2008 SURI Intern
Year: Sophomore
Major: Neuroscience/Psychology
School: Ohio Wesleyan University,
Delaware, OH
Mentor: Karen Anderson, Ph.D.
Dept: Psychology
Research Project: Effect of Repeated Administration of d-amphetamine on Impulsive Choice
Assessment of the factors that influence impulsive choice may contribute to the understanding of behavioral conditions that are generally associated with impulsivity, including drug abuse. In the laboratory, impulsive choice is often studied using a delay discounting procedure in which a choice is presented between one food pellet immediately (smaller reinforcer) and three food pellets with increasing delay (larger reinforcer). Studies of choice and delayed outcomes suggest that the value of the reinforcer is discounted when its delivery is delayed. In such a procedure, an impulsive choice is typically defined as the choice for a smaller, immediate reinforcer over a larger, delayed reinforcer. Conversely, a self-controlled choice is exhibited when a subject chooses the larger, delayed reinforcer over the smaller, immediate reinforcer.
The present study is designed to examine delay discounting in eight Sprague-Dawley rats following chronic d-amphetamine administration (0.10 mg/kg – 1.7 mg/kg, i.p.) in order to shed light on the effects of prolonged stimulant administration. The delay discounting model will be tested in a discrete-trials choice procedure that incorporates the use of operant chambers equipped with two levers. Subjects will choose (FR 1) between one food pellet delivered immediately (impulsive choice) and three food pellets delivered after an increasing delay (self-controlled choice). The sessions will consist of five blocks of eight trials, each with the delay to the larger reinforcer successively increasing across blocks. Each block will consist of two forced-choice and six free-choice trials.
A previous study on the acute effects of the drug found that lower doses of d-amphetamine (0.10 mg/kg, 0.30 mg/kg) generally increased larger-reinforcer choice, while higher doses (1.0 mg/kg, 1.7 mg/kg) decreased larger-reinforcer choice. The dose of d-amphetamine that had the most robust effect on choice for the larger reinforcer following acute administration will be administered prior to each test session for three weeks or until choice stability is reached. Following this three week exposure, other doses of d-amphetamine will be substituted for the repeated dose and compared to the acute drug effects. Analysis of shifts in delay discounting functions may suggest the development of tolerance or sensitization. After repeated exposure, drug administration will be terminated, and subsequent sessions will allow the observation of any residual effects of the long-term drug exposure.
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