Question

Pick two sexual dimorphisms in the brain. For each one, explain how hormones determine the development – summarize the observation or experiment.

Answer 1

Sexual dimorphism defines the morphologic differences between two sexes. There are certain evidences from fruit flies humans which demonstrate sexual dimorphism in structure, functiona nd regulation of brain. Sexual dimophism is clearly more evident in the cortical region with women having larger volumes relative to cerebrum size particularly in the frontal and medial cortices whereas males have larger volume relative to cerebrum size particularly in those regions having amygdala and hippocampus. These sexual dimorphism are homologous with animals showing greater level of sex steroid receptors during stages of brain development. A classic example of sexual dimorphism is the role of aromatization in animals. During initial period of development, testosterone is converted to estradiol by enzyme aromatase. Estradiol is responsible for growth, maturation, normal development of neuronal cells, helps in synapse formation. During early brain development in rodents, monkeys aromatase activity is chiefly found in hippocampus and amygdala where there is a high concentration of sex steroid receptors. The cortical regions show high concentration of these receptors during fetal development stage and gradually there is a diminish of cortical estrogen receptors with subsequent decrease in levels of mRNA which suggest that estradiol mediates the cortical differentiation.

White matter sexual dimorphism of the adult human brain also serves as a classic example. Men have a larger cerebrum than women and there are regiospecific sex differences particularly in the cortical areas. The sex differences in the distribution of androgen receptors in the hypothalamus provide the cumulative effects on sexual dimorphism. Moreover, the spatial organization of estrogen receptors in several parts of brain elucidate the fact of bearing sexual dimorphism. In the cerebral regions which provides early sexual differentiation ratain sexual dimorphism where there is a high concentration of sex steroid receptors as compared to the regions of brain having low density of sex steroid receptors.