Immunohistochemical localization of bombesin/gastrin-releasing peptide and substance P in primary sensory neurons.

The existence of bombesin/gastrin-releasing peptide-like immunoreactivity (BN-GRP-LI) in rat sensory ganglia and spinal cord was confirmed using immunocytochemistry, gel filtration chromatography, and high performance liquid chromatography combined with radioimmunoassay. Immunohistochemical studies showed that in the spinal sensory ganglia of the rat about 5% of the neurons exhibited BN-GRP-LI, whereas about 20% of the neurons exhibited substance P-like immunoreactivity (SP-LI). The two immunoreactivities were found in different cells, but both were located in small ganglion cells. In the posterior horn of the spinal cord, BN-GRP-LI and SP-LI were located in the superficial layers, and this distribution was different from that of Met5-enkephalin-like immunoreactivity. The results are in agreement with the concept that there is a primary sensory pathway from the sensory ganglia to the spinal cord which contains BN-GRP-LI and that these neurons are separate from those containing substance P. In extracts prepared from spinal ganglia, two molecular weight forms of BN-GRP-LI were found using gel filtration chromatography. The high molecular weight form coeluted with porcine GRP and the low molecular weight form was smaller than bombesin. The low molecular weight BN-GRP-LI extracted from spinal cord was more hydrophilic than bombesin or ranatensin.