Chronological appearance of the different hypophysial hormones in the pituitary of sea bass larvae (Dicentrarchus labrax) during their early development: an immunocytochemical demonstration

Antisera raised against chum salmon prolactin (PRL), rainbow trout growth hormone (GH), mammalian adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), and luteinizing hormone (LH) were used to study the chronological appearance of immunoreactivity for PRL, GH, ACTH, TSH, LH, and melanocyte-stimulating hormone (MSH) in the pituitary of sea bass larvae (Dicentrarchus labrax) during the first 26 days after hatching. The anti-ACTH gives positive immunostaining in the ACTH cells as well as in the MSH cells; however, the two cell types can easily be distinguished by their different localization in the pituitary: ACTH in the rostral pars distalis, MSH in the pars intermedia. The first day after hatching cells immunoreactive for TSH, GH and ACTH could already be noticed, ACTH reacted strong in the pars intermedia but very weak in the rostral pars distalis. Cells immunopositive for PRL became visible between Days 9 and 15. With anti-LH, no positive reaction could be obtained during the first 26 days after hatching.     

Immunocytochemical identification of the prolactin- and growth hormone-secreting cells in the teleost pituitary with antisera to tilapia prolactin and growth hormone

Antisera raised to highly purified tilapia (Sarotherodon mossambicus) prolactin (PRL) and growth hormone (GH) were used to locate PRL and GH cells in the adenohypophysis of seven species of teleosts by immunoenzymological methods using horseradish peroxidase. The only pituitary cells in the tilapia that immunologically reacted with anti-tilapia PRL were the PRL cells located in the rostral pars distalis (RPD). In the pituitary glands of two species of salmonids and two species of marine fishes, the tilapia PRL antibodies bound to both PRL and GH cells; no prolactin-immunoreactive cells were identified in the goldfish and eel pituitaries. Antiserum to tilapia GH reacted specifically with the GH cells located in the proximal pars distalis of all teleosts examined in this study, but not with any presumed PRL cells in the RPD. These results indicate that tilapia PRL antisera are specific for tilapia PRL cells but not necessarily for these cells in other teleost species. Tilapia GH antisera showed no species specificity among the teleosts tested.     

Immunohistochemical localization of gonadotropin releasing hormones in the brain and pituitary gland of the Nile perch,Lates niloticus (Teleostei,Centropomidae)

In the present study we investigated the distribution of gonadotropin-releasing hormones (GnRH) in the brain of Lates niloticus and their association with different pituitary cell types using immunohistochemical techniques. We found immunoreactive (ir) chicken GnRH-II (cGnRH-II) and mammalian GnRH (mGnRH) as the main components of the GnRH-ir system within the brain of the Nile perch. The results indicate that mGnRH and cGnRH are localized in different neurons: mGnRH-ir perikaria were observed in the preoptic region particularly in the organum vasculosum laminae terminalis (OVLT) and in the nucleus lateralis tuberis pars posterior (NLTP) of the mediobasal hypothalamus. These cell bodies are located along a continuum of ir-fibers that could be traced from the olfactory nerve to the pituitary. mGnRH-ir fibers were detected in many parts of the brain (olfactory bulbs, ventral telencephalon, hypothalamus, and mesencephalon) and in the pituitary. cGnRH-ir cell bodies are restricted to the optic tract, but few scattered fibers could be detected in different parts of the brain. The pituitary exhibited very few cGnRH-II ir fibers, contrasting with an extensive mGnRH innervation. Moreover, mGnRH-ir fibers were targeting the three areas of the pituitary gland: rostral pars distalis (RPD), proximal pars distalis (PPD), and pars intermedia (PI). Double immunolabeling studies showed GnRH-ir fibers in close proximity with prolactin (PRL)- and adrenocorticotropic hormone (ACTH)-producing cells in the RPD, growth hormone (GH)-producing cells in the PPD, gonadotropins (GTHs)-producing cells in the PPD in the external border of the PI, and with somatolactin (SL)- and alpha-melanocyte stimulating hormone (alpha-MSH)-producing cells in the PI. Our results showed direct morphological evidence for a close association of GnRH-ir fibers with the different adenohypophysial cell types. These results suggest a multiple role of GnRH in the regulation of various pituitary hormones' release.     

Immunocytochemical study of growth hormone, prolactin, and thyroid-stimulating hormone in the adenohypophysis of the sea lamprey, Petromyzon marinus L., during its upstream migration

Immunoreactivity to growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone (TSH) was found in the adenohypophysis of the sea lamprey, Petromyzon marinus L., during its upstream migration, by immunoperoxidase techniques with antisera to mammalian pituitary hormones. Cross-reactivity to GH and PRL was found in two different cell populations in the proximal pars distalis. Specific immunostaining for GH and PRL was absent in other parts of the lamprey pituitary. Immunoreactive TSH cells were located only in the rostral pars distalis, and corresponded in shape and size to the large basophils in this region of the lamprey pituitary. These results suggest that mammalian-like GH, PRL, and TSH are produced in the pituitary of the lamprey.     

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.     

Colocalization of GnRH binding sites with gonadotropin-, somatotropin-, somatolactin-, and prolactin-expressing pituitary cells of the pejerrey, Odontesthes bonariensis, in vitro.

Previous studies in the pejerrey, Odontesthes bonariensis, have demonstrated that fibers with immunoreactivity to gonadotropin-releasing hormone (ir-GnRH) reach all areas of the pituitary gland, the rostral pars distalis (RPD), the proximal pars distalis (PPD), and the pars intemedia (PI). A close association was shown between ir-GnRH fibers and gonadotropin (GtH)-, growth hormone (GH)-, somatolactin (SL)-, and prolactin (PRL)-expressing cells. The presence of only one GnRH variant, suspected to be a novel form, has been shown in pituitary extracts of this fish. In addition, GnRH may stimulate GtHs, GH, SL, and PRL levels in different fish species. The objective of the present study was to seek GnRH receptors and therefore colocalization with GtHs, GH, SL, and PRL cells in O. bonariensis using a pituitary primary cell culture system. GnRH binding sites were revealed by autoradiography of an iodinated superactive GnRH agonist ([(125)I]GnRH-A) and pituitary cells were identified by immunocytochemistry using piscine antisera. Following autoradiography, silver grains representing specific [(125)I]GnRH-A binding were associated with anti GtH, GH, SL, and PRL positive cells. These results demonstrate the presence of GnRH binding sites on these cells. It is suggested that GnRH may play a wide role in the neuroendocrine control of different pituitary hormones in addition to the GtHs.     

Immunocytochemical demonstration of melanotropic and adrenocorticotropic cells from the gilthead sea bream (Sparus aurata L., Teleostei) by light and electron microscopy: an ontogenic study

In the pituitary of gilthead sea bream, Sparus aurata, melanotropic (MSH) and adrenocorticotropic (ACTH) cells were identified at the light and electron microscopic levels using rabbit anti-synthetic alphaMSH (MSH) and anti-human ACTH (1-24) (ACTH) sera. The distribution of these cell types was followed from hatching to 48 months. The techniques used included the peroxidase anti-peroxidase (PAP) method, conventional electron microscopy, and an immunogold technique. Using PAP, MSH (immunoreactive to both anti-MSH and anti-ACTH) and ACTH (immunoreactive to anti-ACTH) cells were detected from hatching onward. These cells were distinguished ultrastructurally in 1-day-old larvae. Immunogold labeling was first detected in MSH cells in 5-day-old larvae, while ACTH cells were only immunogold labeled in adults. In newly hatched larvae, MSH cells were located from the middle to the posterior region of the adenohypophysis, while ACTH cells were found in the dorsoanterior region, next to the hypothalamus. At this age, both cell types were scarce. As the fish developed, these cell types progressively increased in number: MSH cells made up a layer surrounding the neurohypophysis (NH) in the pars intermedia (pi), whereas ACTH cells bordered the developing NH in the rostral pars distalis (rpd). From 82 days onward, a few MSH cells were observed in the proximal pars distalis (ppd) next to the pi and some ACTH cells were seen in the ppd next to the rpd. In adult specimens, both MSH and ACTH cells were adjacent to the stellate cells and showed processes and synaptic-like structures. MSH cells exhibited numerous round secretory granules with a granular content and of varying electron density and compactness. These granules were immunogold labeled with anti-MSH serum. Electron-dense secretory granules near the Golgi complex immunoreacted with anti-MSH, anti-ACTH, or with both antisera. ACTH cells exhibited round secretory granules with a homogeneous, high electron-dense core and a narrow, clear halo. These granules immunoreacted with anti-ACTH serum. The main ultrastructural features that characterize the MSH and ACTH cells of adults appeared early during ontogeny. Involutive MSH and ACTH cells were only observed in adult specimens.     

The dawn and evolution of hormones in the adenohypophysis

The adenohypophysial hormones have been believed to have evolved from several ancestral genes by duplication followed by evolutionary divergence. To understand the origin and evolution of the endocrine systems in vertebrates, we have characterized adenohypophysial hormones in an agnathan, the sea lamprey Petromyzon marinus. In gnathostomes, adrenocorticotropin (ACTH) and melanotropin (MSH) together with beta-endorphins (beta-END) are encoded in a single gene, designated as proopiomelanocortin (POMC), however in sea lamprey, ACTH and MSH are encoded in two distinct genes, proopoicortin (POC) gene and proopiomelanotropin (POM) gene, respectively. The POC and POM genes are expressed specifically in the rostral pars distalis (RPD) and the pars intermedia (PI), respectively. Consequently, the final products from both tissues are the same in all vertebrates, i.e., ACTH from the PD and MSH from the PI. The POMC gene might have been established in the early stages of invertebrate evolution by internal gene duplication of the MSH domains. The ancestral gene might be then inherited in lobe-finned fish and tetrapods, while internal duplication and deletion of MSH domains as well as duplication of whole POMC gene took place in lamprey and gnathostome fish. Sea lamprey growth hormone (GH) is expressed in the cells of the dorsal half of the proximal pars distalis (PPD) and stimulates the expression of an insulin-like growth factor (IGF) gene in the liver as in other vertebrates. Its gene consists of 5 exons and 4 introns spanning 13.6 kb, which is the largest gene among known GH genes. GH appears to be the only member of the GH family in the sea lamprey, which suggests that GH is the ancestral hormone of the GH family that originated first in the molecular evolution of the GH family in vertebrates and later, probably during the early evolution of gnathostomes. The other member of the gene family, PRL and SL, appeared by gene duplication. A beta-chain cDNA belonging to the gonadotropin (GTH) and thyrotropin (TSH) family was cloned. It is expressed in cells of the ventral half of PPD. Since the expression of this gene is stimulated by lamprey gonadotropin-releasing hormone, it was assigned to be a GTHbeta. This GTHbeta is far removed from beta-subunits of LH, FSH, and TSH in an unrooted tree derived from phylogenetic analysis, and takes a position as an out group, suggesting that lampreys have a single GTH gene, which duplicated after the agnathans and prior to the evolution of gnathostomes to give rise to LH and FSH.     

Immunohistochemistry of the pituitary pars distalis of the musk shrew, Suncus murinus.

Immunocharacteristics of the pituitary pars distalis cell types of the musk shrew, Suncus murinus, were studied by the unlabeled antibody enzyme technique, using peroxidase-antiperoxidase or avidin-biotin-peroxidase complex. The thyrotropin (TSH)-, gonadotropin (GTH)-, corticotropin (ACTH)-, prolactin (PRL)-, and growth hormone (GH)-secreting cells of the PD were identified on the basis of their immunoreactivity with different heterologous antisera. The TSH cells showed specific immunoreactivity with antisera against human (h) TSH beta and rat (r) TSH beta. Cells showing immunoreactivity with the antisera against hLH beta and ovine (o) LH beta were designated as GTH cells as no immunoreactivity was observed with antisera against hFSH beta and oFSH beta. The ACTH cells as well as the cells of the pars intermedia were revealed by anti-ACTH1-24 and anti-ACTH1-10 sera. Whereas the PRL cells were recognized by their immunoreactivity with antisera against hPRL and oPRL, the GH cells were identified with anti-hGH, anti-oGH, and anti-bovine (b) GH sera. TSH and GTH, TSH and ACTH, GTH and ACTH, ACTH and GH, ACTH and PRL, and GH and PRL cells were visualized in the same section using the dual immunoperoxidase technique. Comparison of the immunohistochemically identified cells with those described histochemically reveals several discrepancies, which expose the limitations of the latter techniques identifying adenohypophysial cells.     

Ontogenesis of the three parts of the fetal rat adenohypophysis. A detailed immunohistochemical analysis

The sequential changes in the histological pattern of anterior pituitary cytodifferentiation of the rat are described. The first labeled cells were ACTH positive and were detected in the pars tuberalis on postconceptual day 13. On day 14 ACTH cells also appeared in the ventral periphery of the pars distalis. On fetal day 15 the pars tuberalis anlage was characterized by numerous well-stained ACTH cells and by some weakly labeled FSH-beta, LH-beta, TSH-beta, GH and PRL cells while the pars distalis showed only ACTH positivity. On day 16 of gestation the ACTH cells were equally distributed throughout the whole pars distalis, while LH-beta, FSH-beta, TSH-beta, PRL and GH immunoreactive cells were localized either in the ventral region of the pars distalis only or were evenly distributed throughout the pars distalis. The present immunocytochemical data suggest that in the pars distalis the hypophyseal cell differentiation follows a clear rostrocaudal, ventrodorsal direction and that the time sequence of the functional differentiation of the adenohypophysis is pars tuberalis, pars distalis and pars intermedia.     

Identification and distribution of the cell types in the pituitary gland of Austromenidia laticlavia (Teleostei, Atherinidae)

By using antisera against human pituitary hormones in immunocytochemistry in combination with classical cytochemical techniques, we have been able to identify the different cell types in the adenohypophysis of the Austromenidia laticlavia and to determine their location. Antisera against prolactin and growth hormones did not stain cells in the pituitary of Austromenidia, whereas antisera against beta-endorphin, LH, and beta-TSH selectively cross-reacted with cells which have a specific location within the adenohypophysis. The beta-endorphin antiserum stained the periodic acid-Schiff (PAS)-negative cells in the pars intermedia and also, though faintly, the PAS-negative cells in the internal border of the rostral pars distalis (RPD). Human beta-TSH antiserum showed a discrete population of small PAS-positive cells in the proximal pars distalis (PPD). Antiserum against human LH stained PAS-positive cells located in the most ventral zone of the PPD and around the pars intermedia (PI). The distribution of the different cell types is similar to that of other teleosts. The phylogenetic implications of the degree of cross-reactivity of the antisera against human pituitary hormones with specific cells of the teleost fish pituitary is discussed.     

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.     

Transplantation of the pituitary pars distalis induces the corticotrophs to store melanocyte-stimulating hormone, an effect reversed by the administration of corticotropin-releasing factor.

Corticotrophs of the pituitary pars distalis do not contain immunohistochemically detectable alpha-melanocyte-stimulating hormone (MSH). After grafting the glands beneath the renal capsule for 25 days, this hormone could be demonstrated in corticotrophs, coexisting with corticotropin. The administration of corticotropin-releasing factor deprived these cells of the content of MSH but did not apparently affect the presence of adrenocorticotropin (ACTH). It is suggested that the histological appearance of MSH in the corticotrophs may be due to a diminished rate of corticotropin release, which may provide time for splitting the former hormone in amounts larger than the negligible ones normally present in the pars distalis, or to the hypothetical fact that some hypothalamic factor may inhibit the cleavage of ACTH into MSH.     

Localization and characterization of prolactin-like immunoreactivity in the pituitary of the frog Rana ridibunda

Distribution and quantification of PRL in the pituitary gland of the frog Rana ridibunda were investigated using a high-affinity antiserum raised against bullfrog prolactin (PRL). The immunoreactive PRL-producing cells were distributed throughout the pars distalis, the highest density of cells being observed in the rostral region of the adenohypophysis facing the neurointermediate lobe. The dorsal region of the pars distalis contained only a few scattered PRL-immunoreactive cells. At the electron microscopic level, PRL-containing cells were visualized using the immunogold procedure. PRL-immunoreactive material was exclusively stored in secretory granules (size ranging from 200 to 700 nm in diameter). Neither the rough endoplasmic reticulum nor the Golgi apparatus were immunolabeled. Using a radioimmunoassay method we have compared the displacement curves obtained with bullfrog PRL and acetic extracts from Rana ridibunda pituitary. The two binding curves were not completely parallel, suggesting the existence of slight variations of the amino acid sequences of PRL in the two species. The concentration of PRL in the green frog adenohypophysis appeared somewhat higher (35.3 +/- 8.8 micrograms/mg protein) than that in the bullfrog pituitary. These results validate the use of an antiserum to bullfrog PRL to investigate the regulation of PRL secretion in Rana ridibunda.     

Distribution of immunoreactive adenohypophysial cell types in the pituitaries of the Atlantic and the Pacific hagfish, Myxine glutinosa and Eptatretus burgeri

The hagfish is considered the most primitive vertebrate known, living or extinct. It remains an enigma whether adenohypophysial hormones similar to those of more advanced vertebrates are present in the hagfish pituitary gland or not. The present study aimed to detect immunoreactive adenohypophysial hormones in the hagfish pituitary gland, using antisera to tetrapod and fish adenohypophysial hormones as immunohistochemical probes. For this purpose, two species of hagfish, the Atlantic hagfish, Myxine glutinosa, and the Pacific hagfish, Eptatretus burgeri, were used. In both species, three different types of immunoreactive cells were detected in the adenohypophysis. (1) The first type of cells was gonadotropin (GTH)-like cells which were stained by antisera to LH-related GTHs, such as ovine LHbeta, human LHbeta, bullfrog LH, salmon LHbeta and sturgeon LHbeta in both species of hagfish. (2) The second type of cells that were detected was growth hormone (GH)/prolactin (PRL)-like cells. In M. glutinosa the cells were stained by antisera to salmon GH, salmon PRL, sturgeon GH, sturgeon PRL, blue shark GH, and lamprey GH. In E. burgeri the cells were only stained by anti-human GH and anti-sturgeon PRL. (3) The last type of cells was adrenocorticotropin (ACTH)-like cells. These cells were stained by antisera to lamprey ACTH and human beta-endorphin. In both species of hagfish, GTH-like cells were relatively abundant, and were distributed throughout the adenohypophysis, whereas GH/PRL-like and ACTH-like cells were few in number in the adenohypophysis. Based on these findings, we suggest that hagfish may have retained ancestral characteristics of key anterior pituitary hormones.     

Immunocytochemical demonstration of pituitary cell types in the teleost Poecilia latipinna, by light and electron microscopy

Using the unlabelled antibody method at the light microscope level, and the immunogold method at the electron microscope level, the distribution of the different adenohypophysial cells was demonstrated in the teleost Poecilia latipinna, by means of antisera to both teleostean and mammalian pituitary hormones and their subunits. Anti-salmon prolactin, but not anti-rat or -ovine prolactin, gave a specific staining of the acidophils of the rostral pars distalis (RPD), while anti-trout growth hormone (GH), but not anti-rat GH, stained similar but always separate cells in the proximal pars distalis (PPD). Antisera to the whole molecules of mammalian glycoprotein hormones stained the entire population of basophils in the PPD, but separate populations of gonadotrophs and thyrotrophs could be discriminated using anti-salmon gonadotrophin and anti-human thyrotrophin beta subunit. Antisera to ACTH (1-24) and (11-24) sequences, as well as beta-endorphin and met-enkephalin, stained the lead haematoxylin-positive cells of the RPD and pars intermedia (PI), whereas anti-alpha-MSH stained only the PI cells. Ultrastructural examination showed that these immunoreactivities were present in the same secretory granules, and were always greater in pale granules rather than electron dense granules. In the RPD, blebs of ACTH-immunoreactive cytoplasm were found to protrude through the gaps in the basement membrane into the neurohypophysis. The second "PAS-positive" cell type of the PI showed a strong cross-reaction with anti-salmon gonadotrophin, suggesting that it may produce a glycoprotein chemically related to the gonadotrophin(s).     

Cytological responses of the pituitary (rostral pars distalis) and immunoreactive corticotropin-releasing factor (CRF) in the goldfish treated with dopamine antagonists

The in vivo effects of three dopamine (DA) antagonists on the cytology of the rostral pars distalis (RPD) were investigated in young goldfish (Carassius auratus L.). Pimozide, sulpiride, and domperidone were injected for 5 (low dose, Experiment I) and 7 days (higher dose, Experiment II). Cytological and immunocytochemical techniques using antisera to (1-24) ACTH and (1-39) ACTH, human beta-thyrotropin (TSH beta), and synthetic (1-41) CRF were applied to pituitary and brain sections. Cytometrical studies showed that the three drugs induced similar quantitative changes in the cells of the RPD. Prolactin (PRL)-secreting cell hypertrophy was significant in Experiment II, whereas the nuclear enlargement was significant in both experiments. The numbers of cytoplasmic granules were similar in control and treated goldfish. Thyrotropic (TSH) cells and their nuclei were significantly enlarged in both experiments; their content in immunoreactive TSH was not clearly modified. Corticotropic (ACTH) cells showed significant nuclear and cellular hypertrophy, and labeled granules were often concentrated along the cell membrane. The amount of immunoreactive CRF present in the rostral neurohypophysial ramifications was reduced in the majority of treated fish. Solvent-injected controls showed no significant changes in the RPD. These results suggest that DA inhibits PRL cell activity in goldfish. TSH and ACTH cells appear stimulated by DA-receptor blockers, although differential effects on synthesis and release cannot be evaluated in in vivo experiments. A release of corticotropin-releasing factor may be involved in the ACTH cell stimulation. These data are compared with those obtained in other vertebrates.     

Immunocytochemical demonstration of close relationships between neuropeptidergic nerve fibers and hormone-producing cell types in the adenohypophysis of the sea bass (Dicentrarchus labrax)

Light microscopic double immunocytochemical stainings, performed on sea bass hypothalamo-hypophysial sections, revealed the projection of different neuropeptide-immunoreactive neurons innervating the hormone-producing cell populations in the pituitary gland. In the rostral pars distalis (PD) the ACTH cells were found in close proximity to fibers immunoreactive for somatostatin (SRIF), growth hormone-releasing hormone (GRF), corticotropin-releasing hormone (CRF), vasotocin (VT), isotocin (IT), substance P (SP), neurotensin, and galanin (GAL), while the PRL cell zone seemed only innervated by nerve fibers immunopositive for GAL. In the proximal PD, fibers immunoreactive for SRIF, GRF, VT, IT, cholecystokinin, SP, neuropeptide Y, and GAL formed a close relationship with the growth hormone cells. The gonadotrophs were observed near nerve fibers immunostained for gonadotropin-releasing hormone, IT, and less obviously GRF and VT, while fibers positive for GRF, CRF, VT, IT, SP, and GAL penetrated between and formed a close association with the thyrotrophs. In the pars intermedia the MSH cells and the PAS-positive (PAS+) cells seemed both innervated by separate nerve fibers immunoreactive for GRF, CRF, melanin concentrating hormone, VT, IT, and SP. All these results suggest a functional role of the neuropeptides in the adenohypophysis of the sea bass, possibly in the synthesis and/or release of hypophysial hormones from the different cell types.     

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.