Gonadotropin-releasing hormones in the brain and pituitary of the teleost,the white sucker

The present study investigated GnRH forms within the brain of a representat ive of the order Cypriniformes, the white sucker, Catostomus commersoni, us ing HPLC, RIA, and immunocytochemistry. Several immunoreactive (ir) GnRH fo rms were identified in the brain of the white sucker by chromatography and radioimmunoassay, including ir-salmon GnRH, ir-lamprey GnRH-I and -III, and ir-chicken GnRH-II. Results from immunocytochemical studies were consisten t with multiple GnRH forms distributed in different patterns, particularly for fibers. Neuronal perikarya containing ir-salmon GnRH and ir-lamprey-lik e GnRH were found laterally within the preoptic area and rostral hypothalam us. Cells containing exclusively ir-salmon GnRH appeared slightly more rost rally but in the same region. Fibers containing ir-salmon GnRH and ir-lampr ey-like GnRH were seen throughout the caudal telencephalon and extended int o the diencephalon, toward the pituitary. Fibers containing ir-chicken-II-l ike GnRH were also seen in the caudal telencephalon, but were concentrated more dorsally in the diencephalon. Within the pituitary, fibers containing ir-salmon GnRH and ir-lamprey-like GnRH entered the neurohypophysis, but di ffered in their destinations. Fibers containing ir-salmon GnRH remained wit hin the neurohypophysis, while fibers containing ir-lamprey-like GnRH targe ted adenohypophyseal tissue. These findings are consistent with the hypothe sis that multiple GnRH forms with multiple functions exist within the brain and pituitary of teleosts and provide further evidence of a lamprey-like G nRH within an early evolved teleost species. (C) 2000 Academic Press.