Thyrotropin-releasing hormone (TRH)-immunoreactive neuron populations in the rat olfactory bulb.

Thyrotropin-releasing hormone (TRH)-like immunoreactivity was examined in the rat olfactory bulb by an immunohistochemical method using antiserum against the tripeptide TRH. TRH-immunoreactive neurons and neuronal processes were localized in both main and accessory olfactory bulb, including the glomerular layer, external plexiform layer, mitral cell body layer, internal plexiform layer and granule cell layer. However, no TRH-positive structures were observed in the olfactory nerve layer. The present study demonstrates that TRH is located in several neuronal populations in the olfactory bulb, and that this peptide thus may be involved in the processing of information in the olfactory system.