Tetanus toxin binding to isolated and cultured rat retinal glial cells.

The presence of immunocytochemically detectable membrane receptors for tetanus toxin, supposedly composed of higher gangliosides, is widely accepted as a marker of neuronal cells. We now demonstrate that Muller cells, a unique glial cell type of the vertebrate retina, possess specific tetanus toxin (TT)-binding sites. Single cell suspensions were prepared from adult rat retina by a gentle dissociation method, and the Muller cells, unequivocally identified by their morphology, could be immunocytochemically double-labeled by antisera to vimentin and to TT. The expression of complex gangliosides by identified Muller cells was also demonstrated by immunofluorescence labeling with the monoclonal antibody A2B5. Using the double-immunolabeling method for the identification of Muller cells we show that specific tetanus toxin binding is acquired by these cells during postnatal maturation both in vivo and in vitro. In vivo the percentage of tetanus toxin-positive Muller cells increases from 0% in 4-day-old animals to 10% on postnatal day 8, reaching the adult level of about 95–100% around day 30. In retinal monolayer cultures prepared from newborn rats, the majority (65%) of vimentin-positive non-neuronal cells became TT-positive during a 2-week culture period, indicating that this population of non-neuronal cells represents differentiating Muller cells. Again, comparable results were obtained with A2B5, supporting the conclusion that Mullerian glia expresses surface molecules, which are normally regarded as neuronal markers.