Mechanisms for brain sex diff erentiation

概要

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Distinctive sex diff erences in reproductive behavior and physiology have been attributed not to diff erencesin hormones gonad secretes in each sex but differences in particular brain structures. Interestingly enough, brainsex difference is determined mostly by gonadal hormones during ontogeny independent of genetic sex. In manylaboratory mammals, brain sex can be manipulated at a particular stage of ontogeny called critical period for brain sexdiff erentiation, by endocrine treatments. Thus, neonatal orchidectomy or administration of gonadal hormones to femalepups reverses brain sex phenotype which culminates in sex-specifi c functions. The early, transient exposure to gonadalhormones or its absence leaves indelible marks on brain phenotype. This organizing action of gonadal hormones,combined with activational action of the hormones after puberty, accomplishes sex specific functions. Brain wouldundergo sex diff erentiation through neurogenesis, migration, or survival in addition to regulation of ion channels andother functional molecule. Two distinct structures, the sexually dimorphic nucleus of the preoptic area, which is largerin male rats than in males and the anteroventral periventricular nucleus, which furnish opposite characteristics, willprovide good opportunity to understand the mechanism of brain sex diff erentiation.