Sexual dimorphism in brain weight of meadow voles: role of gonadal hormones.

ABSTRACT

In most adult mammals, brain weights of males exceed those of females. The role of androgens in the genesis of this sex difference was assessed in meadow voles by acute neonatal or chronic postweaning manipulation of testosterone titers. Female voles given a single injection of testosterone propionate (TP) on the second day of postnatal life had brain weights in adulthood that were indistinguishable from those of male voles and significantly heavier than those of control females. Whole brain DNA content, a measure of cell number, was not increased by neonatal TP treatment. Females treated with TP from day 19 to 70 had lower brain weights than control females and males gonadectomized at 19 days of age had greater brain weights than did intact male voles at day 70. The sex dimorphism in brain weight reflects organizational effects of testosterone during perinatal development. Beginning at weaning, and continuing through postpubertal development, testosterone decreases brain weight in both sexes. We suggest that testosterone affects brain weight by altering cell size or non-cellular components rather than cell number.