Studies on brain lesion by administration of monosodium L-glutamate to mice. I. Brain lesions in infant mice caused by administration of monosodium L-glutamate.

Light-microscopic examination was performed on the brain lesions induced by monosodium L-glutamate (MSG) in neonatal and infant mice of ICR strain. Lesions characterized as cytoplasmic balooning, chromatin clumping, pyknosis and karyorrhexis of neurons were recognized in the arcuate nucleus (AN), subfornical organ, preoptic area, area postrema and cerebral cortex. The most vulnerable region was the AN in which the region near the root of the median eminence was easily damaged. The changes in the AN were severest in 7-day-old mice, but only slight in 20-day-old mice. Thresholds of inducing AN lesions in 10-day-old mice after intraperitoneal injection and force-tube feeding were 0.4 and 0.7-0.8 g/kg body weight, respectively. The threshold of retinal changes was about 2.5-fold that of AN in force-tube feeding. In neonatal mice injected daily with 4 g MSG/kg body weight, the neurons of the AN disappeared almost completely by the 4th day of intraperitoneal administration.