REGIONAL DISTRIBUTION OF GROWTH HORMONE-RELEASING HORMONE (GHRH) RECEPTOR MESSENGER-RNA IN THE RAT-BRAIN

We examined the tissue distribution of growth hormone-releasing hormon e (GHRH) receptor mRNA in the rat brain because several lines of evide nce have suggested that GHRH plays a functional role in the brain. GHR H receptor mRNA was detected in the hypothalamus as well as pituitary, but not in olfactory bulb, caudate putamen, cerebral cortex, hippocam pus, cerebellum, or brainstem by RNase protection assay. To clarify th e precise localization of GHRH receptor mRNA in the hypothalamus, reve rse transcription-polymerase chain reaction (RT-PCR) was used. A PCR p roduct of the predicted size (564 bp) was detected in the periventricu lar, arcuate, and ventromedial nuclei, and the anterior hypothalamic a rea, but not in the paraventricular nucleus in the hypothalamus. These areas where GHRH receptor mRNA was detected are possible sites of GHR H action. Another band, smaller in size than that of the predicted PCR amplification product, was detected in the anterior hypothalamic area and arcuate nucleus, respectively. Hybridization analysis with a cDNA probe for GHRH receptor demonstrated that the smaller bands as well a s that of the predicted size corresponded to GHRH receptor cDNA. The r ole of the short form of the GHRH receptor remains unknown.