Investigation of the linkages between GnRH neurons and other areas in male quail brain

Reproduction of every species is the result of complex interactions of both external and internal environmental factors. Because the gonadotropin releasing hormone (GnRH) system appears to have a central role in regulating reproductive physiology and behavior of animals, the environmental factors must reach the GnRH neurons to modulate reproduction. A series of three studies were conducted to investigate the possible linkages between GnRH neurons and other areas of male quail brain. In study 1, immunocytochemistry was used to compare the distribution of nerve fibers and neurons containing GnRH in male quail housed under long day (LD) or short day (SD) photoperiods. A cluster of cGnRH-I ir-neurons was found in the caudal septal area of sexually active (LD) males. In contrast, fewer cGnRH-I ir-neurons were found in this area of sexually inactive (SD) males. In study 2, double immunocytochemistry of vasoactive intestinal peptide (VIP) and cGnRH-I was conducted to investigate possible interaction of cGnRH-I with VIP which has been suggested as a transducer of putative encephalic photoreceptors to the hypothalamo-pituitary-gonadal axis. A cluster of cGnRH-I-ir neurons in the caudal septal area was heavily innervated by VIP-ir fibers; VIP-ir fibers appeared to contact cGnRH-I-ir cells directly at this location. Study 3 was conducted to investigate the linkages of cGnRH-I neurons and other areas of brain using a neural tracing technique with a fluorescent dye, because comprehensive understanding of the ways in which environmental factors regulate reproduction requires verification of such connections. The caudal septal area containing cGnRH-I neurons has connections with the limbic system or the areas closely associated with it. Considering that the telencephalic limbic system receives vast sensory projections directly or indirectly, the cGnRH-I system appears to receive environmental information via the limbic system to coordinate reproduction