Behavioral alterations induced by Toxoplasma gondii during different stages of infection in mice

Abstract

Acute, chronic and reactivation of Toxoplasma gondii (T. gondii) infections are approximately found in 30-60% of population world-wide. T. gondii is a pathogen relevant to psychiatric disorders. We have recently found that reactivation of chronic T. gondii induced depressive-like behaviors in mice. In the present study, we aimed to illustrate the behavioral alterations in mice during acute, chronic and after reactivation of chronic T. gondii. Behavioral battery included sucrose preference and forced swim, and fear conditioning tests, and measurement of locomotor activity following T. gondii infection in mice. First, we prepared an ethogram and confirmed that specific pathogen free-BALB/c mice exhibited sickness-like behaviors during acute infection. In addition, reduced sucrose preference and increased immobility in forced swim test (putative indicators to anhedonic and despair-like behaviors, respectively) were exhibited in acute phase. While in chronic stage such symptoms were not exhibited at all. In turn, relapse of depressive- and some of sickness-like symptoms noticed after reactivation of chronic T. gondii infection. Interestingly, increased freezing time in fear conditioning was displayed during acute and reactivated T. gondii but not during chronic infection. Further, despite the well-known contribution of neurotransmitters; serotonin and dopamine in major depressive disorder, low levels of these neurotransmitters were observed in the brain not only in acute but also during chronic infection. Without interpolation of these symptoms to human psychiatric disorders, collectively, our results demonstrated the crucial changes induced by acute and reactivated T. gondii in modifying the behavior of mice.