Immunocytochemical demonstration of glial fibrillary acidic protein in mouse tanycytes

Summary Immunohistochemical techniques were used to stain for the astrocytespecific glial fibrillary acidic protein (GFAP) in the cells lining the third ventricle of the developing and mature mouse brain. Before birth immunoreactive tanycytes were only observed in the infundibular recess of the median eminence, where they could first be seen at embryonic day 17. They possessed long processes running towards the ventral surface of the brain. During the early postnatal period GFAP-positive tanycytes gradually appeared throughout the third ventricle, although the ependymal cells themselves remained unstained. The tanycytes retained their immunoreactivity for anti-GFAP serum in the adult, and were also evident in the adult rat third ventricle. It is suggested that the presence of GFAP in these specialised cells of the third ventricle indicates that they, the transient radial glia of the developing cerebral cortex, the persistent Bergmann glia of the cerebellum, similar astrocytes with radial processes in the hippocampal dentate gyrus and conventional astroglia are all closely related cell types.