Distribution of substance P immunoreactive nerve terminals within the nucleus tractus solitarius of the rat.

The relative density of the substance P (SP) immunoreactive nerve terminals in the subnuclei of the nucleus tractus solitarius (NTS) of the rat was examined by immunohistochemical light and electron microscopy. A higher density of SP immunoreactive terminals was observed in the medial and dorsolateral subnuclei of the rostral levels to the obex, while SP immunoreactive terminals were only sparsely found in the medial, ventrolateral and interstitial subnuclei from levels 1 mm rostral to 0.5 mm caudal to the obex. Most other parts of the NTS were moderately innervated by SP immunoreactive nerve terminals.