New research indicates that stress might do more than simply gray hair.

Psychiatry professor Therese Kosten and her colleagues have developed a method of stressing rat pups in early stages of life, from birth through the beginning of adulthood, in order to investigate the long-term effects of stress, she said. They found that female rats that experienced early-life stress had a higher tendency toward drug addiction and overeating.

Kosten’s research was supported by Women’s Health Research at Yale, a faculty training grant focusing on women and drug abuse and is funded by the National Institute on Drug Abuse and the National Institutes of Health.

Stressful conditions were created by taking the pups away from their mothers for about one hour each day during their developmental years. University of California, Irvine Academic Administrator Priscilla Kehoe, who co-authored the paper, said this form of stress was psychological but not physical, ensuring that the rats’ health was not compromised.

“I tried to make it subtle so they didn’t go hungry and cold,” she said. “The tests were based on early stress, so there was no weight loss or physical illness.”

When they were tested at adulthood, the rats that underwent stress in their youth had greater neurochemical responses in the areas of the brain associated with drug reward, specifically due to cocaine and methamphetamines, which were administered directly to the rats.

“When the rats grow up, they cannot handle stress well, which makes them vulnerable to addiction,” Kehoe said.

Kosten said that while adult female rats exposed to stress continually sought cocaine and food, male rats that were put through the same early life conditions exhibited a less pronounced reaction. The male rats did exhibit some need for an increased amount of cocaine, but not nearly as strongly as their female counterparts.

“We charted new territory by using female rats,” Kosten said.

Several Yale undergraduate women said they see the need for such research. Maggie Doherty ’07, who serves on the board of the Yale Women’s Center, said it is important that gender be made a focus in major health studies, citing studies on aspirin and heart disease, in which women were not specifically investigated for some time.

“When gender is not taken into account, women are definitely at a disadvantage,” she said, “Studies like this … when men are not simply considered the norm, are important.”

Allyson Goldberg ’08, who is also on the Women’s Center board, said she thinks more research needs to be done to solidify results in the case of humans.

“While rats are often used as model organisms for research on humans, there is still much that needs to be examined before such a big leap can be made in applying these findings to ourselves,” Goldberg said.

This type of research could have significant medical and societal effects because it shows that people who develop an addiction without early life stress may have different brain chemistry, Kosten said. An implication of her research could result in the development of more effective treatment for these cases.

“I would like to see more prevention measures that would target children with early life stress,” Kosten said. “Not everyone comes to addiction the same way, and that needs to be addressed.”

Kosten said the model of early life stress she studied also resulted in the stressing of the mother rat. When the pup was brought back to the mother, she gave it a significantly greater amount of attention, illustrating family members’ tendency to support one another during times of major stress. This principle could be used to explain the adult psychology of those who went through childhood trauma, Kosten said.

“It would be interesting to think about children who have survived natural disasters as well as unnatural disasters, such as war,” she said.

Kosten’s team is now exploring how easily humans acquire addictions and looking at models of drug addiction relapse, which is often triggered by stress.

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