These MPCs might normally relocate in this way to deal with an infection or an injury in the brain, but in this case, they moved solely because of the response to a social stressor, he said. The experiments showed that the number of these cells more than tripled in the brain following the stress.

Other immune cells called microglia, normally residing in the brain, also triggered an inflammatory response because of the stress. The researchers also noted that the stressor caused a particular activation pattern of neurons, or nerve cells, within the brain.

The response to social stress also caused an increase in the amounts of some inflammatory cytokines in the brain, including interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-a) which are linked to inflammation. These cytokine responses correlated with an insensitivity of MPCs to glucocorticoids, hormones that normally inhibit inflammation in the body.

So the research team saw these and other cellular changes occurring in the brain following the stress, at the same time they were seeing the behavioral changes – the anxiety-like behavior.

The findings are evidence of a two-way communication that’s existing between the body and the brain in times of stress, Sheridan said.

To test that apparent connection, they gave the mice injections of propranolol - a so-called “beta-blocker” drug often used for cardiac conditions - before they encountered the more aggressive mouse. In this case, the researchers saw no increase in IL-1 or TNF-a, no glucocorticoid insensitivity, and no long-lasting anxiety-like behavior in the test animals.

“If we treated the animal with a beta-blocker each night before we put the intruder in, it completely blocked the signal. The anxiety-like behavior never developed,” Godbout said.

“What this basically argues is that we may now have a new target for individuals who have extended anxiety-like behavior,” Sheridan said. “We may have a new target cell to think about in terms of new therapies.

“And since that cell (the MPCs traveling from the bone marrow) is coming from the periphery of the body, we might not need to resort to psychoactive drugs that can have adverse effects on the brain.”

Proving that, however, will take more animal studies and subsequent large studies using humans before this approach could be used clinically, he said.

The research was supported in part by the National Institute of Mental Health, the National Institute on Aging and the National Institute of Dental and Craniofacial Research.

Working with Sheridan and Godbout on the research were Eric Wohleb, Mark Hanke, Angela Corona, Nicole Powell, LaTonia Stiner, Michael Bailey and Randy Nelson, all of Ohio State.

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Source: Ohio State University