[Immunocytological study of corticotropic cells in several species of teleost fish: Gasterosteus aculeatus L., Carassius auratus L., Lebistes reticulatus P., Salmo irideus Gibbs and Perca fluviatilis L]

Immunocytochemical study of cell type distribution in the pituitary of Barbus barbus (Teleostei, Cyprinidae)

Antisera to mammalian pituitary and placental hormones have been used to identify and localize the different cell types in the pituitary of the barbel (Barbus barbus, L.). The immunocytochemical labeling employed the immunoperoxidase technique or the immunogold silver staining procedure. Corticotrophic and prolactin cells, visualized using antisera to human adrenocorticotropic hormone and ovine prolactin (PRL), respectively, occur in the rostral pars distalis (RPD). Antisera against mammalian gonadotropins [ovine follicle-stimulating hormone (FSH); bovine luteinizing hormone] or porcine growth hormone selectively cross-react with two different cell populations occupying the major part of the proximal pars distalis (PPD). Thyrotropic cells, stained by an antiserum to whole human thyroid-stimulating hormone preabsorbed with porcine FSH, are scattered throughout the PPD and found amongst growth hormone and gonadotrophic cells. The majority of pars intermedia cells are stained with anti-melanophore stimulating hormone whereas the scattered PAS positive cells are revealed by both anti-ovine PRL and anti-bovine placental lactogen (or chorionic somatomammotropin). The latter antiserum also cross-reacts with the PRL cells of the RPD. Our results indicate that the distribution of the different cell types in Barbus barbus is similar to that described in other families of teleosts. This report is also the first demonstration of antigenic similarity between mammalian placental lactogen and fish prolactin.

Immunocytochemical location of pituitary cells containing ACTH, alpha-MSH, and beta-endorphin in Acipenser transmontanus, Lepisosteus spatula, and Amia calva

This immunocytochemical study of the pituitaries of the primitive actinopterygians, Acipenser transmontanus, Lepisosteus spatula, and Amia calva, showed a strict delineation between the hormonal fragments of proopiomelanocorticotropin (POMC) produced by corticotropes of the pars distalis and the melanotropes of the pars intermedia. Corticotropes were immunoreactive only for ACTH and not to either of the further degradation products, alpha-MSH or beta-endorphin. Melanotropes were shown to be immunoreactive to all three antisera but it is argued that immunoreactivity of melanotropes to ACTH antiserum is due to that antiserum's cross-reactivity with the cleavage product corticotropin-like intermediate peptide. The PAS positivity of both the corticotropes and the melanotropes of all three primitive fish argues for an ancient origin of a carbohydrate component of POMC and for its loss or reduction in teleosts where these cells are PAS negative.

Immunocytochemical and ultrastructural characterization of the cell types in the adenohypophysis of Sparus aurata L. (teleost)

The structure and immunocytochemistry of the adenohypophysis of sexually mature male specimens of Sparus aurata (gilthead sea bream) were studied. The adenohypophysis was composed of rostral pars distalis (RPD), proximal pars distalis (PPD), and pars intermedia (PI). In the RPD the prolactin cells were organized into follicles which occupied a very reduced area as corresponds to that in saltwater fishes; the corticotropic cells were surrounding the pars nervosa branches and the prolactin follicles. The PPD showed somatotropic, gonadotropic, and thyrotropic cells. The somatotropic cells were isolated, clustered, or surrounding the pars nervosa branches. Only one polymorphic cell type of gonadotropic cells was found in the PPD ventral and dorsal areas and around the PI. The PI was composed mainly of melanotropic cells and a PAS-positive cell layer adjacent to the neurohypophysis. The ultrastructure of the presumptive endocrine cells was reported and their distribution was discussed in relation to those of other teleosts.

Immunohistochemical investigation of the pituitary of the sturgeon (Acipenser baeri, Chondrostei)

An immunohistochemical study of the sturgeon (Acipenser baeri) pituitary was undertaken using antisera directed against hormones from various classes of vertebrates, including the only pituitary hormone available from sturgeon, gonadotrophin. A positive reaction was obtained after application of antisera towards the following hormones 1-24 synthetic ACTH (1-24 ACTH), melanophore stimulating hormone (MSH), ovine prolactin (oPRL), ovine growth hormone (oGH), salmon growth hormone (sGH), carp gonadotrophin (cGTH) and its beta subunit (βcGTH), sturgeon gonadotrophin (aciGTH), carp thyrotrophin (cTSH) and β subunit of the human thyrotrophin (βhTSH). The results demonstrate that, in general, the sturgeon pituitary resembles that of teleosts as regards the distribution of the different cell types: ACTH and PRL cells in the rostral pars distalis, GTH, TSH and GH cells in the proximal pars distalis and MSH and PAS-cells in pars intermedia. In addition to the topographical organization of the sturgeon pituitary, this study provides data on the immunological relationships between sturgeon pituitary hormones and those of other vertebrates.

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.

Immunocytochemical identification of the proopiocortin-producing cells in the chum salmon pituitary with antisera to endorphin and NH2-terminal peptide of salmon proopiocortin

The proopiocortin-containing cells were identified immunocytochemically in the chum salmon pituitary using specific antibodies raised against NH2-terminal peptide (sNPP) and COOH-terminal peptide, endorphin (sEP), of salmon proopiocortin. Immunoreactivity for both sNPP and sEP was observed in the same cells, melanotrops, in the pars intermedia. In the pars distalis, on the other hand, corticotrops were stained only with antibody to sNPP but not with that to sEP. The present results indicate that proopiocortin or a precursor molecule for NH2-terminal peptide and endorphin is biosynthesized in both melanotrops of the pars intermedia and corticotrops of the pars distalis. However, the absence of immunoreactivity of corticotrops with sEP antibody suggests that the processing of the precursor molecule in the pars distalis differs significantly from that in the pars intermedia in the chum salmon pituitary as the processings established in the two lobes in the mammalian pituitaries.

Immunocytochemical identification of CRF-like and SRIF-like peptides in the brain and the pituitary of cyprinid fish

Single and double immunocytochemical techniques were applied to the brain and pituitary of carps and goldfish. With the use of antiserum raised against synthetic corticotropin-releasing factor (CRF), immunoreactive perikarya were observed in the nucleus praeopticus and the nucleus praeopticus periventricularis. CRF-like-immunoreactive hypothalamic nerve fibers reach the pituitary. In cyprinids, some fine fibers enter the rostral neurohypophysis bordered by prolactin- and ACTH cells. Other thicker fibers extend ventrocaudally into the neurointermediate lobe. This CRF-like system appears to differ from the SRIF-like system, which is restricted to the proximal pars distalis of the pituitary containing somatotrophs.

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.

Immunocytological study on the differentiation of chick and quail adenohypophysis epithelial rudiments, grafted or cultivated in vitro: evidence for polypeptidic hormones

Epithelial rudiments of adenohypohysis were removed from chick and quail embryos between days 3 and 5 of development. Chick rudiments were grafted for 11--13 days onto the chorioallantoic membrane of decapitated chick embryo hosts. Quail rudiments were cultivated in vitro for 6 days. Both grafted and cultivated Rathke's pouches differentiated into adenohypophyseal tissue. The adenohypophyseal tissue cultured on chorio-allantoic membrane exhibited cells reacting with the following immune sera: anti-beta-(1--24)ACTH, anti-alpha-(17--39)-ACTH, anti-alpha-endorphin, anti-beta-endorphin and anti-beta-LPH, which also gave a positive reaction when applied to adenohypophysis of corresponding age which had differentiated in situ. In situ, corticotrophs were located exclusively in the cephalic lobe of adenohypophysis. Therefore, the differentiation of corticotrophs in the whole graft, i.e., from both cephalic and caudal lobes of Rathke's pouch, showed that the cells of the caudal lobe, or at least some of them, were uncommitted when the rudiment was removed. In vitro, tissue derived from Rathke's pouch contained cells reacting with antibodies to beta-(1--24)-ACTH, alpha-(17--39)-ACTH, and beta-LPH, as did adenohypophysis from quail embryos of corresponding age (9--10 days), differentiated in situ. The differentiation of quail Rathke's pouch in vitro corroborates that differentiation can occur without influence from hypothalamus and, moreover, shows that at least some kinds of cells can differentiate without influence exerted by any other encephalic factors, and in the absence of mesenchyme. The question arises whether fibroblastic cells derived from Rathke's pouch cells act as feeder-cells and/or secrete some factors promoting differentiation.