THURSDAY, May 21 (HealthDay News) -- The mere presence of breast tumors in rats is associated with depression and anxiety, according to a study published online May 18 in the Proceedings of the National Academy of Sciences.

Leah M. Pyter, Ph.D., and colleagues from the University of Chicago examined whether the presence of chemically-induced mammary tumors in rats affected behavior.

The researchers found that the presence of the tumors induced depressive- and obsessive-compulsive anxiety-like behaviors. Rats with tumors also had increased levels of the proinflammatory cytokines interleukin-1-β, interleukin-6, tumor necrosis factor-α, and interleukin-10 in the hippocampus, which had been previously linked to depressive behaviors. Rats with tumors had lower stress-induced levels of corticosterone, which inhibits cytokine signaling, and increased levels of mineralocorticoid and glucocorticoid receptors in the hippocampus.

"The results establish that tumors alone are sufficient to trigger changes in emotional behaviors," Pyter and colleagues conclude. "Dampened glucocorticoid responses to stressors may exacerbate the deleterious effects of tumor-induced cytokines on affective states."

Abstract
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