Histologic changes in the inner retina of albino rats following intravitreal injection of monosodium L-glutamate.

Monosodium L-glutamate is known to cause intracellular swelling, necrosis, and disappearance of most inner retinal neurons, with concomitant thinning of inner retinal layers within hours after subcutaneous injection into neonatal rodents. A similar process can be observed in adult rat retina after intravitreal glutamate injection. To better describe and compare this process with that reported after systemic application, adult Sprague-Dawley rat eyes were intravitreally injected with 1 mumol monosodium L-glutamate and the retinas studied by LM and EM over a 2-month period. Results demonstrated that adult rat retina experienced severe degenerative changes which progressed in two stages: an initial stage of massive intracellular swelling and a second stage of necrosis and cell loss. Degeneration involved ganglion and inner nuclear layer cells. Inner retinal thickness decreased concurrently. By 2 months post-injection, degenerative changes in rod spherules and some loss of photoreceptor nuclei were observed. Both time course and severity of the lesion differed from that described in prior studies after systemic treatment.