The wounds of rats heal better when the rodents are living in a comfortable, less stressful environment, according to new research from the Benson-Henry Institute for Mind Body Medicine at Massachusetts General Hospital and Shriners Burns Hospital.
Allowing rats living in isolation to build nests led to more efficient and thorough healing of their burn injuries than was seen in isolated rats without access to nest-building materials. This effect could also be observed in the brain, where stress-associated structures displayed altered gene expression.
"These findings are consistent with other animal studies that show how stress and social deprivation reduce physical well being, but our study is novel in showing that the detrimental effects on physical health can be reversed by environmental stimulation," said senior author John B. Levine of the MGH Department of Psychiatry, in a press release announcing the findings.
Earlier studies had indicated that the mothering behavior of rats could be improved by placing them in more stimulating environments — most likely because of the effects of oxytocin, a hormone associated with maternal attachment and bonding. And members of the MGH/Shriners research team had also previously found that rats reared in isolation displayed poor wound healing. The current study looked at whether environmental enhancement can reduce the impact of stress on wound healing and associated brain patterns.
For the study, young rats that had been recently weaned were placed either in cages shared with other rats or into cages alone. They received standard bedding materials, but some of the isolated rodents also got small squares of cotton called Nestlets, which the rats would rip up and arrange into nests. Whenever the nesting materials were replaced, about twice a week, the rats constructed new nests.
An experiment designed to test wound healing found major differences among these groups. About a month after a burn injury was administered under anesthesia, 92 percent of the rats reared in groups had healed well, compared with only 12 percent of the rats living in isolation without nesting materials. But among the isolation-reared rats given nesting materials, 64 percent were determined to have healed well.
A daily dose of oxytocin had the same effect on wound healing as did the access to nest-building materials, the researchers found. In addition, giving the isolation-reared rats the chance to build nests reduced their hyperactive behavior, which could be traced through altered gene expression in the hippocampus — a brain structure known to be crucial to stress regulation.
"The fact that giving these animals a behavioral intervention changed not only their behavior but also their physical health raises important mind-body questions that require further investigation in humans as well as animal models," said study author Gregory Fricchione, director of the Benson-Henry Institute, in the press release. "It sets the stage for further studies to identify the mechanism accounting for this phenomenon."
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