IMMUNOHISTOCHEMICAL LOCALIZATION OF CHICKEN GONADOTROPIN-RELEASING HORMONE-I AND HORMONE-II (CGNRH-I AND CGNRH-II) IN TURKEY HEN BRAIN

The distribution of cells and fibers immunoreactive (ir) for either ch icken gonadotropin-releasing hormone I (cGnRH I; [Gln8]GnRH) or II ([H is5,Trp7,Tyr8]GnRH) was determined in brains of turkey hens to reveal whether these peptides occur in separate neuronal systems. ir-cGnRH I cells were located: along the medial aspect of the ventriculus lateral is, nucleus accumbens, and bed nucleus of the stria terminalis; ventra l to the tractus septomesencephalicus and extending medially to the th ird ventricle, and caudally into the lateral hypothalamic area; and in a diffuse band extending from the nucleus preopticus medialis to the nucleus dorsomedialis anterior thalami. cGnRH I fibers were evident in these areas in addition to the hippocampus, nucleus subhabenularis me dialis, nucleus ventromedialis hypothalami, and median eminence. Two g roups of ir-cGnRH II cells were observed: a magnocellular group lying between the substantia grisea centralis and the nucleus ruber; and a p arvicellular group lying medial to the nucleus of the basal optic root and extending into the lateral hypothalamic area. ir-cGnRH II fibers were prominent in limbic structures (cortex piriformis, lateral to nuc leus taeniae, hippocampus); olfactory areas (tuberculum olfactorium, n ucleus subhabenularis lateralis, nucleus septalis lateralis); areas th at in other avian species have steroid-concentrating cells or receptor s (medial edge of lobus parolfactorius, nucleus septalis medialis, nuc leus periventricularis magnocellularis, nucleus dorsomedialis posterio r thalami); and areas containing ir-GnRH I cells or fibers but not in median eminence. These results suggest that cGnRH I and II occur in se parate neuronal systems and that cGnRH II does not directly promote pi tuitary gonadotropin secretion.