Montserrat Navarro

Prior multiple ethanol withdrawals enhance stress-induced anxiety-like behavior: inhibition by CRF1- and benzodiazepine-receptor antagonists and a 5-HT1a-receptor agonist.

Repeated withdrawals from chronic ethanol induce a persistent adaptive change. Further, stress substitutes for the initial two withdrawals of a multiple-withdrawal protocol to sensitize rats to withdrawal-induced anxiety-like behavior (‘anxiety’). Therefore, it was tested whether the persistent adaptation induced by multiple-withdrawal exposures allows stress to elicit anxiety after a period of abstinence. Social interaction was used to assess the degree of anxiety induced by 45 min of restraint stress 3, 7, or 14 days after rats were exposed to multiple withdrawals from a chronic 4.5% ethanol diet. Restraint stress reduced social interaction (ie anxiety-like behavior) at 3, but not at 7 or 14 days, after the multiple withdrawals. No anxiety response was observed in animals that received multiple withdrawals without stress or in animals that received stress when exposed only to control liquid diet. Drugs (ie a CRF1-receptor antagonist, a benzodiazepine receptor antagonist, and a 5-HT1A-receptor agonist) previously demonstrated to block the cumulative adaptation, when administered during repeated withdrawals, prevented stress-induced anxiety-like behavior during abstinence. Additionally, these drugs applied prior to stress in the rats previously exposed to the repeated withdrawal protocol, likewise, minimized stress-induced anxiety. The anxiety following stress during abstinence from previous chronic ethanol exposure is indicative of an interaction of stress with the persistent adaptive change caused by repeated withdrawals. Stress eliciting anxiety-like behavior during abstinence from previous ethanol exposures in rats is consistent with stress inducing anxiety during recovery (sobriety) in the alcoholic, a circumstance that can facilitate craving and relapse.

CRF-1 antagonist and CRF-2 agonist decrease binge-like ethanol drinking in c57bl/6j mice independent of the HPA axis

Recent evidence suggests that corticotropin-releasing factor (CRF) receptor (CRFR) signaling is involved in modulating binge-like ethanol consumption in C57BL/6J mice. In this report, a series of experiments were performed to further characterize the role of CRFR signaling in binge-like ethanol consumption. The role of central CRFR signaling was assessed with intracerebroventricular (i.c.v.) infusion of the nonselective CRFR antagonist, α-helical CRF9–41 (0, 1, 5, 10 μg/1 μl). The contribution of central CRF type 2 receptor (CRF2R) signaling was assessed with i.c.v. infusion of the selective CRF2R agonist, urocortin (Ucn) 3 (0, 0.05, 0.1, or 0.5 μg/1 μl). The role of the hypothalamic–pituitary–adrenal (HPA) axis was assessed by pretreating mice with intraperitoneal (i.p.) injection of (1) the corticosterone synthesis inhibitor, metyrapone (0, 50, 100, 150 mg/kg) or (2) the glucocorticoid receptor antagonist, mifepristone (0, 25, 50 mg/kg), and (3) by using radioimmunoassay to determine whether binge-like ethanol intake influenced plasma corticosterone levels. Finally, we determined whether the ability of the CRF1R antagonist, CP-154,526 (CP; 0, 10, 15 mg/kg, i.p.), to blunt binge-like drinking required normal HPA axis signaling by comparing the effectiveness of CP in adrenalectomized (ADX) and normal mice. Results showed that i.c.v. infusion of a 1 μg dose of α-helical CRF9–41 significantly attenuated binge-like ethanol consumption relative to vehicle treatment, and i.c.v. infusion of Ucn 3 dose-dependently blunted binge-like drinking. On the other hand, metyrapone nonselectively reduced both ethanol and sucrose consumption, mifepristone did not alter ethanol drinking, and binge-like drinking did not correlate with plasma corticosterone levels. Finally, i.p. injection of CP significantly attenuated binge-like ethanol intake in both ADX and normal mice. Together, these results suggest that binge-like ethanol intake in C57BL/6J mice is modulated by CRF1R and CRF2R signaling, such that blockade of CRF1R or activation of CRF2R effectively reduces excessive ethanol intake. Furthermore, normal HPA axis signaling is not necessary to achieve binge-like drinking behavior.

Corticotropin Releasing Factor Signaling in the Central Amygdala is Recruited during Binge-Like Ethanol Consumption in C57BL/6J Mice

A well established body of work indicates a crucial role for corticotropin-releasing factor (CRF) in neurobiological responses associated with excessive dependence-like ethanol drinking in ethanol-vapor-exposed rodents. Recent evidence demonstrates a role for CRF in the modulation of binge-like ethanol consumption by nondependent mice, a behavior that can precede ethanol dependence. The CRF circuitry that is engaged by binge-like ethanol exposure, however, is unknown. Using converging approaches, we provide evidence that, similar to ethanol-vapor-induced increases in ethanol intake, CRF signaling in the central nucleus of the amygdala (CeA) is engaged during binge-like ethanol consumption by C57BL/6J mice. Specifically, we found that binge-like consumption of an ethanol solution (20% ethanol v/v) was attenuated by pretreatment with the CRF1R antagonists antalarmin, 4-ethyl-[2,5,6-trimethyl-7-(2,4,6-trimethylphenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-yl]amino-1-butanol, and NBI-27914 at doses (30 mg/kg, i.p.) that did not alter nonbinge-like ethanol consumption. Binge-like ethanol consumption resulted in significant increases of CRF immunoreactivity in the CeA immediately following ethanol drinking and 18–24 h following ethanol removal and also blocked the ability of CRF to enhance GABAergic transmission in the CeA 18–24 h following ethanol removal. Pretreatment with bilateral injections of antalarmin (1 μg/0.5 μl per side) into the CeA, but not the adjacent basolateral amygdala, significantly attenuated binge-like ethanol consumption. These findings suggest that CRF signaling in the CeA is recruited during excessive ethanol intake, before the development of dependence. We hypothesize that plastic changes in CRF signaling develop with repeated binge-like drinking episodes, contributing to the transition to dependence.

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.

Corticotropin-Releasing Factor (CRF) Sensitization of Ethanol Withdrawal-Induced Anxiety-Like Behavior is Brain Site Specific and Mediated by CRF-1 Receptors: Relation to Stress-Induced Sensitization

In abstinent alcoholics, stress induces negative affect—a response linked to craving and relapse. In rats, repeated stresses at weekly intervals before 5-day ethanol diet sensitize withdrawal-induced anxiety-like behavior (“anxiety”) that is blocked by a corticotrophin-releasing factor 1 (CRF-1)-receptor antagonist. Current experiments were performed to identify brain sites that support CRF involvement in stress sensitization of ethanol withdrawal-induced anxiety-like behavior. First, different doses of CRF microinjected weekly into the central amygdala (CeA) before ethanol exposure produced a dose-related sensitization of anxiety during ethanol withdrawal. Subsequently, CRF microinjection into the basolateral amygdala, dorsal raphe nucleus (DRN), or dorsal bed nucleus of the stria terminalis (d-BNST) also sensitized ethanol withdrawal-induced anxiety. In contrast, sensitization of ethanol withdrawal-induced anxiety was not observed after weekly CRF administration into the ventral-BNST, CA1-hippocampal region, or hypothalamic-paraventricular nucleus. Then, experiments documented the CRF receptor subtype responsible for CRF and stress sensitization of withdrawal-induced anxiety. Systemic administration of a CRF-1 receptor antagonist before CRF microinjection into the CeA, DRN, or d-BNST prevented CRF-induced sensitization of anxiety during ethanol withdrawal. Furthermore, repeated microinjections of urocortin-3, a CRF-2 receptor agonist, into the CRF-positive sites did not sensitize anxiety after withdrawal from ethanol. Finally, microinjection of a CRF-1 receptor antagonist into the CeA, DRN, or d-BNST before stress blocked sensitization of anxiety-like behavior induced by the repeated stress/ethanol withdrawal protocol. These results indicate that CRF released by stress acts on CRF-1 receptors within specific brain regions to produce a cumulative adaptation that sensitizes anxiety-like behavior during withdrawal from chronic ethanol exposure.

Serotonin engages an anxiety and fear-promoting circuit in the extended amygdala

Serotonin (also known as 5-hydroxytryptamine (5-HT)) is a neurotransmitter that has an essential role in the regulation of emotion. However, the precise circuits have not yet been defined through which aversive states are orchestrated by 5-HT. Here we show that 5-HT from the dorsal raphe nucleus (5-HTDRN) enhances fear and anxiety and activates a subpopulation of corticotropin-releasing factor (CRF) neurons in the bed nucleus of the stria terminalis (CRFBNST) in mice. Specifically, 5-HTDRN projections to the BNST, via actions at 5-HT2C receptors (5-HT2CRs), engage a CRFBNST inhibitory microcircuit that silences anxiolytic BNST outputs to the ventral tegmental area and lateral hypothalamus. Furthermore, we demonstrate that this CRFBNST inhibitory circuit underlies aversive behaviour following acute exposure to selective serotonin reuptake inhibitors (SSRIs). This early aversive effect is mediated via the corticotrophin-releasing factor type 1 receptor (CRF1R, also known as CRHR1), given that CRF1R antagonism is sufficient to prevent acute SSRI-induced enhancements in aversive learning. These results reveal an essential 5-HTDRN→CRFBNST circuit governing fear and anxiety, and provide a potential mechanistic explanation for the clinical observation of early adverse events to SSRI treatment in some patients with anxiety disorders.

Repeated Lipopolysaccharide (LPS) or Cytokine Treatments Sensitize Ethanol Withdrawal-Induced Anxiety-Like Behavior

Previous investigations demonstrated that repeated stresses before an ethanol exposure sensitize ethanol withdrawal-induced anxiety-like behavior (‘anxiety’). In addition to activating the hypothalamic–pituitary–adrenal axis, acute stress also elevates cytokines in brain. Initially, to test possible cytokine involvement in this stress/withdrawal protocol, cytokines were increased in brain with 2 weekly repeated lipopolysaccharide (LPS) administrations (1000 μ/kg) (LPS/withdrawal protocol) or with twice weekly intracerebroventricular (i.c.v.) administrations of the cytokines IL-1β, CCL2 (MCP-1) or TNFα (cytokine/withdrawal protocol) before exposure and withdrawal from a 5-day cycle of chronic ethanol diet. Both protocols sensitized withdrawal-induced anxiety and confirm cytokine involvement in the sensitized anxiety response. Testing of various doses of LPS (16–1000 μg/kg) and TNFα (3–100 ng, i.c.v.) demonstrated the dose-related nature of these protocols to sensitize withdrawal-induced anxiety. The sensitized anxiety was not produced by a single 5-day ethanol diet cycle or by repeated LPS or cytokine treatments alone. Likewise, sensitized anxiety in these protocols could not be attributed to differences in ethanol ingestion. When challenged with a subsequent re-exposure to a 5-day ethanol diet cycle 16 days after completion of the LPS/withdrawal or cytokine/withdrawal protocols, an increase in withdrawal-induced anxiety was observed—an indication of induction of an underlying persistent adaptive change. Finally, just as found previously with the stress/withdrawal protocol, administration of the benzodiazepine receptor antagonist flumazenil before the LPS or TNF treatments prevented anxiety sensitization. Together, these findings indicate that increased cytokine activity induces adaptive change that supports sensitization of ethanol withdrawal-induced anxiety that may be linked to GABAA-receptor function.

Effects of Melanocortin Receptor Activation and Blockade on Ethanol Intake: A Possible Role for the Melanocortin-4 Receptor

BACKGROUND The melanocortin (MC) system is composed of peptides that are cleaved from the polypeptide precursor pro-opiomelanocortin. A growing body of literature suggests that the MC system modulates neurobiological responses to drugs of abuse. Because ethanol has direct effects on central pro-opiomelanocortin activity, it is possible that MC neuropeptides participate in the control of voluntary ethanol consumption. Here we assessed the possibility that MC receptor (MCR) agonists modulate ethanol intake via the MC3 receptor (MC3R) and/or the MC4 receptor (MC4R) and whether the MCR antagonist AgRP-(83-132) controls ethanol consumption. METHODS Mc3r-deficient (Mc3r) and wild-type (Mc3r) littermate mice were given intraperitoneal (10 mg/kg) and intracerebroventricular (1.0 microg ICV) doses of melanotan II (MTII), a nonselective MCR agonist. To assess the role of MC4R, C57BL/6J mice were given an ICV infusion of the highly selective MC4R agonist cyclo(NH-CH2-CH2-CO-His-d-Phe-Arg-Trp-Glu)-NH2 (1.0 or 3.0 microg). Finally, naïve C57BL/6J mice were given an ICV infusion of AgRP-(83-132) (0.05 and 1.0 microg). RESULTS MTII was similarly effective at reducing ethanol drinking in Mc3r-deficient (Mc3r) and wild-type (Mc3r) littermate mice. Furthermore, ICV infusion of the MC4R agonist significantly reduced ethanol drinking, whereas ICV infusion of AgRP-(83-132) significantly increased ethanol drinking in C57BL/6J mice. Neither MTII nor AgRP-(83-132) altered blood ethanol levels at doses that modulated ethanol drinking. CONCLUSIONS The present results suggest that MC4R, and not MC3R, modulates MCR agonist-induced reduction of ethanol consumption and that ethanol intake is increased by the antagonistic actions of AgRP-(83-132). These findings strengthen the argument that MCR signaling controls ethanol consumption and that compounds directed at MCR may represent promising targets for treating alcohol abuse disorders in addition to obesity.

MTII-induced reduction of voluntary ethanol drinking is blocked by pretreatment with AgRP-(83-132)

Over the last 30 years, evidence has emerged indicating that the central melanocortin (MC) peptide system is involved with neurobiological responses to drugs of abuse. Recently, rats selectively bred for high ethanol preference were shown to have altered brain levels of MC receptor (MCR) and central infusion of the potent non-selective MCR agonist, melanotan-II (MTII), attenuates their high ethanol drinking. The goal of the present report was to further characterize the effects of MTII on voluntary ethanol consumption. In alcohol preferring C57BL/6 mice with an established history of ethanol drinking, intracerebroventricular (i.c.v.) infusion of a 5.0 microg dose of agouti-related protein (AgRP)-(83-132), a non-selective MCR antagonist, has no effect on 8-h ethanol drinking or food intake. However, pre-treatment with a 5.0 microg dose of (AgRP)-(83-132) significantly blocks MTII-induced (1.0 microg) reduction of 8-h ethanol drinking and food intake, consistent with a competitive antagonist action. I.c.v. infusion of MTII does not cause alteration of blood ethanol levels 2- or 4-h following intraperitoneal (i.p.) injection of a 4.0 g ethanol/kg dose. Finally, when given in an i.p. injection, a 150 microg dose of MTII reduces 8-h ethanol drinking. These data extend recent findings by showing that both central and peripheral administration of MTII reduces ethanol drinking by mice. Additionally, the ability of (AgRP)-(83-132) to block the effects of MTII implies that MTII-induced reduction of ethanol drinking is receptor mediated.

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.