Sex differences in binge-like EtOH drinking, corticotropin-releasing hormone and corticosterone: effects of β-endorphin

Binge drinking is an increasingly common pattern of risky use associated with numerous health problems, including alcohol use disorders. Because low basal plasma levels of βendorphin (β-E) and an increased β-E response to alcohol are evident in genetically at-risk human populations, this peptide is thought to contribute to the susceptibility for disordered drinking. Animal models suggest that the effect of β-E on consumption may be sex-dependent. Here, we studied binge-like EtOH consumption in transgenic mice possessing varying levels of β-E: wild-type controls with 100% of the peptide (β-E +/+), heterozygous mice constitutively modified to possess 50% of wild-type levels (β-E +/−) and mice entirely lacking the capacity to synthesize β-E (−/−). These three genotypes and both sexes were evaluated in a 4-day, two-bottle choice, drinking in the dark paradigm with limited access to 20% EtOH. β-E deficiency determined sexually divergent patterns of drinking in that β-E −/− female mice drank more than their wild-type counterparts, an effect not observed in male mice. β-E −/− female mice also displayed elevated basal anxiety, plasma corticosterone and corticotropin-releasing hormone mRNA in the extended amygdala, and all of these were normalized by EtOH self-administration. These data suggest that a heightened risk for excessive EtOH consumption in female mice is related to the drug\u27s ability to ameliorate an overactive anxiety/stress-like state. Taken together, our study highlights a critical impact of sex on neuropeptide regulation of EtOH consumption

Sex and β-Endorphin Influence the Effects of Ethanol on Limbic Gabra2 Expression in a Mouse Binge Drinking Model

Binge drinking is a widespread problem linked to increased risk for alcohol-related complications, including development of alcohol use disorders. In the last decade, binge drinking has increased significantly, specifically in women. Clinically, sexually dimorphic effects of alcohol are well-characterized, however, the underlying mechanisms for these dimorphisms in the physiological and behavioral effects of alcohol are poorly understood. Among its many effects, alcohol consumption reduces anxiety via the inhibitory neurotransmitter GABA, most likely acting upon receptors containing the α-2 subunit (Gabra2). Previous research from our laboratory indicates that female mice lacking the endogenous opioid peptide β-endorphin (βE) have an overactive stress axis and enhanced anxiety-like phenotype, coupled with increased binge-like alcohol consumption. Because βE works via GABA signaling to reduce anxiety, we sought to determine whether sexually dimorphic binge drinking behavior in βE deficient mice is coupled with differences in CNS Gabra2 expression. To test this hypothesis, we used βE knock-out mice in a drinking in the dark model where adult male and female C57BL/6J controls (βE +/+) and βE deficient (βE -/-; B6.129S2-Pomctm1Low/J) mice were provided with one bottle of 20% ethanol (EtOH) and one of water (EtOH drinkers) or two bottles of water (water drinkers) 3 h into the dark cycle for four consecutive days. Following a binge test on day 4, limbic tissue was collected and frozen for subsequent qRT-PCR analysis of Gabra2 mRNA expression. Water-drinking βE +/+ females expressed more Gabra2 in central nucleus of the amygdala and the bed nucleus of the stria terminalis than males, but this sex difference was absent in the βE -/- mice. Genotype alone had no effect on alcohol consumption or drug-induced increase in Gabra2 expression. In contrast, βE expression had bi-directional effects in females: in wildtypes, Gabra2 mRNA was reduced by binge EtOH consumption, while EtOH increased expression in βE -/- females to levels commensurate with drug-naïve βE +/+ females. These results support the contention that βE plays a role in sexually dimorphic binge-like EtOH consumption, perhaps through differential expression of GABAA α2 subunits in limbic structures known to play key roles in the regulation of stress and anxiety

Sex and β-Endorphin Influence the Effects of Ethanol on Limbic Gabra2 Expression in a Mouse Binge Drinking Model

Binge drinking is a widespread problem linked to increased risk for alcohol-related complications, including development of alcohol use disorders. In the last decade, binge drinking has increased significantly, specifically in women. Clinically, sexually dimorphic effects of alcohol are well-characterized, however, the underlying mechanisms for these dimorphisms in the physiological and behavioral effects of alcohol are poorly understood. Among its many effects, alcohol consumption reduces anxiety via the inhibitory neurotransmitter GABA, most likely acting upon receptors containing the α-2 subunit (Gabra2). Previous research from our laboratory indicates that female mice lacking the endogenous opioid peptide β-endorphin (βE) have an overactive stress axis and enhanced anxiety-like phenotype, coupled with increased binge-like alcohol consumption. Because βE works via GABA signaling to reduce anxiety, we sought to determine whether sexually dimorphic binge drinking behavior in βE deficient mice is coupled with differences in CNS Gabra2 expression. To test this hypothesis, we used βE knock-out mice in a “drinking in the dark” model where adult male and female C57BL/6J controls (βE +/+) and βE deficient (βE -/-; B6.129S2-Pomctm1Low/J) mice were provided with one bottle of 20% ethanol (EtOH) and one of water (EtOH drinkers) or two bottles of water (water drinkers) 3 h into the dark cycle for four consecutive days. Following a binge test on day 4, limbic tissue was collected and frozen for subsequent qRT-PCR analysis of Gabra2 mRNA expression. Water-drinking βE +/+ females expressed more Gabra2 in central nucleus of the amygdala and the bed nucleus of the stria terminalis than males, but this sex difference was absent in the βE -/- mice. Genotype alone had no effect on alcohol consumption or drug-induced increase in Gabra2 expression. In contrast, βE expression had bi-directional effects in females: in wildtypes, Gabra2 mRNA was reduced by binge EtOH consumption, while EtOH increased expression in βE -/- females to levels commensurate with drug-naïve βE +/+ females. These results support the contention that βE plays a role in sexually dimorphic binge-like EtOH consumption, perhaps through differential expression of GABAA α2 subunits in limbic structures known to play key roles in the regulation of stress and anxiety

Locomotor sensitization to ethanol: Contribution of b-Endorphin

Alcohol use disorders, like all drug addictions, involve a constellation of adaptive changes throughout the brain. Neural activity underlying changes in the rewarding properties of alcohol reflect changes in dopamine transmission in mesolimbic and nigrostriatal pathways and these effects are modulated by endogenous opioids such as b-Endorphin. In order to study the role of b-Endorphin in the development of locomotor sensitization to repeated EtOH exposure, we tested transgenic mice that vary in their capacity to synthesize this peptide as a result of constitutive modification of the Pomc gene. Our results indicate that mice deficient in b-Endorphin show attenuated locomotor activation following an acute injection of EtOH (2 g/kg) and, in contrast to wildtype mice, fail to demonstrate locomotor sensitization after 12 days of repeated EtOH injections. These data support the idea that b-Endorphin modulates the locomotor effects of EtOH and contributes to the neuroadaptive changes associated with chronic use

Never Enough : the Neuroscience and Experience of Addiction

Judith Grisel was a daily drug user and college dropout when she began to consider that her addiction might have a cure, one that she herself could perhaps discover by studying the brain. Now, after twenty-five years as a neuroscientist, she shares what she and other scientists have learned about addiction, enriched by captivating glimpses of her personal journey. In Never Enough, Grisel reveals the unfortunate bottom line of all regular drug use: there is no such thing as a free lunch. All drugs act on the brain in a way that diminishes their enjoyable effects and creates unpleasant ones with repeated use. Yet they have their appeal, and Grisel draws on anecdotes both comic and tragic from her own days of using as she limns the science behind the love of various drugs, from marijuana to alcohol, opiates to psychedelics, speed to spice. With more than one in five people over the age of fourteen addicted, drug abuse has been called the most formidable health problem worldwide, and Grisel delves with compassion into the science of this scourge. She points to what is different about the brains of addicts even before they first pick up a drink or drug, highlights the changes that take place in the brain and behavior as a result of chronic using, and shares the surprising hidden gifts of personality that addiction can expose. She describes what drove her to addiction, what helped her recover, and her belief that a “cure” for addiction will not be found in our individual brains but in the way we interact with our communities. Set apart by its color, candor, and bell-clear writing, Never Enough is a revelatory look at the roles drugs play in all of our lives and offers crucial new insight into how we can solve the epidemic of abuse. -- publisherhttps://digitalcommons.bucknell.edu/books/1061/thumbnail.jp

Beta-Endorphin Modulates the Effect of Stress on Novelty-Suppressed Feeding

Although stress is implicated in the pathophysiology of mood and anxiety disorders, not all individuals who suffer stressful life events develop psychopathology. Differential susceptibility to stress may be influenced by genetically mediated differences in hypothalamic-pituitary-adrenal (HPA) axis activity and moderation of the stress response by the opioid peptide beta-endorphin (beta-E). The present study investigated genetic contributions to coping behavior by examining anxious behavior of transgenic mice with varying capacities to synthesize beta-E [B6.129S2-Pomc(tm1Low)/J; regulated by insertion of a premature stop codon into one or both copies of the proopiomelanocortin (POMC) gene], both under normal conditions and following 3 min of forced swim (FS). Ten minutes after this stress exposure or a control manipulation, acutely food-deprived female and male transgenic mice were subjected to a novelty-suppressed feeding (NSF) test, during which their interaction with an almond slice located in the center of an open field box was measured. There was an interaction between genotype and stress for latency to approach the almond and whether or not the almond was approached, such that mice with low or absent beta-E displayed a stronger aversion to novelty-feeding after stress exposure than did mice with normal levels. These data provide evidence for a moderating effect of beta-E on the behavioral response to stress. Genotypic differences in anxious behavior emerged when mice were stressed prior to behavioral assessment, suggesting that beta-E plays a role in coping behavior. These findings indicate that genetic variability in sensitivity of the beta-E system to stress may contribute, at least in part, to heritable differences in stress reactivity as well as vulnerability to stress-related psychopathology

Oral Self-Administration Of EtOH In Transgenic Mice Lacking Beta-Endorphin

EtOH modifies the production and/or release of endogenous opioid peptides, including -endorphin (Gianoulakis, 2004; Przewlocka et al., 1994; Schulz et al., 1980). Opioids subsequently influence the reinforcing properties of EtOH and the development of alcoholism (Terenius, 1996; Van Ree, 1996). In this study, beta-endorphin deficient mutant mice were used to examine the effects of a specific opioid peptide on EtOH consumption. Mice were obtained from The Jackson Laboratory, Bar Harbor, ME, USA. Male and female, adult naïve mice were single housed in Plexiglas cages with corn cob bedding and ad lib access to food (mouse chow) and water. A two-bottle free choice EtOH oral self-administration paradigm was administered to homozygous mutant mice (void of all beta-endorphin), heterozygous mice (50% beta-endorphin expression), and sibling wildtype mice (C57BL/6J). Subjects received increasing concentrations of EtOH (0%, 3%, 6%, 12%, and 15%) each given over an eight day span, and were evaluated for preference and consumption each day. Bottles were switched every other day to avoid the development of a side preference. Overall, females drank more than males. Homozygous mutant mice (KO) showed decreased preference for EtOH at all concentrations, and self-administered significantly less than heterozygous mice (HT) and wildtype mice (C57). The HTs had a tendency to drink the most followed by the C57s, and the KOs drank the least. These data support the hypothesis that beta-endorphin influences the reinforcing effects of EtOH

β-Endorphin and sex differentially modulate the response to EtOH in a sitespecific manner

The effects of alcohol are multifaceted, involving brain circuits regulating reward, motivation, and stress, frequently via the endogenous opioid, beta-endorphin (β-E). It is currently unknown how alcohol affects neural circuit activation in females and how β-E affects ethanol\u27s ability to induce neuronal activation. Therefore, we investigated the impact of acute alcohol treatment on neuronal activation in reward-and stress-related brain circuitry in a sex-and β-E dependent manner. In this study, male and female control (C57BL/6J; β-E+/+) and β-E null (−/−) mice were injected intraperitoneally with 2 g/kg ethanol (EtOH) or saline. Post-injection, animals were sacrificed using ketamine/xylazine and perfused with saline followed by 4% paraformaldehyde. Brain sections (35 μm) were immunohistochemically processed for tyrosine hydroxylase (TH), dopamine\u27s ratelimiting enzyme, and c-fos, a neuronal activation marker. The number of c-fos immunoreactive cell nuclei, THimmunoreactivity, and TH/c-fos-ir cells were quantified in the nucleus accumbens (NAc), ventral tegmental area (VTA), paraventricular nucleus (PVN), central nucleus of the amygdala (CeA), paraventricular thalamic nucleus (PVA) and Edinger-Westphal nucleus (EW). In females, EtOH increased c-fos expression in the CeA, PVN, EW and NAc shell, while c-fos expression in the VTA, and TH expression in the VTA and NAc, depended on a genotype and treatment interaction. In males, EtOH increased c-fos in the CeA and PVN. EtOH also increased the number of double-labeled cells in the Arc, but only in females. These results suggest that the neurons in females are inherently more sensitive to EtOH, emphasizing the importance of studying the relationship between sex and alcohol addiction