Induction of c-fos mRNA in the arcuate nucleus of normal and mutant growth hormone-deficient mice by a synthetic non-peptidyl growth hormone secretagogue.

We have studied by in situ hybridization histochemistry the mRNA expression of the c-fos immediate early gene in the brains of wild type and dwarf(dw/dw) and little(lit/lit) mutant mice after systemic injections of the synthetic GH secretagogues GHRP-6 and L-163,191. Both GH secretagogues induced a marked c-fos mRNA expression in the arcuate-ventromedial hypothalamus (ARC-VMH) of both control and mutant mice indicating a possible action on growth hormone releasing hormone (GHRH) neurones in the ARC-VMH. Both dw/dw and lit/lit mice showed a 5-fold elevation in GHRH mRNA expression in the ARC-VMH compared with control animals under basal conditions. Since lit/lit mice have a reduced ability to secrete GH and lack a functional GHRH receptor while dw/dw mice lack both GH and presumably GHRH receptors, the GH-secretagogue-induced c-fos mRNA in the brain of these mutants are unlikely to be mediated by an indirect action of GH or a interaction of the synthetic GH-secretagogue with the GHRH receptor.