Lateralized action of androgen on development of behavior and brain sex differences

Androgens have been linked to asymmetric brain development. Our results show that in sexually active male gerbils, the volume of the sexually dimorphic area, pars compacta (SDApc) of the preoptic region was positively correlated with the emission rate of an ultrasonic courtship vocalization. Day 1 postnatal treatment of female gerbils with testosterone propionate (TP, 100 micrograms, n = 16) or diethylstilbestrol (DES, 5 micrograms, n = 22) followed by ovariectomy and implantation of testosterone (T) filled silastic capsules in adulthood (day 120-130), increased mean volumes of the SDApc (TP, 1.21: DES, 0.84 mm3 x 10(-3)) and a second sexually dimorphic nucleus, the suprachiasmatic nucleus (SCN) (TP, 295: DES, 287.7 mm3 x 10(-3] compared to control females (n = 13) also given T in adulthood (SDApc = 0.37, SCN = 197.0 mm3 x 10(-3)). Rates of sexually dimorphic ultrasonic calls emitted during sexual interactions with estrous females (TP, 39.3: DES, 28.1 per min) were also increased relative to female controls (22.5 per min). With both treatments, significant covariances were revealed between vocalization rates and the left SDApc volumes [TP (rho), rho = .74: DES, rho = .43], but not the contralateral nucleus. Asymmetric development was absent in control females which received T as adults. Lateralization was specific to the SDApc, since no relationship was seen between either rates of calling and SCN volumes, or frequencies of nonvocal sexual components and the volumes of the SDApc or SCN. We conclude that steroid sex hormones influence lateralization of brain structure related to vocal behavior. The hormonal effect, which is likely to involve estrogen, occurs during neonatal development.