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.     

Quail Rathke''s pouch differentiation an electron microscopic study

Summary Adenohypophyseal region of quail embryo has been examined by electron microscopy from stage 12 to stage 21 of Zacchei (1961).The Seessel's pouch develops prior to the early stages of adenohypophysis formation, then regresses while Rathke's pouch proliferates and differentiates.From Rathke's pouch formation by stage 12 (48 h of incubation) until appearance of the first secretory granules by stage 21 (6 days of incubation), there are no major ultrastructural modifications in adenohypophyseal cells. Mitochondria, Golgi vesicles, polysomic ribosomes, pinocytotic vesicles, and mitotic figures become more numerous while nucleocytoplasmic ratio and the number of ribosomes and lipid droplets decreases. The major change is the appearance of secretory granules by day 6 of incubation. This phenomenon occurs at the same time as in chick embryo, despite an incubation period shorter for quail than for chick. Mitotic figures are mainly distributed near the pouch lumen, while secretory granules are first located in the peripheral cells of the cephalic part ofpars distalis primordium. The hypothetical role of mesenchyme and vascularization is discussed.This work has been supported by a grant from DGRST, no. 77.7.9665     

Embryonic development of the pituitary gland in the chick

Pituitary glands of chicken, from stages 20 (70 approximately 72 h of incubation) to 46 (20 days) of Hamburger and Hamilton (1951), were studied by immunocytochemical and histological stainings and India ink injection into blood vessels. Using the distribution pattern of 6 types of immunoreactive adenohypophyseal cells and the location of pituitary stalk as guideposts, we found how specific areas in the epithelium of Rathke's pouch differentiate into specific regions of the adenohypophysis at 20 days. In the sagittal plane, the walls of Rathke's pouch were tentatively divided into the upper part (A(1) + A(2)) and lower part (A(3)) of the anterior wall, and the posterior wall (P(1) + P(2) + P(3)). The cephalic lobe was mainly assembled by the proliferation of parenchymal cells in the areas A(2) + A(3) + P(2) of Rathke's pouch epithelia at 3 days of incubation. The caudal lobe was derived from A(1) + P(1) + P(3). The pars tuberalis was derived from A(1) + A(2). Thus, the avian adenohypophysis is established at 13 days, though the blood supply to the pars distalis is established at 20 days. Therefore, the cephalic lobe and caudal lobe of the pars distalis and the pars tuberalis of the chicken adenohypophysis are derived from specific areas of the cell cords of Rathke's pouch at 3 days of incubation.     

Immunohistological analysis in the distribution of cells in the fetal porcine adenohypophysis.

Adenohypophyses of porcine fetuses from 25 to 110 days of gestation were studied by immunohistochemical staining to ascertain the ontogeny of specific cell types and their spatial distribution in the pars distalis. No hormone-containing cells were found before 30 days of gestation. ACTH cells were observed first at 40 days, while GH and LH cells appeared first at 60 days. PRL cells were initially detected at 105 days. ACTH immunoreactive cells were also observed in the pars intermedia at 40 days. Blood capillaries were interposed between cell cords of the pars distalis after 40 days of gestation. ACTH cells were evenly distribution in all areas of the pars distalis except the rostral area (sex zone). GH cells were densely distributed in lateral wings of the pars distalis and immediately anterior to Rathke's lumen. PRL cells resembled GH cells in their distribution pattern, but PRL cells were fewer in number. LH cells were scattered in the sex zone of the pars distalis from 60 to 80 days of gestation. After 90 days, they became scattered throughout the pars distalis but were more numerous in the sex zone than in other areas. The inductive elements of adenohypophysial cells from Rathke's pouch epithelia are discussed. We hypothesize that cell cords of specific areas facing Rathke's lumen may differentiate into specific cell types of the pars distalis during fetal life.     

Ontogenesis of the rabbit pituitary intermediate lobe

Summary The development of the intermediate lobe of the rabbit pituitary was investigated by light and electron microscopy and by using immunocytological techniques. The first immunoreactive melanotrophic cells were detected at the fetal day 17 in the dorsal zone of Rathke's pouch epithelium facing the neural lobe; this coincided ultrastructurally with the appearance in this area of a few cells exhibiting secretory vesicles and granular condensations in the Golgi saccules. The differentiation of the gland probably required an infundibular inductive effect. Secretory cells increased in number following a dorsoventral gradient during the next fetal and neonatal stages until postnatal day 20, the stage at which the intermediate lobe exhibited its definitive organization. The gland innervation occurred during the first days after birth. The advent of these oxytocin- and neurophysin-immunoreactive fibres coincided with an obvious stimulation of the synthetic activity of the melanotrophic cells. The possible neurotrophic effect of these cells on their innervating system remains to be established.This article is dedicated to the memory of Georgette Haller     

The development and morphogenesis of the human pituitary gland

Summary In order to clarify the environmental factors which are involved in the development of the primordium of the pituitary gland such as cell-cell interactions, a three-dimensional reconstruction of this organ and its surrounding tissues was carried out. Pituitary material was obtained from human fetuses mainly during the period of organogenesis. Rathke's diverticulum was found to stretch rostrally from the stomodeal epithelium to the middle of the mesoderm, and already by the 5th week of fetal growth, it was clearly seen to be involved with the diencephalon. The area of contact between Rathke's pouch and the diencephalon gradually moved from the rostral to caudal regions and, after 13 weeks of development, had a position similar to that found in the newborn infant.Among the cells forming Rathke's pouch, it was found that the closer their relationship was to the diencephalon, the greater were their epithelial characteristics. When the relationship of such cells to the diencephalon was weaker, their differentiation to endocrine cells occurred earlier. Immunohistochemically, that portion of the pituitary primordium which has a close relationship with the diencephalon, later to become the pars intermedia, showed an adrenocorticotropic hormone (ACTH) immunoreactivity later than that of the pars anterior. On the other hand, in the 21st fetal week, nearly all of the cells of the pars intermedia were found to be ACTH-positive. This finding is thought to indicate a close connection between the physical contact between the brai (diencephalon) and the pituitary primordium and the development of the pars intermedia; the differentiation of ACTH cells. The surface of the epithelium of Rathke's cavity continues to increase at least until the 21st fetal week, so the growth of the epithelium of Rathke's pouch is thought to be heavily involved in the growth of the primordium of the pituitary gland in the early stages of development.     

Distribution of calbindin and parvalbumin in the developing somatosensory cortex and its primordium in the rat: an immunocytochemical study

Summary Immunocytochemical techniques were used to analyze the distribution of the calcium-binding proteins calbindin and parvalbumin during the pre- and postnatal development of the rat somatosensory cortex. Calbindin occurs in most early differentiated neurons that form the primordial plexiform layer at embryonic day 14. This expression in transient; during the perinatal period, calbindin becomes immunologically undetectable within the structures derived from the primordial plexiform layer, i.e., the prospective layers I and VIb. Immunoreactive neurons are also absent from adult layers I and VIb. Calbindin is also detected in a second population of neurons which, from embryonic day 18 onwards, distributes diffusely within the cortical plate. Some neurons of this population show morphological traits of immaturity, while others show complete dendritic arborization. The definitive pattern of distribution of calbindin-immunoreactive neurons is achieved by postnatal day 22. Infragranular layers contain intensely-immunoreactive cells whose numerical density decreases during postnatal development, whereas in supragranular layers similar neurons are interspersed among numerous faintly-stained neurons.Parvalbumin is detected for the first time at postnatal day 6, within a small group of neurons located in cortical layer V, and extends afterwards through the whole thickness of the cerebral cortex. At this same postnatal stage, groups of immunoreactivepuncta are also found in layer IV of the somatosensory cortex; these puncta increase in density progressively and, at embryonic day 13, immunoreactive cells appear also grouped at this level. At this postnatal age, parvalbumin immunostaining delineates the somatosensory map in cortical layer IV. From this stage to adulthood, the number of immunoreactive neurons increases in the whole thickness of the somatosensory cortex. Barrels in layer IV become less distinct as immunoreactive cells and processes invade the septa. Layer IV in the adult somatosensory cortex appears more densely populated by parvalbumin immunoreactive neurons and puncta than in the surrounding areas.     

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.     

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     

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.     

Cysts in the rat adenohypophysis: incidence and histology

The incidence and histology of cysts in the adenohypophysis of adult male Wistar rats are reported. Of sixty pituitaries studied 13 of them (21.6%) presented a single cyst located in the pars distalis. The cysts varied in shape and size and were usually multilocular. Two of them were connected with the subdural space at the ventral surface of the adenohypophysis. Histology demonstrated that the cysts were filled with mucinous material and foamy macrophages and were lined by flat and cuboidal ciliated and nonciliated epithelial cells, goblet cells as well as several adenohypophysial endocrine cells such as somatotrophs, thyrotrophs, and gonadotrophs. The ciliated cells were the most numerous. Histologic and immunohistochemical studies of the uninvolved areas of the adenohypophysis showed no abnormalities and the weights and histology of the adenohypophyses and peripheral endocrine glands were within normal range, suggesting that the cysts did not impair the adenohypophysial endocrine activity. Although the morphogenesis of the cysts remained obscure, the histological and immunohistochemical findings support the hypothesis that during embryonic development, the future cysts coming from the pharyngeal epithelium is fused with the stomodeum before or during the formation of the Rathke's pouch.     

Ontogeny of vasotocinergic and mesotocinergic systems in the brain of the South African clawed frog Xenopus laevis

For a better understanding of the development of neurotransmitter systems and of their putative functional significance during ontogenesis, the development of the vasotocin (AVT) and mesotocin (MST) systems in the brain of Xenopus laevis was studied by means of immunohistochemical techniques. Weakly immunoreactive fibers were already present at late embryonic stage 38 in the caudoventral part of the telencephalon and in the ventral part of the diencephalon. The earliest immunodetectable AVT and MST immunoreactive cell bodies were found in the developing preoptic area at late embryonic stage 43. At the end of the embryonic period (stage 45), AVT immunoreactive fibers have reached the future medial amygdala, the midbrain tegmentum, the median eminence and the neural lobe of the pituitary. When compared with AVT immunoreactive fibers, the development of MST fibers shows some temporal delay. During the premetamorphosis (stages 45–52), AVT immunoreactive cell bodies appear in the medial part of the suprachiasmatic nucleus, the dorsal infundibular region, and the midbrain tegmentum, whereas fibers can now be traced to the nucleus accumbens, the septum and the medial amygdala in the forebrain, to the midbrain tegmentum, the reticular formation, the raphe nuclei, and the solitary tract nucleus in the brainstem, and to the spinal cord. Further maturation of the AVT system during prometamorphosis (stages 53–58) includes the appearance of immunoreactive cell bodies in the lateral part of the suprachiasmatic nucleus, the ventral preoptic area, and the dorsal infundibular region. By the end of the metamorphosis (stage 65), the maturation of the AVT/MST systems reaches an almost adult-like pattern. It should be noted that in amphibians, in contrast to mammals, the early appearance of the AVT/MST systems, including their extensive extrahypothalamic component, suggests that the two neuropeptidergic systems may play a significant role during development.     

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.     

Patterns of proliferation in the hypophysis of the mouse embryo

Summary The process of proliferation and growth in the neurohypophysis and adenohypophysis of the mouse embryo was studied by means of tritiated thymidine autoradiography. the percent of cells labeled (labelings index, LI) was determined in embryos ranging from 9 through 16 days of gestation one hour after an intraperitoneal injection of ³H-thymidine in the mother. The infundibular region of the diencephalon showed an early abd dramatic decrease in proliferation between the tenth and eleventh days of gestation, in contrast to the hypophyseal (Rathke's) pouch which showed a consistently high level of activity during these stages. During days 12–16 the infundibulum was very sparsely labeled but continued to exhibit a low rate of mitotic activity as it developed into the neurohypophysis. The dorsal wall of the hypophyseal pouch which represents the intermediate lobe of the hypophysis was well labeled, and even at 16 days of gestation its labeling index was approximately 25%. The major portion of the hypophyseal pouch representing the pars distalis showed a highly active proliferation, particularly in its lateral regions at early stages, but by 13 and 14 days of gestation many of the cells failed to incorporate the label as they became grouped into loose clusters. By 15 days' gestation much of the hypophyseal pouch, particularly its ventral and lateral portions, became highly vascularized, and the majority of its labeled nuclei represented those of endothelial cells.This research was supported by NIH grant no. HD12308 from the National Institute of Child Health and Human Development, USPHS     

The occurrence and developmental origin of epithelial cysts in the rat and mouse adenohypophysis.

The adenohypophysis occasionally contains cysts of epithelial nature. The present study describes the incidence and immunohistochemical characteristics of these epithelial cysts in the adenohypophysis of rats at different ages and in young mice. Epithelial cysts were found in about 10% of the partes distales irrespective of age and animal species. Their incidence in the pars tuberalis was higher: 22% and 58% in young rats and mice, respectively. Immunohistochemically, cells composing these cysts failed to contain S-100 protein. Although cysts found in the pars tuberalis frequently possessed immunoreactive luteinizing hormone-producing cells, most cysts in the pars distalis were immunonegative when stained with antisera to several different adenohypophysial hormones. Examination of fetal rat hypophysis has shown a close topographical relationship between cysts and the pharyngeal duct. This fact, together with the frequent occurrence of cysts in the ventro-medial region of the pars distalis in neonatal and young animals, indicates that these cysts are probably derived from a part of oral epithelium that is otherwise destined to degenerate at the time when Rathke's pouch closes.     

The Embryological development and cytodifferentiation of the pars distalis of the golden hamster (Mesocricetus auratus)

Summary The embryological development and cytodifferentiation of the hamster pars distalis was investigated using light and electron microscope techniques in order to obtain basic information for comparison with pituitary development in other mammalian species. The normal chronological events in the development of the hamster pars distalis closely paralleled the pituitary organogenesis of other laboratory rodents. Rathke's pouch formed and touched the infundibulum at 8 1/2 days of gestation and separated from the stomodeum 3 days later. Penetration of vascular elements from the developing hypophysial portal system into the pars distalis occurred at 12 1/2 days gestation. This was also the first day that small secretory granules were seen in any of the parenchymal cells. Further cytodifferentiation during the following prenatal, and first few postnatal days of life revealed granulated cells which, in most cases, could not be identified using morphological criteria or granule size as may be done in the adult. An orderly sequence of inductive and morphological events appears to take place in the developing hamster adenohypophysis paralleling similar events observed in other animals.Submitted by the senior author to the Graduate School of Louisiana State University, Baton Rouge, in partial fulfilment for the Ph.D.     

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 embryological development and cytodifferentiation of the anterior pituitary in the marsupial, Isoodon macrourus

Summary Light and electron microscopy were used to study the development of the anterior pituitary gland from fetal stages to the end of pouch life in the marsupial I. macrourus.The early morphological development of the anterior pituitary in I. macrourus follows a similar pattern of events to that described for cutherians. Rathke's and Seesel's pouches were present in 101/2 day old embryos. At birth these pouches had formed a multi-chambered vesicle which was still connected to the stomodeum by a thin cord of tissue. A small number of granules (200–400 nm dia.) were found in cells at birth. These cells could not be classified on ultrastructural features but alcian blue-periodic acid Schiffs-orange G staining suggested one cell type was possibly a presumptive thyrotroph. There were no capillaries in the pars distalis at birth.The cords connecting Rathke's and Seessel's pouches to the stomodeum were located at the site of the periosteal bud of the developing basisphenoid which commenced to ossify at 7 days. At this stage presumptive thyrotrophs, gonadotrophs, and somatotrophs could be distinguished using alcian blue-periodic acid Schiffs-orange G staining. However, five cell types could be categorised at the same age using ultrastructural characteristics alone. Precise names for these cells are unavailable but two closely resemble presumptive mammotrophs and thyrotrophs described for another marsupial M. eugenii.By 13 days after birth the anterior pituitary of I. macrourus had become vascular and acidophils were concentrated in a posterior zone. There was little gross morphological change from 13 to 66 days after birth by which the time weaning has occurred.Cilia were seen in cells of the anterior pituitary and mitosis of granulated cells was observed from birth onwards.There is a considerable range of variation in pituitary cytogenesis amongst marsupials, and its functional significance awaits further investigation.     

Identification and responsiveness of prolactin-containing secretory granules in clonal rat mammotrophs

Clonal pituitary cells (2B8) derived from embryonic Rathke's pouch epithelium of Wistar-Imamichi rats established by Ishikawa et al. (1977) were used in this study. Late-passage 2B8 cells were found to contain small secretory granules which contained immunoreactive prolactin as demonstrated by electron microscopic immunocytochemistry. When 2B8 cells were incubated in the presence of various agents that are known to stimulate or inhibit prolactin secretion, the volume density of the secretory granules in the cytoplasm was shown to be altered.     

Evidence for a Local Action of Growth Hormone in Embryonic Tooth Development in the Rat

Abstract

Studies in non-dental embryonic tissues have suggested that an interaction between growth hormone and its receptor may play a role in growth and development before the foetal pituitary gland is competent. This study reports the distribution of growth hormone, its rezceptor and binding protein in developing rat tooth germs from embryonic day 17 to 21 and postnatal day 0 using antibodies specific for each of these proteins. Four foetal rats were processed at each time point (E17, EM, E20/21 and postnatal day 0). Following routine fixation and paraffin embedding, sections were treated with antisera to rat growth hormone, rat growth hormone binding protein and growth hormone receptor. Localization of antibody/antigen complexes was subsequently visualized by addition of biotinylated IgG and reaction with streptavidin peroxidase and diaminobenzidine. Assessment of the level of staining was qualitative and based on a subjective rankings ranging from equivocal to very strong staining. Overall, growth hormone and its binding protein were located both in the cellular elements and throughout the extracellular matrix, whereas the growth hormone receptor showed an exclusively intra-cellular location. All three proteins were detectable in cells of the dental epithelium and mesenchyme at the primordial bud stage (E17) which occurs prior to expression of pituitary growth hormone. At the cap stage of odontogenesis (E18-19), numerous cells in both the dental epithelium and mesenchyme were intensely immunoreactive for growth hormone, its binding protein and receptor. In the succeeding early bell stage (E20-21), most of the mesenchymal cells in the dental pulp were mildly positive for these proteins, while the dental epithelium and adjacent mesenchyme were more immunoreactive. At the late bell stage (postnatal day 0), all three proteins were localized in dental epithelium, differentiating mesenchymal cells the cuspal surface facing the epithelial-mesenchymal interface, preodontoblasts, and odontoblasts forming dentine. From these observations, immunoreactive growth hormone, its receptor and binding protein appear to be expressed in odontogenic cells undergoing histodiierentiation, morphodifferentiation and dentinogenesis in a cell-type and stage-specific pattern throughout embryonic tooth development. This suggests the possibility that growth hormone, or a growth hormone-like protein, plays a paracrindautocrine role in tooth development in utero.