Without a companion, an animal's wounds won't heal nearly as fast, according to a recent study on the effect social contact had on healing wounds on stressed hamsters.

In fact, wounds on hamsters living with a sibling healed almost twice as quickly as those left alone and produced lesser amounts of cortisol, a stress hormone. This was one of several tests conducted by researchers to determine how social interaction affects the state of health and to better understand the mechanisms for healing.

Scientists treated a group of hamsters with oxytocin, a hormone released during social contact that is associated with bonding in monogamous animals, and others without the treatment. Those with oxytocin healed about 25 percent faster than hamsters that weren't treated.

During the study, female Siberian hamsters were isolated or shared space with a sibling. Each animal experienced minor skin wounds the size of a seed on their necks. Some were locked up in small tubes for two hours each day for as long as two weeks. Although the hamsters were too big to turn around, they could move forward or backward, stand up or lie down.

Of the four groups in which hamsters were divided, the wounds of those that were isolated and stressed were some 25 percent larger than the rest and remained that way for a week.

A second experiment compared the cortisol levels of paired, stressed pairs of hamsters versus single stressed ones in separate blood tests completed 45 minutes apart. Cortisol levels in isolated hamsters were about 1.5 times higher than paired hamsters.

A third test measured the kind of response hamsters had to stress when the adrenal gland (cortisol's main source) was removed. Interestingly, the lack of cortisol in some of the isolated hamsters was as beneficial as having a nearby companion with wounds on stressed or nonstressed hamsters healing at the same rate.

In the final test, scientists treated two groups of isolated hamsters with oxycotin or a substance that blocks its production. Hamsters in the oxytoxin group had injections for five straight days prior to receiving their wounds and restraining their access.

Finally, the researchers experimented with the effects of treating two groups of socially isolated hamsters with either oxytocin or a substance that blocks its production. Hamsters in the oxytocin treatment group were given injections daily for five days prior to wounding and control animals were given just a saline placebo. The treated animals' wounds healed at a faster rate than the wounds did on the control animals. Moreover, treatment with oxycotin delayed the healing process, even in paired animals.

EurekAlert August 3, 2004