Immunocytochemical evidence for peptidergic (GnRH) and dopaminergic innervation of the gonadotropic cells in the pituitary of the African catfish, Clarias gariepinus

Abstract

The proximal pars distalis (PPD) of the pituitary of the African catfish, Clarias gariepinus, was studied with immunocytochemical methods at the ultrastructural level. Anti-serum raised against synthetic mammalian luteinizing hormone-releasing hormone (LHRH) was applied on Lowicryl-embedded pituitaries and the antigenic sites were visualized with protein A-gold. In nerve fibers contacting the gonadotropic cells, granulated vesicles with a diameter of 90-120 nm were labeled after this procedure, whereas the glandular cells were not labeled. For the immunocytochemical demonstration of dopaminergic fibers, the preembedding method was performed on Vibratome sections, using highly specific antibodies against dopamine. Immunoreactivity was restricted to fibers containing granulated vesicles with a diameter of approximately 80 nm and terminating on gonadotropic cells. The present data support the results of earlier in vivo and in vitro studies on the catfish pituitary, indicating a dual neuroendocrine regulation of the gonadotropic cells.