IMMUNOREACTIVE GONADOTROPIN-RELEASING-HORMONE (GNRH) IS DETECTED ONLYIN THE FORM OF CHICKEN GNRH-II WITHIN THE BRAIN OF THE GREEN ANOLE, ANOLIS-CAROLINENSIS

The presence of multiple forms of gonadotropin-releasing hormone (GnRH ) within a single brain is common among vertebrate species. In previou s studies of reptiles, two forms of GnRH were isolated from the brain of alligators and the primary structure was determined to be that of c hicken (c)GnRH-I and cGnRH-II. GnRH has also been detected by indirect methods in other reptiles including turtles, lizards, and snakes. We used a combination of high-performance liquid chromatography (HPLC) an d radioimmunoassay to determine the number and molecular form(s) of Gn RH in the brain of a lizard, Anolis carolinensis, that was reported to lack GnRH cells in the forebrain. Immunoreactivity was detected in th e same HPLC elution position in which synthetic cGnRH-II elutes, but n ot in any other position. Detection was based on five antisera that am ong them detect the 12 known forms of GnRH; these antisera include one s that are specific to cGnRH-I and cGnRH-II. We conclude that the liza rd A. carolinensis contains cGnRH-II, but not cGnRH-I or another known form of GnRH. These data, coupled with our earlier immunocytochemical study, suggest that the lizard studied here lacks cGnRH-I, the form t hat is found in the terminal nerve, olfactory bulb, and forebrain in n onsquamate reptiles and in birds. Our hypothesis is that the presence of both cGnRH-I and cGnRH-II in the brain is ancestral in the reptilia n lineage and retained in the orders that include turtles (Chelonia) o r alligators (Crocodilia). However, the pattern in the order Squamata varies: in A. carolinensis, only cGnRH-II is present in the brain and cGnRH-I is absent, whereas in the snake Thamnophilis sirtalis, cGnRH-I is retained and cGnRH-II is absent in the brain, as recently reported . This raises the question of how reproduction is controlled in reptil es that lack one form of GnRH. (C) 1997 Academic Press.