Immunoreactive glial fibrillary acidic protein in pituicytes of the rat neurohypophysis

The glial fibrillary acidic protein (GFAP) has been associated with glial filaments. Electron microscopic examination of rat pituicytes in our laboratory has revealed few of these 8–9 nm filaments that are present in other astrocytes. Since the literature is inconsistent on the existence of filaments in pituicytes, we investigated the content of GFAP in these cells. Immunocytochemical methods revealed a strong positivity for GFAP in pituicytes. Furthermore, the primary antiserum dilution required for optimal staining suggests that there may be more GFAP in pituicytes than in other glial elements. The significance of immunoreactive GFAP in pituicytes is discussed in terms of possible functions and embryonic origins.