Ethanol consumption and resistance are inversely related to neuropeptide Y levels

Genetic linkage analysis of rats that were selectively bred for alcohol preference identified a chromosomal region that includes the neuropeptide Y (NPY) gene. Alcohol-preferring rats have lower levels of NPY in several brain regions compared with alcohol-non-preferring rats. We therefore studied alcohol consumption by mice that completely lack NPY as a result of targeted gene disruption. Here we report that NPY-deficient mice show increased consumption, compared with wild-type mice, of solutions containing 6%, 10% and 20% (v/v) ethanol. NPY-deficient mice are also less sensitive to the sedative/hypnotic effects of ethanol, as shown by more rapid recovery from ethanol-induced sleep, even though plasma ethanol concentrations do not differ significantly from those of controls. In contrast, transgenic mice that overexpress a marked NPY gene in neurons that usually express it have a lower preference for ethanol and are more sensitive to the sedative/hypnotic effects of this drug than controls. These data are direct evidence that alcohol consumption and resistance are inversely related to NPY levels in the brain.

"Drinking in the dark" (DID) procedures: a model of binge-like ethanol drinking in non-dependent mice

This review provides an overview of an animal model of binge-like ethanol drinking that has come to be called "drinking in the dark" (DID), a procedure that promotes high levels of ethanol drinking and pharmacologically relevant blood ethanol concentrations (BECs) in ethanol-preferring strains of mice. Originally described by Rhodes, Best, Belknap, Finn, and Crabbe (2005), the most common variation of the DID procedure, using singly housed mice, involves replacing the water bottle with a bottle containing 20% ethanol for 2-4 h, beginning 3 h into the dark cycle. Using this procedure, high ethanol drinking strains of mice (e.g., C57BL/6J) typically consume enough ethanol to achieve BECs greater than 100 mg/dL and to exhibit behavioral evidence of intoxication. This limited access procedure takes advantage of the time in the animal's dark cycle in which the levels of ingestive behaviors are high, yet high ethanol intake does not appear to stem from caloric need. Mice have the choice of drinking or avoiding the ethanol solution, eliminating the stressful conditions that are inherent in other models of binge-like ethanol exposure in which ethanol is administered by the experimenter, and in some cases, potentially painful. The DID procedure is a high throughput approach that does not require extensive training or the inclusion of sweet compounds to motivate high levels of ethanol intake. The high throughput nature of the DID procedure makes it useful for rapid screening of pharmacological targets that are protective against binge-like drinking and for identifying strains of mice that exhibit binge-like drinking behavior. Additionally, the simplicity of DID procedures allows for easy integration into other paradigms, such as prenatal ethanol exposure and adolescent ethanol drinking. It is suggested that the DID model is a useful tool for studying the neurobiology and genetics underlying binge-like ethanol drinking, and may be useful for studying the transition to ethanol dependence.

"Drinking in the Dark" (DID): a simple mouse model of binge-like alcohol intake

One of the greatest challenges that scientists face when studying the neurobiology and/or genetics of alcohol (ethanol) consumption is that most preclinical animal models do not voluntarily consume enough ethanol to achieve pharmacologically meaningful blood ethanol concentrations (BECs). Recent rodent models have been developed that promote binge-like levels of ethanol consumption associated with high BECs (i.e., ≥100 mg/dl). This unit describes procedures for an animal model of binge-like ethanol drinking which has come to be called "drinking in the dark" (DID). The "basic" variation of DID involves replacing the water bottle with a bottle containing 20% ethanol for 2 to 4 hr, beginning 3 hr into the dark cycle, on cages of singly-housed C57BL/6J mice. Using this procedure, mice typically consume enough ethanol to achieve BECs >100 mg/dl and to exhibit behavioral evidence of intoxication. An alternative two-bottle (ethanol and water) procedure is also described.

Blockade of the corticotropin releasing factor type 1 receptor attenuates elevated ethanol drinking associated with drinking in the dark procedures

BACKGROUND

Drinking in the dark (DID) procedures have recently been developed to induce high levels of ethanol drinking in C57BL/6J mice, which result in blood ethanol concentrations (BECs) reaching levels that have measurable affects on physiology and/or behavior. The present experiments determined whether the increased ethanol drinking caused by DID procedures can be attenuated by pretreatment with CP-154,526; a corticotropin releasing factor type-1 (CRF1) receptor antagonist.

METHODS

In Experiment 1, male C57BL/6J mice received ethanol (20% v/v) in place of water for 4 hours, beginning with 3 hours into the dark cycle. On the fourth day, mice were given an intraperitoneal injection of one of the 4 doses of CP-154,526 (0, 1, 3, 10 mg/kg) 30 minutes before receiving their ethanol bottle. In Experiment 2, C57BL/6J mice had 2 hours of access to the 20% ethanol solution, beginning with 3 hours into the dark cycle on days 1 to 3, and 4 hours of access to the ethanol bottle on day 4 of DID procedures. Mice were given an intraperitoneal injection of one of the 4 doses of CP-154,526 (0, 1, 3, 10 mg/kg) 30 minutes before receiving their ethanol bottle on day 4. Tail blood samples were collected immediately after the 4-hour ethanol access period on the fourth day of each experiment. Additional control experiments assessed the effects of CP-154,526 on 4-hour consumption of a 10% (w/v) sucrose solution and open-field locomotor activity.

RESULTS

In Experiment 1, the vehicle-treated group consumed approximately 4.0 g/kg/4 h of ethanol and achieved BECs of approximately 30 mg%. Furthermore, pretreatment with the CRF1 receptor antagonist did not alter ethanol consumption. On the other hand, procedures used in Experiment 2 resulted in vehicle-treated mice consuming approximately 6.0 g/kg/4 h of ethanol with BECs of about 80 mg%. Additionally, the 10 mg/kg dose of CP-154,526 significantly reduced ethanol consumption and BECs to approximately 3.0 g/kg/4 h and 27 mg%, respectively, relative to vehicle-treated mice. Importantly, the 10 mg/kg dose of the CRF1R antagonist did not significantly alter 4-hour sucrose consumption or locomotor activity.

CONCLUSIONS

These data indicate that CRF1R signaling modulates high, but not moderate, levels of ethanol drinking associated with DID procedures.

Insular cortex lesions and taste aversion learning: effects of conditioning method and timing of lesion

The specific role of insular cortex in acquisition and expression of a conditioned taste aversion was assessed using two different conditioning methods, which vary mode of taste delivery. Involvement of insular cortex in the induction of c-Fos-immunoreactivity in the nucleus of the solitary tract, a cellular correlate of the behavioral expression of a conditioned taste aversion, was also assessed. Electrolytic lesions of insular cortex blocked behavioral expression of a conditioned taste aversion and this was evident not only when lesions were placed prior to conditioning, but also when they were made after conditioning but before testing. In contrast to the effects on behavior, lesions did not completely block the c-Fos-immunoreactivity which accompanies re-exposure to the aversive taste. In addition, the blocking of behavioral evidence of aversion conditioning by cortical lesions was seen both in animals trained under an intraoral acquisition procedure and those trained with bottle-conditioning. This contrasts with previous work with amygdala lesions which showed that amygdala was absolutely necessary for taste aversions conditioned with the intraoral method but not for those conditioned using bottle presentation of the taste. Overall, these findings imply that the details of the neural circuitry involved in taste aversion learning, including its anatomical distribution, complexity and degree of redundancy, vary with the type of conditioning method employed.

c-Fos induction in rat brainstem in response to ethanol- and lithium chloride-induced conditioned taste aversions

When consumption of a novel taste (conditioned stimulus; CS) is followed by exposure to a toxin, organisms will avoid consumption of that taste in the future. This learned response, known as a conditioned taste aversion (CTA), can be demonstrated using a variety of drugs, including lithium chloride (LiCl) and ethanol. c-Fos immunohistochemistry was used to examine neural activation in the rat brainstem associated with drug administration and with a CS taste previously paired with these drugs. Relative to saline controls, animals injected with either LiCl (76 mg/kg) or ethanol (3.5 g/kg) displayed greater c-Fos expression in area postrema, nucleus of the solitary tract (NTS), and lateral parabrachial nucleus. At these doses, LiCl- and ethanol-injected groups did not differ from each other. For establishing a CTA, intraoral infusion of a 0.15% saccharin solution was followed by injection of either LiCl or ethanol. Both LiCl and ethanol produced quantitatively similar CTAs. Relative to unpaired control groups, saccharin paired with either drug induced significant c-Fos expression in NTS. Thus, like LiCl, ethanol and tastes that have become aversive by virtue of their association with ethanol activate brainstem regions hypothesized to play a role in CTA learning.

Glucagon-like peptide-1 (7-36) amide: a central regulator of satiety and interoceptive stress

Glucagon-like peptide-1 (7-36) amide (GLP-1) is processed from proglucagon in the distal ileum as well as in the CNS. In the periphery, GLP-1 acts as an incretin factor and profoundly inhibits upper gastrointestinal motility ('ileal brake'), the latter presumably involving the CNS. Within the CNS, GLP-1 has a satiating effect, since administration of GLP-1 into the third cerebral ventricle reduces short-term food intake (and meal size), while administration of GLP-1 antagonists have the opposite effect. In addition, activation of GLP-1 receptors in certain brain regions elicits strong taste aversions. Similarities between toxin- and GLP-1-induced neuronal activity in the CNS (brain stem) suggest a role for central GLP-1 receptors in relaying interoceptive stress. Thus, regionally distinct GLP-1 receptor populations in the CNS may be involved in satiety or malaise. It is argued that the satiating and aversive aspects of GLP-1 serve homeostatic and nonhomeostatic functions with respect to maintenance of nutrient balance.

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

Binge alcohol (ethanol) drinking is a destructive pattern of ethanol consumption that may precipitate ethanol dependence-a chronic, debilitating, and prevalent health problem. While an abundance of research has focused on the neurochemical underpinnings of ethanol dependence, relatively little is known about the mechanisms underlying the heavy consumption characteristic of binge ethanol drinking. Recently, a simple preclinical model termed "drinking in the dark" (DID) was developed to examine binge-like ethanol consumption in a rodent population. This assay capitalizes on the predisposition of C57BL/6J mice to voluntarily consume substantial quantities of a high concentration (20% v/v) ethanol solution, resulting in pharmacologically relevant blood ethanol concentrations (BECs). This review provides a comprehensive overview of recent literature utilizing this model to investigate the neuromodulatory systems that may influence binge ethanol drinking. Studies examining the glutamatergic and opioidergic systems not only provide evidence for these systems in the modulation of binge-like ethanol consumption, but also suggest this preclinical model has predictive validity and may be an appropriate tool for screening novel pharmacological compounds aimed at treating binge ethanol drinking in the human population. Additionally, this review presents evidence for the involvement of the GABAergic, dopaminergic, nicotinic, and endocannabinoid systems in modulating binge-like ethanol consumption. Finally, recent evidence shows that corticotropin-releasing factor (CRF), agouti-related protein (AgRP), neuropeptide Y (NPY), and ghrelin are also implicated as impacting this pattern of ethanol consumption.

Comparison of central administration of corticotropin-releasing hormone and urocortin on food intake, conditioned taste aversion, and c-Fos expression

Corticotropin-releasing hormone (CRH) is a potent regulator of the hypothalamic-pituitary-adrenal axis, and reduces food intake when administered into the third cerebral ventricle (i3vt). However, CRH also promotes conditioned taste aversion (CTA) learning which indicates that its anorectic effects are accompanied by aversive consequences that would reduce food intake independently of energy regulation. Urocortin (Ucn) is a closely related mammalian peptide that binds to both identified CRH receptor subtypes and also reduces food intake when administered i3vt. The present experiments compared the aversive consequences of i3vt administration of CRH and Ucn at doses that produced comparable decrements in food intake. Experiment 1 found that 1.0 microg Ucn and 2.0 microg CRH produced similar reductions in food intake. Experiment 2 demonstrated that, at these doses, CRH but not Ucn promoted robust and reliable CTA learning. A third experiment showed comparable increased c-Fos-like immunoreactivity after Ucn and CRH in forebrain and hindbrain structures associated with food intake. It is concluded that Ucn, at doses that reduce food intake to levels like that observed after administration of CRH, do not produce similarly aversive consequences.

Ethanol consumption in rats selectively bred for differential saccharin intake

Rat lines selectively bred for high ethanol consumption consume more saccharin solution than do their low-ethanol-consuming counterparts. The present study utilized the technique of reciprocal selection to examine the reliability of the saccharin/ethanol relationship; specifically, consumption of 1-10% ethanol solution was measured in rats selectively bred for high vs. low saccharin consumption (Occidental HiS and LoS lines). HiS rats consumed more ethanol than did LoS rats. These results support the idea that individual differences in ethanol and saccharin consumption share some common mechanism(s).

Central infusion of GLP-1, but not leptin, produces conditioned taste aversions in rats

Leptin (ob protein) and glucagon-like peptide-1-(7-36) amide (GLP-1) are peptides recently proposed to be involved in the regulation of food intake. Although the ability of exogenous leptin and GLP-1 to modulate consummatory behavior is consistent with the suggestion that these peptides are endogenous regulatory agents, central administration of these peptides may have aversive side effects, which could explain the anorexia. In the present experiment, exposure to a saccharine taste was immediately followed by central administration of leptin or GLP-1 to determine if these drugs could produce a conditioned taste aversion (CTA) in rats. At doses equated for producing comparable reductions in short-term food intake, GLP-1, but not leptin, generated a robust CTA. Although leptin caused no aversion, this peptide was the only drug to cause relatively long-term reductions in food consumption (16 h) and body weight (24 h). Hence, the results indicate that central GLP-1 produces aversive side effects, and it is argued that these nonspecific effects may explain the anorectic actions of GLP-1.

Neurobiological responses to ethanol in mutant mice lacking neuropeptide Y or the Y5 receptor

We have previously shown that voluntary ethanol consumption and resistance are inversely related to neuropeptide Y (NPY) levels in NPY-knockout (NPY -/-) and NPY-overexpressing mice. Here we report that NPY -/- mice on a mixed C57BL/6Jx129/SvEv background showed increased sensitivity to locomotor activation caused by intraperitoneal (ip) injection of 1.5 g/kg of ethanol, and were resistant to sedation caused by a 3.5-g/kg dose of ethanol. In contrast, NPY -/- mice on an inbred 129/SvEv background consumed the same amount of ethanol as wild-type (WT) controls at 3%, 6%, and 10% ethanol, but consumed significantly more of a 20% solution. They exhibited normal locomotor activation following a 1.5-g/kg injection of ethanol, and displayed normal sedation in response to 2.5 and 3.0 g/kg of ethanol, suggesting a genetic background effect. Y5 receptor knockout (Y5 -/-) mice on an inbred 129/SvEv background showed normal ethanol-induced locomotor activity and normal voluntary ethanol consumption, but displayed increased sleep time caused by 2.5 and 3.0 g/kg injection of ethanol. These data extend previous results by showing that NPY -/- mice of a mixed C57BL/6Jx129/SvEv background have increased sensitivity to the locomotor activation effect caused by a low dose of ethanol, and that expression of ethanol-related phenotypes are dependent on the genetic background of NPY -/- mice.

Central infusion of glucagon-like peptide-1-(7-36) amide (GLP-1) receptor antagonist attenuates lithium chloride-induced c-Fos induction in rat brainstem

Central infusion of glucagon-like peptide-1-(7-36) amide (GLP-1) and intraperitoneal (i.p.) injection of lithium chloride (LiCl) produce similar patterns of c-Fos induction in the rat brain. These similarities led us to assess the hypothesis that neuronal activity caused by i.p. injection of LiCl involves activation of central GLP-1 pathways. We therefore determined if third-ventricular (i3vt) infusion of a GLP-1 receptor antagonist would block LiCl-induced c-Fos expression in the brainstem. Relative to rats pretreated with i3vt infusion of vehicle, pretreatment with the potent GLP-1 receptor antagonist, des His1 Glu9 exendin-4 (10.0 microgram), significantly attenuated LiCl-induced (76 mg/kg; i.p.) c-Fos expression in several brainstem regions, including the area postrema, the nucleus of the solitary tract, and the lateral parabrachial nucleus. While central infusion of des His1 Glu9 exendin-4 also blocked GLP-1-induced (10.0 microgram) anorexia and c-Fos expression, the antagonist produced no independent effects on food intake or c-Fos expression. These results suggest that LiCl-induced c-Fos expression in the rat brainstem is mediated, at least in part, by GLP-1 receptor signaling.

Alcoholism and obesity: overlapping neuropeptide pathways?

Ethanol is a caloric compound, and ethanol drinking and food intake are both appetitive and consummatory behaviors. Furthermore, both ethanol and food have rewarding properties. It is therefore possible that overlapping central pathways are involved with uncontrolled eating and excessive ethanol consumption. A growing list of peptides has been shown to regulate food intake and/or energy homeostasis. Peptides such as the melanocortins, corticotropin releasing factor, and cholecystokinin promote reductions of food intake while others such as galanin and neuropeptide Y stimulate feeding. The present review highlights research aimed at determining if ingestive peptides also regulate voluntary ethanol intake, with an emphasis on the melanocortins and neuropeptide Y. It is suggested that research directed at ingestive peptides may expand our understanding of the neurobiological mechanisms that drive ethanol self-administration, and may reveal new therapeutic candidates for treating alcohol abuse and alcoholism.

Central infusion of melanocortin agonist MTII in rats: assessment of c-Fos expression and taste aversion

Like leptin (OB protein), central infusion of the nonspecific melanocortin agonist MTII reduces food intake for relatively long periods of time (i.e., 12 h; W. Fan, B. A. Boston, R. A. Kesterson, V. J. Hruby, and R. D. Cone, Nature; 385: 165-168, 1997). To test the hypothesis that MTII may influence ingestive behavior via mechanisms similar to those that mediate the effects of leptin, we infused a single dose of MTII into the third ventricle (i3vt) of Long-Evans rats and examined three dependent measures that have been studied following i3vt infusion of leptin: 1) effects on long-term food intake and body weight (48 h), 2) patterns of c-Fos expression in the brain, and 3) conditioned taste aversion learning. Similar to leptin, MTII reduced 48-h food intake (1.0 nmol dose), reduced body weight at 24 and 48 h (0.1 and 1.0 nmol doses, respectively), and induced c-Fos expression in the paraventricular nucleus of the hypothalamus and the central nucleus of the amygdala. In contrast to leptin, MTII was found to produce conditioned taste aversions. These results are consistent with the hypothesis that MTII may influence regulatory behavior via mechanisms similar to those that mediate the effects of leptin.

Central neuropeptide Y modulates binge-like ethanol drinking in C57BL/6J mice via Y1 and Y2 receptors

Frequent binge drinking has been linked to heart disease, high blood pressure, type 2 diabetes, and the development of ethanol dependence. Thus, identifying pharmaceutical targets to treat binge drinking is of paramount importance. Here we employed a mouse model of binge-like ethanol drinking to study the role of neuropeptide Y (NPY). To this end, the present set of studies utilized pharmacological manipulation of NPY signaling, immunoreactivity (IR) mapping of NPY and NPY receptors, and electrophysiological recordings from slice preparations of the amygdala. The results indicated that central infusion of NPY, a NPY Y1 receptor (Y1R) agonist, and a Y2R antagonist significantly blunted binge-like ethanol drinking in C57BL/6J mice (that achieved blood ethanol levels >80 mg/dl in control conditions). Binge-like ethanol drinking reduced NPY and Y1R IR in the central nucleus of the amygdala (CeA), and 24 h of ethanol abstinence after a history of binge-like drinking promoted increases of Y1R and Y2R IR. Electrophysiological recordings of slice preparations from the CeA showed that binge-like ethanol drinking augmented the ability of NPY to inhibit GABAergic transmission. Thus, binge-like ethanol drinking in C57BL/6J mice promoted alterations of NPY signaling in the CeA, and administration of exogenous NPY compounds protected against binge-like drinking. The current data suggest that Y1R agonists and Y2R antagonists may be useful for curbing and/or preventing binge drinking, protecting vulnerable individuals from progressing to the point of ethanol dependence.

Central infusions of leptin and GLP-1-(7-36) amide differentially stimulate c-FLI in the rat brain

Recently, glucagon-like peptide-1-(7-36) amide (GLP-1) and leptin have been implicated in the regulation of food intake. In the present study, we compared the effects of third ventricular administration (i3vt) of leptin (3.5 micrograms) and GLP-1 (10.0 micrograms) on short-term food intake and c-Fos-like immunoreactivity (c-FLI) in hypothalamic, limbic, and hindbrain areas in the rat. Relative to controls, infusion of leptin or GLP-1 (3 h before lights off) significantly reduced food intake over the first 2 h in the dark phase (53 and 63%, respectively). In different rats, infusion of leptin or GLP-1 elevated c-FLI in the paraventricular hypothalamus and central amygdala. Furthermore, leptin selectively elevated c-FLI in the dorsomedial hypothalamus, whereas GLP-1 selectively elevated c-FLI in the nucleus of the solitary tract, area postrema, lateral parabrachial nucleus, and arcuate hypothalamic nucleus. The fact that most of the c-FLI after leptin or GLP-1 administration was observed in separate regions within the central nervous system (CNS) suggests different roles for leptin and GLP-1 in the CNS regulation of food intake and body weight.

IL-1 receptor signaling in the basolateral amygdala modulates binge-like ethanol consumption in male C57BL/6J mice

Proinflammatory cytokines have been implicated in alcohol-induced neurodegeneration, but the role of the neuroimmune system in alcohol related behaviors has only recently come to the forefront. Herein, the effects of binge-like drinking on IL-1β mRNA and immunoreactivity within the amygdala were measured following the "drinking in the dark" (DID) paradigm, a model of binge-like ethanol drinking in C57BL/6J mice. Moreover, the role of IL-1 receptor signaling in the amygdala on ethanol consumption was assessed. Results indicated that a history of binge-like ethanol drinking promoted a significant increase of IL-1β mRNA expression within the amygdala, and immunohistochemistry analyses revealed that the basolateral amygdala (BLA), but not central amygdala (CeA), exhibited significantly increased IL-1β immunoreactivity. However, Fluoro-Jade® C labeling indicated that multiple cycles of the DID paradigm were not sufficient to elicit neuronal death. Bilateral infusions of IL-1 receptor antagonist (IL-1Ra) reduced ethanol consumption when infused into the BLA but not the CeA. These observations were specific to ethanol drinking as the IL-1Ra did not alter either sucrose drinking or open-field locomotor activity. The current findings highlight a specific role for IL-1 receptor signaling in modulating binge-like ethanol consumption and indicate that proinflammatory cytokines can be induced prior to dependence or any evidence of neuronal cell death. These findings provide a framework in which to understand how neuroimmune adaptations may alter ethanol consumption and therein contribute to alcohol abuse.

The CRF-1 receptor antagonist, CP-154,526, attenuates stress-induced increases in ethanol consumption by BALB/cJ mice

BACKGROUND

Corticotropin-releasing factor (CRF) signaling modulates neurobiological responses to stress and ethanol, and may modulate observed increases in ethanol consumption following exposure to stressful events. The current experiment was conducted to further characterize the role of CRF1 receptor (CRF1R) signaling in stress-induced increases in ethanol consumption in BALB/cJ and C57BL/6N mice.

METHODS

Male BALB/cJ and C57BL/6N mice were given continuous access to 8% (v/v) ethanol and water for the duration of the experiment. When a baseline of ethanol consumption was established, animals were exposed to 5 minutes of forced swim stress on each of 5 consecutive days. Thirty minutes before each forced swim session, animals were given an intraperitoneal injection of a 10 mg/kg dose of CP-154,526, a selective CRF1R antagonist, or an equal volume of vehicle. The effect of forced swim stress exposure on consumption of a 1% (w/v) sucrose solution was also investigated in an ethanol-naïve group of BALB/cJ mice.

RESULTS

Exposure to forced swim stress significantly increased ethanol consumption by the BALB/cJ, but not of the C57BL/6N, mice. Stress-induced increases in ethanol consumption were delayed and became evident approximately 3 weeks after the first stressor. Additionally, forced swim stress did not cause increases of food or water intake and did not promote delayed increases of sucrose consumption. Importantly, BALB/cJ mice pretreated with the CRF1R antagonist showed blunted stress-induced increases in ethanol intake, and the CRF1R antagonist did not influence the ethanol drinking of non-stressed mice.

CONCLUSIONS

The present results provide evidence that CRF1R signaling modulates the delayed increase of ethanol consumption stemming from repeated exposure to a stressful event in BALB/cJ mice.

Pre-clinical evidence that corticotropin-releasing factor (CRF) receptor antagonists are promising targets for pharmacological treatment of alcoholism

Alcoholism is a chronic disorder characterized by cycling periods of excessive ethanol consumption, withdrawal, abstinence and relapse, which is associated with progressive changes in central corticotropin-releasing factor (CRF) receptor signaling. CRF and urocortin peptides act by binding to the CRF type 1 (CRF1R) or the CRF type 2 (CRF2R) receptors, both of which have been implicated in the regulation of neurobiological responses to ethanol. The current review provides a comprehensive overview of preclinical evidence from studies involving rodents that when viewed together, suggest a promising role for CRFR antagonists in the treatment of alcohol abuse disorders. CRFR antagonists protect against excessive ethanol intake resulting from ethanol dependence without influencing ethanol intake in non-dependent animals. Similarly, CRFR antagonists block excessive binge-like ethanol drinking in non-dependent mice but do not alter ethanol intake in mice drinking moderate amounts of ethanol. CRFR antagonists also protect against increased ethanol intake and relapse-like behaviors precipitated by exposure to a stressful event. Additionally, CRFR antagonists attenuate the negative emotional responses associated with ethanol withdrawal. The protective effects of CRFR antagonists are modulated by CRF1R. Finally, recent evidence has emerged suggesting that CRF2R agonists may also be useful for treating alcohol abuse disorders.

The Role of Neuropeptide Y (NPY) in Alcohol and Drug Abuse Disorders

Neuropeptide Y (NPY) is a neuromodulator that is widely expressed throughout the central nervous system (CNS) and which is cosecreted with classic neurotransmitters including GABA and glutamate. There is a long history of research implicating a role for NPY in modulating neurobiological responses to alcohol (ethanol) as well as other drugs of abuse. Both ethanol exposure and withdrawal from chronic ethanol have been shown to produce changes in NPY and NPY receptor protein levels and mRNA expression in the CNS. Importantly, manipulations of NPY Y1 and Y2 receptor signaling have been shown to alter ethanol consumption and self-administration in a brain region-specific manner, with Y1 receptor activation and Y2 receptor blockade in regions of the extended amygdala promoting robust reductions of ethanol intake. Similar observations have been made in studies examining neurobiological responses to nicotine, psychostimulants, and opioids. When taken together with observations of potential genetic linkage between the NPY system and the human alcohol abuse disorders, NPY represents a promising target for treating problematic alcohol and drug use, and in protecting individuals from relapse during abstinence.

Repeated cycles of binge-like ethanol (EtOH)-drinking in male C57BL/6J mice augments subsequent voluntary EtOH intake but not other dependence-like phenotypes

BACKGROUND

Recently, procedures have been developed to model specific facets of human alcohol abuse disorders, including those that model excessive binge-like drinking (i.e., "drinking-in-the-dark," or DID procedures) and excessive dependence-like drinking (i.e., intermittent ethanol [EtOH] vapor exposure). Similar neuropeptide systems modulate excessive EtOH drinking stemming from both procedures, raising the possibility that both paradigms are actually modeling the same phenotypes and triggering the same central neuroplasticity. Therefore, the goal of this present project was to study the effects of a history of binge-like EtOH drinking, using DID procedures, on phenotypes that have previously been described with procedures to model dependence-like drinking.

METHODS

Male C57BL/6J mice first experienced 0 to 10 four-day binge-like drinking episodes (3 days of rest between episodes). Beginning 24 hours after the final binge-like drinking session, mice were tested for anxiety-like behaviors (with elevated plus maze [EPM] and open-field locomotor activity tests), ataxia with the rotarod test, and sensitivity to handling-induced convulsions (HICs). One week later, mice began a 40-day 2-bottle (water vs. EtOH) voluntary consumption test with concentration ranging from 10 to 20% (v/v) EtOH.

RESULTS

A prior history of binge-like EtOH drinking significantly increased subsequent voluntary EtOH consumption and preference, effects most robust in groups that initially experienced 6 or 10 binge-like drinking episodes and completely absent in mice that experienced 1 binge-like drinking episode. Conversely, a history of binge-like EtOH drinking did not influence anxiety-like behaviors, ataxia, or HICs.

CONCLUSIONS

Excessive EtOH drinking stemming from DID procedures does not initially induce phenotypes consistent with a dependence-like state. However, the subsequent increases in voluntary EtOH consumption and preference that become more robust following repeated episodes of binge-like EtOH drinking may reflect the early stages of EtOH dependence, suggesting that DID procedures may be ideal for studying the transition to EtOH dependence.

The paraventricular thalamus provides a polysynaptic brake on limbic CRF neurons to sex-dependently blunt binge alcohol drinking and avoidance behavior in mice

Bed nucleus of the stria terminalis (BNST) neurons that synthesize corticotropin-releasing factor (CRF) drive binge alcohol drinking and anxiety. Here, we found that female C57BL/6J mice binge drink more than males and have greater basal BNSTCRF neuron excitability and synaptic excitation. We identified a dense VGLUT2 + synaptic input from the paraventricular thalamus (PVT) that releases glutamate directly onto BNSTCRF neurons but also engages a large BNST interneuron population to ultimately inhibit BNSTCRF neurons, and this polysynaptic PVTVGLUT2-BNSTCRF circuit is more robust in females than males. Chemogenetic inhibition of the PVTBNST projection promoted binge alcohol drinking only in female mice, while activation reduced avoidance behavior in both sexes. Lastly, repeated binge drinking produced a female-like phenotype in the male PVT-BNSTCRF excitatory synapse without altering the function of PVTBNST neurons per se. Our data describe a complex, feedforward inhibitory PVTVGLUT2-BNSTCRF circuit that is sex-dependent in its function, behavioral roles, and alcohol-induced plasticity.