Abstract: AIM:To investigate the relationship between the acetylcholinesterase (AchE) activity in hippocampus and the effect of ketamine on spatial learning and memory of the early developing rats.METHODS:Forty one-month old male SD rats were randomly divided into two groups with 20 rats each: ketamine group in which rats received intraperitoneal-ketamine 40 mg/kg and then 20 mg/kg every 15 min 3 times in total; control group (received normal saline 5mL). The two groups were further divided into 2 subgroups according to the time when Morris water maze (MWM) testing were started in the 1st week (C1, K1) or the 3rd week (C2, K2) after the injection. MWM testing was performed in the 1st week and the 3rd week after the injection. The hippocampus was dissected away from the brains, then the AchE activity was detected with the colorimetric method, and the changes in morphology were observed with HE.RESULTS:(1) For MWM: The latent period of group K1 was significantly longer than group C1 (P<0. 05 or P<0. 01), but there was no significant difference between group K2 and group C2. In the spatial probe test, the time across the original platform of group K1 was shorter than the group C1 (P<0. 05), but there was no significant difference between group K2 and group C2. (2) For AchE activity: the AchE activity of group K1 was significantly lower than group C1 (P<0. 05), but there was no significant difference between group K2 and group C2. (3) For HE assay: light microscopy showed no abnormal changes of hippocampal neurons in two groups.CONCLUSION: Ketamine administration impairs spatial learning andmemory in short time, and a decrease in AchE activity in hippocampus of the rats may have a link with the impairment. However, there is no impairment to learning and memory in long time.

Key words: acetyleholinesterase, hippocampus, ketamine, learning and memory