Sex differences in response to amphetamine in adult Long–Evans rats performing a delay-discounting task

The use of animal models to investigate experimental questions about impulsive behavior can provide valuable insight into problems that affect human health. The delay-discounting paradigm involves subjects choosing between smaller reinforcers delivered immediately and larger reinforcers that are delivered after a delay. This is an important experimental paradigm for examining impulsive choice in both laboratory species and humans. However, a shortcoming of previously published delay-discounting studies in animals is that typically only males were studied, reducing the applicability of these studies to human populations. In the present study, both female and male adult Long–Evans rats were trained to perform a delay-discounting task, with delays of 0, 5, 10, 20 and 40s before delivery of the larger reinforcer. Because dopaminergic signaling is important in mediating this task, the effects of d-amphetamine and the dopamine receptor antagonist, cis-flupenthixol, on task performance were then examined. The main experimental measure was percent larger-reinforcer choice, which was defined as the percentage of experimental trials at each delay in which the delayed, larger reinforcer was chosen. There was no sex difference in percent larger-reinforcer choice during baseline performance of the task. However, d-amphetamine administration disrupted choice in females, as evidenced by