( Certain behaviors such as eating drin...)Brainstem blocks pain to protect key behaviors

A report from researchers at the University of Chicago, published early online in the Proceedings of the National Academy of Sciences, shows that by activating "OFF" cells and shutting down "ON" cells in the ventromedial medulla (VMM) ?a small region in the brain stem ?animals provide themselves with a form of "eating-induced analgesia," allowing them to complete essential tasks even in a difficult situation.

"Escaping pain and potential dangers may be important protective behaviors, but eating, drinking, and eliminating wastes are absolutely essential," said study author Peggy Mason, Ph.D., professor in the department of neurobiology, pharmacology and physiology (NPP) at the University of Chicago. "What we found was a very effective system that lets these animals focus on the essentials and postpone concerns that are slightly less pressing. It's as if they could give themselves a six-second dose of morphine, allowing hunger to override pain."

Mason and colleague Hayley Foo, research associate in NPP, studied adult male rats in containers with a wire mesh floor that enabled them to deliver radiant heat to one hind paw. The heat caused no damage but was annoying enough to make the animal withdraw that paw within seconds.

When the rats ate, however, they postponed retracting the heated paw for six to eight seconds and continued to eat.

Food choice made no difference. Rats focused just as intently on standard rat chow as when munching chocolate chips, yogurt drops or butter cookies.

Although earlier studies found that eating took precedence over pain in food-deprived animals, this is the first study to show that feeding suppressed pain in well-fed animals.

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Source:University of Chicago Medical Center