Persistence of visual responsiveness in the lateral geniculate nucleus of rats treated with monosodium-L-glutamate

Normal treatment of rats with monosodium-L-glutamate (MSG) resulted in extensive degeneration of the inner nuclear layer of the retina. The retino-hypothalamic projection was still functional as these rats entrained their circadian food intake rhythm to the light-dark cycle. A normal proportion of dorsal lateral geniculate nucleus (LGNd) cells in MSG rats responded to visual stimulation. The response pattern, latency and variability of LGNd cells at different times (3-18 months) after treatment were comparable to those of normal rats. These results demonstrate the MSG-induced retinal damage does not lead to blindness in the rat. The similarity in pathophysiology between MSG lesioned rats and animals exposed to constant illumination is discussed.