Substance P- and enkephalin-containing projections from the interpeduncular nucleus to the dorsal tegmental region in the rat

Abstract

A combination of fluorescent retrograde tracing and immunohistochemical staining for substance P (SP) and Leu-enkephalin (Enk) was used to study the projections from the interpeduncular nucleus (IP) to the dorsal tegmental region, i.e. the dorsal tegmental nucleus of Gudden, the dorsolateral tegmental nucleus and the caudal extension of the dorsal raphe nucleus. After injections of ‘Granular Blue’ (GB) in the dorsal tegmental region, followed one or two days later by a colchicine injection near the IP, and subsequently two days later by the immunohistochemical procedure, populations of neurons double labeled for Enk and GB, or SP and GB, cells that only showed GB labeling, and a number of cells stained only for one of the peptides could be identified in the rostral subnucleus of the IP. This study demonstrates the existence of both Enk- and SP-containing projections from the IP to the dorsal tegmental region.