EXPRESSION AND DISTRIBUTION OF 2 GONADOTROPIN-RELEASING HORMONES IN THE CATFISH BRAIN

The expression of prepro-catfish GnRH mRNA and prepro-chicken GnRH-II mRNA was investigated by means of in situ hybridization. The different ial distribution of cells expressing the respective mRNAs was compared with the distribution of cells immunoreactive for (1) catfish (cf) Gn RH and chicken (c) GnRH-II and (2) both GnRH-associated peptides (GAPs ). It was found that the prepro-cfGnRH mRNA expressing cells were loca ted in the ventral forebrain, with a similar distribution of the cfGnR H- and cfGAP-immunoreactive perikarya. The prepro-cGnRH-II mRNA expres sing cells were exclusively located in the midbrain tegmentum, at the same position as a group of large cGnRH-II- and CIIGAP-immunoreactive perikarya. It was concluded that the peptidergic neurons in the ventra l forebrain contain cfGnRH, whereas cGnRH-II perikarya are restricted to the midbrain. The proximal pars distalis of the pituitary, containi ng the gonadotropin cells, is innervated by fibers immunoreactive for both cfGnRH and cfGAP and originating from the cfGnRH neurons in the v entral forebrain. We could, however, not detect fibers innervating the pituitary that were immunoreactive for cIIGAP.