New research in hamsters now suggests that without companionship, wounds on the animals don't heal as fast.
Researchers looked at the effect social contact had on wound healing in stressed hamsters. Results showed that skin wounds healed nearly twice as fast in the hamsters paired with a sibling. These animals also produced less of the stress hormone cortisol than unpaired hamsters.
"Stress delays wound healing in humans and other animals, and social contact helps counteract this delay," said Courtney DeVries, the study's lead author and an assistant professor of psychology and neuroscience at Ohio State University. "Our goal is to understand the physiological mechanisms by which social support improves health."
She and her colleagues also treated a group of socially isolated hamsters with oxytocin, a hormone released during social contact and associated with social bonding in monogamous animals. Oxytocin treatment seemed to ameliorate the effects stress had on wound healing, as the treated animals healed about 25 percent faster than the untreated lone animals.
The study appears in a recent issue of the journal Psychoneuroendocrinology.
The researchers conducted a series of experiments to learn how social interaction affects health, and to better understand the mechanisms by which it does so. Female Siberian hamsters were housed with a sibling or isolated during the three-week study. All animals received minor skin wounds about the size of a sunflower seed on the backs of their necks. The researchers photographed and measured the wounds each day.
Some of the hamsters were confined to small Plexiglas tubes for two hours a day for up to 14 consecutive days. Other studies have shown that such confinement causes stress and also delays wound healing. While the animals couldn't turn around in the tubes, they could move back and forth and stand up or lie down.
Hamsters were separated into four groups for one of the experiments: socially isolated, non-stressed; socially isolated, stressed; paired, non-stressed; and paired, stressed. As soon as a single day after injury, the wounds on the socially isolated, stressed animals remained about 25 percent larger than the wounds of the other three groups, and stayed this way for about a week.
In a second experiment, the researchers compared levels of cortisol – the stress hormone – of paired animals to those in isolated animals. Blood samples were collected immediately after the hamsters were stressed, and again 45 minutes later. Right after stress, the cortisol levels of the isolated animals were one-and-a-half times greater than those of the paired animals.
"We expected cortisol concentration to increase substantially in stressed and lone animals," DeVries said. But cortisol levels didn't increase in the paired, stressed hamsters.