Experimental Chronic Toxoplasmosis Model in Mice: Brain Lesions and Related Behavioral Changes

Objective: In this study, it is aimed to constitute a chronic toxoplasmosis model using toxoplasma gondii (T. gondii) ME49 strain that is supposed to produce tissue cysts, to compare healthy and infected mice in terms of behavioral changes. In addition, the relationship between behavioral changes and brain lesions was questioned. Method: Before experimental application, out of a total of twenty-one 2-month-old Swiss albino mice, T. gondii antibody-free, 14 were infected by intraperitoneal (IP) (n=8) or oral (n=6) inoculation of 2x102 Toxoplasma gondii ME49 oocysts. Four months later, fear-and anxiety-related behavioral changes in infected and healthy control groups were comparatively evaluated with plus-maze test. At the end of the experiment (45 day after inoculation), euthanasia was carried out on all mice and their brains were examined histopathologically and immunohistochemically for the presence of T. gondii tissue cysts. Results: Infected mice had low levels of anxiety, they have entered the open arms more frequently and have spent more time in the open arms of the maze compared to controls. Pathologically, in the infected group, high rates of gliosis, perivascular cell infiltration, meningitis, and neuron necrosis were observed especially in the parietal and temporal lobes, cornu ammonis, amygdala, and thalamus compared to the other parts of the brain. A higher number of tissue cyst formations were positively correlated with the lesion severity in these parts of the brain. Conclusion: It can be suggested that, tissue cysts and neuropathological changes in chronically infected mice brains have direct concern with behavioral manipulation which results from low anxiety levels. (Archives of Neuropsychiatry 2012; 49: 139-144)