Behavioral effects of Toxoplasma gondii infection in mice: Anxiety, memory, and risk-taking alterations: A controlled experimental study

Background: Toxoplasma gondii causes chronic infections in the central nervous system that are linked to alterations in host behavior. This study aimed to investigate the behavioral effects of a chronic T. gondii infection in mice and its association with the quantity of T. gondii cysts in the brain. Methods: Sixty Swiss Webster mice were included. Behavioral testing was done by open field test, elevated plus maze, light-dark box, and novel object recognition. The brain was extracted after euthanasia and homogenized to count T. gondii cysts. Results: All mice developed a chronic infection (mean brain cyst burden: 1,247±1,176 cysts/g tissue). Compared to controls, infected mice showed significant behavioral changes in several domains. A 27% increase in locomotor activity was observed. Infected mice spent 51% more time in the anxiety-inducing core zones and 57% more time in the elevated plus maze's open arms, indicating a significant decrease in anxiety-related behaviors. Reduced latency to enter bright surroundings indicated an enhanced risk-taking propensity. Infected mice exhibited 55% lower discrimination indices than controls, indicating a severe impairment in recognition memory. Both sexes exhibited these behavioral changes, and they were significantly positively correlated with brain tissue cyst density, suggesting dose-dependent effects. Conclusion: Chronic T. gondii infection induced significant, dose-dependent behavioral alterations (r =.34-.41 for anxiety measures; r =-.38 for memory), with behavioral changes proportional to brain parasite burden. This provides strong evidence for parasite-mediated host behavioral manipulation and highlight the need for further neuropsychiatric research on toxoplasmosis, especially its potential relevance to human neuropsychiatric disorders.