Immunocytochemical identification and distribution of the cell types in the pituitary gland of Bagrus bayad (Teleostei, Bagridae)

Immunocytochemical identification of the different cell types in the pituitary gland of Bagrus bayad was performed using antisera against mammalian (human and rat) and piscine hormones. The adenohypophysis was composed of rostral pars distalis (RPD), proximal pars distalis (PPD) and pars intermedia (PI). Prolactin and adrenocorticotrophic cells were located in the rostral pars distalis of the pituitary. Gonadotrophic and growth hormone cells were distributed in the proximal pars distalis, but gonadotrophic cells appear also at the border of the pars intermedia. Somatolactin cells, as well as alpha-melanotrophic cells were located in the pars intermedia of B. bayad pituitary. The prolactin (PRL) cells were distributed in the RPD stained with orange G and showed strong immunoreactivity with antiserum to chum salmon. The adrenocorticotrophic (ACTH) cells were lead hematoxylin-positive (PbH) and showed strong immunoreactivity with anti-human ACTH; these cells bordered the neurohypophysis and grouped in islets between PRL cells in the RPD. Growth hormone (GH) cells were densely distributed with the gonadotrophic (GTH) cells in the PPD. They were orange G positive and reacted with antiserum to chum salmon. GTH cells were located in the central area of the PPD and in the external border of the PI. These cells were Alcyan Blue and PAS positive, and immunostained with anti-chum salmon GTH Iβ and anti-chum salmon GTH IIβ. In addition, antiserum to rat thyrotropin stimulating hormone β (TSHβ) reacted positively to the GTH cells. These results suggest that GTH I, GTH II and TSH are synthesized in the same cells in the pituitary of B. bayad. The PI was composed mainly of PbH cells and a PAS cell adjacent to the neurohypophysis. The PAS cells from the PI bound specifically to anti-chum somatolactin. Anti-alphamelanin stimulating hormone (MSH) stained only the PbH (alpha-melanotrophic) cells of the PI.