Immunocytochemical localization of gonadotropin-releasing hormones in the brain of a viviparous caecilian amphibian, Typhlonectes natans (Amphibia : Gymnophiona)

The molecular forms and brain distribution of gonadotropin-releasing hormon e (GnRH) have been well studied in the amphibian orders Urodela (salamander s and newts) and Anura (frogs and toads). In the order Gymnophiona (caecili ans), however, few species have been investigated. Antibodies against diffe rent molecular forms of GnRH were used to immunohistochemically localize th e GnRH-containing neurons in the brain of the caecilian, Typhlonectes natan s which differs from most other amphibians in that it is viviparous. An ant ibody selective for mammalian GnRH recognized cell bodies predominantly in the septo-preoptic area but only with occasional cell bodies in the lateral hypothalamus and ventral thalamic eminence. Thick, prominent fibers in the septal region and fibers within the terminal nerve were also labeled. An a ntibody selective for chicken-it GnRH labeled a population of cell bodies i n the dorsal hypothalamus, ventral thalamus and midbrain tegmentum. Thin fi bers projected laterally from these cells. An antibody specific for salmon GnRH did not label cell bodies but did show intense terminal field immunore activity. The brain of this caecilian, therefore, contains three antigenica lly distinct forms of GnRH. The mammalian and chicken-II GnRH peptides have been shown in other amphibians but the distribution of cells and fibers wa s unique in this caecilian. Copyright (C) 2000 S. Karger AG, Basel.