Immunoreactive gonadotropin-releasing hormone (Gn-RH) during maturation in the rat: Ontogeny of regional hypothalamic...

The developmental appearance of immunoreactive gonandotropin releasing hormone (Gn-RH) was measured by radioimmunoassay in male and female rats from the 12th day of gestation to adulthood. Gn-RH content of the whole hypothalamus of both sexes increased from birth to 21 days of age. By the 28th day, Gn-RH content in females had approximately reached adult levels, while that in males continued to increase. Adult male rats exhibited significantly higher levels than adult females. The ontogeny of the regional differences previously observed in cycling female rats (4) was also studied. Regional analysis of Gn-RH development was characterized in the anterior hypothalamus by the rapid attainment of adult levels by day 7. In striking contrast, in the mid-hypothalamic region, Gn-RH content increased gradually, rising dramatically just prior to vaginal opening. The developmental pattern of Gn-RH content is consistent with the maturation of those hypothalamic structures concerned with synthesis, transport and storage of Gn-RH. The regional patterns observed may thus represent sequential maturation of the neural pathways involved.