Increase in D2 dopamine receptors in the substantia nigra after chronic (-)-sulpiride treatment.

Changes in D2 dopamine (DA) receptors in the substantia nigra (SN) and caudate nucleus (CN) homogenates were studied in rats following chronic treatment with the specific D2 receptor antagonist (-)-sulpiride (50 mg/kg s.c. twice daily for 8 days). Sixty hours after (-)-sulpiride withdrawal, the Bmax of [3H]spiroperidol binding (in the presence of 30 Nm ketanserin) was found to be increased by 76% and 38% in the SN and CN, respectively. No changes in the KdS were observed. The findings suggest that chronic (-)-sulpiride results in the upregulation of DA autoreceptors in the SN.