Immunocytochemical identification of thyrotropin (TSH)-producing cells in pituitary glands of several species of teleosts with antiserum to human TSH beta subunit

Expression of Tshb and Tshr in the ricefield eel Monopterus albus: Potential paracrine/autocrine roles in gonads

Thyroid stimulating hormone (TSH), a glycoprotein synthesized and secreted from thyrotrophs of the pituitary gland, is composed of a glycoprotein hormone common alpha subunit (CGA) and a specific beta subunit (TSHB). The major biological function of TSH is to stimulate thyroidal follicles to synthesize and secrete thyroid hormones through activating its cognate receptor, the thyroid stimulating hormone receptor (TSHR). In the present study, polyclonal antisera against ricefield eel Tshb and Tshr were generated respectively, and the expression of Tshb and Tshr was examined at mRNA and protein levels. RT-PCR analysis showed that tshb mRNA was expressed mainly in the pituitary as well as in some extrapituitary tissues including the ovary and testis. Tshr mRNA was also expressed in a tissue-specific manner, with transcripts detected in tissues including the kidney, ovary, and testis. The immunoreactive Tshb signals in the pituitary were shown to be localized to the inner areas of adenohypophysis which are close to the neurohypophysis of adult ricefield eels. Tshb-immunoreatvie cells in the pituitary of ricefield eel larvae were firstly observed at hatching. The expression of immunoreactive Tshb and Cga was also detected in ricefield eel ovary and testis together with Tshr. In the ovary, immunoreactive Tshb, Cga, and Tshr were observed in oocytes and granulosa cells. In the testis, immunoreactive Tshb was mainly observed in Sertoli cells while immunoreactive Cga and Tshr were detected in germ cells as well as somatic cells. Results of the present study suggest that Tsh may be synthesized both in the ovary and testis locally, which may play paracrine and/or autocrine roles in gonadal development in ricefield eels.

Functional divergence of thyrotropin beta-subunit paralogs gives new insights into salmon smoltification metamorphosis

Smoltification is a metamorphic event in salmon life history, which initiates downstream migration and pre-adapts juvenile salmon for seawater entry. While a number of reports concern thyroid hormones and smoltification, few and inconclusive studies have addressed the potential role of thyrotropin (TSH). TSH is composed of a α-subunit common to gonadotropins, and a β-subunit conferring hormone specificity. We report the presence and functional divergence of duplicated TSH β-subunit paralogs (tshβa and tshβb) in Atlantic salmon. Phylogeny and synteny analyses allowed us to infer that they originated from teleost-specific whole genome duplication. Expression profiles of both paralogs in the pituitary were measured by qPCR throughout smoltification in Atlantic salmon from the endangered Loire-Allier population raised in a conservation hatchery. This revealed a striking peak of tshβb expression in April, concomitant with downstream migration initiation, while tshβa expression remained relatively constant. In situ hybridization showed two distinct pituitary cell populations, tshβa cells in the anterior adenohypophysis, and tshβb cells near to the pituitary stalk, a location comparable to the pars tuberalis TSH cells involved in seasonal physiology and behaviour in birds and mammals. Functional divergence of tshβ paralogs in Atlantic salmon supports a specific role of tshβb in smoltification.

Immunocytochemical identification and ontogeny of adenohypophyseal cells in a cave fish, Phreatichthys andruzzii (Cypriniformes: Cyprinidae)

The morphogenesis of the pituitary gland and the chronological appearance of adenohypophyseal cells were investigated for the first time in the Somalian cave fish Phreatichthys andruzzii by immunocytochemistry. The adult adenohypophysis contained: a rostral pars distalis, with prolactin (PRL) cells arranged in follicles and adrenocorticotropic (ACTH) cells, a proximal pars distalis with somatotropic (GH), β-thyrotropic (TSH), β-gonadotropic type I (FSH) and type II (LH) cells and a pars intermedia with α-somatolactin (SL), α-melanotropic (MSH) and β-endorphin (END) cells. All regions were deeply penetrated by neurohypophyseal branches. At hatching (24 h post-fertilization) the pituitary was an oval cell mass, close to the ventral margin of diencephalon. The first immunoreactive cells appeared as follows: PRL at 0·5 days after hatching (dah), GH and SL at 1·5 dah, END at 2 dah, TSH, ACTH and MSH at 2·5 dah, FSH at 28 dah and LH at 90 dah. The neurohypophysis appeared at 5 dah and branched extensively inside the adenohypophysis at 130 dah, but there was no boundary between rostral pars distalis and proximal pars distalis at this stage. The potential indices of prolactin and growth hormone production increased until 28 and 60 dah, respectively. The potential index of growth hormone production correlated positively with total length. Activity of PRL and GH cells, measured as ratio of cell area to nucleus area, was significantly higher in juveniles than in larvae.

Effects of the anti-thyroidal compound potassium-perchlorate on the thyroid system of the zebrafish

The increasing pollution of aquatic habitats with anthropogenic compounds has led to various test strategies to detect hazardous chemicals. However, information on effects of pollutants in the thyroid system in fish, which is essential for growth, development and parts of reproduction, is still scarce. Other vertebrate groups such as amphibians or mammals are well-studied; so the need for further knowledge especially in fish as a favored vertebrate model test organism is evident. Modified early life-stage tests were carried out with zebrafish exposed to the known thyroid inhibitor potassium perchlorate (0, 62.5, 125, 250, 500 and 5000 μg/L) to identify adverse effects on the hypothalamic-pituitary-thyroid axis. Especially higher perchlorate concentrations led to conspicuous alterations in thyroidal tissue architecture and to effects in the pituitary. In the thyroid, severe hyperplasia at concentrations ≥ 500 μg/L together with an increase in follicle number could be detected. The most sensitive endpoint was the colloid, which showed alterations at ≥ 250 μg/L. The tinctorial properties and the texture of the colloid changed dramatically. Interestingly, effects on epithelial cell height were minor. The pituitary revealed significant proliferations of TSH-producing cells resulting in alterations in the ratio of adeno- to neurohypophysis. The liver as the main site of T4 deiodination showed severe glycogen depletion at concentrations ≥ 250 μg/L. In summary, the thyroid system in zebrafish showed effects by perchlorate from concentrations ≥ 250 μg/L, thus documenting a high sensitivity of the zebrafish thyroid gland for goitrogens. In the future, such distinct alterations could lead to a better understanding and identification of potential thyroid-disrupting chemicals.

Alterations along the Hypothalamic-Pituitary-Thyroid Axis of the Zebrafish (Danio rerio) after Exposure to Propylthiouracil

In the past, various approaches have been developed to detect adverse effects of pollutants on the thyroid of vertebrates, most of these with special emphasis on the South African clawed frog, Xenopus laevis. Although fish are primarily affected by thyroid-disrupting chemicals, studies into alterations of the thyroid of fish are scarce. Therefore, effects of the reference compound propylthiouracil on histopathology of the thyroid axis were analyzed in a modified early life-stage test with zebrafish (Danio rerio) exposed to propylthiouracil. The test substance induced dose-dependent alterations of thyroidal tissue concomitant with increases in the number of surrounding blood vessels. Despite this massive proliferation of the thyroid, zebrafish were not able to maintain thyroxin concentrations. The pituitary was affected displaying significant alterations in thyroid-stimulating hormone cell counts. Quantitative evaluation of pituitary surface areas revealed a dose-dependent increase of adenohypophyseal tissue. Distinct histopathological effects may contribute to a more easy identification and interpretation of alterations induced by thyroid-disrupting chemicals.

Immunocytochemical identification of adenohypophyseal cells in the pirarucu (Arapaima gigas), an Amazonian basal teleost

The adenohypophysis (AH) of juvenile pirarucu (Arapaima gigas), a representative species of the Osteoglossomorpha (bonytongue fishes, one of the oldest living groups of the teleosts), was studied using histochemical and immunocytochemical methods. The AH is comprised of the pars distalis (PD), without a clear distinction between rostral pars distalis (RPD) and proximal pars distalis (PPD), and the pars intermedia (PI). The neurohypophysis (NH) is positioned on top of the PD and penetrates and branches into the PI. In the most rostral dorsal portion of the PD, adrenocorticotropic cells and fusiform gonadotropic cells were found. In the central PD, scarce prolactin-producing cells and growth-hormone-producing cells were located mainly in the dorsal part, whereas round gonadotropic cells were abundant in the ventral portion of this region. Human thyrotropin immunoreactive cells were not found in the entire AH. In the PI, melanotropic, some adrenocorticotropic, and somatolactin-producing cells were located intermingled surrounding the neurohypophyseal branches. Our results showed that the A. gigas pituitary has some basal characteristics between the ancient Actinopterygii and the more derived teleosts.

Immunocytochemical characterization of adenohypophyseal cells in the greater weever fish (Trachinus draco)

The adenohypophysis of the greater weever fish (Trachinus draco) was studied using histochemical and immunocytochemical methods. The adenohypophysis comprised the rostral pars distalis (RPD), the proximal pars distalis (PPD), and the pars intermedia (PI). Neurohypophysis showed a patent hypophyseal stalk which was divided into several branches intermingled with the adenohypophysis. Salmon prolactin (PRL)-immunoreactive (ir) cells, arranged in follicles, resided in the RPD and the most rostral part of the ventral PPD. Human adrenocorticotropin (ACTH)-ir cells were located in the RPD between PRL-ir cells and the neurohypophyseal processes. Salmon and seabream somatotropin (GH)-ir cells were located in both the dorsal and the ventral PPD. Some GH-ir cells were seen in surrounding and in contact with neurohypophyseal branches, whereas other isolated or clustered GH-ir cells were embedded in adenohypophyseal cells of the PPD. In addition, isolated or clustered GH-ir cells were also detected in the tissue of the PPD covering the most rostral part of PI. Only one class of salmon and carp gonadotropin (GTH)-ir cells was detected. Isolated or clustered GTH-ir cells resided in both the dorsal and the ventral PPD and were seen surrounding the PI and in the tissue of the PPD covering the most rostral part of PI. In addition, a few scattered GTH-ir cells were observed in the ventral RPD. Scattered groups of thyrotropin (TSH)-ir cells were present in the anteroventral PPD. Salmon and seabream somatolactin (SL)-ir and bovine melanotropin (MSH)-ir cells were intermingled surrounding the neurohypophyseal tissue. SL-ir cells were negative to periodic acid-Schiff technique. MSH-ir cells showed a very weak immunoreactivity to anti-human ACTH((1-24)) serum. In addition to the PI location, few isolated or clustered SL- and MSH-ir cells were observed in the dorsal PPD.

Identification and localization of eight distinct hormone-producing cell types in the pituitary of male Atlantic halibut (Hippoglossus hippoglossus L.)

The eight distinct hormone-producing cell types in the adenohypophysis of male Atlantic halibut (Hippoglossus hippoglossus L.) were identified and localized using immunohistochemistry and in situ hybridization. Lactotropes either occupied most of the rostral pars distalis (RPD) or they were arranged in follicular structures located along the periphery of the RPD. Corticotropes were confined to a thin layer of RPD cells bordering the pars nervosa (PN). The somatotropes were arranged in multicellular layers bordering the highly convoluted PN penetrating the proximal pars distalis (PPD), while thyrotropes, scattered in small islets in between the somatotropes, were located in the centro-dorsal part of the PPD. Gonadotropes were found throughout the PPD. Immunoreactivity to glycoprotein-alpha and luteinizing hormone beta-subunit was also observed along the periphery of the pars intermedia (PI), indicating that a thin extension of the PPD surrounded the PI. In situ hybridization showed that follicle-stimulating hormone and luteinizing hormone were produced in distinct cells of the PPD. PI contained somatolactotropes bordering the highly convoluted PN, and melanotropes that showed positive immunostaining against both anti-alpha-melanocyte-stimulating hormone and anti-beta-endorphin. The general cellular organization was similar to that of other teleost fish. These results lay the basis for future investigations on Atlantic halibut pituitary physiology.

An immunocytochemical study of the pituitary gland of the white seabream (Diplodus sargus)

The adenohypophysis of the white seabream (Diplodus sargus) was studied using histochemical and immunocytochemical techniques. The adenohypophysis was composed of rostral pars distalis, proximal pars distalis and pars intermedia. Prolactin (anti-chum salmon prolactin positive) and adrenocorticotropic (anti-human ACTH positive) cells were found in the rostral pars distalis. Prolactin cells were organized into follicles, while ACTH cells were arranged in cords around neurohypophyseal tissue branches that penetrated the rostral pars distalis. In the proximal pars distalis, somatotropic (anti-chum salmon and anti-gilthead seabream growth hormone positive), gonadotropic (anti-chum salmon beta-gonadotrophin II and anti-carp beta-gonadotrophin II positive, but anti-chum salmon beta-gonadotrophin I negative) and thyrotropic (anti-human beta-thyrotropin positive) cells were observed. Growth hormone cells were restricted to the dorsal and ventral part of the proximal pars distalis. They were clustered or surrounded the neurohypophyseal branches. Only one type of gonadotrophin cell was identified and they were clustered or isolated in the proximal pars distalis. Scattered groups of thyrotropin cells were located throughout the proximal pars distalis. In the pars intermedia somatolactin (anti-chum salmon and anti-gilthead seabream somatolactin positive) and melanotropic (anti-alpha-melanotropic hormone positive) cells were localized. In addition, gonadotrophin cells surrounded the pars intermedia or distributed evenly between somatolactin and melanotropic hormone cells. Somatolactin cells were periodic acid-Schiff negative and surrounded the neurohypophyseal branches intermingled with melanotropic cells. These cells were also immunoreactive to anti-human ACTH antiserum.

Salmon thyroid-stimulating hormone: isolation, characterization, and development of a radioimmunoassay

Coho salmon (Oncorhynchus kisutch) thyroid-stimulating hormone (TSH) was isolated by ethanol extraction of pituitary glands from mature coho salmon. Extraction was followed by gel-filtration chromatography on Sephadex G-100 superfine, anion-exchange chromatography on a Whatman DE-52 column, and finally by reverse-phase high-performance liquid chromatography. Fractions were monitored for TSH content by a homologous in vivo bioassay and by immunoblots using anti-human TSH beta-subunit antisera. In vivo treatment of coho salmon parr with coho salmon TSH caused a dose-dependent increase in plasma thyroxine level similar to that induced by bovine TSH. The N-terminal sequence (25 residues) of the salmon TSH beta subunit has 56% sequence identity to that of human TSH beta subunit and is identical to the deduced amino acid sequence of trout TSH beta subunit. The N-terminal sequence (25 residues) of the salmon TSH alpha subunit is identical to gonadotropin alpha-II subunit. Molecular sizes of the alpha and beta subunits are 18,000 and 24,000 daltons, respectively, as estimated by SDS-PAGE. Antiserum generated against salmon TSH, which was preadsorbed with alpha subunit using an alpha-subunit affinity column, detected only salmon TSH beta subunit by immunoblot and specifically stained thyrotropin-producing cells of the pituitary gland. A homologous radioimmunoassay (RIA) was developed using purified salmon TSH standard, iodinated TSH beta subunit, and antiserum generated against salmon TSH. Cross-reactivities of GTH I, GTH II, GTH I beta and GTH II beta subunits, alpha subunit, growth hormone, prolactin, and somatolactin were less than 1%. Displacement curves for serial dilutions of plasma and pituitary extracts of various salmonid species, as well as coho salmon pituitary cell culture medium, were parallel to the coho salmon TSH standards. In contrast, plasma of hypophysectomized juvenile coho salmon and pituitary extracts of Pacific tomcod (Microgadus proximus) did not displace bound radiolabeled salmon TSH. Finally, in vivo injection of juvenile coho salmon with triiodothyronine decreased plasma TSH levels, whereas the goitrogen, methimazole, increased plasma TSH levels. Injection of gonadotropin-releasing hormone agonist did not alter plasma TSH. These data suggest that the RIA is specific for TSH and confirm a negative-feedback relationship between the thyroid hormones and TSH.

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.

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.

Immunocytochemistry of gonadotropic cells in the pituitary of Pomadasys jubelini (teleost fish)

An antibody specific for the beta subunit of carp gonadotropin was applied to pituitary sections from Pomadasys jubelini in order to characterize and localize the gonadotropic cells by immunocytological means. It reveals the gonadotropic zone lying mainly at the periphery of the proximal pars distalis with lateral extensions around the pars intermedia. The separation between the pars proximalis and the pars intermedia is irregular. Short finger-like extensions of the gonadotropic zone protrude more or less into the pars intermedia. The immunocytological results corroborate previous tentative identifications of the gonadotropic cells by classical cytological methods and suggest that the gonadotropic hormone produced is immunologically related with several previously studied fish gonadotropins.

The development of monoclonal antibodies against salmon (Oncorhynchus kisutch and O. keta) pituitary hormones and their immunohistochemical identification

Monoclonal antibodies (MCAs) directed against several salmon pituitary hormones were generated by the fusion of myeloma cells with spleen cells from mice that had been immunized with either chum salmon (Oncorhynchus keta) growth hormone (GH) or prolactin (PRL), or one of two purified protein preparations from coho salmon (O. kisutch) pituitaries. Hybridoma were cloned by limiting dilution and screened for MCA production using immunohistochemical procedures. MCAs were generated that bound specifically to GH, PRL, or gonadotropic cells. MCAs were generated that bound to either fine granular material or large globular inclusions in the cytoplasm of the "classical" strongly PAS-positive globular gonadotropic cell type found in mature fish. This suggests that these MCAs are directed against gonadotropin II (GTH II). A MCA was also generated that bound both granular and globular material in the globular gonadotrops and granular material in the weakly PAS-positive vesicular gonadotrops in pituitaries from mature fish and to a cell type in immature rainbow trout pituitaries which is tentatively identified as the gonadotropin I (GTH I) cell type. This MCA did not bind to thyrotrops in immature rainbow trout pituitaries.

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.

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.

The relation between pituitary gland and thyroid growth during the lifespan of the annual fish Cynolebias whitei and Nothobranchius korthausae: gonadotropic and thyrotropic cells

In the annual cyprinodont Cynolebias whitei the cell types responsible for the increase of pituitary growth at the onset of maturation and for pituitary hyperplasia in old specimens were identified as gonadotropic cells and thyrotropic cells, respectively. The gonadotropic cells showed a high affinity to anti-carp alpha beta-GTH serum, both at light- and electron-microscopical levels. The allometric relation of total gonadotropic cell volume to body length, determined for fish from six weeks up to six months of age, showed no inflections. Therefore pituitary growth in maturing fish may be partly a result of proliferation of gonadotropes, although gonadotropic cells do not contribute to pituitary hyperplasia in old fish. Thyrotropic cells showed a weak affinity to anti-carp alpha beta-GTH serum at light-microscopical level. Under the electron microscope thyrotropic cells displayed signs of activation in maturing fish and signs of proliferation in old fish. The allometric relation of thyroid gland volume to body length paralleled that of pituitary volume to body length. Histologically the thyroid gland showed signs of inactivity in adult fish and of hyperplasia in old fish. The possibility, that gonadal maturation, pituitary thyrotropic activity, and growth of the thyroid in maturing fish are related through the inhibitory action of gonadal steroids on thyroid hormone release, is discussed. Pituitary hyperplasia in old fish is the result of proliferation of thyrotropic cells. Similar hyperplasia of pituitary and thyroid glands was observed in old Nothobranchius korthausae.

Development and aging of the teleost pituitary: qualitative and quantitative observations in the annual cyprinodont Cynolebias whitei

The rapidly aging annual cyprinodont Cynolebias whitei (maximum age under natural conditions: approximately six months) was used to study the histology and growth of the pituitary gland throughout the entire lifespan of a teleost fish. Immunoreactive prolactin and corticotropic cells were present in the prehatching larvae. Somatotropic cells and pars intermedia could be distinguished by histological staining in five days old fish. After three weeks basophilic, GTH-immunoreactive, cells could be observed in the proximal pars distalis while in five weeks old fish PAS-positive and melanotropic cells could be distinguished in the pars intermedia. A weakly chromophilic and GTH-immunoreactive cell type appeared in the proximal pars distalis of 6 weeks old fish. These cells were identified as thyrotropic cells. In fish older than four months cysts and haemorrhagia appeared in all parts of the pituitary gland. Allometric (log-log) plots of fish length and pituitary volume revealed two inflections in the slope of the regression line. Such inflections indicate stanzas (stages or periods) in fish growth. Both inflections found in this study reflect an increased rate of pituitary growth in relation to the growth rate of body length in the subsequent stanzas. The first inflection occurs at about three weeks, coincides with the appearance of GTH-immunoreactive cells and probably represents the onset of maturation. The second inflection occurs at four months and is followed by pituitary hyperplasia and histological deteriorations. This inflection is considered to reflect the onset of aging.

Immunoelectron microscope observations on secretion of human placental lactogen (hPL) in the human chorionic villi

Immunoelectron microscope localization of human placental lactogen (hPL) was investigated in the chorionic villi from week 7 to full-term gestation with the protein A-gold technique. With specific antiserum against hPL, immuno-reactive gold particles were found to be preferentially located in Golgi-derived, electron-dense small granules of 80-180 nm in the syncytiotrophoblast. Our electron micrographs indicate that these small granules increase in number in the course of gestation and are released by exocytosis from the apical cell surface. The present study reveals that hPL is segregated from the Golgi apparatus, stored in the syncytiotrophoblast as secretory granules, and released into the maternal blood.

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).

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.