Histochemical and immunocytochemical identification of the pituitary cell types in three sciaenid fishes: Atlantic croaker ( Micropogonias undulatus), spotted seatrout ( Cynoscion nebulosus), and red drum ( Sciaenops ocellatus)

Abstract

The adenohypophysial cell types in three species of sciaenid teleosts were identified using a combination of classical histochemical techniques and immunocytochemistry with antisera raised against piscine and human pituitary hormones. In general greater specificity for the different cell types was observed with antisera to the piscine pituitary hormones than with antisera raised against the human hormones. The distribution of the cell types did not differ significantly among the three species, Atlantic croaker ( Micropogonias undulatus), spotted seatrout ( Cynoscion nebulosus), and red drum ( Sciaenops ocellatus), and was similar to that reported in several other teleosts. A major portion of the rostral pars distalis was composed of acidophilic prolactin cells which showed specific binding to antisera to carp, coho salmon, and chinook salmon prolactins. The acidophilic corticotrops formed cords of cells which bordered the prolactin cells and showed strong immunoreactivity with anti-human ACTH. This antiserum also cross-reacted with the lead hematoxylin-positive cells in the pars intermedia. The acidophilic growth hormone cells were restricted to the dorsal part of the proximal pars distalis in close contact with the neurohypophysis and were specifically bound by anti-carp and anti-chum salmon growth hormone. The basophilic thyrotrops were located in the dorsal-anterior part of the proximal pars distalis and showed strong immunoreactivity to antiserum to the human thyrotropin β subunit. This antiserum also bound weakly to the basophilic gonadotrops which were concentrated in the ventral part of the proximal pars distalis and also extended posteriorly to form a border around the pars intermedia. Antiserum to croaker maturational gonadotropin, which recognizes two distinct gonadotropins in sciaenids, bound strongly and specifically to the gonadotrops. The gonadotrops were also bound specifically by antisera to the α and β subunits of human luteinizing hormone. Antisera to the β subunits of two recently isolated coho salmon gonadotropins, GTH-I and GTH-II, failed to bind the gonadotrops strongly or differentially in the three sciaenid species. Consequently, the number of gonadotropin cell types in sciaenid fishes remains unresolved.