Comparative distribution of bombesin/GRP- and substance-P-like immunoreactivities in rat hypothalamus

Immunohistochemical localization of bombesin/gastrin-releasing peptide ( GRP )-like immunoreactivity (BN/ GRP -LI) and substance P-like immunoreactivity (SP-LI) in consecutive sections of rat hypothalamus was studied. Bombesin/ GRP -like immunoreactivity in the hypothalamus was partially characterized by gel filtration chromatography followed by radioimmunoassay. In the hypothalamus, SP-LI was more widely distributed than BN/ GRP -LI. Only the anterior and medial parvocellular parts of the nucleus paraventricularis and the nucleus suprachiasmaticus contained numerous cell bodies which exhibited BN/ GRP -LI. Neurons in these areas did not exhibit SP-LI. In contrast, cell bodies exhibiting SP-LI were numerous in the nucleus preopticus medialis and lateralis, nucleus anterior, nucleus ventromedialis and dorsomedialis, nucleus lateralis, nucleus arcuatus, and nucleus premamillaris ventralis and dorsalis. Only occasional cell bodies in these areas exhibited BN/ GRP -LI. It is concluded that the neuronal systems in the hypothalamus containing BN/ GRP -LI and SP-LI are separate, though the terminal fields in many areas overlap. Two peaks of BN/ GRP -LI were detected after gel filtration chromatography from extracts of the rat nucleus paraventricularis. The high molecular weight form coeluted with synthetic GRP (1-27), and the small molecular weight form eluted after synthetic bombesin. Thus, the endogenous BN/ GRP -LI is probably not authentic bombesin.