The effect of serotonin depletion on motor activity habituation, and [ [formula omitted]]muscimol binding in the rat hippocampus

Abstract

The effect of serotonin depletion ( p-chlorophenylalanine pretreatment) on habituation of exploratory motor activity, and on cortical and hippocampal [ 3 H ]muscimol binding in vitro, was examined in rats. It appeared that the very strong decrease in serotonin concentration abolished motor habituation in the open field and decreased [ 3 H ]muscimol binding to cortical and hippocampal brain slices. The GABA A receptor down-regulation was due to a decrease in the apparent affinity of the radioligand for the receptors. p-Chlorophenylalanine-induced biochemical changes were selective and most probably secondary to serotonin depletion, as the serotonin synthesis inhibitor did not displace [ 3 H ]muscimol from its binding sites in neural membranes taken from the occipital cortex. It is concluded that there is a functional interaction between brain serotonin and GABA (γ-aminobutyric acid) systems, both at behavioral and biochemical levels, that is involved in the motor activity habituation process.