Neuropeptides in striato-nigral pathways.

The existence of a neuronal pathway containing Leu-enkephalin and connecting the neostriatum with the globus pallidus has been confirmed combining immunohistochemistry with microinjections of neurotoxic agents (kainic acid, colchicine) and discrete knife lesions. The presence of substance P in nerve terminals of the substantia nigra was demonstrated by the application of a monoclonal antibody against this peptide. Electron microscopic studies revealed immunoreactive sites for substance P in nerve terminals establishing symmetric and asymmetric synapses, mainly over dendritic profiles. The possible peptide-containing neuronal pathways in the nigro-striatal system are discussed.