CHARACTERIZATION AND LOCALIZATION OF 2 FORMS OF GONADOTROPIN-RELEASING-HORMONE (GNRH) IN THE SPINAL-CORD OF THE FROG RANA-RIDIBUNDA

Two molecular variants of gonadotropin-releasing hormone (GnRH) have b een previously characterized in the brain of amphibians, i.e., mammali an GnRH (mGnRH) and chicken GnRH-II (cGnRH-II). The aim of the present study was to identify the molecular forms of gonadotropin-releasing h ormone and to localize gonadotropin-releasing hormone-containing eleme nts in the spinal cord of the frog Rana ridibunda using highly specifi c antisera against mGnRH and cGnRH-II. High-performance liquid chromat ography (HPLC) analysis combined with radioimmunoassay (RIA) detection revealed that frog spinal cord extracts contained both mGnRH and cGnR H-II. Immunohistochemical labeling revealed that the frog spinal cord was devoid of GnRH-containing cell bodies. In contrast, numerous GnRH- immunoreactive fibers were observed throughout the entire length of th e cord. mGnRH immunoreactivity was only detected in the rostral region of the cord and consisted of varicose processes located in the vicini ty of the central canal. cGnRH-II-positive fibers were found throughou t the spinal cord, the density of immunoreactive processes decreasing gradually toward the caudal region. Two main cGnRH-II-positive fiber t racts with a rostrocaudal orientation were observed: a relatively dens e fiber bundle surrounding the central canal, and a more diffuse plexu s in the white matter. In addition, short, varicose cGnRH-II-positive processes with a radial orientation were present throughout the gray m atter. These fibers were particularly abundant ventromedially and form ed a diffuse network that ramified laterally to end in the vicinity of motoneurons. Taken together, these data indicate that the frog spinal cord, like the frog brain, contains two forms of GnRH. The presence o f numerous cGnRH-II-immunoreactive fibers in the ventral horn suggests that cGnRH-II may influence the activity of a subpopulation of motone urons.