The effects of glutamate and kainate on cell proliferation in retinal cultures

Two different monolayer culture preparations were used to investigate the effects of glutamate and kainate on retinal cell proliferation. Glial monolayer cultures were produced from 8-day-old chick embryo neural retina. Glial monolayers were exposed to glutamate (5 mM) or kainate (0.4 mM) at either 3 or 5 days in vitro. It was found that exposure to glutamate at 3 days in vitro significantly reduced the number of glia present at 6 days, but a day 5 exposure or exposure to kainate did not significantly affect the number of glia. This glutamate-induced decrease in cell number was seen even though thymidine kinase (EC 2.7.75) and thymidylate synthetase (EC 2.1.1-) activities were higher in treated cultures. Neuroblast monolayer cultures were produced from 6-day-old chick embryo neural retina. These cultures also were exposed to glutamate (5 mM) or kainate (0.4 mM) Glutamate, but not kainate treated cultures, showed a decrease in neuroblast survival and proliferation compared with controls. Thus, at the concentrations tested, glutamate appears to be a general retinal toxin, while the survival of immature neurons or glia is not affected by kainate.