Regional distribution of growth hormone-releasing hormone (GHRH) receptor mRNA in the rat brain.

We examined the tissue distribution of growth hormone-releasing hormone (GHRH) receptor mRNA in the rat brain because several lines of evidence have suggested that GHRH plays a functional role in the brain. GHRH receptor mRNA was detected in the hypothalamus as well as pituitary, but not in olfactory bulb, caudate putamen, cerebral cortex, hippocampus, cerebellum, or brainstem by RNase protection assay. To clarify the precise localization of GHRH receptor mRNA in the hypothalamus, reverse transcription-polymerase chain reaction (RT-PCR) was used. A PCR product of the predicted size (564 bp) was detected in the periventricular, arcuate, and ventromedial nuclei, and the anterior hypothalamic area, but not in the paraventricular nucleus in the hypothalamus. These areas where GHRH receptor mRNA was detected are possible sites of GHRH 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 as that of the predicted size corresponded to GHRH receptor cDNA. The role of the short form of the GHRH receptor remains unknown.