DISTRIBUTION OF GONADOTROPIN-RELEASING-HORMONE IMMUNOREACTIVITY IN THE BRAIN OF ICHTHYOPHIS-BEDDOMEI (AMPHIBIA, GYMNOPHIONA)

From a comparative viewpoint, we have investigated the presence and ne uroanatomical distribution of gonadotropin-releasing hormone (GnRH)-im munoreactive material in the brain of a gymnophione amphibian, Ichthyo phis beddomei. Immunocytochemical analysis of the adult brain and term inal nerves in both sexes shows the presence of neurons and fibers con taining mammalian GnRH (mGnRH)- and chicken GnRH-II (cGnRH-II)-like pe ptides. With respect to GnRH-immunoreactive material, there are two di stinct neuronal systems in the brain: one containing mGnRH, which is l ocated in the forebrain and terminal nerve, and the other containing c GnRH-II, which is restricted to the midbrain tegmentum. Basically, thi s distribution pattern parallels that of many species of anurans and a urodele. Whereas the presence of cGnRH-II-immunoreactive fibers in th e dorsal pallium of I. beddomei is a feature in common with a urodele amphibian, the total absence of cGnRH-II-like material in the median e minence is unique to this species. It is suggested here that the distr ibution profile of GnRH-like material within the brain and terminal ne rve of I. beddomei represents a primitive pattern. (C) 1997 Wiley-Liss , Inc.