Coloration de l'hypophyse avec l'hématoxyline au plomb (H.Pb): Données nouvelles chez les Téléostéens et comparaison avec les résultats obtenus chez d'autres Vertébrés

Immunocytochemical identification and localization of the different cell types in the pituitary of the seabass (Dicentrarchus labrax)

Antisera raised against chum salmon prolactin (PRL), trout growth hormone (GH), mammalian adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), luteinizing hormone (LH), and alpha-melanophore-stimulating hormone (alpha-MSH) were used to localize PRL, GH, ACTH, gonadotropic, TSH, and MSH cells in the hypophysis of the teleost Dicentrarchus labrax using the unlabeled peroxidase anti-peroxidase method. In the rostral pars distalis, ACTH cells stained very intensively with anti-ACTH; so did the MSH cells in the pars intermedia. The prolactin cells stained very specifically with anti-prolactin without staining the growth hormone cells. In the proximal pars distalis anti-GH, anti-TSH beta, and anti-LH stained selectively the corresponding cells; with these antisera no cross-reaction with any other cell type was observed. Anti-alpha-MSH only stained cells in the pars intermedia. Some cells in the pars intermedia did not react at all; these could correspond to the PAS-positive cells. A characteristic feature was positive staining with anti-LH in some cell groups encircling the pars intermedia, indicating the fact that in the seabass some cells of the proximal pars distalis surround the pars intermedia.

Preparation of enriched populations of corticotrophs from goldfish rostral pars distalis

A mammalian isolated adrenal cell system was validated as a bioassay for goldfish ACTH; the log dose-response curve for the goldfish hormone is parallel to that for synthetic mammalian ACTH1-24, and the two ACTHs induce the same maximum rate of corticosterone production. Using this assay, it was observed that (1) there is a marked and consistent biphasic change in pituitary ACTH content as related to the length of time the fish are held in laboratory aquaria, and (2) the absolute and relative (to tissue wt) ACTH content of the rostral pars distalis is considerably greater than that of the proximal portion of the gland. Using a trypsin technique, isolated pituitary cells were prepared from both (rostral and proximal) portions of the gland; bioassay data indicate that cell suspensions prepared from the rostral pars distalis are enriched with respect to corticotrophs. The implications of these findings with regard to formulating an advantageous in vitro system for studying ACTH secretion are discussed.

Effect of pimozide on the cytology of the eel pituitary. II. MSH-secreting cells

Pimozide, a specific blocker of dopaminergic receptors, was injected for 4 or 9 days in freshwater (FW) eels or eels acclimated to sea water (SW) for 10 or 30 days. The daily dose was 100 or 200 microgram/100 g. Melanophore index values increase in FW and in 1 month-SW injected eels. All the treated fish react by a total or subtotal degranulation of the lead-hematoxylin positive cells in the pars intermedia. These cells were previously identified as alpha-MSH-secreting cells. The MSH cell nuclear area is significantly increased, nucleoli are larger and the endoplasmic reticulum more developed. The intensity of the response is similar in FW and SW eels, but it does not increase with the higher dose. The rapid release of pituitary alpha-MSH is also visualized by immunofluorescence and immunoenzymologic techniques. No effect on the second cell type of the pars intermedia (PAS-positive cell) is detected. The amount of neurosecretory material is often reduced in the neurohypophysis. These results suggest that the hypothalamic inhibitory control of MSH release and synthesis is mediated through dopaminergic fibers in the eel, but other factors cannot be ignored in this regulation.