"These results differ somewhat from our previous study conducted with male rats," said Therese Kosten, research scientist, Department of Psychiatry, and lead author of the study. "Early life stress produces a greater increase in cocaine self-administration in female versus male rats."

In addition, the neonatal stress enhances responding for food treats in female, but not male, rats, she said. "We believe this may suggest that women with early life stress have an enhanced risk of developing drug addiction, as well as eating disorders," Kosten said.

Of the rats in the research, some were isolated from their mothers as "infants." The rats were studied as adults who had learned to self-administer cocaine and food treats. The researchers found the rats that had been kept in isolation worked harder to obtain food and drug rewards.

"The results of the cocaine self-administration study along with our previous work demonstrating enduring effects of neonatal isolation in female rats point to the possibility that women with early life stress experience may be at increased risk of initiating and maintaining drug addiction," Kosten said. "The fact that early isolation enhances responding for food in female rats, but not male rats, may provide an insight into the role of early life stress on gender differences in vulnerability to develop eating disorders."

Co-authors include Xiang Yang Zhang of Yale and Priscilla Kehoe of the University of California at Irvine. The study was funded, in part, by the Yale Interdisciplinary Women's Health Research Scholar Program on Women and Drug Abuse. This program is part of Women's Health Research at Yale (www.yalewhr.org), which supports research on sex and gender differences in health and disease.

Neuropsychopharmacology 31: 70-76 (January 2006)

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