not been fully adapted to study forms of binging behavior that are not alcohol-driven. In the present study, we used a modified version of DID that uses multiple bottle availability to promote even higher levels of EtOH drinking in male C57BL/6J mice and allows a thorough investigation of tastant preferences. We assessed whether administration of systemic naltrexone could reduce binging on EtOH, sucrose, and saccharin separately as well as in combination. Our multiple bottle DID procedure resulted in heightened levels of consumption compared with previously reported data using this task. We found that administration of the opioid receptor antagonist naltrexone reduced intakes of preferred, highly concentrated EtOH, sucrose, and saccharin. We also report that naltrexone was able to reduce overall intakes when animals were allowed to self-administer EtOH, sucrose, or saccharin in combination. Our modified DID procedure provides a novel approach to study binging behavior that extends beyond EtOH to other tastants (i.e. sucrose and artificial sweeteners), and has implications for the study of the neuropharmacology of binge drinking.

Environmental Enrichment During Adolescence Mitigates Cognitive Deficits and Alcohol Vulnerability due to Continuous and Intermittent Perinatal Alcohol Exposure in Adult Rats

Perinatal alcohol exposure affects ontogenic neurodevelopment, causing physical and functional long-term abnormalities with limited treatment options. This study investigated long-term consequences of continuous and intermittent maternal alcohol drinking on behavioral readouts of cognitive function and alcohol vulnerability in the offspring. The effects of environmental enrichment (EE) during adolescence were also evaluated. Female rats underwent continuous alcohol drinking (CAD)—or intermittent alcohol drinking paradigm (IAD), along pregestation, gestation, and lactation periods—equivalent to the whole gestational period in humans. Male offspring were reared in standard conditions or EE until adulthood and were then assessed for declarative memory in the novel object recognition test; spatial learning, cognitive flexibility, and reference memory in the Morris water maze (MWM); alcohol consumption and relapse by a two-bottle choice paradigm. Our data show that perinatal CAD decreased locomotor activity, exploratory behavior, and declarative memory with respect to controls, whereas perinatal IAD displayed impaired declarative memory and spatial learning and memory. Moreover, both perinatal alcohol-exposed offspring showed higher vulnerability to alcohol consummatory behavior than controls, albeit perinatal IAD rats showed a greater alcohol consumption and relapse behavior with respect to perinatal-CAD progeny. EE ameliorated declarative memory in perinatal CAD, while it mitigated spatial learning and reference memory impairment in perinatal-IAD progeny. In addition, EE decreased vulnerability to alcohol in both control and perinatal alcohol-exposed rats. Maternal alcohol consumption produces drinking pattern-related long-term consequences on cognition and vulnerability to alcohol in the offspring. However, increased positive environmental stimuli during adolescence may curtail the detrimental effects of developmental alcohol exposure.

Leveraging Neural Networks in Preclinical Alcohol Research

Alcohol use disorder is a pervasive healthcare issue with significant socioeconomic consequences. There is a plethora of neural imaging techniques available at the clinical and preclinical level, including magnetic resonance imaging and three-dimensional (3D) tissue imaging techniques. Network-based approaches can be applied to imaging data to create neural networks that model the functional and structural connectivity of the brain. These networks can be used to changes to brain-wide neural signaling caused by brain states associated with alcohol use. Neural networks can be further used to identify key brain regions or neural "hubs" involved in alcohol drinking. Here, we briefly review the current imaging and neurocircuit manipulation methods. Then, we discuss clinical and preclinical studies using network-based approaches related to substance use disorders and alcohol drinking. Finally, we discuss how preclinical 3D imaging in combination with network approaches can be applied alone and in combination with other approaches to better understand alcohol drinking.

Differential patterns of alcohol and nicotine intake: Combined alcohol and nicotine binge consumption behaviors in mice

Late adolescence and young adulthood, corresponding to the high school and college years, are vulnerable periods for increased alcohol and nicotine use. The dramatic increase in the prevalence of electronic cigarette use is particularly concerning in these age groups. Late adolescents and young adults are more likely to engage in cycles of binge drug consumption, and alcohol and nicotine are frequently used together. However, there are few data examining the combination of alcohol and nicotine in binge models in animal models. In this study, our objectives were to determine how voluntary nicotine consumption beginning in late adolescence influenced subsequent binge alcohol consumption in young adulthood, how a combination of alcohol and nicotine binge consumption differed from alcohol-only binge consumption, and whether nicotine would be consumed when presented in a binge procedure. Male C57BL/6J mice voluntarily consumed unsweetened alcohol and nicotine in continuous-access bottle-choice procedures in combination with cycles of drinking-in-the-dark. Our results show that experience with voluntary nicotine consumption in late adolescence did not affect subsequent binge alcohol consumption in early adulthood. However, mice that consumed nicotine in adolescence showed an initial decrease in alcohol preference, and consequently increase in nicotine preference, on the first session of combined ethanol and nicotine binge consumption in adulthood compared with mice that drank only water during late adolescence. Lastly, we found that mice readily consumed unsweetened nicotine when presented in a binge procedure, and the level of consumption exceeded the nicotine consumption observed in the combination alcohol and nicotine binge. Our data show that expansion of the patterns of alcohol and nicotine co-consumption in a mouse models is possible, which will enable us to dissect relevant molecular targets underlying these consumption patterns and better inform drug development efforts.

An Animal Model of Alcohol Binge Drinking: Chronic-Intermittent Ethanol Administration in Rodents

Binge drinking (BD), characterized by intermittent consumption of large quantities of alcohol in short periods of time, is the main alcohol consumption pattern in adolescents and young adults. BD has serious biomedical consequences, and it is a prominent risk factor for later development of alcohol use disorders. Rodent models offer exceptional power to study these negative consequences of BD. This chapter focuses on one of these BD models: the chronic-intermittent ethanol administration (CIEA) paradigm. Essentially, CIEA consists of the administration in rats or mice of i.p. injections of ethanol (doses: 3-4 g/kg) for several consecutive days each week, in alternation with several days without injections, during several weeks. Due to our interest in the neurobehavioral effects of BD, a combination of the CIEA model with a battery of behavioral tests is described, with emphasis on the effects of alcohol BD on different kinds of memory. The CIEA model, in combination with behavioral tasks, seems to be a useful tool for studying the neurobehavioral effects of BD as well as for developing potential prevention and treatment strategies.

A Preliminary, Open-Label Study of Naltrexone and Bupropion Combination Therapy for Treating Binge Drinking in Human Subjects

AIMS

The combination of bupropion and naltrexone has shown efficacy in reducing binge drinking in animal models. This study assessed the tolerability and potential utility of combined naltrexone and bupropion in reducing binge drinking in human subjects.

METHODS

This preliminary study employed an open-label, single-arm, 12-week, prospective design. Twelve men and women who exhibited a minimum of five (men) or three (women) binge drinking episodes per month over the past 3 months were recruited. All subjects received both bupropion-extended release 300 mg/day and naltrexone 50 mg/day and were monitored throughout the 3-month treatment period. Binge drinking was assessed using the timeline follow-back method.

RESULTS

Treatment with combined naltrexone and bupropion reduced the average number of drinks per binge drinking day from 7.8 drinks to 6.4 drinks and reduced the average percentage of binge drinking days per month from 19% (5.7 days/month) to 5% (1.5 days/month). Naltrexone and bupropion were generally well tolerated, with insomnia, headache and nausea/diarrhea being the most common side effects. Six subjects elected to stay on medication after the trial.

CONCLUSIONS

This study suggests that combined naltrexone and bupropion therapy should be further investigated for tolerability and efficacy in reducing binge drinking in humans.

Alcohol Binge Drinking and Anxiety-Like Behavior in Socialized Versus Isolated C57BL/6J Mice

BACKGROUND

Binge alcohol drinking has been characterized as a key feature of alcoholism. The drinking-in-the-dark (DID) preclinical model, a procedure that promotes high levels of ethanol (EtOH) intake in short periods of time, has been extensively used to investigate neuropharmacological and genetic determinants of binge-like EtOH consumption. Using DID methodology, alcohol-preferring strains of mice such as C57BL/6J (B6) mice consume enough EtOH to achieve blood concentrations (≥1.0 mg/ml) associated with behavioral intoxication (i.e., motor incoordination). DID procedures typically involve the use of socially isolated animals (single-housed prior to and during the experiment). Previous research indicates that stress associated with social isolation can induce anxiety-like behavior and promote increases in EtOH intake. The present study investigates the role of housing conditions in anxiety-like behavior and binge-like EtOH intake using a DID procedure.

METHODS

Male and female B6 mice were isolated or pair-housed for a period of 6 weeks prior to evaluation of anxiety-like (elevated plus maze, light and dark box, open field) and drinking (water, 10% sucrose, 10 to 30% EtOH) behavior. In order to measure intake, a variation of the standard DID procedure using a removable, transparent, and perforated plastic barrier strip (designed to temporarily divide the cage in 2) was introduced. This allowed for individual intake records (2-hour test) of isolated and socially housed animals.

RESULTS

Increased anxiety-like behavior and reduced sucrose consumption were found in isolated mice. The effects of housing conditions on EtOH intake were sex- and concentration-dependent. In male mice, isolation increased 20 and 30% EtOH intake. In females, however, an increased intake of EtOH (30%) was found in socialized animals. No effects of housing or sex were found at EtOH 10%.

CONCLUSIONS

Together with previous literature, the present study suggests that social isolation can promote anxiety-associated behavior and produce sex-dependent changes in binge-like EtOH consumption.

Dynorphin-kappa opioid receptor activity in the central amygdala modulates binge-like alcohol drinking in mice

Although previous research has demonstrated a role for kappa opioid receptor-mediated signaling in escalated alcohol consumption associated with dependence and stress exposure, involvement of the dynorphin/kappa opioid receptor (DYN/KOR) system in binge-like drinking has not been fully explored. Here we used pharmacological and chemogenetic approaches to examine the influence of DYN/KOR signaling on alcohol consumption in the drinking-in-the-dark (DID) model of binge-like drinking. Systemic administration of the KOR agonist U50,488 increased binge-like drinking (Experiment 1) while, conversely, systemic administration of the KOR antagonist nor-BNI reduced drinking in the DID model (Experiment 2). These effects of systemic KOR manipulation were selective for alcohol as neither drug influenced consumption of sucrose in the DID paradigm (Experiment 3). In Experiment 4, administration of the long-acting KOR antagonist nor-BNI into the central nucleus of the amygdala (CeA) decreased alcohol intake. Next, targeted "silencing" of DYN+ neurons in the CeA was accomplished using a chemogenetic strategy. Cre-dependent viral expression in DYN+ neurons was confirmed in CeA of Pdyn-IRES-Cre mice and functionality of an inhibitory (hM4Di) DREADD was validated (Experiment 5). Activating the inhibitory DREADD by CNO injection reduced binge-like alcohol drinking, but CNO injection did not alter alcohol intake in mice that were treated with control virus (Experiment 6). Collectively, these results demonstrate that DYN/KOR signaling in the CeA contributes to excessive alcohol consumption in a binge-drinking model.

Medial prefrontal cortex neuropeptide Y modulates binge-like ethanol consumption in C57BL/6J mice

Neuropeptide Y (NPY) signaling via limbic NPY1 and 2 receptors (NPY1R and NPY2R, respectively) is known to modulate binge-like ethanol consumption in rodents. However, the role of NPY signaling in the medial prefrontal cortex (mPFC), which provides top-down modulation of the limbic system, is unknown. Here, we used "drinking-in-the-dark" (DID) procedures in C57BL/6J mice to address this gap in the literature. First, the impact of DID on NPY immunoreactivity (IR) was assessed in the mPFC. Next, the role of NPY1R and NPY2R signaling in the mPFC on ethanol consumption was evaluated through site-directed pharmacology. Chemogenetic inhibition of NPY1R+ neurons in the mPFC was performed to further evaluate the role of this population. To determine the potential role of NPY1R+ neurons projecting from the mPFC to the basolateral amygdala (BLA) this efferent population was selectively silenced. Three, 4-day cycles of DID reduced NPY IR in the mPFC. Intra-mPFC activation of NPY1R and antagonism of NPY2R resulted in decreased binge-like ethanol intake. Silencing of mPFC NPY1R+ neurons overall, and specifically NPY1R+ neurons projecting to the BLA, significantly reduced binge-like ethanol intake. We provide novel evidence that (1) binge-like ethanol intake reduces NPY levels in the mPFC; (2) activation of NPY1R or blockade of NPY2R reduces binge-like ethanol intake; and (3) chemogenetic inhibition of NPY1R+ neurons in the mPFC and NPY1R+ mPFC neurons projecting to the BLA blunts binge-like drinking. These observations provide the first direct evidence that NPY signaling in the mPFC modulates binge-like ethanol consumption.

Murine Drinking Models in the Development of Pharmacotherapies for Alcoholism: Drinking in the Dark and Two-bottle Choice

Alcohol Use Disorder (AUD) is a major problem with more than an estimated 76 million people worldwide meeting the diagnostic criteria. Current treatments are limited to three FDA-approved medications that are largely ineffective even when combined with psychosocial intervention, as is evident by the high relapse rate. As such, the search for more novel treatments represents an important public health goal. To this end, the following protocol utilizes two simple rodent drinking models to assess the preclinical efficacy of lead anti-alcohol compounds: two-bottle choice (TBC) and drinking in the dark (DID). The former allows mice to voluntary drink in moderation while the latter induces mice to voluntary consume a large amount of alcohol in a short period that mimics binge drinking. The simple and high throughput nature of both of these paradigms allow for rapid screening of pharmacological agents or for identifying strains of mice that exhibit certain voluntary drinking behavior.

Characterization of the Hippocampal Neuroimmune Response to Binge-Like Ethanol Consumption in the Drinking in the Dark Model

OBJECTIVES

Alcohol dependence leads to dysregulation of the neuroimmune system, but the effects of excessive alcohol consumption on key players of the neuroimmune response after episodic binge drinking in nondependence has not been readily assessed. These studies seek to determine how the neuroimmune system within the hippocampus responds to binge-like consumption prior to dependence or evidence of brain damage.

METHODS

C57BL/6J mice underwent the drinking in the dark (DID) paradigm to recapitulate binge consumption. Immunohistochemical techniques were employed to determine the effects of ethanol on cytokine and astrocyte responses within the hippocampus. Astrocyte activation was also assessed using qRT-PCR.

RESULTS

Our results indicated that binge-like ethanol consumption resulted in a 3.6-fold increase in the proinflammatory cytokine interleukin (IL)-1β immunoreactivity in various regions of the hippocampus. The opposite effect was seen in the anti-inflammatory cytokine IL-10. Binge-like consumption resulted in a 67% decrease in IL-10 immunoreactivity but had no effect on IL-4 or IL-6 compared with the water-drinking control group. Moreover, astrocyte activation occurred following ethanol exposure as GFAP immunoreactivity was increased over 120% in mice that experienced 3 cycles of ethanol binges. PCR analyses indicated that the mRNA increased by almost 4-fold after one cycle of DID, but this effect did not persist in abstinence.

CONCLUSIONS

Altogether, these findings suggest that binge-like ethanol drinking prior to dependence causes dysregulation to the neuroimmune system. This altered neuroimmune state may have an impact on behavior but could also result in a heightened neuroimmune response that is exacerbated from further ethanol exposure or other immune-modulating events.

A comparison of hippocampal microglial responses in aged and young rodents following dependent and non-dependent binge drinking

Alcoholism is a highly visible and prevalent issue in the United States. Although binge-drinking is assumed to be a college-age problem, older adults (ages 65+) consume binge amounts of alcohol and have alcohol use disorders (AUDs). Moreover, individuals with alcohol dependence in their youth often continue to drink as they age. As such, this study tested the hypothesis that the effects of alcohol on hippocampal microglia are exacerbated in aged versus younger rodents in two AUD models. Briefly, adult (2-3 months) and aged (15+ months) Sprague-Dawley rats were administered alcohol or control diet using the Majchrowicz model to study alcohol-induced neurodegeneration. To study the effects of non-dependent binge consumption on microglia, adolescent (6-8 weeks) and aged (18+ months) C57/BL6N were subjected to the Drinking in the Dark paradigm. Microglia number and densitometry were assessed using immunohistochemistry. Hippocampal subregional and model/species-specific effects of alcohol were observed, but overall, aging did not appear to increase the alcohol-induced microglia reactivity as measured by Iba-1 densitometry. However, analysis of microglial counts revealed a significant decrease in the number microglia cells in both the alcohol-induced neurodegeneration and DID model across age groups. In the dentate gyrus, the loss of microglia was exacerbated by aging, particularly in mice after DID, non-dependent model. Using qRT-PCR, the persistence of alcohol and aging effects was assessed following the DID model. Allograft Inflammatory Factor 1 mRNA was increased in both young and aged mice by alcohol exposure; however, only in the aged mice did the alcohol effect persist. Overall, these data imply that the microglial response to alcohol is complex with evidence of depressed numbers of microglia but also increased reactivity with advanced age.

Sex Differences in Binge-Like and Aversion-Resistant Alcohol Drinking in C57BL/6J Mice

BACKGROUND

Alcohol use disorder is characterized by compulsive alcohol intake, or drinking despite negative consequences. Previous studies have shown that female rodents have a heightened vulnerability to drug use across different stages of the addictive cycle, but no previous studies have studied females in a model of aversion-resistant alcohol intake. Here, we investigated sex differences in binge-like and aversion-resistant alcohol drinking in C57BL/6J mice using a modified drinking-in-the-dark (DID) paradigm.

METHODS

In Experiment 1, 24-hour aversion to quinine (0, 100, or 250 μM) was assessed. In Experiment 2, male and female adult C57BL/6J mice consumed 15% ethanol (EtOH) or water in a 2-bottle limited-access DID paradigm for 2 h/d for 15 days. The EtOH was next adulterated with quinine (0, 100, or 250 μM) over 3 consecutive drinking sessions to test aversion-resistant intake. In Experiment 3, intake of quinine-adulterated (100 μM) EtOH was assessed across all 15 drinking sessions.

RESULTS

Quinine was equally aversive to both sexes in Experiment 1. In Experiment 2, female mice consumed significantly more alcohol than male mice during the final 6 drinking sessions. Levels of aversion-resistant intake did not differ between the sexes. In Experiment 3, quinine suppressed consumption in all mice, though females drank significantly more on the final 2 sessions.

CONCLUSIONS

The results of this study demonstrate that while female mice escalate and consume more EtOH than males, both sexes exhibit similar levels of aversion-resistant drinking. These results inform our understanding of how sex interacts with vulnerability for addiction and argue for the inclusion of females in more studies of aversion-resistant alcohol drinking.

Oxytocin and Rodent Models of Addiction

Interest for the use of oxytocin as a treatment for addiction began over 40years ago. Better known for its roles in parturition, lactation and pair bonding, oxytocin also has anxiolytic properties, reduces immune and inflammatory responses, and has a role in learning and memory. In this chapter, oxytocin effects on addiction processes are described by highlighting research findings that have used oxytocin within current preclinical animal models of addiction, relapse, or craving. First, we provide a brief background of the endogenous oxytocin system followed by descriptions of the behavioral models used to study addiction, including models of drug taking and seeking. Then we review recent preclinical studies that have used oxytocin as a therapeutic intervention throughout multiple stages of the addiction cycle from a behavioral and neurobiological perspective. These models encompass the entire range of the addiction cycle including acquisition and maintenance of drug taking, withdrawal and craving during periods of drug abstinence, and ultimately relapse. We then posit several theories about how oxytocin interacts with both drug and social reward, as well as presenting a mechanistic account of how specific oxytocin receptor localization may contribute to oxytocin's efficacy as an addiction therapeutic.

Advancing Pharmacotherapy Development from Preclinical Animal Studies

Animal models provide rapid, inexpensive assessments of an investigational drug's therapeutic potential. Ideally, they support the plausibility of therapeutic efficacy and provide a rationale for further investigation. Here, I discuss how the absence of clear effective-ineffective categories for alcohol use disorder (AUD) medications and biases in the clinical and preclinical literature affect the development of predictive preclinical alcohol dependence (AD) models. Invoking the analogical argument concept from the philosophy of science field, I discuss how models of excessive alcohol drinking support the plausibility of clinical pharmacotherapy effects. Even though these models are not likely be completely discriminative, they are sensitive to clinically effective medications and have revealed dozens of novel medication targets. In that context, I discuss recent preclinical work on GLP-1 receptor agonists, phosphodiesterase inhibitors, glucocorticoid receptor antagonists, nociception agonists and antagonists, and CRF1 antagonists. Clinically approved medications are available for each of these drug classes. I conclude by advocating a translational approach in which drugs are evaluated highly congruent preclinical models and human laboratory studies. Once translation is established, I suggest the burden is to develop hypothesis-based therapeutic interventions maximizing the impact of the confirmed pharmacotherapeutic effects in the context of additional variables falling outside the model.

Pre-conceptional and Peri-Gestational Maternal Binge Alcohol Drinking Produces Inheritance of Mood Disturbances and Alcohol Vulnerability in the Adolescent Offspring

Although binge drinking is on the rise in women of reproductive age and during pregnancy, the consequences in the offspring, in particular the inheritance of alcohol-related mood disturbances and alcohol abuse vulnerability, are still poorly investigated. In this study, we modeled both Habitual- and Binge Alcohol Drinking (HAD and BAD) in female rats by employing a two-bottle choice paradigm, with 20% alcohol and water. The exposure started 12 weeks before pregnancy and continued during gestation and lactation. The consequences induced by the two alcohol drinking patterns in female rats were assessed before conception in terms of behavioral reactivity, anxiety- and depressive-like behavior. Afterwards, from adolescence to young-adulthood, male offspring was assessed for behavioral phenotype and alcohol abuse vulnerability. At pre-conceptional time BAD female rats showed higher mean alcohol intake and preference than HAD group; differences in drinking trajectories were attenuated during pregnancy and lactation. Pre-conceptional BAD induced a prevalent depressive/anhedonic-like behavior in female rats, rather than an increase in anxiety-like behavior, as observed in HAD rats. In the adolescent offspring, peri-gestational BAD did not affect behavioral reactivity in the open field and anxiety-like behavior in the elevated plus maze. Rather, BAD dams offspring displayed higher despair-behavior and lower social interaction with respect to control- and HAD dams progeny. Notably, only binge drinking exposure increased offspring vulnerability to alcohol abuse and relapse following forced abstinence. This is the first report showing that binge-like alcohol consumption from pre-conceptional until weaning induces relevant consequences in the affective phenotype of both the mothers and the offspring, and that such effects include heightened alcohol abuse vulnerability in the offspring. These findings highlight the need for more incisive public education campaigns about detrimental consequences of peri-gestational alcohol exposure.

Voluntary Binge-like Ethanol Consumption Site-specifically Increases c-Fos Immunoexpression in Male C57BL6/J Mice

The assessment of binge ethanol-induced neuronal activation, using c-Fos immunoreactivity (IR) as a marker of neuronal activity, is typically accomplished via forced ethanol exposure, such as intraperitoneal injection or gavage. Neuronal activity using a voluntary binge-like drinking model, such as "drinking-in-the-dark" (DID), has not been thoroughly explored. Additionally, studies assessing ethanol-elicited neuronal activation may or may not involve stereotaxic surgery, which could impact c-Fos IR. The experiments detailed herein aimed to assess the effects of voluntary binge-like ethanol consumption on c-Fos IR in brain regions implicated in ethanol intake in animals with and without surgery experience. Age-matched male C57BL/6J mice underwent either stereotaxic surgery (Study 1) or no surgery (Study 2). Then, mice experienced one 4-day DID cycle, tail blood samples were collected immediately after test conclusion on day 4, and mice were subsequently sacrificed. In each study, mice that drink ethanol were sorted into those that achieved binge-equivalent blood ethanol concentrations (BECs ≥ 80 mg/dl) versus those that did not. Relative to water-consuming controls, mice with BECs ≥ 80 mg/dl showed significantly elevated c-Fos IR in several brain regions implicated in neurobiological responses to ethanol. In general, the brain regions exhibiting binge-induced c-Fos IR were the same between studies, though differences were noted, highlighting the need for caution when interpreting ethanol-induced c-Fos IR when subjects have a prior history of surgery. Altogether, these results provide insight into the brain regions that modulate binge-like ethanol intake stemming from DID procedures among animals with and without surgery experience.

Modulation of Binge-like Ethanol Consumption by IL-10 Signaling in the Basolateral Amygdala

Excessive ethanol consumption alters the neuroimmune system and particularly impacts the cytokine milieu of the CNS. Cytokine dysregulation has been shown to underlie addictive-like behaviors including alcohol abuse; however, many studies focus primarily on the proinflammatory cytokine profile during alcohol dependence. The current study furthers this research by determining the impact of excessive ethanol consumption on interleukin-10 (IL-10) and interleukin-4 (IL-4) activity in a model of non-dependent binge consumption called the "drinking in the dark" (DID) paradigm. Furthermore, the ability of IL-10 to modulate ethanol consumption was tested using site-directed pharmacology. Immunohistochemistry analyses determined that ethanol decreased IL-10 by 50 % in the basolateral amygdala (BLA) but had no effect on IL-4. Neither IL-10 nor IL-4, however, were altered in the central amygdala (CEA). Enzyme linked immunosorbent assays confirmed that IL-10 was decreased in the amygdala but not in the serum, suggesting changes of this cytokine with the DID paradigm are restricted to the central nervous system. Finally, bilateral infusions of IL-10 into the BLA, but not CeA, reduced binge-like drinking and corresponding blood ethanol concentrations without impacting either locomotor activity or anxiety-like behavioral correlates. Together, these data support the idea that alcohol abuse dysregulates specific anti-inflammatory cytokines; however, ameliorating alcohol-induced effects on cytokines, like IL-10, may prove to be an effective therapy in curbing excessive consumption.

Ethanol Induced Brain Lipid Changes in Mice Assessed by Mass Spectrometry

Alcohol abuse is a chronic disease characterized by the consumption of alcohol at a level that interferes with physical and mental health and causes serious and persistent changes in the brain. Lipid metabolism is of particular interest due to its high concentration in the brain. Lipids are the main component of cell membranes, are involved in cell signaling, signal transduction, and energy storage. In this study, we analyzed lipid composition of chronically ethanol exposed mouse brains. Juvenile (JUV) and adult (ADU) mice were placed on a daily limited-access ethanol intake model for 52 days. After euthanasia, brains were harvested, and total lipids were extracted from brain homogenates. Samples were analyzed using high resolution mass spectrometry and processed by multivariate and univariate statistical analysis. Significant lipid changes were observed in different classes including sphingolipids, fatty acids, lysophosphatidylcholines, and other glycerophospholipids.

Lateral hypothalamic melanocortin receptor signaling modulates binge-like ethanol drinking in C57BL/6J mice

Binge ethanol drinking is a highly pervasive and destructive behavior yet the underlying neurobiological mechanisms remain poorly understood. Recent work suggests that overlapping neurobiological mechanisms modulate feeding disorders and excessive ethanol intake, and converging evidence indicates that the melanocortin (MC) system may be a promising candidate. The aims of the present work were to examine how repeated binge-like ethanol drinking, using the 'drinking in the dark' (DID) protocol, impacts key peptides within the MC system and if site-specific manipulation of MC receptor (MCR) signaling modulates binge-like ethanol drinking. Male C57BL/6J mice were exposed to one, three or six cycles of binge-like ethanol, sucrose or water drinking, after which brain tissue was processed via immunohistochemistry (IHC) for analysis of key MC peptides, including alpha-melanocyte stimulating hormone (α-MSH) and agouti-related protein (AgRP). Results indicated that α-MSH expression was selectively decreased, while AgRP expression was selectively increased, within specific hypothalamic subregions following repeated binge-like ethanol drinking. To further explore this relationship, we used site-directed drug delivery techniques to agonize or antagonize MCRs within the lateral hypothalamus (LH). We found that the nonselective MCR agonist melanotan-II (MTII) blunted, while the nonselective MCR antagonist AgRP augmented, binge-like ethanol consumption when delivered into the LH. As these effects were region-specific, the present results suggest that a more thorough understanding of the MC neurocircuitry within the hypothalamus will help provide novel insight into the mechanisms that modulate excessive binge-like ethanol intake and may help uncover new therapeutic targets aimed at treating alcohol abuse disorders.

Considerations in the Evaluation of Potential Efficacy of Medications for Alcohol and Drug Use Disorders: An Editorial

The societal burden created by alcohol and drug use disorders is estimated to be on the order of hundreds of billions of dollars, creating a need for effective medications to reduce use and prevent relapse. While there are FDA-approved medications to facilitate abstinence and prevent relapse for some indications including, alcohol, tobacco, and opiate use disorders, there are no approved treatments for other abused substances, including cocaine, methamphetamine, and cannabis, leaving these critical medical needs unmet. The development of such medications has fallen largely to the government with efforts spearheaded by the National Institute on Drug Abuse and the National Institute on Alcoholism and Alcohol Abuse. Both agencies have medication development programs with preclinical components that include the standardized evaluation of compounds using animal models. This chapter describes the rationale and considerations involved in the use of such models, including reinstatement of drug self-administration.

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

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