The olfactory bulb is rich in TRH immunoreactivity

We report that the rat olfactory bulb is rich in thyrotropin releasing hormone (TRH) immunoreactivity. TRH content was determined according to the radioimmunoassay method of Bassiri and Utiger. The concentration (mean +/- SEM., n = 10) of TRH in olfactory bulb (60 +/- 10 pg/mg wet weight) was 23% of the concentration in the hypothalamus, and was at least twice that of other brain regions examined. The 2 olfactory bulbs (mean wet weight 65 mg/2 bulbs) contained 3.9 +/- 0.3 ng TRH. The TRH immunoreactivity could be separated into high and low molecular weight forms. The low molecular weight form co-chromatographed with authentic TRH (mol. wt. 362) on gel filtration and thin layer adsorption chromatography and caused the release of thyrotropin from pituitary tissue incubated in vitro. Since the neuronal organization and functions of the olfactory bulb are well described, studies of the localization and metabolism of TRH in this region may help to clarify the role of this tripeptide in the central nervous system.