Protective effect of all-trans retinoic acid on NMDA-induced neuronal cell death in rat retina

We histologically examined the effects of all-trans retinoic acid (ATRA) on neuronal injury induced by intravitreous injection of N-methyl-d-aspartic acid (NMDA) (200 nmol/eye). Treatment with ATRA for 7 days (15 mg/kg for the first two days and 10 mg/kg for the following five days, p.o.) reduced the decrease of cell number in the ganglion cell layer and the inner nuclear layer 7 days after NMDA injection. TUNEL staining 6 h after NMDA injection showed that treatment with ATRA (15 mg/kg, p.o.) 1 h prior to NMDA injection reduced the number of apoptotic cells in the ganglion cell layer and inner nuclear layer. The anti-apoptotic effect of ATRA was vanished by intravitreous injection of U0126, an extracellular signal-regulated kinase/mitogen-activated protein kinase kinase inhibitor (1 nmol/eye). These results suggest that ATRA has a protective effect, which is medicated by extracellular signal-regulated kinase pathway, on NMDA-induced apoptosis in the rat retina. ATRA may be useful as a therapeutic drug against retinal diseases that cause glutamate neurotoxicity.