It is not surprising that a deadly disease like cancer can make you depressed. But if the tumors are the source of depression? That's what a new study in rats suggests. Animals with breast tumors showed depressivelike behavior and anxiety, although unlike humans, they do not know the psychological burden that comes with a serious illness.
Up to 60% of women with breast cancer also have depression, and this figure generally holds true for other cancers. In addition to anxiety and fear, some studies suggest that treatments like chemotherapy can trigger an inflammatory cascade that is linked to depression, social isolation, and related symptoms. But no one had focused on the impact of the tumors themselves for a very simple reason: It is difficult to disentangle the psychological burden of cancer, the effects of treatment, and biochemical effects of the disease
So Leah Pyter. , A behavioral neuroscientist at the University of Chicago, Illinois, turned to rats, which do not share our mental burden of being diagnosed with cancer. Working with his mentor, systems biologist Brian Prendergast, and their colleagues, Pyter induced mammary tumors in rats and then put 12 sick animals, with 12 healthy controls, through various tests that indicate depressive behaviors. In a standard test, the rats placed in a cylinder of water were considered more depressed if they spent more time sitting, as opposed to the paddling pool. In another, researchers counted how much sucrose consumed rats. (Eating less suggests that animals are down in the dumps.) The team also examined anxiety. Rats that buried more marbles were considered more obsessive-compulsive - and therefore more anxious
tumors affected rats were more likely to show depressive behaviors and anxiety, reports of team online this week in the Proceedings of the national Academy of sciences . For example, tumors with rats spent about 80% of their time floating in water, compared to 50% for healthy rats.
levels to determine what caused low animal spirits, the researchers measured cytokines, molecules that can be released by tumors or immune cells that fight against their signaling. Sick animals showed higher levels in the blood and in the hippocampus of the brain that controls emotional behavior. "Cytokines in the brain can induce depressivelike behavior," said Pyter. The levels of certain cytokines were more than double normal levels, the group reports. The rats with tumors also had an insufficient response to stress, producing fewer glucocorticoid hormones that dampen natural inflammation and may remove cytokines. Why the release of glucocorticoids is altered, she does not know, but there are reports of the same effect in people with a dispersed cancer.
"It was not really a research center in this field, [and] I think it is increasingly important," said Charles Cleeland, psychopharmacologist at MD Anderson Cancer center in Houston, Texas, which has examined the link between chemotherapy and depression. it also notes that "some patients come to the clinic treatment with behavioral changes," saving the results found here.
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