Relative withdrawal of GFAPa component of brain evolution

Mihály Kálmán^1,2*

• ¹Faculty of Medicine, Semmelweis University, Budapest, Hungary
• ²Semmelweis University, Budapest, Hungary

The glial fibrillary acidic protein (GFAP) is the main intermediate filament protein and histochemical marker of astroglia. It seems to be a contradiction that there are extended GFAP-poor or even -free areas in the brains of animals in different vertebrate clades: cartilaginous and ray-finned fishes, and amniotes. The part "Relevant Subsections" of the present study reviews our GFAP mapping studies on the brains of 58 species of these clades as well as mappings of other authors, and demonstrates that these areas appeared independently from each other in the more advanced groups of different clades; it raised the supposal that the lack of GFAP is an apomorphic phenomenon The GFAP expression has withdrawed mainly relatively: the GFAP-immunonegative areas increased more than the immunopositive ones. Mainly areas which enlarged and got growing complexity during evolution are devoid of GFAP immunopositivity (except their perivascular glia). The lack of GFAP expression, however, does not mean the lack of astroglia. In the areas immunonegative to GFAP astrocytes were visualized using other markers, e.g. glutamine synthetase or S-100 protein. In birds and mammals lesions induced GFAP expression in these areas. It proves that the capability of GFAP expression is not lost just became facultative. These data raised the supposal that the lack of GFAP production might have an evolutionary advantage. The next part, "Discussion" relates the GFAP ”withdrawal” to other steps of evolution: the growing complexity and thickening of the brain wall, and the appearance of the astrocytes especially the protoplasmic astrocytes and then considers the supposed evolutionary advantages and disadvantages of the absence of GFAP. What was the role of the relative "withdrawal" of GFAP expression in the brain evolution, it cannot be answered yet definitely. The most probable candidates can be the devoid of the synthesis of an unnecessary protein, a better adaptation of astrocytes to the demands of neurons, and an increased allowance of synaptic plasticity. On the other hand, one must take into consideration that the withdrawal of GFAP may not be a primary phenomenon but a consequence of the evolution of neural networks.