Infect Immun. 2016 Jul 25. pii: IAI.00217-16. [Epub ahead of print]
Abstract
Chronic infection with Toxoplasma gondii becomes established in tissues of the central nervous system, where parasites may directly or indirectly modulate neuronal function. Epidemiological studies reveal that chronic infection in humans is a risk factor for developing mental diseases. However, the mechanisms underlying parasite-induced neuronal dysfunction in the brain remain unclear. Here, we examined memory associated with conditioned fear in mice and found that T. gondii infection impairs consolidation of conditioned fear memory. To examine brain pathology induced by T. gondii infection, we analyzed parasite load and histopathological changes. T. gondii infects all brain areas, yet the cortex exhibits more severe tissue damage than other regions. We measured neurotransmitter levels in the cortex and amygdala because these regions are involved in fear memory expression. Levels of dopamine metabolites, but not dopamine, were increased in the cortex of infected mice compared with those in uninfected mice. By contrast, serotonin levels were decreased in the amygdala and norepinephrine levels were decreased in the cortex and amygdala of infected mice. The levels of cortical dopamine metabolites were associated with the time spent freezing in the fear-conditioning test. These results suggest that T. gondii infection affects fear memory through dysfunction of the cortex and amygdala. Our findings provide insight into the mechanisms underlying neurological changes during T. gondii infection.
Copyright © 2016, American Society for Microbiology. All Rights Reserved.
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