To evaluate the involvement of apoptosis in N-methyl-D-aspartate (NMDA)-induced excitotoxicity in the rabbit retina.

After intravitreal injection of 680 and 2,000 nmoles of NMDA in rabbit eyes, the eyes were enucleated at 2, 16, and 60 hours and 1 and 2 weeks. The apoptotic cell death was determined with TdT-mediated biotin-dUTP nick end labeling (TUNEL) stain, and immunohistochemical stains of Bcl-2, Bax, and caspase-3 were performed.

TUNEL showed increased labeling scattered in the ganglion cell layer and inner nuclear layer from 16 to 60 hours. The number of TUNEL-positive nuclei decreased at 60 hours, and none was observed at 2 hours, 1 week, and 2 weeks. More TUNEL-positive nuclei were seen with injection of 2,000 nmoles compared to 680 nmoles. Bcl-2, Bax, and caspase-3 were seen histologically as early as 2 hours in the ganglion cell layer and inner nuclear layer; there was no stained nuclei with the TUNEL stain. At 2 hours after intravitreal NMDA injection, Bcl-2, Bax, and caspase-3 were also stained in Muller cells.

This study showed that apoptosis is involved in NMDA-induced excitotoxicity in the rabbit retina. Bcl-2, Bax, and caspase-3 may play important roles in modulating the apoptosis in NMDA-induced excitotoxicity, and Muller cells are involved in the apoptotic pathway.