Pharmacological modulation of repeated ethanol withdrawal-induced anxiety-like behavior differs in alcohol-preferring P and Sprague-Dawley rats

Theoretical Frameworks and Mechanistic Aspects of Alcohol Addiction: Alcohol Addiction as a Reward Deficit/Stress Surfeit Disorder

Alcohol use disorder (AUD) can be defined by a compulsion to seek and take alcohol, the loss of control in limiting intake, and the emergence of a negative emotional state when access to alcohol is prevented. Alcohol use disorder impacts multiple motivational mechanisms and can be conceptualized as a disorder that includes a progression from impulsivity (positive reinforcement) to compulsivity (negative reinforcement). Compulsive drug seeking that is associated with AUD can be derived from multiple neuroadaptations, but the thesis argued herein is that a key component involves the construct of negative reinforcement. Negative reinforcement is defined as drug taking that alleviates a negative emotional state. The negative emotional state that drives such negative reinforcement is hypothesized to derive from the dysregulation of specific neurochemical elements that are involved in reward and stress within basal forebrain structures that involve the ventral striatum and extended amygdala, respectively. Specific neurochemical elements in these structures include decreases in reward neurotransmission (e.g., decreases in dopamine and opioid peptide function in the ventral striatum) and the recruitment of brain stress systems (e.g., corticotropin-releasing factor [CRF]) in the extended amygdala, which contributes to hyperkatifeia and greater alcohol intake that is associated with dependence. Glucocorticoids and mineralocorticoids may play a role in sensitizing the extended amygdala CRF system. Other components of brain stress systems in the extended amygdala that may contribute to the negative motivational state of withdrawal include norepinephrine in the bed nucleus of the stria terminalis, dynorphin in the nucleus accumbens, hypocretin and vasopressin in the central nucleus of the amygdala, and neuroimmune modulation. Decreases in the activity of neuropeptide Y, nociception, endocannabinoids, and oxytocin in the extended amygdala may also contribute to hyperkatifeia that is associated with alcohol withdrawal. Such dysregulation of emotional processing may also significantly contribute to pain that is associated with alcohol withdrawal and negative urgency (i.e., impulsivity that is associated with hyperkatifeia during hyperkatifeia). Thus, an overactive brain stress response system is hypothesized to be activated by acute excessive drug intake, to be sensitized during repeated withdrawal, to persist into protracted abstinence, and to contribute to the compulsivity of AUD. The combination of the loss of reward function and recruitment of brain stress systems provides a powerful neurochemical basis for a negative emotional state that is responsible for the negative reinforcement that at least partially drives the compulsivity of AUD.

Attenuation of ethanol abstinence-induced anxiety- and depressive-like behavior by the phosphodiesterase-4 inhibitor rolipram in rodents

RATIONALE

Withdrawal symptoms stand as a core feature of alcohol dependence. Our previous results have shown that inhibition of phosphodiesterase-4 (PDE4) decreased ethanol seeking and drinking in alcohol-preferring rodents. However, little is known about whether PDE4 is involved in ethanol abstinence-related behavior.

OBJECTIVE

The objective of this study was to characterize the role of PDE4 in the development of anxiety- and depressive-like behavior induced by abstinence from ethanol exposure in different animal models.

METHODS

Using three rodent models of ethanol abstinence, we examined the effects of rolipram, a prototypical, selective PDE4 inhibitor, on (1) anxiety-like behavior induced by repeated ethanol abstinence in the elevated plus maze test in fawn-hooded (FH/Wjd) rats, (2) anxiety-like behavior in the open-field test and light-dark transition test following acute ethanol abstinence in C57BL/6J mice, and (3) anxiety- and depressive-like behavior induced by protracted ethanol abstinence in the elevated plus maze, forced-swim, and tail-suspension tests in C57BL/6J mice.

RESULTS

Pretreatment with rolipram (0.1 or 0.2 mg/kg) significantly increased entries and time spent in the open arms of the elevated plus maze test in rats with repeated ethanol abstinence. Similarly, in mice with acute ethanol abstinence, administration of rolipram (0.25 or 0.5 mg/kg) dose-dependently increased the crossings in the central zone of the open-field test and duration and transitions on the light side of the light-dark transition test, suggesting anxiolytic-like effects of rolipram. Consistent with these, chronic treatment with rolipram (0.1, 0.3, or 1.0 mg/kg) increased entries in the open arms of the elevated plus maze test; it also reduced the increased duration of immobility in both the forced-swim and tail-suspension tests in mice after protracted ethanol abstinence, suggesting antidepressant-like effects of rolipram.

CONCLUSIONS

These results provide the first demonstration for that PDE4 plays a role in modulating the development of negative emotional reactions associated with ethanol abstinence, including anxiety and depression. PDE4 inhibitors may be a novel class of drugs for treatment of alcoholism.

Genetic correlation between alcohol preference and conditioned fear: Exploring a functional relationship

Post-traumatic stress disorder (PTSD) and alcohol-use disorders have a high rate of co-occurrence, possibly because they are regulated by common genes. In support of this idea, mice selectively bred for high (HAP) alcohol preference show greater fear potentiated startle (FPS), a model for fear-related disorders such as PTSD, compared to mice selectively bred for low (LAP) alcohol preference. This positive genetic correlation between alcohol preference and FPS behavior suggests that the two traits may be functionally related. This study examined the effects of fear conditioning on alcohol consumption and the effects of alcohol consumption on the expression of FPS in male and female HAP2 and LAP2 mice. In experiment 1, alcohol consumption (g/kg) under continuous-access conditions was monitored daily for 4 weeks following a single fear-conditioning or control treatment (foot shock and no shock). FPS was assessed three times (once at the end of the 4-week alcohol access period, once at 24 h after removal of alcohol, and once at 6-8 days after removal of alcohol), followed by two more weeks of alcohol access. Results showed no change in alcohol consumption, but alcohol-consuming, fear-conditioned, HAP2 males showed increased FPS at 24 h during the alcohol abstinence period compared to control groups. In experiment 2, alcohol consumption under limited-access conditions was monitored daily for 4 weeks. Fear-conditioning or control treatments occurred four times during the first 12 days and FPS testing occurred four times during the second 12 days of the 4-week alcohol consumption period. Results showed that fear conditioning increased alcohol intake in both HAP2 and LAP2 mice immediately following the first conditioning session. Fear-conditioned HAP2 but not LAP2 mice showed greater alcohol intake compared to control groups on drinking days that occurred between fear conditioning and FPS test sessions. FPS did not change as a function of alcohol consumption in either line. These results in mice help shed light on how a genetic propensity toward high alcohol consumption may be related to the risk for developing PTSD and co-morbid alcohol-use disorders in humans.

Prazosin Prevents Increased Anxiety Behavior That Occurs in Response to Stress During Alcohol Deprivations

AIMS

Stress-induced anxiety is a risk factor for relapse to alcohol drinking. The aim of this study was to test the hypothesis that the central nervous system (CNS)-active α₁-adrenergic receptor antagonist, prazosin, would block the stress-induced increase in anxiety that occurs during alcohol deprivations.

METHODS

Selectively bred male alcohol-preferring (P) rats were given three cycles of 5 days of ad libitum voluntary alcohol drinking interrupted by 2 days of alcohol deprivation, with or without 1 h of restraint stress 4 h after the start of each of the first two alcohol deprivation cycles. Prazosin (1.0 or 1.5 mg/kg, IP) or vehicle was administered before each restraint stress. Anxiety-like behavior during alcohol deprivation following the third 5-day cycle of alcohol drinking (7 days after the most recent restraint stress ± prazosin treatment) was measured by performance in an elevated plus-maze and in social approach/avoidance testing.

RESULTS

Rats that received constant alcohol access, or alcohol access and deprivations without stress or prazosin treatments in the first two alcohol deprivations did not exhibit augmented anxiety-like behavior during the third deprivation. In contrast, rats that had been stressed during the first two alcohol deprivations exhibited increased anxiety-like behavior (compared with control rats) in both anxiety tests during the third deprivation. Prazosin given before stresses in the first two cycles of alcohol withdrawal prevented increased anxiety-like behavior during the third alcohol deprivation.

CONCLUSION

Prazosin treatment before stresses experienced during alcohol deprivations may prevent the increased anxiety during subsequent deprivation/abstinence that is a risk factor for relapse to alcohol drinking.

SHORT SUMMARY

Administration of prazosin before stresses during repetitive alcohol deprivations in male alcohol-preferring (P) rats prevents increased anxiety during a subsequent deprivation without further prazosin treatment. Prazosin treatment during repeated alcohol deprivations may prevent the increased anxiety that is a risk factor for relapse to alcohol drinking.

An Update on CRF Mechanisms Underlying Alcohol Use Disorders and Dependence

Alcohol is the most commonly used and abused substance worldwide. The emergence of alcohol use disorders, and alcohol dependence in particular, is accompanied by functional changes in brain reward and stress systems, which contribute to escalated alcohol drinking and seeking. Corticotropin-releasing factor (CRF) systems have been critically implied in the transition toward problematic alcohol drinking and alcohol dependence. This review will discuss how dysregulation of CRF function contributes to the vulnerability for escalated alcohol drinking and other consequences of alcohol consumption, based on preclinical evidence. CRF signaling, mostly via CRF1 receptors, seems to be particularly important in conditions of excessive alcohol taking and seeking, including during early and protracted withdrawal, relapse, as well as during withdrawal-induced anxiety and escalated aggression promoted by alcohol. Modulation of CRF1 function seems to exert a less prominent role over low to moderate alcohol intake, or to species-typical behaviors. While CRF mechanisms in the hypothalamic-pituitary-adrenal axis have some contribution to the neurobiology of alcohol abuse and dependence, a pivotal role for extra-hypothalamic CRF pathways, particularly in the extended amygdala, is well characterized. More recent studies further suggest a direct modulation of brain reward function by CRF signaling in the ventral tegmental area, nucleus accumbens, and the prefrontal cortex, among other structures. This review will further discuss a putative role for other components of the CRF system that contribute for the overall balance of CRF function in reward and stress pathways, including CRF2 receptors, CRF-binding protein, and urocortins, a family of CRF-related peptides.

Persistent adaptation by chronic alcohol is facilitated by neuroimmune activation linked to stress and CRF

This review updates the conceptual basis for the association of alcohol abuse with an insidious adaptation that facilitates negative affect during withdrawal from chronic intermittent alcohol (CIA) exposure - a change that later supports sensitization of stress-induced anxiety following alcohol abstinence. The finding that a CRF1-receptor antagonist (CRF1RA) minimized CIA withdrawal-induced negative affect supported an association of alcohol withdrawal with a stress mechanism. The finding that repeated stresses or multiple CRF injections into selected brain sites prior to a single 5-day chronic alcohol (CA) exposure induced anxiety during withdrawal provided critical support for a linkage of CIA withdrawal with stress. The determination that CRF1RA injection into positive CRF-sensitive brain sites prevented CIA withdrawal-induced anxiety provided support that neural path integration maintains the persistent CIA adaptation. Based upon reports that stress increases neuroimmune function, an effort was undertaken to test whether cytokines would support the adaptation induced by stress/CA exposure. Twenty-four hours after withdrawal from CIA, cytokine mRNAs were found to be increased in cortex as well as other sites in brain. Further, repeated cytokine injections into previously identified brain sites substituted for stress and CRF induction of anxiety during CA withdrawal. Discovery that a CRF1RA prevented the brain cytokine mRNA increase induced by CA withdrawal provided critical evidence for CRF involvement in this neuroimmune induction after CA withdrawal. However, the CRF1RA did not block the stress increase in cytokine mRNA increases in controls. The latter data supported the hypothesis that distinct mechanisms linked to stress and CA withdrawal can support common neuroimmune functions within a brain site. As evidence evolves concerning neural involvement in brain neuroimmune function, a better understanding of the progressive adaptation associated with CIA exposure will advance new knowledge that could possibly lead to strategies to combat alcohol abuse.

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.

The "Prediction of Alcohol Withdrawal Severity Scale" (PAWSS): systematic literature review and pilot study of a new scale for the prediction of complicated alcohol withdrawal syndrome

BACKGROUND

To date, no screening tools for alcohol withdrawal syndromes (AWS) have been validated in the medically ill. Although several tools quantify the severity of AWS (e.g., Clinical Institute Withdrawal Assessment for Alcohol [CIWA]), none identify subjects at risk of AWS, thus missing the opportunity for timely prophylaxis. Moreover, there are no validated tools for the prediction of complicated (i.e., moderate to severe) AWS in the medically ill.

OBJECTIVES

Our goals were (1) to conduct a systematic review of the published literature on AWS to identify clinical factors associated with the development of AWS, (2) to use the identified factors to develop a tool for the prediction of alcohol withdrawal among patients at risk, and (3) to conduct a pilot study to assess the validity of the tool.

METHODS

For the creation of the Prediction of Alcohol Withdrawal Severity Scale (PAWSS), we conducted a systematic literature search using PRISMA (preferred reporting items for systematic reviews and meta-analyses) guidelines for clinical factors associated with the development of AWS, using PubMed, PsychInfo, MEDLINE, and Cochrane Databases. Eligibility criteria included: (i) manuscripts dealing with human subjects, age 18 years or older, (ii) manuscripts directly addressing descriptions of AWS or its predisposing factors, including case reports, naturalistic case descriptions, and all types of clinical trials (e.g., randomized, single-blind, or open label studies), (iii) manuscripts describing characteristics of alcohol use disorder (AUD), and (iv) manuscripts dealing with animal data (which were considered only if they directly dealt with variables described in humans). Obtained data were used to develop the Prediction of Alcohol Withdrawal Severity Scale, in order to assist in the identification of patients at risk for complicated AWS. A pilot study was conducted to assess the new tool's psychometric qualities on patients admitted to a general inpatient medicine unit over a 2-week period, who agreed to participate in the study. Blind to PAWSS results, a separate group of researchers retrospectively examined the medical records for evidence of AWS.

RESULTS

The search produced 2802 articles describing factors potentially associated with increased risk for AWS, increased severity of withdrawal symptoms, and potential characteristics differentiating subjects with various forms of AWS. Of these, 446 articles met inclusion criteria and underwent further scrutiny, yielding a total of 233 unique articles describing factors predictive of AWS. A total of 10 items were identified as correlated with complicated AWS (i.e., withdrawal hallucinosis, withdrawal-related seizures, and delirium tremens) and used to construct the PAWSS. During the pilot study, a total of 68 subjects underwent evaluation with PAWSS. In this pilot sample the sensitivity, specificity, and positive and negative predictive values of PAWSS were 100%, using the threshold score of 4.

DISCUSSION

The results of the literature search identified 10 items which may be correlated with risk for complicated AWS. These items were assembled into a tool to assist in the identification of patients at risk: PAWSS. The results of this pilot study suggest that PAWSS may be useful in identifying risk of complicated AWS in medically ill, hospitalized individuals. PAWSS is the first validated tool for the prediction of severe AWS in the medically ill and its use may aid in the early identification of patients at risk for complicated AWS, allowing for prophylaxis against AWS before severe alcohol withdrawal syndromes develop.

Neurocircuitry of alcohol addiction: synthesis from animal models

Alcoholism, more generically drug addiction, can be defined as a chronically relapsing disorder characterized by: (1) compulsion to seek and take the drug (alcohol); (2) loss of control in limiting (alcohol) intake; and (3) emergence of a negative emotional state (e.g., dysphoria, anxiety, irritability), reflecting a motivational withdrawal syndrome, when access to the drug (alcohol) is prevented (defined here as dependence). The compulsive drug seeking associated with alcoholism can be derived from multiple neuroadaptations, but the thesis argued here, derived largely from animal models, is that a key component involves decreased brain reward function, increased brain stress function, and compromised executive function, all of which contribute to the construct of negative reinforcement. Negative reinforcement is defined as drug taking that alleviates a negative emotional state. The negative emotional state that drives such negative reinforcement is hypothesized to derive from decreases in reward neurotransmission in the ventral striatum, such as decreased dopamine and opioid peptide function in the nucleus accumbens (ventral striatum), but also recruitment of brain stress systems, such as corticotropin-releasing factor (CRF), in the extended amygdala. Data from animal models that support this thesis show that acute withdrawal from chronic alcohol, sufficient to produce dependence, increases reward thresholds, increases anxiety-like responses, decreases dopamine system function, and increases extracellular levels of CRF in the central nucleus of the amygdala. CRF receptor antagonists also block excessive drug intake produced by dependence. Alcoholism also involves substantial neuroadaptations that persist beyond acute withdrawal and trigger relapse and deficits in cognitive function that can also fuel compulsive drinking. A brain stress response system is hypothesized to be activated by acute excessive drug intake, to be sensitized during repeated withdrawal, to persist into protracted abstinence, and to contribute to the compulsivity of alcoholism. Other components of brain stress systems in the extended amygdala that interact with CRF and may contribute to the negative motivational state of withdrawal include increases in norepinephrine function, increases in dynorphin activity, and decreases in neuropeptide Y. The combination of impairment of function in reward circuitry and recruitment of brain stress system circuitry provides a powerful neurochemical basis for the negative emotional states that are responsible for the negative reinforcement that drives the compulsivity of alcoholism.

Theoretical frameworks and mechanistic aspects of alcohol addiction: alcohol addiction as a reward deficit disorder

Alcoholism can be defined by a compulsion to seek and take drug, loss of control in limiting intake, and the emergence of a negative emotional state when access to the drug is prevented. Alcoholism impacts multiple motivational mechanisms and can be conceptualized as a disorder that includes a progression from impulsivity (positive reinforcement) to compulsivity (negative reinforcement). The compulsive drug seeking associated with alcoholism can be derived from multiple neuroadaptations, but the thesis argued here is that a key component involves the construct of negative reinforcement. Negative reinforcement is defined as drug taking that alleviates a negative emotional state. The negative emotional state that drives such negative reinforcement is hypothesized to derive from dysregulation of specific neurochemical elements involved in reward and stress within the basal forebrain structures involving the ventral striatum and extended amygdala, respectively. Specific neurochemical elements in these structures include not only decreases in reward neurotransmission, such as decreased dopamine and γ-aminobutyric acid function in the ventral striatum, but also recruitment of brain stress systems, such as corticotropin-releasing factor (CRF), in the extended amygdala. Acute withdrawal from chronic alcohol, sufficient to produce dependence, increases reward thresholds, increases anxiety-like responses, decreases dopamine system function, and increases extracellular levels of CRF in the central nucleus of the amygdala. CRF receptor antagonists also block excessive drug intake produced by dependence. A brain stress response system is hypothesized to be activated by acute excessive drug intake, to be sensitized during repeated withdrawal, to persist into protracted abstinence, and to contribute to the compulsivity of alcoholism. Other components of brain stress systems in the extended amygdala that interact with CRF and that may contribute to the negative motivational state of withdrawal include norepinephrine, dynorphin, and neuropeptide Y. The combination of loss of reward function and recruitment of brain stress systems provides a powerful neurochemical basis for a negative emotional state that is responsible for the negative reinforcement driving, at least partially, the compulsivity of alcoholism.

Effects of a stressor and corticotrophin releasing factor on ethanol deprivation-induced ethanol intake and anxiety-like behavior in alcohol-preferring P rats

RATIONALE

Stress may elevate ethanol drinking and anxiety associated with ethanol drinking. Studies to identify relevant neurobiological substrates are needed.

OBJECTIVE

To assess roles of brain regions in corticotrophin releasing factor (CRF) effects on stressor-enhanced, ethanol deprivation-induced drinking and anxiety-like behavior.

METHODS

Ethanol-preferring rats (P rats) were exposed to three cycles of a two-bottle choice paradigm with two 2-day deprivation periods that included 1 h exposure to a restraint stressor. To assess the role of CRF and to identify relevant brain regions, a CRF-1 receptor antagonist (SSR125543; 10 ug) was injected into the nucleus accumbens (NAC), amygdala (Amyg), or dorsal raphe nucleus (DRN) prior to exposure to the restraint stressor. In a second study, CRF (0.5 ug) was injected into one of these regions, or the ventral tegmental area (VTA), or paraventricular nucleus of the hypothalamus (PVN).

RESULTS

Applying the restraint stressor during deprivation increased voluntary intake and sensitized anxiety-like behavior. Antagonist injection into the NAC prevented increased drinking without affecting anxiety-like behavior, whereas injection into the Amyg or DRN prevented the anxiety-like behavior without affecting drinking. To confirm CRF actions in the stressor effect, CRF was injected into selected brain regions. NAC injections (but not the VTA, Amyg, DRN, or PVN) facilitated drinking but did not change anxiety-like behavior. Injections into the DRN or Amyg (but not PVN or VTA) enhanced anxiety-like behavior.

CONCLUSIONS

Results emphasize that a restraint stressor elevates ethanol intake and sensitizes ethanol deprivation-induced anxiety-like behavior through CRF1 receptors in the NAC and Amyg/DRN, respectively.

Chronic alcohol neuroadaptation and stress contribute to susceptibility for alcohol craving and relapse

Alcoholism is a chronic relapsing disorder. Major characteristics observed in alcoholics during an initial period of alcohol abstinence are altered physiological functions and a negative emotional state. Evidence suggests that a persistent, cumulative adaptation involving a kindling/allostasis-like process occurs during the course of repeated chronic alcohol exposures that is critical for the negative symptoms observed during alcohol withdrawal. Basic studies have provided evidence for specific neurotransmitters within identified brain sites being responsible for the negative emotion induced by the persistent cumulative adaptation following intermittent-alcohol exposures. After an extended period of abstinence, the cumulative alcohol adaptation increases susceptibility to stress- and alcohol cue-induced negative symptoms and alcohol seeking, both of which can facilitate excessive ingestion of alcohol. In the alcoholic, stressful imagery and alcohol cues alter physiological responses, enhance negative emotion, and induce craving. Brain fMRI imaging following stress and alcohol cues has documented neural changes in specific brain regions of alcoholics not observed in social drinkers. Such altered activity in brain of abstinent alcoholics to stress and alcohol cues is consistent with a continuing ethanol adaptation being responsible. Therapies in alcoholics found to block responses to stress and alcohol cues would presumably be potential treatments by which susceptibility for continued alcohol abuse can be reduced. By continuing to define the neurobiological basis of the sustained alcohol adaptation critical for the increased susceptibility of alcoholics to stress and alcohol cues that facilitate craving, a new era is expected to evolve in which the high rate of relapse in alcoholism is minimized.

Neuropeptide Y (NPY)-induced reductions in alcohol intake during continuous access and following alcohol deprivation are not altered by restraint stress in alcohol-preferring (P) rats

Administration of neuropeptide Y (NPY) reduces anxiety-like behavior and alcohol intake in alcohol-preferring rats. The present experiment examined whether the effects of NPY on alcohol drinking are modulated by stress exposure during continuous access or following ethanol deprivation. Female P rats underwent 6 weeks of continuous access to 15% v/v ethanol and water prior to intracerebroventricular (ICV) cannula implantation. Deprived rats underwent two cycles of 5 days of ethanol exposure followed by 2 days of ethanol deprivation, while non-deprived rats had uninterrupted access to ethanol. Stressed rats in both ethanol access groups were exposed to restraint stress for 1h 4-6h after ethanol was removed from the deprived group in both cycles. ICV infusions of 5.0 μg NPY or aCSF were administered 48 h following the deprivation/stress procedure, after which ethanol was returned. Rats showed increased ethanol intake following ethanol deprivation compared to non-deprived controls. Food and water intake were increased, while ethanol intake was decreased, in rats infused with NPY. Stress did not increase ethanol intake or alter the response to NPY. Although no stress effects were found, the present experiment replicates previous findings regarding the effectiveness of NPY in reducing ethanol consumption. Future studies aimed at determining the extent to which stress may affect relapse to ethanol drinking and response to NPY would benefit from implementing different stress paradigms and varying the pattern of ethanol access.

Effects of CRF1-receptor and opioid-receptor antagonists on dependence-induced increases in alcohol drinking by alcohol-preferring (P) rats

BACKGROUND

Selective breeding of rats over generations and induction of alcohol dependence via chronic vapor inhalation both enhance alcohol consumption in animal models. The purpose of this study was to determine whether dependence-induced increases in alcohol consumption by P rats is sensitive to naltrexone, a general opioid receptor antagonist (but with highest affinity at the mu-opioid receptor at low doses), and the recently characterized small molecule CRF(1)-receptor antagonist MPZP (N,N-bis(2-methoxyethyl)-3-(4-methoxy-2-methylphenyl)-2,5-dimethyl-pyrazolo[1,5-a]pyrimidin-7-amine).

METHODS

P rats (n = 20) were trained to respond for alcohol and water in a 2-lever operant situation during daily 30-minute sessions. P rats were then matched for alcohol intake and exposed to chronic intermittent alcohol vapor (n = 10) or ambient air (n = 10) for approximately 10 weeks. All rats were then administered MPZP and naltrexone in 2 separate and consecutive Latin-square designs.

RESULTS

MPZP attenuated dependence-induced increases in alcohol intake by P rats while having no effect on alcohol consumption by nondependent controls. Conversely, operant alcohol responding was reduced similarly in dependent and nondependent P rats by naltrexone.

CONCLUSIONS

These results confirm a role for brain CRF(1)-receptor systems in dependence-induced changes in the reinforcing properties of alcohol, and CRF(1)-receptor blockade appears to suppress dependence-induced drinking at lower doses in P rats relative to other rat lines. Therefore, brain CRF(1)-receptor systems are important in the regulation of dependence-induced alcohol consumption, whereas brain opioid systems are important in the regulation of basal alcohol consumption by rats.

Decreased immunoreactivity of the melanocortin neuropeptide alpha-melanocyte-stimulating hormone (alpha-MSH) after chronic ethanol exposure in Sprague-Dawley rats

BACKGROUND

The melanocortin (MC) system is composed of peptides that are cleaved from the polypeptide precursor proopiomelanocortin (POMC). Recent pharmacologic and genetic evidence suggests that MC receptor (MCR) signaling modulates neurobiologic responses to ethanol and ethanol intake. Because ethanol decreases POMC mRNA levels, we determined if exposure to an ethanol-containing diet (ED) would significantly reduce central immunoreactivity of the MC peptide alpha-MSH in rats. We also determined if ethanol exposure would alter the immunoreactivity of agouti-related protein (AgRP), an endogenous MCR antagonist.

METHODS

Male Sprague-Dawley rats were given 18 days of access to normal rodent chow or a control diet (CD), or short-term (4 days) or long-term (18 days) access to an ED. At the end of the study, rats were perfused with 4% paraformaldehyde and their brains were sectioned into two sets for processing with alpha-MSH or AgRP immunohistochemistry.

RESULTS

Rats exposed to an ED showed significant reductions of central alpha-MSH immunoreactivity relative to rats exposed to a control diet (CD) or normal rodent chow. Ethanol-induced reductions of alpha-MSH immunoreactivity were site-specific and were noted in regions of the hypothalamus and extended amygdala, as well as the paraventricular nucleus of the thalamus. Because there were no differences in body weights or caloric intake between the CD and ED groups, reductions of alpha-MSH immunoreactivity in ED-treated rats are best explained by ethanol exposure rather than altered energy balance. No significant ethanol-induced alterations in hypothalamic AgRP immunoreactivity were detected.

CONCLUSIONS

The present study shows that ethanol site specifically reduces alpha-MSH immunoreactivity in rat brain. These observations, in tandem with recent pharmacologic and genetic studies, suggest that the endogenous MC system modulates neurobiologic responses to ethanol. Thus, compounds which target MCRs may prove to have therapeutic value in the treatment of excessive ethanol consumption and/or the symptoms associated with ethanol withdrawal.

Drug challenges reveal differences in mediation of stress facilitation of voluntary alcohol drinking and withdrawal-induced anxiety in alcohol-preferring P rats

BACKGROUND

There is controversy over whether exposure to stress precipitates relapse and/or increases alcohol (ethanol) intake. Our laboratory has demonstrated that repeated stress prior to withdrawal from a brief forced exposure to alcohol results in withdrawal-induced anxiety-like behavior. Because anxiety is often regarded as a precipitating factor in relapsing alcoholics, we decided to examine the consequences of stressing alcohol-preferring P rats on both voluntary alcohol drinking and withdrawal-induced anxiety.

METHODS

P rats were subjected to 3 cycles of 5 days of voluntary alcohol drinking and 2 days of deprivation. Restraint stress (60 min) was applied to some animals during the first and second deprivations/withdrawals (at 4 h). Drugs (flumazenil, buspirone, SB242,084, CP154,526, CRA1000, naloxone, haloperidol, olanzapine, naloxone, and haloperidol) were given to some rats 30 min prior to restraint stress.

RESULTS

Stressed, deprived P rats exhibited both a longer duration of elevated alcohol drinking and anxiety-like behavior in the social interaction test upon withdrawal after the third cycle of voluntary alcohol drinking. When given prior to each of the restraint stresses, the benzodiazepine receptor antagonist flumazenil (5 mg/kg), the corticotrophin releasing factor receptor antagonists CRA1000 (3 mg/kg) and CP154,526 (10 mg/kg), the serotonin 5-HT(1A) receptor partial agonist buspirone (0.6 mg/kg), and the mixed 5-HT(2C)/D2 receptor antagonist olanzapine were effective in reducing the increased duration of elevated alcohol drinking and the withdrawal-induced anxiety-like behavior. In contrast, while the opiate receptor antagonist naloxone (20 mg/kg), the 5-HT(2C) receptor antagonist SB242084 (3 mg/kg), and the dopamine receptor antagonist haloperidol (0.1 mg/kg) also reduced drinking, they did not significantly alter anxiety like behavior.

CONCLUSION

These results suggest that stress-induced facilitation of alcohol drinking and withdrawal-induced anxiety-like behavior in P rats may be closely but imperfectly linked.

Dependence-induced increases in ethanol self-administration in mice are blocked by the CRF1 receptor antagonist antalarmin and by CRF1 receptor knockout

Models of dependence-induced increases in ethanol self-administration will be critical in increasing our understanding of the processes of addiction and relapse, underlying mechanisms, and potential therapeutics. One system that has received considerable attention recently is the CRF(1) system that may mediate the link between anxiety states and relapse drinking. C57BL/6J mice were trained to lever press for ethanol, were made dependent and then were allowed to self-administer ethanol following a period of abstinence. The effect of the CRF(1) antagonist, antalarmin, was examined on this abstinence-induced self-administration in a separate group of mice. Finally, dependence-induced changes in ethanol self-administration were examined in CRF(1) knockout and wild type mice. The results indicated that ethanol self-administration was increased following the induction of dependence, but only after a period of abstinence. This increase in ethanol self-administration was blocked by antalarmin. Furthermore, CRF(1) knockout mice did not display this increased ethanol self-administration following dependence and abstinence. These studies, using both a pharmacological and genetic approach, support a critical role for the CRF(1) system in ethanol self-administration following dependence. In addition, a model is presented that may be useful for studies examining underlying mechanisms of the ethanol addiction process as well as for testing potential therapeutics.

Reduction in repeated ethanol-withdrawal-induced anxiety-like behavior by site-selective injections of 5-HT1A and 5-HT2C ligands

RATIONALE

Anxiety-like behavior resulting from repeated withdrawals from chronic ethanol diets is counteracted by systemic administration of a 5-HT2C receptor antagonist or a 5-HT1A receptor partial agonist.

OBJECTIVES

This study investigated whether prior treatment with these agents into the amygdala, dorsal raphe nucleus, nucleus accumbens, or paraventricular nucleus during early withdrawals would ameliorate the social interaction deficits observed after a subsequent withdrawal.

METHODS

Sprague-Dawley rats were exposed to three cycles of 5 days of forced ethanol diet (4.5%, w/v), with 2 days of control diet after the first and second cycles. Drugs were administered into one of four brain sites 4 h after removal of ethanol on the first and 2nd cycles but not the third. The social interaction test was performed 5 h after removal of ethanol on the third cycle. Drugs tested included SB-243213, a 5-HT2C receptor inverse agonist; buspirone, a 5-HT1A receptor partial agonist; and Ro 60 1075, a 5-HT2C receptor agonist.

RESULTS

Only SB-243213 (at 3 microg, but not at 1 and 0.3 microg) counteracted the social interaction deficits after injections into the amygdala, while buspirone (at 0.3 and 1 microg but not at 0.1 microg) reduced deficits only when given into the dorsal raphe nucleus. In contrast, the 5-HT2C receptor agonist, Ro 60 1075, accentuated the behavioral deficit after two weekly injections into the amygdala.

CONCLUSIONS

These results are consistent with the involvement of 5-HT2C receptors in the amygdala and 5-HT1A autoreceptors in the dorsal raphe nucleus in repeated ethanol withdrawal-induced sensitization of anxiety-like behavior.