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 mammalianspecies. The dorsal region of a multichambered pituitary vesicle, which forms from Rathke's pouch, comes to lie adjacent to the presumptive ipfundibulum by the 10 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 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 laminaand 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 folliculostellate cells also are observed within the epithelial cords of the pars distalis. © 1990, VEB Gustav Fischer Verlag Jena. All rights reserved.