Topographical distribution of substance P in the cat substantia nigra.

The substance P (SP) content in cat substantia nigra (SN) was estimated by radioimmunoassay in microdiscs punched on successive frontal sections. Only slight differences were seen in the regional distribution of SP within the SN. The highest content was found in the pars reticulata (20.7 pmol/mg protein) which was two times higher than in the pars compacta and pars lateralis. Identical results were found in the right and left part of the SN. Out of this area, as pedunculus cerebri and zona incerta, very low concentrations were detected.