Cocaine Trumps Food for Female Rats

Study may help explain addiction differences between males and females.

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By Laura Sanders, Science News

SAN DIEGO—Presented with a choice between cocaine and food, female rats choose the drug while male rats go for the grub, a new study finds. The result may help clarify differences in addiction between men and women, scientists reported November 14 at the annual Society for Neuroscience meeting.

Kerry Kerstetter of the University of California, Santa Barbara and colleagues trained rats to press one lever to receive food or a separate lever to receive cocaine. Later, the rats were presented with the food lever and the cocaine lever at the same time.

At the time of the choice, all of the rats were hungry, so they should have been motivated to choose the food. Male rats clearly preferred the food. But female rats chose the cocaine over the food about half of the time. "Females and males seem to be very different when it comes to the incentive value of cocaine," Kerstetter said.

When the researchers more than doubled the dose of cocaine delivered with each lever push, male rats grew more likely to choose the cocaine. But females still edged them out for cocaine craving, choosing cocaine about 75 to 80 percent of the time compared with less than 50 percent of the time for the males.

"I think these comparisons with the sex differences are particularly interesting," says neuroscientist Ralph DiLeone of the Yale University School of Medicine. "People have noticed these differences with drug addiction, and it starts to make sense to incorporate the food intake, because these drug systems evolved for feeding."

Scientists don't know yet know the reason for the observed sex difference, but Kerstetter and her colleagues think female hormones play a role. Female rats that had their ovaries removed after puberty behaved more like males, choosing food more frequently. Sex hormones produced by the ovaries might be setting up or regulating the cocaine preference in the brains of females, the researchers propose.

The study may eventually help researchers explain observations that women are more sensitive to cocaine, have a greater cocaine craving and are more likely to relapse than men. Understanding why men and women respond to the allure of drugs differently may lead to more effective, sex-specific drug treatment programs, Kerstetter said.

"Male and female brains are organized differently," says Adam Perry of the University of Michigan in Ann Arbor, who studies the roles of sex hormones in drug responses and who was not involved in the study. "If you don't understand how they're different, you can't address the individual needs of the sexes."

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