Early organization of the pituitary gland in Sparus aurata L. (Teleostei) An ultrastructural study

The cell organization of the pituitary gland and the relationship between neurohypophysis and adenohypophysis in the early developmental stages of the gilthead sea bream, Sparus aurata, were studied by electron microscopy. In newly hatched larvae, the pituitary gland was embedded in the ventral floor of the diencephalon and separated from the hypothalamus by a continuous basal lamina. Elongated mesenchymal cells next to the ventral surface were observed. At this stage, there was no neurohypophysis and the adenohypophysis consisted of undifferentiated endocrine cells with small scarce secretory granules and a few stellate cells, with no distinctive zonation. An incipient neurohypophysis was present in 1-day-old larvae. The first evagination of the neurohypophysis into the adenohypophysis were observed in 2-day-old larvae and developed progressively with age, being deeper in the caudal zone. Two regions in the adenohypophysis, one anterior — the presumptive pars distalis — and one posterior — the presumptive pars intermedia — were found in 2-day-old larvae. Three regions (rostral and proximal pars distalis and pars intermedia) were clearly distinguishable in 4-day-old larvae. The ultrastructural features of the pituitary endocrine cells varied during gland differentiation, with the secretory granules gradually increasing in number and size, accompanying organelle development. Nevertheless, even in the oldest larvae studied (65 days), undifferentiated cells similar to those in the earliest stages were observed. The first blood vessels appeared in the neurohypophysis around 16 days after hatching. During early development, the pituitary gland progressively emerged from the ventral floor of the brain. By 16 days, the principal pattern of the pituitary gland architecture appeared to be established.     

Early development of the pituitary gland in Acipenser naccarii (Chondrostei, Acipenseriformes): an immunocytochemical study

The distribution and appearance of secretory cells in the pituitary gland were investigated for the first time in a chondrostean species, Acipenser naccarii, from embryos to juveniles, by immunohistochemistry with mammalian and teleost hormone antisera. On 5.5 day post-fertilization (2.5 days pre-hatching), the pituitary of embryos appears as an oval cell mass with a narrow central cavity (hypophysial cleft), close to the ventral border of diencephalon under the third ventricle. At that time no neurohypophysis is observed, the adenohypophysis is not yet structurally divided into pars intermedia (PI) and pars distalis (PD) and only immunoreactive growth hormone cells are detectable. Seven days post-fertilization (1 day pre-hatching) the immunoreactive thyrotropic cells appear in the ventral region and the immunoreactive adrenocorticotropic cells in the posterior dorsal one. At hatching, some immunoreactive melanotropic (ir-MSH) cells are visible in the posterior dorsal region and some immunoreactive prolactin cells in the anterior one. Eight days later the immunoreactive somatolactin cells appear along the posterior dorsal border and the immunoreactive gonadotropic I (ir-GtH I) cells in the ventral region. Here, a few ir-GtH II cells finally appear in 76–86 day old juveniles. The gland elongates after hatching and in 8-day-old larvae two adenohypophysial regions are identified: a posterior (the presumptive PI) and an anterior one (the presumptive PD). In 156–166-day-old juveniles three regions (rostral and proximal pars distalis and pars intermedia) appear and a high number of ir-MSH cells are visible in the rostral region. The first protrusion of neurohypophysis into adenohypophysis is observed in 76–86-day-old juveniles and increases with age, branching into PI. The rostro-caudal distribution of the immunoreactive cells follows the spatial expression of the corresponding hormone gene families observed in zebra fish, suggesting similar differentiating mechanisms in teleosts and chondrosteans.     

Early development of the pituitary gland in<Emphasis Type="Italic"> Acipenser naccarii</Emphasis> (Chondrostei,Acipenseriformes): an immunocytochemical study

The distribution and appearance of secretory cells in the pituitary gland were investigated for the first time in a chondrostean species, Acipenser naccarii, from embryos to juveniles, by immunohistochemistry with mammalian and teleost hormone antisera. On 5.5 day post-fertilization (2.5 days pre-hatching), the pituitary of embryos appears as an oval cell mass with a narrow central cavity (hypophysial cleft), close to the ventral border of diencephalon under the third ventricle. At that time no neurohypophysis is observed, the adenohypophysis is not yet structurally divided into pars intermedia (PI) and pars distalis (PD) and only immunoreactive growth hormone cells are detectable. Seven days post-fertilization (1 day pre-hatching) the immunoreactive thyrotropic cells appear in the ventral region and the immunoreactive adrenocorticotropic cells in the posterior dorsal one. At hatching, some immunoreactive melanotropic (ir-MSH) cells are visible in the posterior dorsal region and some immunoreactive prolactin cells in the anterior one. Eight days later the immunoreactive somatolactin cells appear along the posterior dorsal border and the immunoreactive gonadotropic I (ir-GtH I) cells in the ventral region. Here, a few ir-GtH II cells finally appear in 76–86 day old juveniles. The gland elongates after hatching and in 8-day-old larvae two adenohypophysial regions are identified: a posterior (the presumptive PI) and an anterior one (the presumptive PD). In 156–166-day-old juveniles three regions (rostral and proximal pars distalis and pars intermedia) appear and a high number of ir-MSH cells are visible in the rostral region. The first protrusion of neurohypophysis into adenohypophysis is observed in 76–86-day-old juveniles and increases with age, branching into PI. The rostro-caudal distribution of the immunoreactive cells follows the spatial expression of the corresponding hormone gene families observed in zebra fish, suggesting similar differentiating mechanisms in teleosts and chondrosteans.     

Ontogeny of immunoreactive somatolactin cells in the pituitary of gilthead sea bream (Sparus aurata L., Teleostei)

This is the first report on the identification of somatolactin (SL) cells during the early developmental stages of the teleost fish Sparus aurata. The SL cells were followed from newly hatched until 46 months. SL cells were immunocytochemically identified at light microscopical level with anti-cod SL in the developing pituitary using the peroxidase-antiperoxidase method. SL cells first appeared in newly hatched specimens, in which the pituitary gland lacked the neurohypophysis. They were scarce and located from the middle to the posterior region of the adenohypophysis. As the fish developed, the cells progressively increased in number and surrounded the developing neurohypophysis, which could be distinguised from 12-day-old larvae onwards in the caudal region of the gland. From 51 days onwards, SL cells were found in a discontinuous layer surrounding the neurohypophysis branches that entered the pars intermedia as clustered or isolated cells among non-SL-immunoreactive cells of the pars intermedia, and in the proximal pars distalis. The somatolactin-immunoreactive cells are periodic acid-Schiff-positive only in the adult stages. These data confirm, previous findings concerning the presence of two molecular forms of SL, glycosylated and nonglycosylated, in this species.     

Ontogeny of immunoreactive somatolactin cells in the pituitary of gilthead sea bream ( Sparus aurata L., Teleostei)

 This is the first report on the identification of somatolactin (SL) cells during the early developmental stages of the teleost fish Sparus aurata. The SL cells were followed from newly hatched until 46 months. SL cells were immunocytochemically identified at light microscopical level with anti-cod SL in the developing pituitary using the peroxidase-antiperoxidase method. SL cells first appeared in newly hatched specimens, in which the pituitary gland lacked the neurohypophysis. They were scarce and located from the middle to the posterior region of the adenohypophysis. As the fish developed, the cells progressively increased in number and surrounded the developing neurohypophysis, which could be distinguised from 12-day-old larvae onwards in the caudal region of the gland. From 51 days onwards, SL cells were found in a discontinuous layer surrounding the neurohypophysis branches that entered the pars intermedia as clustered or isolated cells among non-SL-immunoreactive cells of the pars intermedia, and in the proximal pars distalis. The somatolactin-immunoreactive cells are periodic acid-Schiff-positive only in the adult stages. These data confirm, previous findings concerning the presence of two molecular forms of SL, glycosylated and nonglycosylated, in this species. Accepted: 4 April 1997     

Identification of mammosomatotropes, growth hormone cells and prolactin cells in the pituitary gland of the gilthead sea bream (Sparus aurata L., Teleostei) using light immunocytochemical methods: an ontogenetic study

Growth hormone (GH) and prolactin (PRL) immunoreactivities in the adenohypophysis of Sparus aurata specimens from newly hatched until 48-months-old were detected using the peroxidase-antiperoxidase method. GH cells and PRL cells, and cells that were immunoreactive to both GH and PRL antisera, called mammosomatotropes (MS cells), were found. This is the first report on the identification of MS cells in fish, which were found in newly hatched and older larvae and juvenile specimens. GH and PRL cells appeared from two days after hatching. MS cells were first located in the central region of the adenohypophysis and afterwards in the rostral pars distalis. The GH cells were first identified in the dorsal and ventral areas of the middle-posterior part, and the PRL cells in the ventral region of the middle-anterior part. Later, during development, the sequence of appearance of the GH cells was proximal pars distalis, pars intermedia and rostral pars distalis, while for the PRL cells sequence was rostral pars distalis, proximal pars distalis and pars intermedia. This expansion pattern could be due to a GH- and PRL-cell migration although independent cell differentiation may occur in each region. The present results suggest that GH and PRL cells arise from MS cells at the outset of pituitary development, while MS cells procede from PRL cells in old larvae and juveniles. Accepted: 8 June 2000     

Morphological, developmental and immunohistochemical observations on the opossum pituitary with emphasis on the pars intermedia.

Development of the pituitary in Didelphis follows the general pattern of that described for most mammalian species. The dorsal region of a multichambered pituitary vesicle, which forms from Rathke's pouch, comes to lie adjacent to the presumptive infundibulum by the 10 1/2 d of gestation. The epithelial wall of this vesicle consists of spindle-shaped cells. The dorsal wall of the upper chamber of the pituitary vesicle forms the pars intermedia; the ventral wall of this chamber gives rise to cells of the pars distalis. Corticotropes, somatotropes, and lactotropes are seen in the presumptive adenohypophysis of the 11 1/2 d embryo. Gonadotropes and thyrotropes appear about 1 d later, shortly after birth. By the 2 postnatal week, the adult distribution of all 5 cell types within the pars distalis appears to have been established. The wall bounding the pituitary cleft in the adult represents an epithelial continuum limited by a basal lamina and corresponds to the upper chamber of the original pituitary vesicle. Ultrastructurally, the limiting walls of the pituitary cleft consists of stellate (marginal) cells, large, bulbous cells, and granulated cells. The latter correspond to the various endocrine cell types normally associated with the pars distalis. Non-granular folliculo-stellate cells also are observed within the epithelial cords of the pars distalis.     

Embryonic differentiation of the pituitary in a snake (Thamnophis brachystoma)

Summary The adenohypophysis of Thamnophis is produced from the stomodeal epithelium in two steps: a diverticulum, enlarging by addition of epithelium to its basal end, defines the posterior end of the gland, and a subsequent infolding promoted by mesenchymal movements occurs in epithelium anterior to the original diverticulum and forms the anterior end of the anlage and the hypophyseal stalk. Immediately thereafter the pars intermedia (PI) is demarcated, first by a luminal, subsequently by an external constriction, and secretion granules are found in the gland. At this time granulated cells are rare in the PI, and in the pars distalis (PD) they are more frequent in the anterior end. Secretion granules occur in cells away from the surface of the residual lumen; the lumen is lined by presumptive stellate cells. The early appearance of secretion granules in cells of the embryonic pituitary, and the presence in the hypophyseal stalk of both mucussecreting cells and cells with granules similar to those of the PD suggest that some differentiation occurs in the stomodeal epithelial cells before the definitive pouch is formed.The absence of lateral lobes in the embryonic hypophysis precludes the development of the pars tuberalis in Thamnophis.     

Hypothalamo-hypophysial neurosecretory and vascular system of the teleost Labeo rohita (Ham.)

The paired nucleus preopticus (NPO) lying on either side of the III ventricle gives rise to the left and right main neurosecretory tracts which proceed posteroventrally towards the pituitary and give rise to several finer axons which ramify the infundibular floor adjacent to the pituitary. The bulk of the neurosecretory tracts enter the pars intermedia and few finer ones are seen among the pars distalis. The ventromedian component of the nucleus lateralis tuberis (NLT) is aldehyde fuchsin (AF) positive whereas the anterolateral neurons are AF negative. The internal carotid artery gives rise to the hypophysial and ventral hypothalamic arteries. The ventral hypothalamic artery gives rise to the primary capillary plexus at the infundibular floor region adjacent to the pituitary stalk. Portal vessels formed from this plexus largely irrigate the adenohypophysis. The hypophysial artery enters the neurohypophysis and gives rise to typical teleostean type neuradenointerface vasculature. Morphological contact between the neurosecretory axons and primary capillary plexus at the floor of the infundibulum suggests the possibility of at least some active principles entering the blood vessels. Structurally L. rohita exhibited both tetrapodean and teleostean type of hypothalamo-hypophysial vasculature. Morphological evidences suggest a direct neuroglandular and an indirect neurovasculoglandular pathways of hypothalamic control of hypophysis in L. rohita.     

Fine structural characteristics of the zone of contact between the lower infundibular stem and the pituitary pars distalis in the little brown bat,myotis lucifugus

The purpose of this study was to examine the morphological characteristics of the pituitary gland in the little brown bat that might influence mechanisms of hypothalamic releasing hormone transport. Paraffin sections were prepared from whole crania to examine in situ the orientations of the three parts of the adenohypophysis (pars distalis, pars intermedia, and pars tuberalis) relative to the components of the neurohypophysis (pars nervosa and infundibular stem) and the basal hypothalamus. Of particular interest was the observation that the axis of the infundibular stem is directed posteriorly from the median eminence and occupies a depression in the dorsal surface of the pars distalis as it approaches the pars nervosa. Previous studies have revealed that neuronal projections containing releasing hormones extend into the infundibular stem in this species. Therefore, we conducted a fine structural study to determine whether the zone of contact between the infundibular stem and the pars distalis could represent a site of specialized interaction between hypophysiotropic hormones and their target cells. The results show that the sparse connective tissue along this boundary contains abundant fenestrated capillaries that are exposed on one side to neurosecretory axons and on the other to cells of the pars distalis. Furthermore, secretory cells nearest these capillaries exhibit ultrastructural evidence of heightened secretory activity. We conclude that the fine structural characteristics of this zone are consistent with localized mechanisms of releasing hormone transport. © 1992 Wiley-Liss, Inc.     

Fine structural characteristics of the zone of contact between the lower infundibular stem and the pituitary pars distalis in the little brown bat, Myotis lucifugus.

The purpose of this study was to examine the morphological characteristics of the pituitary gland in the little brown bat that might influence mechanisms of hypothalamic releasing hormone transport. Paraffin sections were prepared from whole crania to examine in situ the orientations of the three parts of the adenohypophysis (pars distalis, pars intermedia, and pars tuberalis) relative to the components of the neurohypophysis (pars nervosa and infundibular stem) and the basal hypothalamus. Of particular interest was the observation that the axis of the infundibular stem is directed posteriorly from the median eminence and occupies a depression in the dorsal surface of the pars distalis as it approaches the pars nervosa. Previous studies have revealed that neuronal projections containing releasing hormones extend into the infundibular stem in this species. Therefore, we conducted a fine structural study to determine whether the zone of contact between the infundibular stem and the pars distalis could represent a site of specialized interaction between hypophysiotropic hormones and their target cells. The results show that the sparse connective tissue along this boundary contains abundant fenestrated capillaries that are exposed on one side to neurosecretory axons and on the other to cells of the pars distalis. Furthermore, secretory cells nearest these capillaries exhibit ultrastructural evidence of heightened secretory activity. We conclude that the fine structural characteristics of this zone are consistent with localized mechanisms of releasing hormone transport.     

Changes in the hypophysis of amphibian larvae after removal of the pre-optic nuclei

Summary A microscopical study was made of the changes occurring in the hypophysis at different times after removal of the anterior hypothalamus (including the pre-optic nuclei); numerous larvae of four anuran species were used. Simultaneous assays of the pituitary glands for thyrotropic hormone were made. The removal of the source of neurosecretion caused a great reduction in the pars posterior and median eminence of the neurohypophysis, and a hypertrophy of the pars intermedia and pars anterior of the adenohypophysis. The basophil cells took up large amounts of water into the cytoplasm, their staining properties changed, and their polysaccharide content was reduced; these changes are attributed to the absence of the thyrotropic effect.Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 52, No. 10, pp. 93–95, October, 1961     

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.     

The innervation of the pars intermedia of the pituitary gland in the toad

Summary The pars intermedia of the pituitary in Bufo arenarum Hensel is innervated by two types of fibers, both coming from the adjacent neurohypophysis: 1. The neurosecretory nerve endings, originating in the neurohypophysis and found along the limit of the pars intermedia with the neurohypophysis. 2. The common nerve endings, which penetrate the pars intermedia as a single bundle from the neurohypophysis and distribute throughout the gland.The present observations report morphological evidence that in the pars intermedia of the pituitary gland in the toad a double nervous control might be involved.     

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

Summary 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.     

Ectopic hypophyseal hormonal cells in benign cystic teratoma of the ovary. Light microscopic histochemical dye staining and immunoperoxidase cytochemistry.

Histologic study of the hypophyseal component of a benign cystic ovarian teratoma disclosed elements that resembled sellar adenohypophysis, pars intermedia, and neurohypophysis. Histochemical dye methods revealed secretory cells with cytologic and granule-staining characteristics of somatotrophs, mammotrophs, melanocorticotrophs, and thyrotrophs. Nongranulated follicular cells and salivary gland rest cells also were present. Indirect immunoperoxidase staining with monospecific antisera to anterior pituitary hormones revealed abundant prolactin-containing cells, which comprised more than 50% of all chromophilic cells, as well as numerous cells that contained growth hormone and thyroid-stimulating hormone. Gonadotrophic cells could not be demonstrated by either tinctorial stains or immunostaining.     

Immunocytochemical and ultrastructural characterization of somatolactin cells from the gilthead sea bream (Sparus aurata L., Teleostei): an ontogenic study (from newly hatched to adults)

For the first time, somatolactin (SL) cells have been ultrastructurally identified and characterized during the ontogeny of gilthead sea bream, Sparus aurata, using specimens ranging in age from hatching to 15 months. The SL cells were identified by an immunogold method using anti-cod SL serum. The SL-immunoreactivity was mostly located on the secretory granules of the cells, although some vesicles of variable size and shape with a medium electron-dense content, and some irregular secretory granules and polymorphic or very irregular masses that can arise from the fusion of several secretory granules, also presented immunogold labeling. In adults, the SL cells were mainly found in the pars intermedia, where they were organized in discontinuous cell cords lying against the neurohypophysis or surrounding the neurohypophyseal branches. Some SL cells, however, appeared isolated or in small groups in the pars intermedia, in the proximal pars distalis and, rarely, in the rostral pars distalis. The SL cells were variable in shape, with processes directed towards the neurohypophysis or blood vessels, or intermingling among other adenohypophyseal cells. The secretory granules were mostly round, although some were oval, bilobate or pear-shaped, with a homogeneous, very electron-dense content and a narrow, dense or clear, halo. Different SL cell populations can be distinguished according to secretory granule size. Our findings indicate that SL is stored in the secretory granules and released by exocytosis. SL cells showing involutive features were only found in adults. SL cells can be ultrastructurally identified in one-day-old larvae although similar characteristics to those found in adults can be positively identified only after 4 days. Secretory granules increased in number, size and heterogeneity during development. Synaptic-like structures between axon terminals of the neurohypophysis and the SL cells were found in larvae from one-day-old onwards. In juveniles of 118 days of age, two different populations of secretory granules (immunogold-labeled and non-immunogold-labeled) can be found in the same or different SL cells, findings that suggest the existence of two different molecular forms of SL at this age. There was a clear increase in the complexity of the pituitary gland and in the heterogeneity of the SL cells during development, the latter observation probably reflecting different functional cell stages or production of SL molecules.     

Immunocytochemical and ultrastructural characterization of somatolactin cells from the gilthead sea bream ( Sparus aurata L., Teleostei): an ontogenic study (from newly hatched to adults)

For the first time, somatolactin (SL) cells have been ultrastructurally identified and characterized during the ontogeny of gilthead sea bream, Sparus aurata, using specimens ranging in age from hatching to 15 months. The SL cells were identified by an immunogold method using anti-cod SL serum. The SL-immunoreactivity was mostly located on the secretory granules of the cells, although some vesicles of variable size and shape with a medium electron-dense content, and some irregular secretory granules and polymorphic or very irregular masses that can arise from the fusion of several secretory granules, also presented immunogold labeling. In adults, the SL cells were mainly found in the pars intermedia, where they were organized in discontinuous cell cords lying against the neurohypophysis or surrounding the neurohypophyseal branches. Some SL cells, however, appeared isolated or in small groups in the pars intermedia, in the proximal pars distalis and, rarely, in the rostral pars distalis. The SL cells were variable in shape, with processes directed towards the neurohypophysis or blood vessels, or intermingling among other adenohypophyseal cells. The secretory granules were mostly round, although some were oval, bilobate or pear-shaped, with a homogeneous, very electron-dense content and a narrow, dense or clear, halo. Different SL cell populations can be distinguished according to secretory granule size. Our findings indicate that SL is stored in the secretory granules and released by exocytosis. SL cells showing involutive features were only found in adults. SL cells can be ultrastructurally identified in one-day-old larvae although similar characteristics to those found in adults can be positively identified only after 4 days. Secretory granules increased in number, size and heterogeneity during development. Synaptic-like structures between axon terminals of the neurohypophysis and the SL cells were found in larvae from one-day-old onwards. In juveniles of 118 days of age, two different populations of secretory granules (immunogold-labeled and non-immunogold-labeled) can be found in the same or different SL cells, findings that suggest the existence of two different molecular forms of SL at this age. There was a clear increase in the complexity of the pituitary gland and in the heterogeneity of the SL cells during development, the latter observation probably reflecting different functional cell stages or production of SL molecules. Accepted: 22 January 2001     

Parathyroid hormone-related protein in tissues of the emerging frog (Rana temporaria): immunohistochemistry and in situ hybridisation

Using antiserum to human parathyroid hormone-related protein (1–16) [PTHrP(1–16)] we have examined tissues of the common frog ( Rana temporaria ) for the presence of immunoreactive PTHrP (irPTHrP) at the stage of emergence from water to land. irPTHrP was detected in dorsal and ventral stratum granulosum of the skin, in the developing ovary, striated muscle and the choroid plexus epithelium of the brain as well as in the olfactory gland epithelium and olfactory lobe neurons of the brain. In the pituitary and hypothalamus irPTHrP protein could be demonstrated in the median eminence, infundibular stem and principally in the neural lobe and pars distalis of the pituitary with weak reaction in the pars intermedia. In situ hybridisation of the same tissues with an oligonucleotide probe to chicken PTHrP 55–65 clearly showed the presence of mRNA for PTHrP-like molecule in all the tissues containing irPTHrP. There was a major inconsistency in the pituitary in that the highest level of gene expression, assessed by in situ hybridisation, was found in the pars intermedia with only very low expression in the pars distalis and neural lobe and undetectable levels in the infundibular stem and median eminence. These observations suggest that tissues of the frog synthesise a PTHrP-like molecule but that in the pituitary the pars intermedia cells may export the protein to cells in other regions of the pituitary and hypothalamus.     

Three-dimensional architecture and distribution of collagen components in the goat hypophysis

The three-dimensional architecture of collagen fibrils in the connective tissue framework and the distribution of collagen types in the goat hypophysis were studied by the cell maceration method in combination with scanning electron microscopy (SEM) and immunohistochemistry. The pars distalis of the adenohypophysis consisted of many cell clusters. SEM revealed that the wall of cell clusters appeared as various-sized flat bundles of collagen fibrils woven in a basket-like configuration. In the pars tuberalis, the aggregates of collagen fibrils were denser and bundles thicker compared to the pars distalis. The density of collagen fibrils changed from the pars tuberalis to pars distalis without a distinct border. The collagen framework in the pars intermedia was mainly divided into three parts, the dorsal region with large hollows, the middle region, and the ventral sheet facing the cavum hypophysis. In the lobus nervosus of the neurohypophysis, the collagen network exhibited a sponge-like appearance at low magnification. Collagen fibrils of various sizes consisted of loose wavy bundles distributed around the cavities. Immunohistochemistry revealed types I, III, IV, V, and VI collagen throughout the hypophysis. It is concluded that to maintain structural and functional integration, the components of collagen are in different configurations throughout the regions of the goat hypophysis.