GFAP- and Vimentin-Containing Stuctures in Human Pineal Gland

The pineal gland plays a key role in coordinating various bodily functions. The main part of the pineal cells are pinealocytes, and the second largest are glial cells, the data on which are contradictory. The purpose of this study is to investigate the astroglial cells in the human pineal gland using immunohistochemistry with transmitted light microscopy and, for the first time, with confocal laser microscopy. Astrocytes were labeled with antibodies to glial fibrillary acidic protein (GFAP) and vimentin. A large number of GFAP- and vimentin-expressing structures were revealed in the human pineal gland. GFAP was localized in polygonal cells located among pinealocytes in lobules, while vimentin was localized in blood vessels and rounded cells localized mainly in trabeculae and partially in pineal lobules. Both GFAP- and vimentin-immunoreactive cells gave rise to several long branching processes that penetrated the entire pineal parenchyma, forming a dense network, and ended on the surface of the pineal gland, blood vessels, and around calcifications. GFAP-immunoreactive fibers tightly entwined all calcifications (single and in groups), while vimentin-immunopositive processes surrounded only a part of them. The study of consecutive sections of the pineal gland showed very rare (if any) coincidence of the localization of GFAP and vimentin in pineal cells. The obtained data suggest that there are two separate populations of astrocyte-like cells in the human pineal gland, that express GFAP or vimentin and differ not only cytochemically, but also in morphological features and localization of cell bodies, as well as in the distribution of processes.