GFAP expression withdraws--a trend of glial evolution?

This study is a summary of investigations in the last decade with several collaborators on representatives of different vertebrate stocks. The results suggest that in the main vertebrate stocks (Agnathi, Chondrichthyes, Actinopterygii, Sarcopterygii-Amniotes), which had their parallel brain evolutions from the laminar brains to the elaborated ones, the astroglia also developed in parallel, and had a common trend of evolution. With growing brain complexity, free astrocytes arose and tended to predominate, and the spontaneous glial fibrillary acidic protein (GFAP)-expression regressed, in several areas. In the mammalian, avian, teleost, and batoid brains, therefore, large areas display a paucity, almost a lack of GFAP-immunoreactivity. The GFAP-expression in the GFAP-free areas seems to be inducible only in the presence of free astrocytes.