Glial and neuronal markers in bass retinal horizontal and Müller cells

Retinal horizontal cells (HCs) are second-order neurons that integrate information from photoreceptors over large retinal areas, mediating the lateral spread of visual signals in the distal retina. The 'glial' vs. 'neuronal' nature of the HC has been widely debated. For example, carbonic anhydrase (CA), glutamine synthetase (GS), and glial fibrillary acidic protein (GFAP) are considered 'glial' markers, yet both CA and GFAP have been previously reported in HCs of the teleost retina in species-specific patterns. In contrast, the neurofilament triplet (NFT) proteins are considered 'neuronal' markers; these proteins have been immunolocalized to a mammalian HC, but are absent from teleost HCs. We have studied these cytochemical characteristics in HCs from the white bass, by immunolabeling both cryosections of intact retina and freshly isolated, identified cells attached to coverslips. We found that both HCs (neurons) and Müller cells (MCs; glia) immunolabeled with antisera to CA. Both type 1 (external) HCs and MCs immunolabeled with an antibody to vimentin. Only MCs immunolabeled with antisera to GS and GFAP. Neither HC perikarya (and their major dendrites) nor MCs immunolabeled with an antibody to the 160-kDa subunit of NFT protein. Thus, bass HCs and MCs share the presence of CA and vimentin epitopes and absence of the NFT 160-kDa epitope. Moreover, retinal cell isolation, by itself, does not affect cell-type specific immunolabeling patterns in identified cells, except for what may be lost with the finer processes of the various cells. Isolated cell studies can aid in interpreting immunolabeling patterns observed in the intact retina, especially in retinal layers where several cell types may be present.