Abstract：To investigate the influence of infection with Toxoplasma gondii upon the capacity of learning and memory in rats attempting to explore its possible mechanism,40 SD rats were randomly divided into 4 groups,i.e.3 experimental groups with T.gondii infection and one control group without infection.In the experimental groups of mice,high,middle and low doses of T.gondii(2×103/ml.2×105/ml and 2×107/ml.)were used and 2 ml of different concentration of T.gondii tachyzoites were injected intra-peritoneally into rats.Then,the passive avoidance test and morris water maze test were performed to observe the behavior changes of animals,such as the ability of learning and memory.Meanwhile,the levels of IL-1β.IL-6 and TNF-αin hippocampus of the infected rats were assayed by radioimmunoassay and the activity of NOS was determined by immunohistochemical assay.The experimental results showed that no influence of the T.gondii infection on the ability of memory of rats could be demonstrated,but the loss of ability in memory of rats injected with high or middle doses of T.gondii tachyzoites appeared more early than those of the normal control rats(P<0.05)and no significant difference could be found between rats injected with low dose of parasites and the normal control rats.(P>0.05).The escape latency of rats in T.gondii infection groups was significantly greater than that of the normal control group and the percentage of the distance between quadrants was decreased(P<0.05).Compared with those of the control group,the levels of IL-1β and TNF-α in hippocampus of rats elevated significantly in the T.gondii infection groups(P<0.05),but no significant difference in the level of IL-6 could be demonstrated between the infection groups and the control group(P>0.05).In addition,the number of the NOS-positive cells in the cerebral cortex of the infected rats increased.It is concluded from these observations that infection with T.gondii can induce harmful effects on the ability of learning and memory of rats obviously and its mechanism of action may be related to the elevation of IL-1β and TNF-α levels in hippocampus of rats.
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