Molecular cloning and differential expression of three GnRH mRNAs in discrete brain areas and lymphocytes in red drum

Three gonadotropin releasing hormones, seabream GnRH (GnRH-I), chicken GnRH-II (GnRH-II) and salmon GnRH (GnRH-III) cDNAs were isolated from the brain of the red drum, Sciaenops ocellatus. The GnRH cDNA sequences of red drum showed more similarity to those of Atlantic croaker, sea bass and sea bream. The real-time quantitative RT-PCR study revealed expression of GnRH-I and GnRH III mRNAs in the olfactory bulb plus telencephalon (OB+TEL), and preoptic-anterior hypothalamic area (POAH), indicating an overlap of the GnRH-I and GnRH-III systems in these fore-brain regions. However, GnRH-II mRNA expression was detected only in the midbrain tegmentum (MT). The GnRH-I mRNA expression in the POAH in fish undergoing gonadal recrudescence was significantly higher than that in gonadally immature individuals, sug-gesting involvement of the POAH GnRH-I in gonadal maturation. On the other hand, GnRH-III mRNA expression was significantly higher in the OB+TEL region compared with that in the POAH. Moreover, the demonstration of GnRH-I mRNA and peptide expres-sion in red drum lymphocytes indicates that the GnRH-I is synthesized in these cells of the immune system similar to the situation in mammals