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Michigan State UniversityBreedlove Jordan lab at MSU

Sexual Dimorphism in the Medial Amygdala

Medial Amygdala Figure 1. The SDN-POA and MeA subregions in rats

The medial amygdala in rats and mice is sexually dimorphic: about 150% larger in volume in males as in females (Figure 4). The individual neurons within the medial amygdala are also larger in males than in females. This sexual dimorphism is not 'organized' by perinatal hormones, because castration of adult males results, a month later, in a medial amygdala that has shrunk to the size of that in normal females. Conversely, treating adult female rats with an androgen such as testosterone for a month causes the medial amygdala to grow to the size seen in normal males. Thus this brain region seems to retain its plasticity throughout life so that it can always be 'organized' in a masculine fashion by androgen.

Medial Amygdala Figure 2. Both androgen and estrogen affect MeA subregion somata

We have evidence that both androgen receptors and estrogen receptors must be activated in order for testosterone to fully masculinize the medial amygdala (Figure 5). We would like to know more about the cellular mechanisms and the sites of action by which steroid hormones alter the structure and function of the medial amygdala.