Sex Differences In Impulsivity In Prepubertal And Adult Rats
The current set of experiments was designed to test the hypothesis that there is a sex difference in impulsivity and in brain areas associated with impulse control in prepubertal and adult rats, such that females have greater inhibitory control than do males. Preliminary studies established that neonatal testosterone exposure is able to masculinize and increase impulsive behavior in prepubertal female rats. In the current study, male and female prepubertal rats exposed to treatments that resulted in either neonatal androgen or estrogen receptor activation made more impulsive choices than did control females and their performance mirrored that of control males. Assessment of impulsivity in adult rats indicated that impulsive choice behavior was similar in males and females whereas impulsive action behavior was greater in males than in females. Analysis of protein levels of markers of dopaminergic and noradrenergic reuptake in the orbital frontal cortex (OFC) and dorsal striatum (dSTR), two brain areas important for impulse control, revealed no differences between male and female prepubertal or adult rats, whereas analysis of protein levels of markers of myelination in the OFC and dSTR revealed similar levels between the sexes in prepubertal rats but increased myelin levels in the OFC but not dSTR of adult female rats as compared to males. Furthermore, analysis of the projections from the OFC to dSTR discovered that the strength of these projections was significantly greater in adult females as compared to males. However, inactivation of the OFC during an impulsive action task in adult rats failed to have an effect on impulsive action responding. Collectively, these results demonstrate for the first time that there is a sex difference in impulsive choice control in prepubertal rats that is organized neonatally by actions of both androgens and estrogens, this sex difference subsides in adulthood, but a sex difference in impulsive action control is present in adulthood. Furthermore, the novel discovery that adult female rats have increased levels of myelination within the OFC and increased strength of projections from the OFC to dSTR as compared to males establishes a molecular sex difference that could underlie the enhanced impulse control in females.