Effects of chronic infection by Toxoplasma gondii on spatial memory, olfactory sensibility, and social behavior in male mice

Introduction

It has been reported that Toxoplasma gondii causes spatial memory, sensitivity, and social behavior impairments. However, the strategy used by the animal to solve the spatial maze has not been studied. On the other hand, olfactory route has not been dissected from the other senses in the social behavior tests, by performing them in total darkness.

Objective

To evaluate spatial memory maze solving strategy, social behavior and olfactory sensitivity in chronic T. gondii infection

Methods

Twenty four BALB/c 10-12 weeks old male mice were used. The control groups were administrated with PBS via i.p. (n=10) while the experimental groups were infected with 1x10⁴ tachyzoites of ME49 strain. At 63-66 days post-infection, the behavioral tests started. Six controls and nine infected mice were tested in the Barnes test for spatial memory, while four control and five infected animals were evaluated in the open field (for "curiosity"), in the Crawley test for social discrimination, and female urine detection for olfactory sensitivity. The last three tests were performed in a red-light room, restricting perception to smell only. Serum specific antibodies against T. gondii were tested by ELISA. Two-factor repeated measures ANOVA with Tukey post hoc analysis, was used in the Barnes maze. For the remaining tests medians and percentiles were compared between controls and experimental animals, by Mann Whitney U test, and Friedman test for repeated measurements.

Results

Five of nine mice of the group tested for memory had α-T. gondii specific antibodies, which also had a longer latency to escape during learning, explored less, and used the direct strategy until the third day, while the four seronegative mice presented a longer latency to escape in the second day, but they improved learning in the third day. All the sociability/sensitivity group mice were negative to antibodies; however, they remained longer time in the center of the open field and showed more curiosity than non-exposed animals. In the Crawley test these animals did not discriminate between new and familiar subjects and showed a deficit in olfactory sensitivity, compared to the controls.

Conclusions

Toxoplasma gondii chronic infection changes Barnes mazeresolution strategy, and was different between seronegative and seropositive animals. The social/olfactory deficit caused by T. gondii could be attributed to a decrease in olfactory sensitivity, but not to an innate curiosity loss.