Postnatal development of the dog pineal gland: electron microscopy.

The ultrastructure of the dog pineal gland from the first postnatal day to the seventh month is described. In the first postnatal stages, pineal parenchyma only shows immature proliferative cells with abundant cytoplasmic glycogen. Nerve fibers are seen in the pineal connective tissue spaces. The differentiation of the dog pineal cell types begins in the first postnatal week. Both pinealocytes and pigmented cells are first seen on the fourth postnatal day. The pineal astrocytes are observed on the tenth day. Immature cells are still found in the pineal gland of 1 mo-old dogs. The differentiation of the dog pineal cell types is completed by the second postnatal month.

Postnatal development of the dog pineal gland. Light microscopy.

The light microscopical morphology of the dog pineal gland from the first postnatal day to maturity is described. In the first postnatal week, the pineal parenchyma shows immature cells and many mitotic figures. In this week, pigmented cells are observed for the first time, both in the pineal gland and in extrapineal nodules. Throughout the second week, the pineal parenchyma shows a cordonal pattern that disappears progressively in the following stages. From the 20-30th day onward, it is feasible to discern the cell types characteristic for the adult pineal gland. In the adult animals, the length of the pineal gland axes almost quadruplies that of the pineal gland in neonatal stages. The light microscopical features of the adult dog pineal gland are also described.

Immunohistochemical localization of intermediate filament and S-100 proteins in several non-endocrine cells of the human pituitary gland.

The presence and distribution of glial fibrillary acidic protein, vimentin, neurofilament protein, cytokeratins No. 8 (52 Kd), No. 18 (45 Kd) and No. 19 (40 Kd) and S-100 protein in pituicytes, folliculo-stellate cells, the epithelium of the Rathke's cysts and squamous cell nests of the pars tuberalis were investigated immunohistochemically by the peroxidase-antiperoxidase (PAP) method in eleven normal human pituitary glands. An identical immunostaining pattern was expressed by both folliculo-stellate cells and pituicytes. In both cell types the immunostaining for glial fibrillary acidic protein (GFAP), S-100 protein and vimentin was strongly positive. These results indicate the probable glial origin of the folliculo-stellate cell, and enlarge the group of glial cell types expressing vimentin. The co-expression of cytokeratins No. 8 and 19, both characteristic for simple epithelia, and S-100 protein was evident in the epithelial cells lining the Rathke's cysts and the squamous cell nests of the pars tuberalis. Furthermore, some epithelial cells of the Rathke's cysts co-expressed cytokeratins, S-100 protein and GFAP, a fact seldom reported and only in relation to rare neoplasms. The cytokeratin No. 18, characteristic for glandular epithelia, was not clearly demonstrated. Finally, the neurofilament protein was detected only in axons of the neurohypophysis; no immunopositive cells could be found throughout the adenohypophysis. Similarities in the antigenic patterns of these cell populations and the possible relation with their origin and nature are discussed.

Immunocytochemical localization of vimentin in stellate cells (folliculo-stellate cells) of the rat, cat and rabbit pituitary pars distalis.

The occurrence of vimentin, a specific intermediate filament protein, has been studied by an indirect immunoperoxidase method in the anterior pituitary gland of adult rats, cats and rabbits of both sexes. In the three species studied, the immunoreaction product was detected in the cytoplasm of stellate-shaped cells scattered throughout the pars distalis. These stellate cells showed long cytoplasmic processes which could be seen between the secretory cells, and occasionally, encircling them. These processes sometimes reach the vasculo-connective septa. The marginal cells lining the anterior layer of the hypophyseal cleft of the rat and the cat pituitary glands also showed a positive immunoreaction. Finally, cyst or follicle-like structures lined by immunostained cells with basal processes could be observed in the anterior lobe of the rat, but not in that of the rabbit or the cat. These findings support the previously held view that folliculo-stellate cells and marginal cells of the anterior pituitary gland have a common nature and suggest that these cell types might be derived from glial neuroectodermic cells.

Immunocytochemical localization of vimentin in the posterior lobe of the cat, rabbit and rat pituitary glands.

The presence and distribution of vimentin, a subunit of intermediate filaments, in the neural lobe and in the pars intermedia of the cat, rabbit and rat pituitary glands were investigated immunocytochemically. In the pars intermedia, our study revealed the presence of vimentin in glial-like cells located between glandular secretory cells of the three species and in the cells of the marginal layer of the cat and rat hypophyseal cleft. In the neural lobe of the cat and rabbit pituitary glands, there was a large amount of cell processes and immunoreactive pituicytes. In contrast, in the rat neural lobe, few pituicytes exhibited immunoreactivity, and these were located principally in the posterior region near the pituitary stalk. The significance of immunoreactive vimentin in these cells is discussed.

Structure and ultrastructure of the pigmented cells in the adult dog pineal gland.

The light and electron microscopic features of pigmented cells in the adult dog pineal gland have been described. The presence of pigmented cells was a constant characteristic of the dog pineal gland, though wide variations in the amount of pigment could be found among different animals. Conversely, the localisation of pigmented cells was very constant on the basal surface of the proximal region of the pineal gland. Frequently, clusters of pigmented cells were seen in the posterior commissure and the neighbour meningeal spaces, near the pigmented pineal zone. The pineal pigment has been identified as melanin according to its morphological features and histochemical properties. Several types of granules were identified ultrastructurally, apparently corresponding to different stages of a maturation process. The pigmented cells were identified as a special type of pinealocyte according to their ultrastructural features.