I. Computer-assisted self-infusion of ethanol (CASE) in humans Self-administration is a hallmark of all addictive drugs, including alcohol. Human alcohol self-administration is typically assessed by measuring the oral intake of alcoholic beverages in a laboratory bar setting. These methods are limited by the high PK variability in alcohol exposures, differences in the definition of standardized drinks and drinking schedules, as well as non-pharmacological influences such as expectancy, beverage preference, and choice of incentives for drinking. The CASE method provides subjects with the flexibility to choose when to push a button to receive alcohol, while providing the investigator with flexibility in controlling the consequent BrAC (and thus brain alcohol exposure) by assuring the same increment across all subjects. Thus, the CASE method assesses behavior driven by the pharmacological effects of alcohol. The first phase of this project was to characterize ad-lib IV alcohol self-administration (IV-ASA) in non-dependent drinkers. During the session, subjects first undergo a directed priming phase, where they are prompted to push a button to receive standardized alcohol infusions, followed by an ad-lib phase, where they have free access to the same infusions. Primary measures include number of button presses, average and peak BrAC. This paradigm was previously shown to be reliable (test-retest correlations >0.6) with high internal consistency among measures (r>0.7). Since then, the sample was expanded to 127 non-dependent drinkers, and confirmed significant associations between IV-ASA measures and drinking history. Self-report measures of liking drug effects and urges following priming predicted ad-lib IV-ASA, and there was a strong association between IV-ASA measures and peak feelings of drug effects, liking drug effects, intoxication and stimulation. Analysis of the early phase (first 30-min) of the IV-ASA session indicated greater sensitivity to priming effects and peak subjective effects. Subjects that had higher initial rates of IV-ASA also scored higher on measures of impulsivity, and reported lower expectancies of cognitive and physical impairment, suggesting personality traits that may underlie this alcohol-seeking behavior. The second phase of this project has focused on developing an operant paradigm, using a progressive ratio (PR) schedule that requires subjects to press the button an increasing number of times for each subsequent alcohol exposure. This PR IV-ASA method assesses motivation for alcohol reward, and is based on the principle that people will work harder for greater rewards. Outcome measures include the total number of rewards earned, and average and peak BrAC. This method has shown high test-retest correlations (r>0.8) for measures. Results from a larger sample (n=92) show significant association between recent drinking history and PR IV-ASA measures, with heavier drinkers showing higher BrACs and total ethanol earned. Subjective measures of alcohol effects and urges after priming were significantly associated with IV-ASA. Exposure-response analysis support the role of the rewarding and motivating effects of alcohol driving alcohol self-administration behavior. Subjects that completed the PR IV-ASA session also participated in the ad-lib IV-ASA thus enabling the comparison of the two operant schedules of IV-ASA within the same individuals. This ongoing analysis will help improve our understanding of individual differences in the rewarding properties of alcohol that drive self-administration behavior. In the past year, the Section has initiated a third phase of this study to examine the influence of stress-cues and alcohol-cues, using a guided-imagery paradigm, on IV-ASA, and the effect of drinking pattern (social vs. binge) on this response. Previous research has shown that craving, particularly in response to stress and alcohol associated cues, can potently trigger alcohol seeking behavior, and can predict relapse to excessive alcohol use in dependent drinkers. However, the relationship between stress and alcohol cues and alcohol craving and subsequent consumption in non-dependent drinkers is less clear. The objective of this study is to characterize acute stress and alcohol-cue reactivity and craving and their relationship with operant IV-ASA in non-dependent drinkers, using a guided imagery script challenge, as well as to compare these relationships in binge vs. non-binge drinkers. This study was initiated in the past year and is ongoing. II. Human Laboratory Models in Medication Development for Alcoholism The Section is invested in developing and utilizing human alcohol self-administration paradigms to examine the effects of pharmacological agents being developed for the treatment of alcohol use disorder (AUD). These studies can complement studies in animal models for alcoholism validated for screening of novel therapeutics to help identify treatments that are likely to succeed in clinical trials, thus facilitating future medication development for AUD. The first experimental medicine initiated by the Section is designed to examine the effect of varenicline, a (nicotinic) acetylcholine receptor partial agonist, on IV-ASA in non-treatment seeking heavy drinkers. Varenicline, an oral medication approved by the FDA for smoking cessation, has demonstrated effectiveness in reducing alcohol consumption in a rodent model of alcohol dependence and in heavy drinking smokers and non-smokers. This study is a randomized, placebo-controlled study in 21-60 year-old non-treatment-seeking heavy drinkers in good physical and psychiatric health. Subjects underwent a baseline IV-ASA session, after which they were randomized to 3 weeks of treatment with varenicline or placebo. Following approximately 2 weeks of treatment, subjects underwent an fMRI scan using a novel Alcohol-Food Incentive Delay task to examine the effect of varenicline on brain reward systems underlying incentive motivation for alcohol. At the end of 3 weeks of treatment, subjects repeated the IV-ASA session to measure changes in self-administration. The sample includes 22 subjects (9 smokers) in the placebo group and 24 subjects (11 smokers) in the varenicline group. Subjects were heavy drinkers with an average of 6 drinks/drinking day, and average AUDIT score of 13.5. Results from the fMRI scan indicate significant BOLD activation in response to cues signaling alcohol reward in the nucleus accumbens, amygdala and posterior insula in the placebo group;this activation was significantly attenuated in the varenicline group. The varenicline group also reported lower feelings of happiness and excitement on subjective mood scales in response to alcohol cues compared with the placebo group. Subjects with higher insula activation in response to alcohol cues showed higher alcohol self-administration behavior across treatment groups. Varenicline decreased BOLD activation in striato-cortico-limbic regions associated with motivation and incentive salience of alcohol reward in heavy drinkers. These findings indicate that medication repurposing of varenicline could be targeted towards reward-drinking individuals seeking help for treatment of AUD. This study also demonstrates the utility of of human laboratory paradigms and the use of fMRI-derived brain biomarkers in medications development for AUD. III. Collaborative Studies: 1) Effects of ghrelin on alcohol administration in non-treatment seeking heavy Drinkers (PI: Lorenzo Leggio, NIAAA). 2) Sleep disturbance and relapse in individuals with alcohol dependence: An exploratory mixed methods study (PI: Gwenyth Wallen, NIH CC). 3) The neurophysiological effects of intravenous alcohol as potential biomarkers of ketamine's rapid antidepressant effects in major depressive disorder (PI: Carlos, Zarate, NIMH)
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