NEUROANATOMICAL ORGANIZATION OF GNRH NEURONAL SYSTEMS IN THE LIZARD (PODARCIS S SICULA) BRAIN DURING DEVELOPMENT

The ontogenesis of the GnRH neuronal systems was studied in the brain of the lizard, Podarcis s. sicula, by immunohistochemistry. The first GnRH neurons were seen in the mesencephalon on the 45th day of incubat ion. One week later GnRH-ir neurons appeared in the infundibulum as we ll. These neurons never appeared to be contiguous with midbrain GnRH n eurons. Thus, the adult pattern of distribution of GnRH neurons was re ached before hatching, which occurred on the 66th day of incubation at a temperature of 28 +/- 2 degrees C. Although mesencephalic and infun dibular GnRH neurons and their fiber projections appeared to be distri buted in anatomically distinct brain areas, both systems showed a posi tive reaction to chicken-I GnRH (cGnRH-I), chicken-II GnRH (cGnRH-II) and salmon GnRH (sGnRH). From the time of hatching, GnRH-ir fibers in the mesencephalon appeared to be reaching the optic tectum, tegmentum, cerebellum and rostral dorsal rhombencephalon, whereas GnRH fibers in the infundibulum were projecting to the caudal basal telencephalon, m edian eminence and rostral basal rhombencephalon. In 60-day-old juveni le lizards, the central area of telencephalon contained neurons reacti ng only with anti-cGnRH-I and anti-sGnRH. Such neurons were absent in the adult. Neither GnRH cells nor fibers were observed in the nasal ar ea, terminal nerve and olfactory bulbs at any stage of development and in the adult. We hypothesize that the two GnRH neuronal systems have separate embryonic origins.