Distribution of neuropeptidelike immunoreactivities in the guinea pig olfactory bulb

The distribution of neuropeptidelike immunoreactivities in the adult guinea pig olfactory bulb was studied immunohistochemically with antisera raised against neurotensin (NT), substance P (SP), methionine-enkephalin-Arg6-Gly7-Leu8 (ENK), somatostatin (SOM), neuropeptide Y (NPY), and cholecystokinin-8 (CCK). In the main olfactory bulb, NT-like immunoreactive (NT-IR) neurons were found among periglomerular cells. In addition, a few periglomerular cells showed ENK-like immunoreactivity. Granule cells displaying SP- or ENK-like immunoreactivities and short axon cells with SOM- or NPY-like immunoreactivities were observed in the deeper half of the granule cell layer. SOM-IR short axon cells were also seen in the external plexiform layer. Dense NT- or NPY-IR fibers were distributed in superficial lamina of the granule cell layer, and sparse SP- or CCK-IR fibers were found in the glomerular layer. In the accessory olfactory bulb, some mitral, periglomerular, and granule cells showed NT-like immunoreactivity. SP- or ENK-IR granule cells were also observed. These results are discussed in relation to laminar organization of the olfactory bulb. The most characteristic features of peptide distribution in guinea pigs, as compared with that of rats in previous studies, were the relative abundance of NT-IR structures and the lack of SP- and CCK-IR juxtaglomerular and tufted cells.