Abstract
Abstract: :
Purpose: To explore the susceptibilities of adult retinal neurons in dissociated culture to treatments with excitotoxic agonists, and the mechanisms of the resultant retinal cell death. Methods: C57B/J mice were used. Retinas were removed, dissociated, plated on a polylysine/laminin substrate, and maintained in vitro for 5 –7 days. Excitotoxic agonists (glutamate, NMDA, or KA) were added for 30 min or 24 h, sometimes in the presence of modified extracellular ion concentrations or potential blocking agents. The next day cells were fixed and immunocytochemically stained to identify ganglion and amacrine cells. Surviving cells were counted. Results: Ganglion cells from adult mouse retinas were much less susceptible to excitotoxic death than those prepared from neonatal retinas. Adult amacrine cells were killed by KA, NMDA, or glutamate. Experiments with selective blockers demonstrated that KA killed through AMPA receptors, while NMDA and glutamate exerted their toxicity through a combination of AMPA and NMDA receptors. The KA–induced death of amacrine cells was not mediated by chloride ions. Removal of extracellular sodium, however, completely prevented cell death, and removal of extracellular calcium prevented about 60% of the death. The mechanism of calcium entry was investigated. Experiments with selective blockers indicated that the lethal calcium entry was via reverse operation of a sodium–calcium exchanger. Conclusions: There is a profound developmental regulation in the sensitivity of retina ganglion cells to excitotoxic insults. Excessive intracellular sodium and calcium are the proximal causes of amacrine cell death. The pathological calcium entry is dependent upon the sodium overload, which then drives a sodium–calcium exchanger to take up calcium.
Keywords: excitatory amino acid receptors • receptors: pharmacology/physiology • retina: neurochemistry