Cancer induces inflammation and depressive-like behavior in the mouse: modulation by social housing.

Considerable data demonstrate a high prevalence of depressive symptoms in cancer patients. This study introduces an experimental model to examine the effect of tumor on depressive-like behavior. Female C57BL/6 mice were injected i.p. with syngeneic ID8 ovarian carcinoma. Experiment 1 measured sucrose intake before and after tumor incubation to assess the effect of tumor on anhedonic depressive-like behavior. Experiment 2 examined effects of tumor and social housing on anhedonia and a second depressive-like behavior, tail suspension test (TST) immobility. Systemic proinflammatory and antiinflammatory cytokines were measured following each experiment. Additional behaviors assessed the specificity of tumor's effect on depressive-like behavior. Tumor caused a reduction in sucrose intake relative to baseline and control levels (P<.05). Moreover, individually-housed tumor-bearing mice exhibited a lower sucrose preference than group-housed tumor-bearing or control mice in either housing condition (P<.05). Although tumor-bearing mice exhibited less locomotion than controls (P<.001), there was no significant effect of tumor on TST immobility. Tumor caused higher levels of systemic proinflammatory and antiinflammatory cytokines and smaller body weight (P<.05), but appetite and motor capacity were not significantly affected. Statistical mediation analysis showed that circulating interleukin-6 partially mediated the effect between tumor and home cage locomotion (P<.01) but not between tumor and sucrose intake. It is concluded that tumor elicits anhedonic depressive-like behavior in a murine model of ovarian cancer. This may have important implications for etiology of depression in the clinical cancer setting.