ANTIBODIES AGAINST DIFFERENT FORMS OF GNRH DISTINGUISH DIFFERENT POPULATIONS OF CELLS AND AXONAL PATHWAYS IN A URODELE AMPHIBIAN, TARICHA-GRANULOSA

Neurons immunoreactive to the peptide hormone gonadotropin-releasing h ormone (GnRH) have been identified in the posterior diencephalon or an terior midbrain of diverse vertebrates. These cells are located caudal to the more well-characterized GnRH neurons in the nervus terminalis and septo-preoptic area, and are believed to express one or more of th e nonmammalian forms of the GnRH. The present study utilized immunocyt ochemical techniques to determine whether the posterior GnRH group is present in a urodele amphibian, the newt Taricha granulosa. Antibodies directed against different molecular forms of GnRH were used to evalu ate the immunological properties of GnRH-containing neurons in amphibi ans. An antibody selective for mammalian GnRH labeled perikarya in the nervus terminalis (terminal nerve) and septo-preoptic region, as desc ribed previously. Thick fibers that arise from terminal nerve and sept o-preoptic neurons project mainly to the median eminence, medial palli um and habenula. An antibody selective for chicken GnRH II labeled cel l bodies in the paraventricular organ and posterior tubercle of the ca udal diencephalon, and thin fibers that project widely throughout the central nervous system. Region-specific staining with different GnRH a ntibodies supports the interpretation that different molecular forms o f GnRH are expressed by neuroanatomically distinguishable systems, (C) 1994 Wiley-Liss, Inc.