Structure of the pars distalis in pouch-young tammar wallabies (Macropus eugenii)

Early onset of ghrelin production in a marsupial

Ghrelin regulates appetite in mammals and can stimulate growth hormone (GH) release from the pituitary. In rats and humans, ghrelin cells appear in the stomach during late fetal life. Nevertheless, the role of ghrelin in early mammalian development is not well understood. Marsupials deliver highly altricial young that weigh less than 1g so they must feed and digest milk at a comparatively immature stage of development. Since they complete their growth and differentiation while in the pouch, they are accessible models in which to determine the time course of ghrelin production during development. We examined the distribution of gastric ghrelin cells, plasma ghrelin concentrations and pituitary expression of the ghrelin receptor (ghsr-1alpha) and GH in the tammar wallaby, Macropus eugenii. There were ghrelin immunopositive cells in the developing mesenchyme of the stomach from day 10 post partum (pp) to day 150pp. Subsequently ghrelin protein in the fore-stomach declined and was absent by day 250pp but remained in the gastric cells of the hind-stomach. Ghrelin was detected in the developing pancreas from day 10pp but was absent by day 150pp and in the adult. Pituitary ghsr-1alpha expression and plasma concentrations of ghrelin increased significantly up to day 70-120pp while GH expression was also elevated, declining with GH to reach adult levels by day 180pp. These results demonstrate an early onset of gastric ghrelin expression in the tammar in concert with a functional stomach at a relatively earlier stage than that of developmentally more mature eutherian young.

Postnatal development of the skin of the marsupial native cat Dasyurus hallucatus

Skin development of the Northern native cat was examined from birth to weaning at 150 days post partum. An outer layer of cells, termed the periderm or epitrichium, is present on the epidermis of the newborn. This layer of cells is not discernible at 7 days post partum. Skin development of the native cat differs from that of the eutherian mammal. The periderm of the eutherian is no longer discernible when the developing hairs first penetrate the epidermis. In the marsupial, this loss of the periderm occurs well before the appearance of follicles. Melanocytes and Langerhans cells are seen at day 23 post partum, follicles at day 30, sebaceous glands at day 59, and sweat glands at day 67. Thus, when the mother first leaves her young in the nest at about days 60 to 70 of lactation, the skin is at a stage of development that will assist the young with thermoregulation. The skin continues to develop throughout lactation and attains an adult appearance by day 150 post partum.

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.

Immunohistochemical study on the development of the adenohypophysial cells in the lizard Gallotia galloti

Immunohistochemical methods have been used to study the embryonic and postnatal development of the hormone-producing cells in the adenohypophysis of the lizard Gallotia galloti. In this species, Rathke's pouch is formed between stages 30 to 32 of the embryonic development, although the first sign of immunoreactivity to antisera against adenohypophysial hormones occurs in stage 33 in the pars distalis anlage. These cells derive from the dorsal face of Rathke's pouch and are immunoreactive to anti-ACTH serum. The cytodifferentiation of ACTH and MSH cells occurs in the pars intermedia in stage 34. The TSH cells appear at stage 35 and the gonadotrope cells at stage 37. These cells derive from both the dorsal and ventral face of the Rathke's pouch. The LTH cells are revealed at stage 39 and are only originated from the dorsal face. The STH cells, which come from the dorsal as well as ventral face, are the last secretory cells differentiated just before hatching. During postnatal development an increase and also a redistribution of the immunoreactive cells occur until acquiring the adult distribution.

The ultrastructure of the pituitary and the adrenal gland of three newborn marsupials (Dasyurus hallucatus, Trichosurus vulpecula and Isoodon macrourus)

The ultrastructure of the pituitary glands of the newborn northern native cat, brushtail possum and the northern brown bandicoot and the adrenal glands of the former two marsupials were examined to determine whether these endocrine glands were functional at birth. The anterior pituitary of all three species was well vascularised and many cells contained electron-dense, membrane bound granules. The adrenal glands were composed of two distinct cell populations. One group of cells possessed dark staining granules, normally observed in catecholamine-secreting cells, and the second group contained large amounts of smooth endoplasmic reticulum and mitochondria with tubulovesicular cristae, indicative of steroid hormone secreting cells. The ultrastructure of the cells of the fetal pituitary and adrenal of all three species would suggest that these glands are functional at birth and, as with many eutherians, the marsupial pituitary and adrenal gland may play an important role in determining the length of gestation.

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

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 eutherians. Rathke's and Seessel's pouches were present in 10 1/2 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.