Immunocytochemical localization of glutamate in normal and detached cat retina.

PURPOSE Glutamate immunoreactivity in the mammalian retina has generally been observed using immersion fixation. The authors investigated glutamate immunoreactivity in the detached cat retina and reevaluated this activity in the normal retina using rapid fixation by perfusion. METHODS Unilateral retinal detachment was produced in cats by injecting 0.25% sodium hyaluronate into the subretinal space using a glass micropipet. The eyes were fixed by perfusion with a mixture of 1% glutaraldehyde and 4% formaldehyde 10 minutes and 60 minutes after detachment, and then they were examined by conventional light and electron microscopic immunocytochemistry. RESULTS In contrast to previous reports based on immersion fixation, the inner segment was not glutamate immunopositive in the normal retina. The inner segment showed intense glutamate immunoreactivity 10 minutes and 60 minutes after retinal detachment. CONCLUSIONS Glutamate immunoreactivity in photoreceptor inner segments may be a postmortem change induced by strong ischemia. Perfusion fixation is of critical importance when studying the immunocytochemical distribution of glutamate in the retina.