Hippocampectomy attenuates the reduction of operant rate produced by d-amphetamine

Abstract

Hippocampal ablations in rats were found to significantly attenuate the response-decreasing effect of d-amphetamine observed when control animals perform on the fixed ratio (FR) component of a multiple FR, extinction (EXT) schedule under the drug’s influence but had no effect on the ability of the drug to facilitate responding on the EXT component. Separate experiments indicated that hippocampal ablation neither increased nor decreased the ability of amphetamine to produce anorexia, stereotypy, or increases in locomotion. The data from these experiments are interpreted to indicate that the hippocampus is one structure involved specifically in the ability of amphetamine to lower response rate on an FR schedule and that the hippocampus may be part of the neural substrate of the phenomenon of “rate dependency,” which is one predictor of the behavioral action of amphetamine. These data may be interpreted within a theoretical framework that ascribes to the hippocampus a function in altering behavior when either the internal or the external environment changes.