[Pathological study of retinal excitotoxicity following subretinal injection of NMDA]

To study neuronal excitotoxicity induced by subretinal injection of glutamate analogues.

We injected 30 mmol/L N-methyl-D-aspartate (NMDA) in 10 microl of DMEM/F12 into subretinal blebs in 24 one-month-old rabbits that were killed 0.5, 1, 2 or 7 days after injection. The retinas were studied histopathologically by light and electronic microscope. The horizontal cells, rod bipolar cells and amacrine cells were labeled by antiserum against calbindin, protein kinase Calpha, and calretinin, respectively. TUNEL labeling was performed to identify apoptotic cells.

Compared with vehicle injected control retina, treated retina showed an early and severe morphological changes in both amacrine and ganglion cells and scattered densification in photoreceptor nuclei at acute stage (<1 d), all retinal neurons damage at the intermediate phase (2 d), and a significant loss of cells in all layers of the retina at the chronic phase (7 d), respectively. Horizontal, amacrine and ganglion cells were reduced after subretinal injection of NMDA. The number of rod bipolar cells had little change. The morphological changes of neuronal death included apoptosis, necrosis, hydropic degeneration and karyorrhectic cell death. TUNEL positive nuclei were significantly (P < 0.01) increased in all retinal layers at the acute phases after NMDA administration.

NMDA administration into sub-retina induces excitotoxicity in photoreceptor, horizontal, rod bipolar, amacrine, and ganglion cells of retina, which is different from the other models of retinal cultures and intravitreal injection that only cause neuronal death in the inner retina.