It was the study on the tracing observation in different living periods after the hippocampal cells in the neonatal rat was damaged after subcutaneous injection with monosodium glutamate (MSG).Injuries were classified into two types.The results were as follows: ①The cell swelling in acute period.Injuries of cell mainly presented in the rats of 11 days.The nuclei was swellen,and the cell degenerated even into death.There were swelling in varying degrees in the pyramidal cells of CA1～CA4 region,especially in that of CA1 region.In CA4 region, as well as swelling, some cells appeared pyknostic.Dentatus gyrus neurons had no significant change in this period.②Delayed cell pyknosis.Nuclei contraction,chromoplasm congulation,cytoplasm contraction and aridity dark for the stain,cell pyknosis and death were observed in CA2～CA4 region of rats of 52 days and 100 days.The activity and number of pyknosis granule cells in the inner layers increased apparently near the door of dentatus gyrus.Although the phenomenon of pyknosis could be observed scarcely in CA1 region, the number of dorsal cells decreased significantly.
