The anterior pituitary gland is composed of granular and agranular cells. The granular cells are composed of five types of endocrine cells (i.e., somatotrophs, lactotrophs, thyrotrophs, gonadotrophs and corticotrophs) and produce pituitary hormones related to metabolism, growth, reproduction, stress response and the immune system. The proper functioning of these cells is dynamically controlled by the hypothalamus by means of hypophysiotrophic hormones. The discovery of hypophysiotrophic hormones was one of the most important events in endocrinology during the last century. However, it is now known that hypophysiotrophic factors alone cannot fully explain the functions of the anterior pituitary gland. Recently, an intrapituitary regulatory system has also been documented.Folliculo-stellate cells (FS-cell) are major agranular cells located in the parenchymal tissue of the anterior pituitary gland that give rise to this additional control. These FS-cells have a characteristic star-like morphology accounting for 5-10% of all pituitary cells and form follicles (1-3). Usually, FS-cells are found lining the lumen of tiny-or pseudo-follicles that are scattered throughout the anterior pituitary gland. Their long slender cytoplasmic processes intermingle in a fashion that produces a three-dimensional (3D) anatomical network, in the meshes of which hormone-secreting cells reside (Fig. 1). By bridging the hypothalamus and endocrine cells, as well as staying closely associated with endocrine cells, FS-cells can actively share the common neuronal message of the extra-and intra-pituitary, which together provide an efficient mechanism to orchestrate anterior pituitary functioning in response to physiological milieu. Discovery of FS-cellsFS-cells in the anterior pituitary gland were first distinguished by electron microscopic observation by Rinehart and Farquhar (1), although they were originally designated as chromophobes. In their observation, they also noted the interdigitised configuration of many cells in the anterior pituitary gland. The name 'folliculostellate cell' had not been proposed until then. Subsequently, FS-cells were reported and described as adrenocorticotroph-like cells lacking secretory granules and arranged around the follicles (2). According to their typical star-like structure and follicle formation capacity, these cells were named folliculo-stellate cells much later in 1972 by Vila-Porcile (4).Many features of FS-cells remained unknown until S-100b protein was reported as a marker protein (5, 6). Because FS-cells are non-endocrine cells, immunohistochemical detection using an antibody against a hormone cannot be used. This fact hampered the study of FS-cells and delayed their investigation compared Journal of NeuroendocrinologyCorrespondence to: Kinji Inoue, Laboratory of Cell Biology, Department of Regulation Biology, Graduate School of Science and Engineering, Saitama University, 255 Shimo-ohkubo, Sakura-ku, Saitama 338-8570, Japan (e-mail: kininoue@mail.saitama-u.ac.jp).Folliculo-stellate cells (FS-cel...

Pituitary folliculostellate (FS) cells are characterized by producing S100B protein, as do brain astrocytes. FS cells have some functions in the pituitary gland, i.e. scavenger functions, sustentacular cell activity through cytokines, and intercellular communication through gap junctions. However, the biological significances of FS cells, especially their differentiation capacities in the anterior pituitary gland, are still under discussion. To understand FS cells with new approaches, we generated a transgenic rat expressing GFP under S100b gene promoter, which regulates tissue-specific expression of S100b gene. Using the transgenic rat, we succeeded in inducing skeletal muscle cells from FS cells by culturing it in serum-free medium containing B-27 supplement, thyroid hormone (tri-iodothyronine), epidermal growth factor, and basic fibroblast growth factor. In this study, we also succeeded in inducing skeletal muscle cells from primary cultured astrocytes and astrocyte cell line, C6 cells. Hence, we concluded that pituitary FS cells have wide differentiation potential and have similar characteristics to astrocytes, which not only support cell activity but also support differentiation capacity.

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Abstract. Glucocorticoids are known to stimulate growth hormone (GH) production but to suppress prolactin (PRL) production. However, previous data were obtained with rather high doses of corticosterone. In this study we examined the effects of various doses (10 -12 -10 -7 M) of corticosterone on GH and PRL production in a rat pituitary somatomammotropic cell line, MtT/SM cells, and found that GH mRNA expression was facilitated by high doses (10 -7 and 10 -8 M). In contrast, a biphasic effect of corticosterone on PRL mRNA expression and secretion was observed, i.e., high doses (10 -7 and 10 -8 M) suppressed and low doses (10 -12 -10 -10 M) facilitated them. In an immunofluorescent staining study, the number of PRL immunopositive cells increased with low doses of corticosterone while it decreased with high doses of it, which corresponded to PRL mRNA expression and hormone secretion, respectively. These effects of corticosterone on PRL production were abolished by a glucocorticoid receptor (GR) antagonist, mifepristone. In addition, co-treatment with low doses of corticosterone (10 -12 -10 -10 M) and 17β-estradiol (E 2 , 10 nM) additively increased the number of PRL immunopositive cells. Moreover, a 24 h BrdU incorporation experiment suggested that the increase in the number of PRL immunopositive cells treated with low dose corticosterone was caused by novel synthesis of PRL while, on the other hand, that of those treated with E 2 resulted from PRL cell proliferation. Thus, we concluded that corticosterone biphasically regulates PRL production and the sensitivity of E 2 to different degrees.

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