Controversial Effects of Diverse Types of lt;i gt;Toxoplasma gondii lt;/i gt; on the Anxiety-like Behavior and Cognitive Impairments in the Animal Model of Alzheimer s Disease

Background: Toxoplasma gondiiis a neurotropic parasite with lifelong persistence in the host brain. Many researchers suggested toxoplasmosis as a risk factor for the development of Alzheimer s disease (AD); however, the link between them has not been fully elucidated. Objectives: The present study was designed to investigate the effects of chronic toxoplasmosis infection with Types I (RH), II (PRU), and III (VEG) strains alone and in combination on cognitive impairments in Alzheimer s rat model. Methods: Seven months after the inoculation of the strains, AD was induced bilaterally in rats by injecting human amyloid beta 1-42 (Aβ1-42) peptide into the brain hippocampus. Behavioral tests, including the elevated plus maze (EPM) and Morris water maze (MWM) were conducted 10 days after the AD induction. Results: Our findings showed that chronic infection with RH strain increased anxiety-like behavior in the Alzheimer s rats in the EPM. In agreement with EPM findings, rats infected with the RH strain exacerbated spatial learning disorders in the MWM test; however, it did not affect the spatial memory. Conversely, infection with the PRU strain significantly enhanced spatial learning without being able to improve memory impairments in the Alzheimer s rat model. Improvement in spatial learning and memory impairments were also observed in rats infected with PRU and VEG strains in combination. Conclusions: Taken together, our findings suggest that chronic infection with PRU strain, as well as PRU and VEG strains in combination, can significantly improve cognitive deficits induced by Aβ1-42 in Alzheimer s rats, while RH strain plays a detrimental role in AD pathogenesis.