[Ultrastructure of folliculo-stellar cells in the hypophyseal pars distalis of the rock squirrel (Citellus variegatus Erxleben), the dormouse (Graphiurus murinus Desmaret), and the hedgehog (Erinaceus europaeus Linnaeus)]

Immunohistochemical study of folliculo-stellate cells in human pituitary adenomas

Folliculo-stellate (FS) cells were studied in 102 human pituitary adenomas by immunohistochemical techniques using antibodies to S-100 protein and intermediate filaments protein. In most pituitary adenomas there were few S-100-positive cells, in contrast, numerous FS cells were found in four of the 54 cases of non-functioning adenomas. Among glial fibrillary acidic protein (GFAP), keratin and vimentin, FS cells showed greatest affinity to vimentin. Stains for desmin or neurofilaments were always negative. Counterstains with GFAP and keratin could demonstrate a small number of double-labelled cells, but mainly disclosed two types of FS cells positive for either GFAP or keratin. Accordingly, FS cells were grossly subdivided into two types: GFAP-positive cells which might be neuroectodermal or glial in origin and keratin-positive cells which might be oral ectodermal or derive from the Rathke's pouch.

Immunohistochemical localization of S-100 protein, glial fibrillary acidic protein, and neuron-specific enolase in the pars distalis of quail, rat, and human hypophyses

In the present study, we have localized immunohistochemically S-100 protein, glial fibrillary acidic (GFA) protein, and neuron-specific enolase (NSE) by the unlabelled antibody peroxidase-antiperoxidase technique. Special attention was paid to the influence of fixation and of pretreatment of sections with proteolytic enzymes. It appeared that the final immunostaining of a given antigen largely depends on the fixative and on the species used. Moreover, pepsin pretreatment proved to be necessary to unmask S-100 protein in quail and GFA protein in rat. S-100 protein (rat, human) and GFA protein (human) immunoreactivities were detected in the folliculo-stellate (FS) cells. In quail, S-100 protein was also found in cells, which were not arranged around a follicular lumen and, in rat, the endothelial cells were immunostained for GFA protein. Clusters of granular cells were weakly immunostained for NSE in all species. An exclusive relationship between FS cells and S-100 protein could not be ascertained from this study.

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

The pars distalis of pouch-young wallabies (Macropus eugenii) aged 1 to 50 days was studied by means of light-microscopic immunohistochemistry and electron microscopy. In the pars distalis of these pouch-young presumptive somatotrops, which constituted up to 70% of the gland, and nongranulated cells were the most numerous cell types. Small numbers (together representing less than 30% of the pars distalis) of immunoreactive mammotrops, thyrotrops, gonadotrops and corticotrops were also found. The presumptive mammotrops, gonadotrops and thyrotrops increased in number and apparent activity between 1 and 50 days postpartum. Presumptive corticotrop cells in 25 to 30 day-old animals were relatively most numerous, and apparently more active than at any other stage of pouch life; these cells decreased in apparent activity and relative number in older animals. The changes in number and activity of cell types in the pars distalis correlated well with major developmental events such as the onset of adrenal activity, the rapid growth phase in the first 100 days postpartum, and the generally low thyroid activity in pouch-young of less than 50 days of age.

An electron microscopic study of stellate cells and cavities in the pars distalis of frog pituitary

Stellate cells in the pars distalis of adult Rana ridibunda were observed electron microscopically under normal and experimental conditions (TRH injection). The stellate cells have lengthy processes extending into the intercellular spaces between the secretory cells and scanty cytoplasm surrounding the nucleus. Occasional desmosomes link stellate cells to adjacent secretory cells. In the pars distalis of animals injected with thyrotropic-releasing hormone (TRH), the stellate cells form large cavities (2-6 mum) filled with heterogeneous material. Their cytoplasm contains well-developed Golgi complexes and some lysosomes; these are the principal morphological alterations as compared to those observed in control animals. It is suggested that stellate cells could play an active role in addition to providing a structural framework for the pars distalis.

Ultrastructure of the nongranulated cells and morphology of the extracellular spaces in the pars distalis of adult and pouch-young tammar wallabies (Macropus eugenii)

Differentiated nongranulated (folliculo-stellate) cells were observed in the centre and periphery of the cords of cells in the pars distalis of the adult tammar wallaby (Macropus eugenii). The nongranulated cells formed follicles containing a small lumen: the cell apices were joined by junctional complexes including zonulae adhaerentes and maculae adhaerentes (desmosomes). Follicles of granulated cells were also occasionally found. Follicles were rarely observed in the adult, but were numerous and generally larger in pouch-young wallabies. Moreover, whereas the involvement of granulated cells in the follicles of the adult was infrequent, they were common components of follicular structures in the pouch-young. The marginal cells at the periphery of the pars distalis in contact with the hypophysial cleft had many of the cytological characteristics of the nongranulated cells in the central pars distalis. In both adult and pouch-young wallabies, nongranulated cells at the periphery of the cell cords were juxtaposed such that they formed "sinusoid-like" spaces or lacunae, presumably as part of the extravascular channel system. The observations are discussed in light of the proposed phagocytotic, metabolite and/or hormone transport and "stem cell" roles attributed to these cells.