• Energy Research

Abstinence from alcohol is associated with the recruitment of neurons in the central nucleus of the amygdala (CeA) in nondependent rats that binge drink alcohol and in alcohol-dependent rats. However, whether the recruitment of this neuronal ensemble in the CeA is causally related to excessive alcohol drinking or if it represents a consequence of excessive drinking remains unknown. We tested the hypothesis that the recruitment of a neuronal ensemble in the CeA during abstinence is required for excessive alcohol drinking in nondependent rats that binge drink alcohol and in alcohol-dependent rats. We found that inactivation of the CeA neuronal ensemble during abstinence significantly decreased alcohol drinking in both groups. In nondependent rats, the decrease in alcohol intake was transient and returned to normal the day after the injection. In dependent rats, inactivation of the neuronal ensemble with Daun02 produced a long-term decrease in alcohol drinking. Moreover, we observed a significant reduction of somatic withdrawal signs in dependent animals that were injected with Daun02 in the CeA. These results indicate that the recruitment of a neuronal ensemble in the CeA during abstinence from alcohol is causally related to excessive alcohol drinking in alcohol-dependent rats, whereas a similar neuronal ensemble only partially contributed to alcohol-binge-like drinking in nondependent rats. These results identify a critical neurobiological mechanism that may be required for the transition to alcohol dependence, suggesting that focusing on the neuronal ensemble in the CeA may lead to a better understanding of the etiology of alcohol use disorders and improve medication development.SIGNIFICANCE STATEMENTAlcohol dependence recruits neurons in the central nucleus of the amygdala (CeA). Here, we found that inactivation of a specific dependence-induced neuronal ensemble in the CeA reversed excessive alcohol drinking and somatic signs of alcohol dependence in rats. These results identify a critical neurobiological mechanism that is required for alcohol dependence, suggesting that targeting dependence neuronal ensembles may lead to a better understanding of the etiology of alcohol use disorders, with implications for diagnosis, prevention, and treatment.

Alcohol use disorder (AUD) is associated with the dysregulation of brain stress and reward systems, including glucocorticoid receptors (GRs). The mixed glucocorticoid/progesterone receptor antagonist mifepristone and selective GR antagonist CORT113176 have been shown to selectively reduce alcohol consumption in alcohol-dependent rats. Mifepristone has also been shown to decrease alcohol consumption and craving for alcohol in humans with AUD. The present study tested the effects of the GR modulators CORT118335, CORT122928, CORT108297, and CORT125134 on alcohol self-administration in nondependent (air-exposed) and alcohol-dependent (alcohol vapor-exposed) adult male rats. Different GR modulators recruit different GR-associated transcriptional cofactors. Thus, we hypothesized that these GR modulators would vary in their effects on alcohol drinking. CORT118335, CORT122928, and CORT125134 significantly reduced alcohol self-administration in both alcohol-dependent and nondependent rats. CORT108297 had no effect on alcohol self-administration in either group. The present results support the potential of GR modulators for the development of treatments for AUD. Future studies that characterize genomic and nongenomic effects of these GR modulators will elucidate potential molecular mechanisms that underlie alcohol drinking in alcohol-dependent and nondependent states.

AbstractElectrophysiological data suggest a dual role of Y2 receptors (Y2Rs) as autoreceptors regulating neuropeptide Y release and heteroceptors regulating gamma‐aminobutyric acid release in the central amygdala (CeA). Here, we report that neither systemic (JNJ‐31020028) nor intra‐CeA (BIIE0246) Y2R antagonism altered operant alcohol responding by alcohol‐dependent or non‐dependent rats. Conversely, BIIE0246 in the CeA reduced anxiety‐like behavior in alcohol‐dependent and alcohol‐naïve rats. The finding that Y2R antagonism reduces anxiety‐like behavior but not alcohol drinking suggests that these two effects may occur via different functions of the Y2R (e.g. autoreceptor versus heteroceptor function).

BackgroundIn humans, emotional and physical signs of withdrawal from ethanol are commonly seen. Many of these symptoms, including anxiety‐like and depression‐like behavior, have been characterized in animal models of ethanol dependence. One issue with several current behavioral tests that measure withdrawal in animal models is that they are often not repeatable within subjects over time. Additionally, irritability, one of the most common symptoms of ethanol withdrawal in humans, has not been well characterized in animal models. The corticotropin‐releasing factor (CRF)‐CRF1 receptor system has been suggested to be critical for the emergence of anxiety‐like behavior in ethanol dependence, but the role of this system in irritability‐like behavior has not been characterized.MethodsThe present study compared the effects of chronic intermittent ethanol (CIE) vapor exposure‐induced ethanol dependence on irritability‐like behavior in rats using the bottle‐brush test during acute withdrawal and protracted abstinence. Rats were trained to self‐administer ethanol in operant chambers and then either left in a nondependent state or made dependent via CIE. Naïve, nondependent, and dependent rats were tested for irritability‐like behavior in the bottle‐brush test 8 hours and 2 weeks into abstinence from ethanol. Separate cohorts of dependent and nondependent rats were used to examine the effect of the specific CRF1 receptor antagonist R121919 on irritability‐like behavior.ResultsDependent rats exhibited escalated ethanol intake compared with their own pre‐CIE baseline and nondependent rats. At both time points of abstinence, ethanol‐dependent rats exhibited increased aggressive‐like responses compared with naïve and nondependent rats. R121919 reduced irritability‐like behavior in both dependent and nondependent rats, but dependent rats were more sensitive to R121919.ConclusionsIrritability‐like behavior is a clinically relevant and reliable measure of negative emotional states that is partially mediated by activation of the CRF‐CRF1 system and remains elevated during protracted abstinence in ethanol‐dependent rats.

The ability of nicotine to suppress body weight is cited as a factor impacting smoking initiation and the failure to quit. Self-administered nicotine in male rats suppresses weight independent of food intake, suggesting that nicotine increases energy expenditure.The current experiment evaluated the impact of self-administered nicotine on metabolism in rats using indirect calorimetry and body composition analysis.Adult male rats with ad libitum access to powdered standard rodent chow self-administered intravenous infusions of nicotine (60 μg/kg/infusion or saline control) in daily 1-h sessions in the last hour of the light cycle. Indirect calorimetry measured respiratory exchange ratio (RER), energy expenditure, motor activity, and food and water consumption for 22.5 h between select self-administration sessions.Self-administered nicotine suppressed weight gain and reduced the percent of body fat without altering the percent of lean mass, as measured by Echo MRI. Nicotine reduced RER, indicating increased fat utilization; this effect was observed prior to weight suppression. Moreover, nicotine intake did not affect motor activity or energy expenditure. Daily food intake was not altered by nicotine self-administration; however, a trend in suppression of meal size, a transient suppression of water intake, and an increase in meal frequency was observed.These data provide evidence that self-administered nicotine suppresses body weight via increased fat metabolism, independent of significant changes in feeding, activity, or energy expenditure.

AbstractA major limitation of the most widely used current animal models of alcohol dependence is that they use forced exposure to ethanol including ethanol-containing liquid diet and chronic intermittent ethanol (CIE) vapor to produce clinically relevant blood alcohol levels (BAL) and addiction-like behaviors. We recently developed a novel animal model of voluntary induction of alcohol dependence using ethanol vapor self-administration (EVSA). In this model, naive outbred rats given intermittent access to alcohol vapor self-administration exhibit BAL in the 150-300 mg% range and develop somatic signs of withdrawal during acute abstinence. However, it is unknown whether EVSA leads to an escalation of alcohol drinkingper se, and whether such escalation is associated with neuroadaptations in brain regions related to stress, reward, and habit. To address these issues, we compared the levels of alcohol drinking during withdrawal between rats passively exposed to alcohol (CIE) or voluntarily exposed to EVSA and measured the number of Fos+ neurons during acute withdrawal (16 h) in the central nucleus of the amygdala (CeA), dorsomedial striatum (DMS), dorsolateral striatum (DLS), nucleus accumbens core (Nacc), periaqueducal grey area (PAG), lateral Habenula (HbL), and the paraventricular nucleus of the thalamus (PVT). The rats were first trained to orally self-administer alcohol in standard operant chambers and then divided in 4 groups (CIE, CI-Air, EVSA and Air-SA) and exposed to intermittent ethanol vapor (passive or active) or intermittent air (passive or active) for 8 h/day, 3 days a week. CIE and EVSA rats exhibited similar BAL (150-300 mg% range) and similar escalation of alcohol drinking during withdrawal, while no changes in terms of drinking were observed in the air exposed rats. CIE and EVSA also increased the motivation for alcohol compared to their respective air control groups under a progressive ratio schedule of reinforcement. Acute withdrawal from EVSA and CIE recruited a similar number of Fos+ neurons in the CeA, however, acute withdrawal from EVSA recruited a higher number of Fos+ neurons in every other brain region analyzed compared to acute withdrawal from CIE. Moreover, acute withdrawal from EVSA specifically recruited the DMS and PVT, a pattern not observed in CIE rats.In summary, these results demonstrate that EVSA produces similar escalation of alcohol drinking, motivation to drink, and blood-alcohol levels than the CIE model, while letting animals voluntary initiate alcohol exposure and maintain alcohol dependence. Moreover, while the behavioral measures of alcohol dependence between the voluntary (EVSA) and passive (CIE) model was similar, the recruitment of neuronal ensembles during acute withdrawal was very different with a higher recruitment of Fos+ neurons in key brain regions important for stress, reward and habit-related processes. The EVSA model may be particularly useful to unveil the neuronal networks and pharmacology responsible for the voluntary induction and maintenance of alcohol dependence and may improve translational studies by providing preclinical researchers with an animal model with better face validity for alcohol use disorder.

BackgroundAlcohol binge drinking in humans is thought to increase the risk for alcohol use disorder (AUD). Unclear is whether drinking patterns (e.g., bingelike or stable drinking) differentially affect the transition to compulsive‐like drinking in dependent individuals. We examined whether chronic bingelike drinking facilitates the transition to compulsive‐like drinking in rats.MethodsMale Wistar rats were given 5 months of intermittent access to ethanol (EtOH) (IAE) or continuous access to EtOH (CAE) in a 2‐bottle choice paradigm. Then, rats were given chronic intermittent EtOH (CIE) vapor exposure. Escalation of EtOH intake and compulsive‐like responding for EtOH, using a progressive‐ratio schedule of reinforcement and quinine‐adulterated EtOH, were measured.ResultsIAE rats escalated EtOH drinking after 2 weeks of 2‐bottle choice, whereas CAE rats exhibited stable EtOH drinking for 5 months. After 8 weeks of CIE, both IAE + CIE and CAE + CIE rats escalated their EtOH intake. However, IAE rats escalated their EtOH intake weeks sooner than CAE rats and exhibited greater EtOH intake. No differences in compulsive‐like responding were found between IAE + CIE and CAE + CIE rats. However, both IAE + CIE and CAE + CIE rats showed strong compulsive‐like responding compared with rats without prior IAE or CAE.ConclusionsChronic EtOH drinking at stable or escalated levels for several months is associated with more compulsive‐like responding for EtOH in rats that are exposed to CIE compared with rats without a prior history of EtOH drinking. Moreover, IAE facilitated the transition to compulsive‐like responding for EtOH after CIE exposure, reflected by the escalation of EtOH intake. These results suggest that IAE may facilitate the transition to AUD. This study indicates that despite a moderate level of EtOH drinking, the IAE animal model is highly relevant to early stages of alcohol abuse and suggests that it may be associated with neuroadaptations that produce a faster transition to alcohol dependence.