Immunocytochemical identification of growth hormone, prolactin, and gonadotropin cells in the pituitary of male plaice (Pleuronectes platessa) during gonadal maturation

A systematic immunohistochemical survey of the distribution patterns of GH, prolactin, somatolactin, beta-TSH, beta-FSH, beta-LH, ACTH, and alpha-MSH in the adenohypophysis of Oreochromis niloticus, the Nile tilapia

Fish pituitary plays a central role in the control of growth, development, reproduction and adaptation to the environment. Several types of hormone-secreting adenohypophyseal cells have been characterised and localised in diverse teleost species. The results suggest a similar distribution pattern among the species investigated. However, most studies deal with a single hormone or hormone family. Thus, we studied adjacent sections of the pituitary of Oreochromis niloticus, the tilapia, by conventional staining and immunohistochemistry with specific antisera directed against growth hormone (GH), prolactin (PRL), somatolactin (SL), thyrotropin (beta-TSH), follicle-stimulating hormone (beta-FSH), luteinising hormone (beta-LH), adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone (alpha-MSH). The pituitary was characterised by a close interdigitating neighbourhood of neurohypophysis (PN) and adenohypophysis. PRL-immunoreactive and ACTH-immunoreactive cells were detected in the rostral pars distalis. GH-immunoreactive cells were present in the proximal pars distalis (PPD). A small region of the PPD contained beta-TSH-immunoreactive cells, and beta-LH-immunoreactive cells covered approximately the remaining parts. Centrally, beta-FSH-immunoreactive cells were detected in the vicinity of the GH-containing cells. Some of these cells also displayed beta-LH immunoreactivity. The pars intermedia was characterised by branches of the PN surrounded by SL-containing and alpha-MSH-immunoreactive cells. The ACTH and alpha-MSH antisera were observed to cross-react with the respective antigens. This cross-reactivity was abolished by pre-absorption. We present a complete map of the distinct localisation sites for the classical pituitary hormones, thereby providing a solid basis for future research on teleost pituitary.

Production, characterization and applications of mouse anti-grass carp (Ctenopharyngodon idellus) growth hormone monoclonal antibodies

Mouse anti-grass carp growth hormone (gcGH) monoclonal antibody (MAb) secretors were produced by PEG-mediated fusion of NS-1 myeloma cells and splenic B-lymphocytes of gcGH hyper-immunized mice. Positive secretors were screened by direct ELISA and cloned by limiting dilution. Three positive secretors, 21D3, 22G5 and 23B3, were obtained in a single fusion trial. Anti-gcGH MAbs were produced by growing hybridomas in the peritoneal cavity of pristane-primed mouse. The three MAbs were isotyped to be IgG2a, IgG2b and IgM, respectively. IgG MAbs were purified from ascitic fluid by Hitrap protein G column and IgM MAb was purified by gel filtration chromatography. The purified MAbs were highly specific and had moderate binding affinity. The MAbs were successfully used for the purification of native gcGH from mature grass carp pituitary extract by one-step immunoaffinity chromatography, for the quantification of gcGH by competitive sandwich ELISA, and for the probing of somatotropes in grass carp pituitary by immunohistochemistry.

Thyroid and pituitary gland development from hatching through metamorphosis of a teleost flatfish, the Atlantic halibut

Fish larval development, not least the spectacular process of flatfish metamorphosis, appears to be under complex endocrine control, many aspects of which are still not fully elucidated. In order to obtain data on the functional development of two major endocrine glands, the pituitary and the thyroid, during flatfish metamorphosis, histology, immunohistochemistry and in situ hybridization techniques were applied on larvae of the Atlantic halibut (Hippoglossus hippoglossus), a large, marine flatfish species, from hatching through metamorphosis. The material was obtained from a commercial hatchery. Larval age is defined as day-degrees (D degrees =accumulated daily temperature from hatching). Sporadic thyroid follicles are first detected in larvae at 142 D degrees (27 days post-hatch), prior to the completion of yolk sack absorption. Both the number and activity of the follicles increase markedly after yolk sack absorption and continue to do so during subsequent development. The larval triiodothyronine (T(3)) and thyroxine (T(4)) content increases, subsequent to yolk absorption, and coincides with the proliferation of thyroid follicles. A second increase of both T(3) and T(4) occurs around the start of metamorphosis and the T(3) content further increases at the metamorphic climax. Overall, the T(3) content is lower than T(4). The pituitary gland can first be distinguished as a separate organ at the yolk sack stage. During subsequent development, the gland becomes more elongated and differentiates into neurohypophysis (NH), pars distalis (PD) and pars intermedia (PI). The first sporadic endocrine pituitary cells are observed at the yolk sack stage, somatotrophs (growth hormone producing cells) and somatolactotrophs (somatolactin producing cells) are first observed at 121 D degrees (23 days post-hatch), and lactotrophs (prolactin producing cells) at 134 D degrees (25 days post-hatch). Scarce thyrotrophs are evident after detection of the first thyroid follicles (142 D degrees ), but coincident with a phase in which follicle number and activity increase (260 D degrees ). The somatotrophs are clustered in the medium ventral region of the PD, lactotrophs in the anterior part of the PD and somatolactotrophs are scattered in the mid and posterior region of the pituitary. At around 600 D degrees , coinciding with the start of metamorphosis, somatolactotrophs are restricted to the interdigitating tissue of the NH. During larval development, the pituitary endocrine cells become more numerous. The present data on thyroid development support the notion that thyroid hormones may play a significant role in Atlantic halibut metamorphosis. The time of appearance and the subsequent proliferation of pituitary somatotrophs, lactotrophs, somatolactotrophs and thyrotrophs indicate at which stages of larval development and metamorphosis these endocrine cells may start to play active regulatory roles.

The brain–pituitary–gonad axis in male teleosts, with special emphasis on flatfish (Pleuronectiformes)

The key component regulating vertebrate puberty and sexual maturation is the endocrine system primarily effectuated along the brain-pituitary-gonad (BPG) axis. By far most investigations on the teleost BPG axis have been performed on salmonids, carps, catfish and eels. Accordingly, earlier reviews on the BPG axis in teleosts have focused on these species, and mainly on females (e.g. 'Fish Physiology, vol. IXA. Reproduction (1983) pp. 97'; 'Proceedings of the Fourth International Symposium on the Reproductive Physiology of Fish. FishSymp91, Sheffield, UK, 1991, pp. 2'; 'Curr. Top. Dev. Biol. 30 (1995) pp. 103'; 'Rev. Fish Biol. Fish. 7 (1997) pp. 173'; 'Proceedings of the Sixth International Symposium on the Reproductive Physiology of Fish. John Grieg A/S, Bergen, Norway, 2000, pp. 211'). However, in recent years new data have emerged on the BPG axis in flatfish, especially at the level of the brain and pituitary. The evolutionarily advanced flatfishes are important model species both from an evolutionary point of view and also because many are candidates for aquaculture. The scope of this paper is to review the present status on the male teleost BPG axis, with an emphasis on flatfish. In doing so, we will first discuss the present understanding of the individual constituents of the axis in the best studied teleost models, and thereafter discuss available data on flatfish. Of the three constituents of the BPG axis, we will focus especially on the pituitary and gonadotropins. In addition to reviewing recent information on flatfish, we present some entirely new information on the phylogeny and molecular structure of teleost gonadotropins.

Immunocytochemical and histological studies on the hypophyseal-gonadal system in the freshwater nile tilapia, oreochromis niloticus (L.), during sexual maturation and spawning in different habitats

The activities of the hypophyseal-gonadal system of O. niloticus in different habitats were investigated using immunocytochemical and histological techniques. The observed physico-chemical results indicated that Lake Nasser water characteristics are within the allowed and desired safety baseline levels. In contrast, Lake Manzalah exhibited high levels of Ca(2+), Mg(2+), SO(4)(2-) and heavy metals (Zn, Pb, and Cd). These water conditions affected the activity of the hypophyseal-gonadal axis of tilapia. The secretory and the synthetic activities of GTH and SL cells in the pituitary gland, in general, underwent obvious normal changes during gonad maturation and spawning of O. niloticus in Lake Nasser. In Lake Manzalah, the secretory activity of GTH and SL cells declined. This may be due to the effect of the high levels of heavy metals which interfere with the release of hormones and disturb the feedback mechanisms. In addition, the activity of both PRL and GH cells in Lake Nasser was higher than that of Lake Manzalah, but the synthetic activity of the ACTH and MSH cells was higher in Lake Manzalah. This may be related to the increased stress on fishes and the dark polluted water in Lake Manzalah. Both the environmental and the endocrine impacts in Lake Manzalah caused a decline in the gonadal activity as reflected by the decrease of sperm amount in the ripe testis, the appearance of oocytes in the testis and the degeneration of ripe oocytes (atresia) during the spawning season. J. Exp. Zool. 284:343-354, 1999. Copyright 1999 Wiley-Liss, Inc.

An immunocytochemical study of pituitary cells of the Senegalese sole, Solea senegalensis (Kaup 1858)

Different antisera directed against mammalian and piscine pituitary hormones, as well as a battery of various conventional histochemical techniques (PAS, Alcian Blue pH 2.5, Bromophenol Blue) and lectins, were used to identify the different hormonal cell types in the pituitary of the Senegalese sole, Solea senegalensis. Prolactin and adrenocorticotrophic cells were located in the rostral pars distalis of the pituitary. Gonadotrophic, thyrotrophic 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 the Solea senegalensis pituitary. The PAS reaction was positive in somatolactin cells, which were unreactive with the lead-Haematoxylin technique, whereas melanotrophic cells were positive. Glycoproteins containing mannose and/or glucose, as well as N-acetyl-glucosamine and sialic acid sugar residues, are synthesized and secreted by gonadotrophic, thyrotrophic and somatolactin cells. Adrenocorticotrophic cells and, especially, the amphiphilic somatolactin and acidophilic growth hormone cells were stained with the Bromophenol Blue technique that identifies proteins in general, but adrenocorticotrophic and growth hormone cells were unreactive towards PAS, Alcian Blue pH 2.5 and lectins (Con A and WGA).

Immunocytochemical and ultrastructural characterization of prolactin, growth hormone, and somatolactin cells from the Mediterranean yellowtail (Seriola dumerilii, Risso 1810)

BACKGROUND

Prolactin (PRL), growth hormone (GH), and somatolactin (SL) are structurally related pituitary hormones that belong to a peptide family. Whereas growth hormone and prolactin are present in the hypophysis of all vertebrates, somatolactin, a recently discovered hormone, has been found only in fish. It has been demonstrated immunocytochemically in a few teleost species; ultrastructurally, cells producing this hormone have been characterized only in one species of salmon. In this paper, we identify and characterize ultrastructurally the cells producing these three hormones in Mediterranean yellowtail (Seriola dumerilii).

METHODS

Pituitaries from adult specimens were dissected out and processed for electron microscopy. The immunogold technique was performed in some ultrathin sections using fish primary antibodies.

RESULTS

PRL cells had round, peripherally distributed, very electron-dense, homogeneous secretory granules of variable size. GH cells had dense, round secretory granules with a conspicuous scalloped membrane, which were grouped in the cell area near the neurohypophysis. SL cells had round, polymorphic, or very irregularly shaped secretory granules, the last seeming to arise from the fusion of various secretory granules. The population of secretory granules varied greatly from one cell to another. In all cases, immunogold labeling was seen exclusively in the secretory granules. Exocytosis was observed in all cell types. Some of the PRL, GH, and SL cells showed involutive features.

CONCLUSIONS

PRL, GH, and SL, although structurally and functionally related, are secreted by ultrastructurally different cells in the pituitary of M. yellowtail.

The adenohypophysis of Mediterranean yellowtail, Seriola dumerilii (Risso, 1810): an immunocytochemical study

The adenohypophysis (ADH) of the Mediterranean yellowtail was studied using the peroxidase-antiperoxidase technique. Human corticotropin (ACTH) (1-24)-immunoreactive (ir) cells were found bordering the neurohypophysis (NH) and salmon prolactin (PRL)-ir cells were arranged in thick cords, both in the rostral pars distalis (RPD). Gonadotropin (GTH)-, thyrotropin (TSH)- and growth hormone (GH)-ir cells were observed in the proximal pars distalis (PPD). Anti-chum salmon GTH I and anti-chum salmon GTH II immunostained the same cells in the outermost part of the ADH at the level of the PPD and the PI. In addition to these cells, some cells grouped in the inner areas of the posterior PPD were revealed by catfish alpha, beta-GTH antiserum. Human beta-TSH-ir cells formed small groups and discontinuous strands in the PPD often in contact with the NH. Tilapia GH-ir cells formed cords mainly surrounding the NH in the central PPD, while cod somatolactin- and alpha MSH-ir cells mainly surrounded the NH branches in the PI.

Growth hormone (GH) and reproduction: a review

Interaction between growth and reproduction occurs in many vertebrates and is particularly obvious at certain stages of the life cycle in fish. Endocrine interactions between the gonadotropic axis and the somatotropic axis are described, the potential role of GH being emphasised. A comparative analysis of these phenomena in mammals, amphibians and fish, suggests a specific role of GH in the physiology of puberty, gametogenesis and fertility. It also shows the original contribution made by studies on the fish model in this field of investigations.

Immunocytochemistry of somatotrophs, gonadotrophs, prolactin and adrenocorticotropin cells in larval sea bream (Sparus auratus) pituitaries

The chronological appearance of endocrine cells in the pituitary of sea-bream (Sparus auratus) larvae was studied using antisera against salmon prolactin, trout growth hormone, salmon gonadotropin and N-terminal human adrenocorticotropin. The larval pituitary (1-12 days after hatching) was oval in shape and was composed of a dense mass of cells with few neurohypophysial fibres. By 60 days after hatching it began to resemble the adult and was divisible into a distinct rostral pars distalis containing prolactin and adrenocorticotropin cells; a proximal pars distalis containing somatotrophs and gonadotrophs and a pars intermedia. Cells immunoreactive with antisera against growth hormone were observed immediately after hatching (2 days post-fertilization). Weakly staining prolactin cells were observed 2 days later in the region corresponding to the rostral pars distalis. Cells immunoreactive with antigonadotropin and anti-adrenocorticotropin sera were observed in the pituitary 6 and 8 days after hatching, respectively. All the cell-types studied were immunoreactive from the time they were first identified until the final samples 90 days after hatching.