Ontogeny of immunoreactive somatolactin, prolactin and growth hormone secretory cells in the developing pituitary gland of Cichlasoma dimerus (Teleostei, Perciformes)

Prolactin, growth hormone and somatolactin constitute a hormone family because they are structurally related and are secreted by acidophilic cells of different regions of the adenohypohyisis. In this work, we report the ontogeny of ir-prolactin, ir-growth hormone and ir-somatolactin cells in the developing pituitary gland of the cichlid fish Cichlasoma dimerus (Teleostei; Perciformes). Antisera raised against fish pituitary hormones were used. In this species hatching occurs 54 hs after fertilization and the three different cell types were recognized two days later. The neurohypophysis was recognized on day 14 after hatching and in later stages it began to show the characteristic deep interdigitations of the adults. On day 42 (juvenile stage) the distribution of ir-PRL, ir-GH and ir-SL showed the pattern described for adults of this species. The ir-SL cells were not PAS-positive in larvae as they are in adults. This would suggest the presence of a nonglycosilated form of somatolactin in early stages of development which may coexist in adults with a glycosilated form. The appearence of these hormones so early in development suggest their importance in the survival of fish larvae but further studies focused on the ontogeny of hypothalamic factors that regulate their synthesis and secretion must be performed.

Immunocytochemical localization of different cell types in the adenohypophysis of the cichlid fish Cichlasoma dimerus (Heckel, 1840)

The adenohypophysis of the cichlid fish Cichlasoma dimerus was studied using the avidin-biotin-peroxidase method with antisera raised against piscine pituitary hormones and heterologous antisera against mammalian pituitary hormones. Antiserum raised against rabbit ACTH recognized a group of cells bordering the neurohypophysis (NH) in the rostral pars distalis (RPD). Anti-chum salmon prolactin (PRL) identified a compact group of cells in the periphery of the RPD. Gonadotropin II (GTH II), thyrotropin (TSH) and growth hormone (GH)-ir cells were localized in the proximal pars distalis. Ir-GTH II cells were also observed in the dorsal area of the pars intermedia (PI). Ir-GTH I cells could not be identified using anti-chum salmon GTH I, this may be due either to a failure of the antisera to recognize the gonadotropin or to a low expression of the hormone in adults of this species. PAS positive cells from the PI bound specifically with three different antisera raised against somatolactin (SL) of four different fish species. These cells surrounded deep branches of the NH in the PI.

The adenohypophysis of the swamp eel, Synbranchus marmoratus, an immunocytochemical analysis

The adenohypophyseal cell types of the protogynous fish Synbranchus marmoratus were studied by histochemical and immunocytochemical staining with antisera raised against piscine and human pituitary hormones to ascertain their distribution. The prolactin (PRL) cells were distributed in the rostral pars distalis and showed specific binding to antisera to carp and chum salmon prolactin. No reaction was observed with antiserum to human prolactin. The corticotrops showed strong immunoreactivity with anti-human ACTH, these cells bordered the neurohypophysis and islets between PRL cells in the rostral pars distalis. Growth hormone (GH) cells were densely distributed and associated with the neurohypophysis only in pars distalis proximal. They reacted with antisera to piscine GH but not with antisera to human growth hormone. The thyrotrops were scattered in the proximal pars distalis and showed strong immunoreactivity to the human thyrotropin Beta subunit antiserum. Gonadotrops were located in the central area of the proximal pars distalis and in the external border of the pars intermedia. These cells were alcian blue and PAS positive, and reacted with anti-croaker GTH and anti-coho GTH I and GTH II. The PAS positive cells from the pars intermedia bound specifically to anti-chum somatolactin.