Glutamate-induced cellular injury in isolated chick embryo retina: Müller cell localization of initial effects

The neurotoxic and gliotoxic effects of glutamate and several glutamate analogues were studied in isolated chick embryo retinas. To facilitate examination of initial pathological events, a short-term incubation system was developed and used for light microscopic and autoradiographic investigation. Low-dose, short-term glutamate treatment of 12-day retinas resulted in a glial-specific lesion in the Müller cells, characterized by extensive cellular edema; at higher concentrations and/or longer treatment times, neurotoxic as well as gliotoxic effects were seen. The early glial damage was identical in appearance to that seen after incubation with DL-alpha-aminoadipate and other reported gliotoxins. No evidence of a similar glial-specific action was seen after administration of kainic acid, although extensive neuronal degeneration did result. Incubation of retinas with tritiated glutamate (3H-glu) revealed a selective uptake of the label by Müller cells. Autoradiographic grains were localized over Müller foot processes at the inner limiting membrane, and by 30 minutes labeled the entire glial system. Prior treatment with neurotoxic levels of glutamate did not alter the autoradiographic localization to glial cells. Possible glial-neuronal interactions and their effect on cytotoxic patterns are discussed.