LOCALIZATION OF GNRH MOLECULAR-FORMS IN THE BRAIN, PITUITARY, AND TESTIS OF THE FROG, RANA-ESCULENTA

In the amphibian brain four molecular forms of GnRH have been identifi ed so far: mammalian GnRH (m- and hydroxyproline(9)m-), chicken II GnR H (cII), and a salmon (s) GnRH-like peptide. In Rana esculenta, cII- a nd s-GnRH-like molecules have been partially characterized in the brai n extracts using HPLC combined with radioimmunoassay. Moreover, since cII-GnRH-like material has been detected in Rana esculenta testis, the present study describes the localization of the above peptides in the brain and testis of the frog. Immunoreactive cII-GnRH and m-GnRH neur ons and fibers were identified in the anterior preoptic area (APOA) an d in the median septal area (MSA). A population of cells located on th e dorsal side of the caudal preoptic region was also stained. Immunopo sitive fibers were seen to overlap the median eminence before ending w ithin the pars nervosa. Moreover, densely packed fibers made close con tact with the vascular complex in the median eminence. Conversely, imm unoreactive s-GnRH-like material was absent in APOA and MSA, but weakl y scattered elements were detected by the anti-s-GnRH serum in the dor sal side of the caudal preoptic region. Using m-GnRH antiserum, a stro ng immunopositivity was observed in the median eminence but not within the pars nervosa, indicating that, besides cII-GnRH and sGnRH-like ma terial, also m-GnRH-like material is present in Rana esculenta brain. In the testis, cells of the interstitial and germinal compartment were detected by anti-cII-GnRH during different periods of the annual cycl e. In particular, in October and February interstitial tissue was inte nsely stained, coinciding with periods of increased androgen productio n and the onset of the new spermatogenic wave, respectively. (C) 1996 Wiley-Liss, Inc.