Immunocytochemical study of substance P-like fibres and cell bodies in the cat diencephalon.

The distribution of fibres and cell bodies containing substance P in the diencephalon of the cat was studied using an indirect immunoperoxidase technique. A high density of both immunoreactive fibres and perikarya was observed in the nuclei habenularis lateralis, periventricularis anterior, arcuatus, supraopticus and supra chiasmaticus, whereas the area hypothalamica dorsalis, the nucleus periventricularis hypothalami and the hypothalamus ventromedialis showed dense plexuses of fibres and moderate concentrations of cell bodies. In the hypothalamus lateralis a low number of fibres and perikarya was found, whereas a rich cluster of substance P cell bodies and scarse fibres were observed in the hypothalamus posterior. Moreover, a dense network of immunoreactive fibres was located in the nuclei lateralis dorsalis, medialis dorsalis, centralis medialis (caudal part) and parataenialis, whereas a moderate number was observed in the nuclei centralis medialis (rostral part), anterior dorsalis, rhomboidens, reuniens, interanteromedialis and filiformis. The hypothalamus anterior had a low density. Finally, a large population of perikarya was observed in the median eminence and regio praeoptica. In the nuclei habenularis medialis, parafascicularis and centrum medianum scarse cell bodies were found.