Immunohistochemical detection, by light and electron microscopy, of pituitary hormones in cold-blooded vertebrates. II. Reptiles

Functional Pituitary Networks in Vertebrates

The pituitary is a master endocrine gland that developed early in vertebrate evolution and therefore exists in all modern vertebrate classes. The last decade has transformed our view of this key organ. Traditionally, the pituitary has been viewed as a randomly organized collection of cells that respond to hypothalamic stimuli by secreting their content. However, recent studies have established that pituitary cells are organized in tightly wired large-scale networks that communicate with each other in both homo and heterotypic manners, allowing the gland to quickly adapt to changing physiological demands. These networks functionally decode and integrate the hypothalamic and systemic stimuli and serve to optimize the pituitary output into the generation of physiologically meaningful hormone pulses. The development of 3D imaging methods and transgenic models have allowed us to expand the research of functional pituitary networks into several vertebrate classes. Here we review the establishment of pituitary cell networks throughout vertebrate evolution and highlight the main perspectives and future directions needed to decipher the way by which pituitary networks serve to generate hormone pulses in vertebrates.

Immunocytochemical localization and ultrastructural study of gonadotroph cells in the female desert lizard Uromastyx acanthinura

The pars distalis from the pituitary gland of adult female desert lizards (Uromastyx acanthinura), captured during vitellogenesis (late may) and hivernal period, was studied with immunocytochemical methods using specific antisera against human FSH (hFSH) and LH (hLH). The immunostaining with anti-hLH and anti-hFSH allowed the identification of only FSH-like containing cells. The FSH-like immunoreactive cells were affected differently by a physiological stage and showed some heterogenous cytological characteristics. During vitellogenesis, four aspects of rostral FSH-like immunoreactive cells could be recognized. The expression of FSH-like in mainly immunoreactive cells was parallel to an intense synthetic activity and to the presence of ultrastructural features indicating an intense release of the hormone. This release was considerably altered in winter, the immunoreactive cells stored an important amount of secretion granules which increased in size and undergo a crinophagic process.

An immunohistochemical study of adenohypophyseal cells in the viviparous reptile Chalcides chalcides

The morphology of the hypophysis and the immunocharacteristics of the adenohypophyseal cells in the viviparous reptile Chalcides chalcides were studied by light microscopy, using conventional staining methods and an indirect antibody technique (ABC method), respectively. The general morphology of the C. chalcides hypophysis was comparable to that of other reptiles, showing three main regions: the pars distalis, the pars intermedia and the pars nervosa. The gland appeared as an elongated body in a cephalic-caudal direction and was almost completely enclosed in the sella turcica. For this reason, the hypophysis was studied in toto with the brain in decalcified specimens. The pars distalis accounted for most of the whole organ. The pars intermedia surrounded the pars nervosa as a goblet. The pars tuberalis was lacking. The immunohistochemical identification of the adenohypophyseal cells was performed using rabbit antisera against mammalian/synthetic hypophyseal hormones. Prolactin cells were clustered in small cellular cordons in the rostral pars distalis and in the medial pars distalis in both male and female specimens. Somatotropic cells were found in the caudal pars distalis. Corticotropic cells were observed in the medio-rostral pars distalis, as well as in the pars intermedia, where melanotropic cells were also present. Melanotropic cells were confined to the pars intermedia. Gonadotropic cells were mostly distributed in the ventral and lateral portions of the pars distalis, where they were found isolated or in small clusters. Thyrotropic cells were detected in the pars distalis with a distribution similar to that of the gonadotropic cells; however, atypically, they were also found in the pars intermedia. Therefore, the cytological characteristics of the adenohypophyseal cells appeared mostly conserved.

Immunohistochemistry and tinctorial affinity of adenohypophysial cells of the rat snake Ptyas mucosus (Colubridae)

Immunocharacteristics of the adenohypophysial cells of the rat snake Ptyas mucosus (Colubridae) were studied with an unlabeled antibody enzyme technique (PAP method) using rabbit antisera against mammalian/synthetic hypophysial hormones. Adenohypophysial cells were identified on the basis of their specific immunoreactivity with various heterologous antisera. As in other reptiles, there was regional localization of pars distalis (PD) cell types in this snake. The gonadotropic (GTH) cells were identified by their specific immunoreactivity with anti-porcine (p)LH beta serum and were distributed uniformly throughout the PD. The thyrotropic (TSH) cells, recognized by their specific immunoreactivity with anti-human (h)TSH beta serum, were found in the medial PD. The prolactin (PRL) and growth hormone (GH) cells were revealed by their specific immunoreactivity with anti-ovine (o)PRL and anti-hGH sera, respectively; the former were confined to the anterior two-thirds of the PD, and the latter were restricted to the posterior third of the PD. The corticotropic (ACTH) cells, identified by their specific immunoreactivity with the anti-ACTH1-24 serum, were localized in the anterior two-thirds of the PD. Though both ACTH and PRL cells were confined to the same area of the PD, they could be distinguished by their distinctive morphology and distribution pattern. Cells of the pars intermedia were revealed by their immunoreactivity to anti-alpha MSH (melanophore-stimulating hormone) and anti-ACTH1-24 sera. Among each adenohypophysial cell type, there was variation in the intensity of immunoreactivity and morphological features, which may be due to their heterogeneity, reflecting various stages of cellular activity. Unlike most other snake species, the occurrence of a rudimentary pars tuberalis in P. mucosus containing a few immunoreactive GTH and TSH cells appeared to be a novel finding. The occurrence of the PRL-like and TSH-like immunoreactivity seen in certain neuronal perikarya and fibers of the hypothalamus and median eminence conforms with earlier observations in other tetrapods. To resolve certain discrepancies in the literature, the tinctorial affinities of immunohistochemically identified adenohypophysial cell types of P. mucosus were studied using various conventional staining methods and were compared with those of other reptilian species studied earlier, including snakes of the family Colubridae.

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.

Effect of pinealectomy on annual testicular cycle of Indian chequered water snake, Natrix piscator

Pinealectomy for 60 days (noted every month of the year), in the tropical Indian chequered water snake. Natrix piscator, caused inhibition of testicular growth during late progressive and active phases and retarded the rate of regression during regressive phase; during sexually inactive phase the testes remain partially active. The weight of the accessory sex organs, vas deferens, and kidney (along with the renal sex segment activity) followed the same pattern as that of the testes. Thus, it may be concluded that the pineal gland of this ophidian participates in the regulation of seasonal testicular cycle, probably via the hypothalamo-hypophyseal axis, and hence the effects of pinealectomy are seasonal and a reproductive phase-dependent phenomenon.

Immunohistochemical localization of thyrotropic cells during amphibian morphogenesis: a stereological study

TSH-like producing cells have been studied using the peroxidase-antiperoxidase (PAP) immunohistochemical technique and rabbit anti-human thyrotropin (TSH) antiserum in the pars distalis of five species of amphibian anuran tadpoles at different stages of development as well as in 1-year-old postmetamorphic animals. This cell type has been identified and located in the pars distalis ventral zone of Bufo calamita showing no changes in its distribution pattern throughout development, and in Rana perezi where TSH-like cells were located in the central zone of the gland in premetamorphic stages, occupying the ventral zone at the end of metamorphosis. No immunoreaction has been observed in the other species studied (Hyla meridionalis, Alytes cisternasii, and Pelobates cultripes). Morphometry and stereology were used to evaluate the changes observed in pars distalis volume and TSH immunoreactive cells during development. Pars distalis volume increased during the larval growth period and decreased throughout the metamorphic climax. TSH volume density and cellular area showed different evolutions in the species studied. The correlation between these parameters suggests a greatly proliferative period followed by an increase in cellular size. The changes observed in TSH total volume as well as the physiological data found by other authors lead us to conclude that there are two phases in amphibian development: first a period of TSH storage (pre- and prometamorphosis) and second a period of TSH release at metamorphic climax.

Immunocytochemical and morphometrical study of thyrotropic cells of Rana ridibunda

Indirect immunofluorescence and PAP techniques for light microscopy as well as the immunogold complex technique for electron microscopy were used to localize and identify thyrotropic (TSH) producing cells in the pars distalis of Rana ridibunda. A double immunostaining procedure was used to distinguish TSH cells from other glycoprotein hormone producing cells. Rabbit anti-human-beta-TSH was used as the primary antiserum and revealed a basophil, PAS and alcian blue positive cell type in the ventro-central zone of the gland. Under the electron microscope, TSH cells show irregular morphology, polymorphic secretory granules with diameters ranging between 120 and 375 nm and poor development of the endoplasmic reticulum and Golgi complex; they are usually polarized towards capillaries. Ultrastructural morphometry (point-counting method) was used to evaluate stereological parameters of rough endoplasmic reticulum, Golgi complex, secretory granules and mitochondria.

Localization of melanotropin-like peptides in the central nervous system of two insect species, the migratory locust, Locusta migratoria, and the fleshfly, Sarcophaga bullata

By use of well characterized antisera in the peroxidase-antiperoxidase method, we were able to demonstrate alpha MSH and beta MSH immunoreactive cells and nerve fibres within the nervous system of adults and larvae of Locusta migratoria and 3-, 5- and 8-day-old adult Sarcophaga bullata. In neither of these insect species, any immunoreaction was obtained with a gamma 3MSH-antiserum. Double immunohistochemical stainings revealed that alpha MSH-like and beta MSH-like substances are located in different cells. These cells show no immunoreactivity to a number of antisera against other POMC-derivatives (anti-beta lipotropin, anti beta endorphin, anti-ACTH1-24); thus they appear to contain alpha MSH- or beta MSH-like material in a specific way. The function of the immunologically detected peptides remains to be demonstrated. The distribution of the immunoreactive material suggests that, like in amphibians and other lower vertebrates, the synthesis or release of melanotropins might be under the influence of external stimuli. The present observations support the recently developed concept that even some of the smallest neuropeptides, the melanotropins, have been highly conserved during a long period of evolution.

Effect of dexamethasone and ACTH on oocyte growth and recruitment in the frog Rana cyanophlyctis during the prebreeding vitellogenic phase

The effects of 5, 25, 50 and 75 micrograms of dexamethasone and 0.1 or 0.5 IU ACTH on oocyte growth and recruitment were studied in Rana cyanophlyctis during prebreeding vitellogenic phase (May). Injections (ip) were given 6 days a week for 31 days and frogs were killed on the 32nd day. Treatment with 5 micrograms dexamethasone had no effect on gonadosomatic index (GSI) or on the number and percentage of different oocytes. Administration of 25 micrograms dexamethasone caused a significant (P less than 0.05) increase in both number and percentage of medium second growth phase (MSGP) oocytes and atretic follicles (AF), and a numerical reduction in number and percentage of large second growth phase (LSGP) oocytes. Frogs which received 50 or 75 micrograms dexamethasone exhibited a significant (P less than 0.05) decrease in GSI, ovarian weight, and number and percentage of LSGP oocytes, while those of MSGP oocytes and AF increased. There was no effect of dexamethasone on first growth phase (FGP) oocytes. The administration of 0.1 IU ACTH had no effect on GSI, percentage of different oocytes, or MSGP and LSGP number. There was a numerical increase in number of FGP oocytes. Treatment with 0.5 IU ACTH caused a significant (P less than 0.05) decrease in GSI, ovary weight, and number and percentage of LSGP oocytes, while those of AF increased. The above findings suggest that lower doses of dexamethasone (5 or 25 micrograms) and of ACTH (0.1 IU) have no effect on oocyte recruitment and growth, but that higher doses (50 or 75 micrograms dexamethasone and 0.5 IU ACTH) impair vitellogenic growth of oocytes and increase follicular atresia.(ABSTRACT TRUNCATED AT 250 WORDS)

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).

In vitro study of frog (Rana ridibunda Pallas) interrenal function by use of a simplified perifusion system. VIII. Structure-activity relationship of synthetic ACTH fragments and gamma-MSH

The present study was undertaken to determine the structure-activity relationships of ACTH analogs on corticosteroid production by frog adrenal gland. Rana ridibunda interrenal dice were perifused with amphibian culture medium for 10 hr. Corticosterone and aldosterone concentrations were measured in the effluent perifusate using sensitive and specific radioimmunoassay methods. Perifusion of interrenal fragments with increasing concentrations of synthetic human ACTH 1-39 (ranging from 6.25 X 10(-11) to 10(-9) M) led to a linear log-dose increase in both corticosterone and aldosterone secretion. Thus, this model made it possible to compare the steroidogenic potency of several ACTH analogs. Synthetic alpha-MSH and its des-N alpha-acetyl derivative were found to be approximately equipotent, and 5 X 10(3) times less active than authentic ACTH. The short-chain analog ACTH 1-10 was 2 X 10(4) times less potent than ACTH whereas ACTH 4-10 was totally inactive. A fragment of the N-terminal region of the proopiomelanocortin molecule, gamma 3-MSH, caused a dose-related stimulation of steroid secretion. However, in contrast to what has been observed in the rat, gamma 3-MSH did not potentiate the corticotropic action of ACTH on frog interrenal gland. Since processing of proopiomelanocortin in frog intermediate lobe generates high amounts of alpha-MSH and des-N alpha-acetyl alpha-MSH, these results suggest that in amphibians, several peptides other than ACTH may be involved in the control of corticosteroidogenesis.

Opiomelanocorticotropic-like hormones in Vipera aspis pituitary

By using immunohistochemical techniques (indirect immunofluorescence and PAP) adrenocorticotropic-like hormone (ACTH), alpha-melanocyte stimulating-like hormone (alpha-MSH), beta-lipotropic-like hormone (beta-LPH), and beta-endorphin-like (beta-EP) have been localized in the pituitary gland of newborn and adult Vipera aspis. The immunolocalization have been compared with the classical histochemical staining and the data show that the opiomelanocorticotropic-like cells resembles the B3 cells of the current literature. In the intermediate lobe both in adults and in newborns the same cells exhibit immunoreactivity for all the peptides considered, while in the rostral region of the pars distalis a difference has been observed between adults and newborns. In the adults, the cells immunostain for ACTH, beta-LPH, and beta-EP but not for alpha-MSH while in the newborns, the same cells show immunoreactivity for ACTH, beta-LPH, alpha-MSH but not for beta-EP. It has been hypothesized that in Vipera during maturation the pars distalis and the intermediate lobe can differently process the common precursor molecule.

Ontogeny and immunocytochemical differentiation of the pituitary gland in a sea turtle, Caretta caretta

In the sea turtle Caretta caretta the dorsal wall of the pituitary anlage and the apex of the hypophyseal angle are derived from stomodeal epithelium adherent to the neural epithelium of the diencephalon; a substantial part of the ventral wall of the anlage is derived from epithelium of mixed origin (stomodeum and foregut). Distribution of immunoreactive cells in the embryonic gland suggests that pituitary peptide hormones (adrenocorticotropin, ACTH; melanotropin, MSH; prolactin, PRL; growth hormone, GH) are synthesized in cells from the dorsal wall, while cells producing glycoprotein hormones (luteinizing hormone, LH; thyrotropin, TSH) trace their lineage to ventral and ventrolateral areas of the anlage that include some endoderm. Mesenchymal movements mold the epithelial anlage in two steps, delineating first the posterior and subsequently the anterior area of the gland. During the former process the lateral lobes are defined, and material immunoreactive with antiserum to ACTH appears in epithelial cells of presumptive pars distalis (PD) and pars intermedia (PI). Delineation of the anterior end of the pituitary gland occurs as the hypophyseal stalk forms, approximately one-fourth through ontogenesis. Shortly thereafter, immunoreactions demonstrate synthetic activity of distinctively distributed cells containing ACTH, PRL, GH, LH and TSH. In Caretta the lateral lobes of the pituitary anlage give rise to a distinct layer of tissue around the PD (pars tuberalis interna, PTint) and a thick layer on the floor of the hypothalamus (juxtaneural pars tuberalis, juxPT). In the pituitaries of late embryos, juxPT tissue proximal to the PD contains many cells immunoreactive with LH antiserum; whereas cells in distal areas of the juxPT do not react with any antisera tested. LH-cells also occur in large numbers in the PTint and in the posterior PD where tissues of the partes tuberalis and distalis are continuous. Cells reactive with antiserum to TSH are found in small numbers in the PTint, and in larger numbers along with the LH-cells in the posterior PD. PRL-cells occur in the anterior PD, GH-cells in the posterior. ACTH-cells are found primarily in the anterior two-thirds of the PD.

Localization of multiple forms of ACTH- and beta-endorphin-related substances in the pituitary of the reptile, Anolis carolinensis

Immunohistochemical studies on the pituitary of Anolis carolinensis detected ACTH-like, beta-endorphin-like, and 16K fragment-like immunoreactivity in distinct clusters of cells in the anterior lobe; ACTH-like, alpha MSH-like, beta-endorphin-like, and 16K fragment-like immunoreactivity was detected in all the cells of the intermediate lobe. Crude acid extracts of both lobes, when analyzed by radioimmunoassay, gave displacement curves in ACTH and beta-endorphin assays which were parallel to the appropriate synthetic standard. Only extracts of the intermediate lobe gave parallel displacement curves in an alpha MSH radioimmunoassay. Extracts of both lobes crossreacted with antiserum to 16K fragment, but the displacement curves were not parallel to that of mouse 16K fragment standard. The levels of immunoreactive ACTH and beta-endorphin in the intermediate lobe were approximately 8-fold higher than in the anterior lobe. Fractionation of anterior lobe and intermediate lobe extracts by either gel filtration on Sephadex G-75 in 10% formic acid or sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed multiple forms of ACTH-related and beta-endorphin-related substances in both lobes. In the anterior lobe the major forms of immunoreactivity were, respectively, ACTH-sized and beta-endorphin-sized. In the intermediate lobe the major forms of immunoreactivity were alpha MSH-sized, CLIP-sized, and beta-endorphin-sized. In both lobes, antisera directed against ACTH and beta-endorphin detected high molecular weight material with an apparent molecular weight slightly less than that of mouse pro-ACTH/endorphin; this material probably represents the putative common precursor for ACTH and beta-endorphin in this species.

Evidence for a common precursor for alpha MSH and beta-endorphin in the intermediate lobe of the pituitary of the reptile Anolis carolinensis

In order to investigate the biosynthesis of alpha MSH and beta-endorphin in a non-mammalian vertebrate, individual lizard intermediate pituitaries were incubated in complete medium containing a radioactive amino acid, using either a steady label or a pulse/chase protocol. Following incubation, acid extracts of the tissue were immunoprecipitated with either an NH2-terminal ACTH antiserum or a beta-endorphin antiserum and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. After a 24 hr steady label in medium containing [3H]tyrosine, multiple molecular weight forms of beta-endorphin-related and NH2-terminal ACTH-related radioactivity were detected. The major peak of beta-endorphin-related radioactivity co-migrated with synthetic beta-endorphin(1-31); minor peaks of beta LPH-sized material and precursor-sized material were also detected. The major peak of NH2-terminal ACTH-related material co-migrated with synthetic alpha MSH; in addition, smaller amounts of material designated ACTH biosynthetic intermediate 1, ACTH biosynthetic intermediate 2, and precursor-sized material were detected. Sequential immunoprecipitation experiments revealed that the precursor-sized material had antigenic determinants for both alpha MSH and beta-endorphin. Pulse/chase experiments established that this material is the common precursor for alpha MSH and beta-endorphin. Based on gel filtration chromatography in 6 M guanidine HCl, the molecular weights of these various peptides are: common precursor, 23,300 daltons; ACTH biosynthetic intermediate 1, 12,200 daltons; ACTH biosynthetic intermediate 2, 4,200 daltons; alpha MSH, 1,500 daltons; beta LPH, 8000 daltons; beta-endorphin, 3,400 daltons. None of the peptides precipitated with either antiserum incorporated [3H]glucosamine; thus glycosylation does not appear to be involved in this biosynthetic pathway in the lizard. The results of the kinetic experiments and molecular weight determinations indicate that the major biosynthetic pathway involves the following events: common precursor is first cleaved to yield ACTH biosynthetic intermediate 1 plus beta LPH; subsequently, beta LPH is cleaved to produce beta-endorphin; ACTH biosynthetic intermediate 1 is cleaved to produce ACTH biosynthetic intermediate 2 which is subsequently cleaved to produce alpha MSH. The pulse/chase experiments indicate minor pathways exist for cleaving beta-endorphin directly from the common precursor or via a high molecular weight form intermediate in size between the common precursor and beta LPH.

Immunohistochemical identification of cells in the pars distalis of the pituitary of the lizard Anolis carolinensis

Immunocharacteristics of the pars distalis cells of the pituitary of the male lizard A. carolinensis are determined by employing the immunoperoxidase technique with antisera to mammalian pituitary hormones. On the basis of their immunoreactivity, 5 different cell types with characteristic anatomical distribution are recognized. ACTH cells are found in the rostral half of the pars distalis, and PRL cells in the rostral two thirds of the pars distalis. GH and TSH cells are located in the caudal half of the pars distalis. GTH cells are distributed throughout the gland. When consecutive sections are stained with antiserum to ovine FSH or its beta-subunit and to ovine LH, the same cells show immunoreactivity to all the three antisera. None of the GTH cells show positive immunoreactivity to ovine beta-LH antiserum. The results suggest the existence of one gonadotropic cell type in the pituitary of this lizard.