Journal
INFECTION AND IMMUNITY
Volume 85, Issue 4, Pages -Publisher
AMER SOC MICROBIOLOGY
DOI: 10.1128/IAI.00007-17
Keywords
Toxoplasma gondii; 1-methyl tryptophan; minocycline; interferon gamma; sickness behavior; anhedonic behavior; despair-like behavior
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Funding
- Japan Society for the Promotion of Science's Funding Program for Next-Generation World- Leading Researchers (NEXT Program)
- Council for Science and Technology Policy [2011/LS003]
- MEXT KAKENHI [15K15118]
- Egyptian Ministry of Higher Education and Scientific Research
- Grants-in-Aid for Scientific Research [15K15118] Funding Source: KAKEN
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Toxoplasma gondii is a pathogen relevant to psychiatric disorders. We recently showed that reactivation of chronic T. gondii infection induced depression-like behaviors in mice. Furthermore, it has been hypothesized that depression-like behaviors are mediated via a host defense mechanism against invading pathogens; proximate mechanisms of this behavioral hypothesis remain unclear. In the present study, we investigate the contribution of indoleamine 2,3-dioxygenase (IDO), inflammation, and interferon gamma (IFN-gamma) to anhedonic and despair-related behaviors in T. gondii-infected mice by using sucrose preference and forced-swim tests, respectively. First, we confirmed that BALB/c mice exhibited both sickness and depression-like behaviors during acute infection. Treatment of infected wild-type mice with minocycline (anti-inflammatory drug) abated sickness and anhedonic and despair-like behaviors, whereas in T. gondii-infected mice, treatment normalized kynurenine/tryptophan (Kyn/Trp) ratios in both plasma and brain tissue. Additionally, T. gondii infection failed to induce anhedonic and despair-like behaviors or increase the Kyn/Trp ratio in immunocompromised (IFN-gamma(-/-)) mice, whereas sickness behavior was observed in both immunocompetent and IFN-gamma(-/-) mice following infection. Furthermore, treatment with 1-methyl tryptophan (an IDO inhibitor) did not affect locomotor activity, attenuated clinical scores and anhedonic and despair-like behaviors, and resulted in normal Kyn/Trp ratios in T. gondii-infected wild-type mice. Although low levels of serotonin and dopamine were observed in the brain during acute and chronic infections, anhedonic and despair-like behaviors were not detected in the chronic stage of infection. Collectively, our results demonstrated that immune enhancement in response to infection with T. gondii resulted in IFN-gamma production, IDO activation, and inflammation associated with anhedonic and despair-like behaviors.
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