Gonadal Hormones Organize the Adolescent Brain and Behavior

Abstract

Sexual differentiation of the nervous system and behavior occurs through organizational effects of gonadal hormones acting during early neural development and again during puberty. In rodents, a transient elevation in testosterone around the time of birth masculinizes and defeminizes the male brain, creating structural sexual dimorphisms and programming sex-typical responses to gonadal hormones in adulthood. A second wave of sexual differentiation occurs when levels of gonadal hormones are elevated at the time of puberty. At this time, both testicular and ovarian hormones further masculinize and feminize the male and female brain, respectively, fine-tuning sex differences in adult behavior. To test the hypothesis that the peripubertal period is a sensitive period for hormone-dependent sexual differentiation that is separate and distinct from the perinatal period, exposure to testosterone was experimentally manipulated in male Syrian hamsters to occur either prepubertally, during puberty, or in young adulthood. This experiment revealed that the perinatal and peripubertal periods of masculinization of male sexual behavior are not two separate critical periods of sensitivity to organizing effects of testosterone. Instead, the two periods of masculinization are driven by the two naturally occurring elevations in gonadal hormones. To explore possible neural mechanisms of peripubertal organizational effects of gonadal hormones, cell birth-dating experiments in male and female rats revealed sex differences in the addition of new cells, including both neurons and glia, to sexually dimorphic cell groups in the hypothalamus and medial amygdala. These sex differences in cell addition were positively correlated with sex differences in the volume of these cell groups. Prepubertal gonadectomy abolished sex differences in the pubertal addition of new cells. These experiments provide evidence that gonadal hormone-dependent sex differences in pubertal cytogenesis contribute to the establishment or maintenance of sexual dimorphisms in the adult brain.KeywordsSexual DimorphismSexual DifferentiationOvarian HormoneGonadal HormoneSensitive PeriodThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.