Sex on the brain

 作者:公冶弄     |      日期:2019-03-08 07:06:02
By Jonathan Knight in San Francisco TESTOSTERONE can reshape the brain of a female rat, making it look like that of a male. This finding could explain brain differences found in transsexuals. The structure of male and female brains differs in several ways. For example, a brain region called the medial amygdala, involved in sexual arousal, is bigger in male rats than females. Such differences were thought to be permanent. But Bradley Cooke and Marc Breedlove at the University of California at Berkeley have challenged this assumption. They implanted a slow-release capsule of testosterone under the skin between the shoulder blades of female rats. Thirty days later, they killed the rats and examined their amygdalas. An amygdala region called the posterodorsal nucleus had grown 30 per cent larger in the female rats, to nearly the size of a male’s (Proceedings of the National Academy of Sciences, vol 96, p 7538). Other amygdala regions, which differ less between sexes, remained unchanged. The same region shrank to roughly female size in castrated males. “We were able to completely sex-reverse these brain nuclei,” says Breedlove. In 1995, researchers found that a brain region called the BST (bed nucleus of the stria terminalis) was half the usual size in men who had undergone sex changes (This Week, 4 November 1995, p 5). They argued that the difference could explain the men’s desire for a sex change, but Breedlove says the castration itself could have caused the BST to shrink. Bruce McEwen, a psychologist at Rockefeller University in New York, cautions that the size changes the Berkeley team found in rats may not cause the brain to work like that of the opposite sex. “If they looked at the brain function, they might find some sex differences,