Effects of d-amphetamine on concurrent self-stimulation of forebrain and brain stem loci

Abstract

Two groups of rats with 3 chronic electrodes were allowed continuous access to self-stimulation on all 3 electrodes in a 3-lever chamber. The rats in Experiment 1 had electrodes aimed at the septal area (SEPT), anterior lateral hypothalamus (ALH) and posterior lateral hypothalamus (PLH). After establishing regular baseline rates of lever-pressing on all 3 electrodes the rats were subjected to a series of d-amphetamine sulfate injections, 0.62, 2.5 and 5.0 mg/kg. Amphetamine increased response rates predominantly on the PLH electrode in all rats. As the dose of amphetamine increased, the rats self-stimulated at higher rates and for longer duration on the PLH electrode. In Experiment 2 the rats had electrodes aimed at the PLH, ventromedial tegmentum (VMT) and locus coeruleus (LC). After establishing baseline rates of lever-pressing on all 3 electrodes, the rats were subjected to two identical series of d-amphetamine sulfate injections, 0.5, 1.0, 2.0 and 4.0 mg/kg. Amphetamine increased response rates predominantly on the PLH and VMT electrodes at 1.0 mg/kg and on the VMT electrode at the 2.0 and 4.0 mg/kg doses. As the dose increased, the rats self-stimulated at higher rates and for longer duration on the VMT electrode. The LC electrode was the least active site for lever-pressing after the 1.0, 2.0 and 4.0 mg/kg doses. Results suggest a differential anatomical sensitivity to d-amphetamine as measured by selective increases in responding and supports the hypothesis that the mesolimbic dopamine pathway has a role in the facilitative effects of amphetamine on self-stimulation.