Multiple marker analysis in the avian optic tectum reveals three classes of neuroglia and carbonic anhydrase-containing neurons.

The distribution and biochemical diversity of neuroglial cells in the avian optic tectum were analyzed using immunohistochemical techniques. Polyclonal and monoclonal antibodies were employed to define the distributions and localizations of four proteins that are considered to be glial-specific in the mammalian central nervous system: glutamine synthetase, carbonic anhydrase-C, glial fibrillary acidic protein, and S-100 protein. The results showed the presence of at least three distinguishable populations of glia: glutamine synthetase/glial fibrillary acidic protein-positive fibrous astrocytes, glutamine synthetase/carbonic anhydrase-C-positive protoplasmic astrocytes, and S-100-positive oligodendroglia. In addition, a distinct population of neurons was observed that showed very intense immunostaining for the presence of carbonic anhydrase-C. The results suggest that the segregation of biochemical functions in the major categories of brain neuroglial cells (oligodendroglia and astroglia) varies significantly between vertebrate species. This observation raises the possibility of using comparative studies to refine our understanding of the roles that glial cells play in nervous tissue.