The Effect of Naltrexone on Goal-Directed and Habit-Directed Ethanol Self-Administration in Rats (2010)

Undergraduates: Rachel Hay, none none none

Faculty Advisor: Donita Robinson
Department: Psychology & Neuroscience

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The purpose of this study is to determine if naltrexone (NTX) differentially affects goal-directed and habit-directed models of alcohol drinking in rats. As an opiate receptor antagonist, NTX is thought to decrease alcohol drinking primarily by diminishing alcohol reward. Thus, we hypothesized that NTX would be more effective at reducing goal-directed than habit-directed self administration in rats trained to press a lever for alcohol. A fixed-ratio(FR5) schedule of reinforcement was used as a model of goal-directed behavior, while a variable interval(VI30) schedule was used as a model of habitual drinking. Higher doses of NTX significantly lowered lever pressing in both VI30- and FR5-trained rats; however, rats responding on the VI30 schedule received significantly more reinforcements than FR5-trained animals. While the median inter-reinforcement interval was significantly higher for VI30 rats than for FR5 rats, the VI30-trained animals pressed steadily and continuously throughout the session, which ultimately allowed for more reinforcements. In contrast, FR5-trained rats exhibited bouts of drinking, and NTX significantly decreased bout length. A satiety-specific devaluation was used to confirm that animals were exhibiting either goal- or habit-directed drinking. These results suggest that NTX differentially affects ethanol self-administration in models of goal-directed and habitual drinking, information which may ultimately help determine who may benefit most from the drug.