Sex-specific behaviors and the rat amygdala
Cooke et al (2007) discuss morphological differences in the medial amygdala (MeA) posterodorsal subnucleus (MeApd). The medial amygdala, according to Cooke et al, "is crucial in the expression of sex-specific social behaviors." Using electron microscopy, Cooke et al found that the left MeApd is larger in male rats than in female rats (both prepubescent and adult). This difference is entirely accounted for by greater dendritic branching, not by a greater number of neurons, although male rats do have a greater number of neurons in the right MeApd. Cooke et al suggest that this indicates a difference in not only how the MeA is used between male and female rats, but in the use of the sides of the MeA in individual rats.
The role of the MeA in rat sex-specific behaviors begins with Mizukami et al (1983), who found the size difference between males and females, and found that this could be manipulated through post-natal hormone treatments. Rowe and Erskine (1993) found that input from the pelvic nerve differentially activated MeA cell groups in female rats following mounting. De Vries and Villalba (1997) also suggest lesion studies implicate the amygdala in intermale aggression in rats.
When I was reading Cooke's study, I was fascinated by the structural differences in male and female rat brains, and the suggestion that they were tied to "sex-specific" behavioral differences. Tracing back into older and older studies, I began to be disappointed that the behaviors studied were all mating behaviors: sex as a verb, not as an adjective. It actually took a fair amount of my attention to realize how difficult it would be to identify sex-specific behaviors that were not associated with the mating act (especially in rats, but not insignificantly in humans). I don't think I've ever really considered my bias against identifying mating behaviors with a particular sex, because of my experience as a LGBT activist.
Introspective musing aside, I'm sure that many of my readers will be eager to discuss the role of post-natal hormones on brain development. I'd like to point out that Mizukami's study only examined the application of hormones in prepubertal rats on brain development -- the sexual dimorphism did not seem to appear until puberty.
The role of the MeA in rat sex-specific behaviors begins with Mizukami et al (1983), who found the size difference between males and females, and found that this could be manipulated through post-natal hormone treatments. Rowe and Erskine (1993) found that input from the pelvic nerve differentially activated MeA cell groups in female rats following mounting. De Vries and Villalba (1997) also suggest lesion studies implicate the amygdala in intermale aggression in rats.
When I was reading Cooke's study, I was fascinated by the structural differences in male and female rat brains, and the suggestion that they were tied to "sex-specific" behavioral differences. Tracing back into older and older studies, I began to be disappointed that the behaviors studied were all mating behaviors: sex as a verb, not as an adjective. It actually took a fair amount of my attention to realize how difficult it would be to identify sex-specific behaviors that were not associated with the mating act (especially in rats, but not insignificantly in humans). I don't think I've ever really considered my bias against identifying mating behaviors with a particular sex, because of my experience as a LGBT activist.
Introspective musing aside, I'm sure that many of my readers will be eager to discuss the role of post-natal hormones on brain development. I'd like to point out that Mizukami's study only examined the application of hormones in prepubertal rats on brain development -- the sexual dimorphism did not seem to appear until puberty.