Denervation supersensitivity for benzodiazepine receptors in the rat substantia nigra.

The injection of kainic acid into the substantia nigra causes, 3 weeks after treatment, a 40% decrease in the total number of binding sites for [3H]diazepam with an increase in the dissociation constant. This decrease was restored to approximately normal by the subsequent injection of kainic acid into the striatum, homolateral to the lesioned substantia nigra. The injection of kainic acid into the striatum of intact animals failed to modify the number of [3H]diazepam binding sites but increased the KD. The results indicate that benzodiazepine binding sites in the substantia nigra are partly located on kainic acid sensitive elements (probably interneurons) and, partly, on kainic acid resistant ones. These binding sites become supersensitive after degeneration of striato-nigral pathways. The possible role of GABAergic denervation of the substantia nigra in the development of benzodiazepine binding sites supersensitivity is discussed.