REGIONAL DISTRIBUTION AND IN-VITRO SECRETION OF SALMON AND CHICKEN-IIGONADOTROPIN-RELEASING HORMONES FROM THE BRAIN AND PITUITARY OF JUVENILE AND ADULT GOLDFISH, CARASSIUS-AURATUS

The content of salmon (sGnRH) and chicken-II (cGnRH-II) gonadotropin-r eleasing hormones was measured in discrete brain regions and pituitari es of juvenile and postspawning adult goldfish, using specific radioim munoassays. In juveniles, the content of both peptides was low. sGnRH was the predominant form in telencephalon-preoptic area (T-POA) (sGnRH :cGnRH-II ratio = 2.06 +/- 0.66) and diencephalon (DIEN) (sGnRH:cGnRH- II ratio = 2.72 +/- 0.32), whereas cGnRH-II was predominant in cerebel lum-brain stem (STEM) (sGnRH:cGnRH-II ratio = 0.47 +/- 0.05). Equal am ounts of the two peptides were present in pituitary (PIT) (sGnRH:cGnRH -II ratio = 1.04 +/- 0.18). In adults, the content of both peptides in all regions was significantly increased. The increase in sGnRH exceed ed that of cGnRH-II in T-POA and PIT, resulting in an increased sGnRH: cGnRH-II ratio in these tissues (T-POA, 3.55 +/- 0.26; PIT, 7.85 +/- 2 .28). In DIEN and STEM, the increase in cGnRH-II content equaled or ex ceeded that of sGnRH; the sGnRH:cGnRH-II ratio was unchanged in STEM ( 0.39 +/- 0.06) and decreased in DIEN (1.23 +/- 0.13). The secretion of sGnRH and cGnRH-II was investigated under static in vitro incubation conditions. Both forms of the peptide were secreted from T-POA slices and PIT fragments from juvenile and adult fish. Secretion was signific antly increased under potassium depolarizing conditions. Secretion of the two peptides was proportional to their content in tissues from bot h juvenile and adult goldfish. (C) 1994 Academic Press, Inc.