The incidence of arcuate neuron damage following 1 to 4 mg/gm oral doses of monosdoium glutamate MSG to neonatal mice was studied. The first morphological manifestation of the lesion involved edematous astrocytic glia and pathological changes in neurons close to the median eminence within 15ndash;20 minutes. The sequence of the lesion involved at least three phases: 1 neuronal edema and death, 2 multiple phagocytic cells, viz. a type of ldquo;denserdquo; cell and an electron ldquo;lucidrdquo; cell astrocyte, and 3 proliferation of astrocytic processes. It was noted that at 4 mg doses, the lesions occurred in other areas such as tectum, habenular nuclei, subfornical organ, dorsolateral surface of the thalamus, dentate-hippocampal gyri, cerebral cortex, and in the lower medulla, the nuclei gracilis and cuneatus and area postrema. In all. these structures, the lesion was initiated superficially and radiated inward, suggesting an inflow of the deleterious agent from the cerebrospinal fluid. Comparison of our neuropathological findings with those of others, emphasized the critical aspects of species variation, developmental age, route of administration, time of examination of brain material after dosage and thoroughness of sampling methods.
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