Evolution of neurohormonal regulation of reproduction in lower vertebrates

Abstract

Immunological and chromatographic studies demonstrate that the gonadotropin (GtH) releasing hormone (GnRH) in the brain of chondrichthyes, teleosts, reptiles and birds is different from luteinizing hormone-releasing hormone (LH-RH) of mammals. LH-RH is present in brain extracts from amphibia. The alterations in the structure of LH-RH found in various of the non-mammalian vertebrates are at positions 7 and 8; the structure of chum salmon GnRH is Trp7-Leu8-LH-RH, and in chickens is Gln8-LH-RH. A response to injection of LH-RH or its agonistic analogues, in terms of increased blood levels of GtH or a gonadal response such asovulation indicative of increased GtH secretion, has been found in all classes of vertebrates, and the cephalochordate amphioxus. This suggests a basic similaritiy of the GnRH receptors throughout vertebrates, and that the ancestral origin of the system was in the invertebrate chordates. Immunohistochemical studies demonstrate that many lower vertebrates have perikarya containing LH-RH-like material in the preoptic and ventrobasal hypothalamic regions. Brain lesioning studies provide functional evidence for GnRH from both locations in amphibia and only the ventrobasal hypothalamus in teleosts. Brain lesioning studies on goldfish suggest the presence of a GtH release-inhibitory factor (GRIF). Dopamine has GRIF activity in goldfish and common carp to modulate the actions of LH-RH and spontaneous release of GtH. How widespread this system for dual neurohormonal regulation of GtH secretion is in vertebrates is not known. © 1983 by the American Society of Zoologists.