A developmental increase in the expression of messenger ribonucleic acid encoding a second form of gonadotropin-releasing hormone in the rhesus macaque hypothalamus

GnRH-I is thought to represent the primary neuroendocrine link between the brain and the reproductive axis. Recently, however, a second molecular form of this decapeptide (GnRH-II) was found to be highly expressed in the brai ns of humans and nonhuman primates. In this study, in situ hybridization wa s used to examine the regional expression of GnRH-II messenger ribonucleic acid in the hypothalamus of immature (0.6 yr) and adult (10-15 yr) male and female rhesus macaques (Macaca mulatta). Overall, no sex-related differenc es were observed. In all of the animals (n = 3 animals/group), intense hybr idization of a monkey GnRH-II riboprobe was evident in the paraventricular nucleus and supraoptic nucleus and to a lesser extent in the suprachiasmati c nucleus, but no age- or sex-related differences were apparent. Intense hy bridization of the riboprobe also occurred in the mediobasal hypothalamus, and this was markedly greater in the adults than in the immature animals. T hese data show that; the expression of GnRH-II messenger ribonucleic acid i ncreases developmentally in a key neuroendocrine center of the brain. Moreo ver, because GnRH-II can stimulate LH release in vivo, it is plausible that changes in its gene expression represent an important component of the mec hanism by which the hypothalamus controls reproductive function.