Evidence that [3H]forskolin binding in the substantia nigra is intrinsic to a striatal-nigral projection: an autoradiographic study of rat brain.

The neuronal localization of binding sites for the diterpene activator of adenylate cyclase, forskolin, has been determined. Kainic or ibotenic acid lesions were administered into the caudate-putamen or substantia nigra of Sprague-Dawley rats. The binding of 20 nM [3H]forskolin was examined autoradiographically and quantitated using computerized densitometry with tritium standards. Neurochemical lesions placed in the caudate-putamen markedly reduced [3H]forskolin binding in this structure and distal to the site of injection in the substantia nigra. Ibotenic acid lesions placed in the substantia nigra did not appreciably alter binding in the substantia nigra, caudate-putamen, nucleus accumbens or olfactory tubercle. These results indicate that 'forskolin-identified' adenylate cyclase in the substantia nigra is located in nerve terminals from the caudate-putamen. In addition, these sites are presumably located on cell bodies or interneurons in the caudate-putamen.