Effect of monosodium glutamate on retinal vessel development and permeability in rats

Monosodium glutamate (MSG) administered to neonatal rats on postnatal days 1 to 10 caused a generalized degeneration of the inner retinal layers. MSG administered only on postnatal days 8, 9, 10, and/or 11 caused a retinopathy limited to more peripheral retinal areas corresponding to currently existing regions of immature retinal vessels. Ink-injected retinal vessel studies showed a delay in development of the retinal vessel network but no alterations in vessel patency. Fluorescence microscopic examination of freeze-dried tissues revealed to abnormalities of the blood-retinal barriers to sodium fluorescein. We conclude, as demonstrated by these methods, that MSG retards development of the retinal vessels but does not affect development of the blood-retinal barriers. The retinotoxic effect of MSG apparently results from a mechanism(s) other than a breakdown of the blood-retinal barrier.