Testosterone implants into the amygdala during the neonatal period masculinize the social play of juvenile female rats.

Implanting androgens directly into the MeA of developing females increases the frequency of their play to that of males.

“Conversely, implanting androgens directly into the MeA of developing females increases the frequency of their play to that of males (Meaney & McEwen, 1986).”

In rats, social play is perinatally organized by androgens.

“In rats, one such behavior that is perinatally organized by androgens is social play.”

The critical time in the rat for organization of play is the early neonatal period, when interactions of androgens with the androgen receptor set up the sex difference observed in juveniles.

“The critical time in the rat for organization of play is the early neonatal period, when interactions of androgens with the AR set up the sex differ- ence observed in juveniles (Meaney et al. 1983; Meaney and McEwen 1986; Pellis and Pellis 1997).”

Play is organized by the perinatal interaction of androgens with the androgen receptor.

“Play is organized by the peri- natal interaction of androgens with the AR (Meaney et al. 1983; Meaney and McEwen 1986; Pellis and Pellis 1997).”

Juvenile social play behavior is classically thought to be due to activation of androgen receptors, with some data suggesting a possible involvement of estrogen receptors.

“Juvenile social play behavior is classically thought to be due to activation of androgen receptors (6,32), with some data suggesting a possible involvement of estrogen receptors (8).”

Masculinization of the male brain may in part be dependent on the effects of androgens on androgen receptors.

“masculinization of the male brain may in part be dependent on the effects of androgens on androgen receptors (Auger, Tetel, & McCarthy, 2000;Bakker, Honda, Harada, & Balthazart, 2002;Meaney & McEwen, 1986;Morris, Jordan, Dugger, & Breedlove, 2005).”

EE2 treatment increased play behavior pinning frequencies in female rats, similar to the increase caused by developmental androgen treatment.

“For example, EE 2 treatment resulted in increased play behavior pinning frequencies by female rats similar to that caused by developmental androgen treatment (Meaney, 1989;Meaney and McEwen, 1986;Tonjes et al., 1987).”

Androgen exposure during the early neonatal time period is responsible for later juvenile rough-and-tumble play behavior, and juvenile hormone levels are not involved in its regulation.

“Therefore, it is believed that androgen exposure during the early neonatal time period is responsible for later juvenile rough-and-tumble play behavior, and that juvenile hormone levels are not involved in its regulation (18, 25).”

High levels of androgen exposure around birth increases the level of rough-and-tumble play behavior during the juvenile period.

“Previous research has shown that high levels of androgen exposure around birth increases the level of rough-and-tumble play behavior during the juvenile period (25).”