6-Hydroxydopamine lesions reduce specific [3H]sulpiride binding in the rat substantia nigra: direct evidence for the existence of nigral D-2 autoreceptors.

[3H]Sulpiride bound to substantia nigra homogenates in a saturable manner and with a pharmacological profile typical of a specific D-2 ligand. Unilateral 6-OH-dopamine (DA) lesions of the nigrostriatal DA neurons reduced by 27-46% the Bmax of the specific [3H]sulpiride binding in substantia nigra homogenates depending on the time after 6-OHDA lesion and significantly increased the Bmax in the caudate. KDs remained unchanged in both areas. The localization of specific [3H]sulpiride binding and its reduction in the substantia nigra of the 6-OHDA-lesioned side were confirmed by quantitative autoradiography. The results provide evidence for the existence of D-2 autoreceptors in substantia nigra.