Morphology of quisqualate-induced neurotoxicity in the chicken retina.

In this study, the acute neurotoxic effects of quisqualic acid on the chick retina were examined 2 hr or 2 days following intravitreal injections of either 100 or 200 nmol quisqualic acid (QUIS). Both doses resulted in marked nuclear pyknosis and cytoplasmic swelling of a large population of cells located in the inner aspect of the inner nuclear layer, consistent with amacrine cells. The associated swelling of the inner plexiform layer was primarily due to swollen processes of amacrine cells. Also affected was a row of cells located in the outer margin of the inner nuclear layer, consistent with horizontal cells. Ganglion cells developed hyperchromic, vacuolated cytoplasm. Bipolar cells appeared to be spared from damage at these doses. Electron microscopy of photoreceptor synapses revealed that QUIS was associated with a decrease in the relative frequency of long synaptic ribbons and an increase in the frequency of short ribbons, granular ribbons, "synaptic stalks," and paranuclear granules. After 2 days survival, most ganglion cells and some amacrine cells appeared normal, while degeneration was observed in a small number of photoreceptors. Remaining photoreceptor terminals appeared normal. QUIS may provide a useful tool in understanding the dynamics of normal photoreceptor ribbon turnover. The results are also discussed in relation to other known classes of excitatory amino acids.