 Reductions in MeCP2 with Small interfering RNA (siRNA) during the first few days of life reduce male levels of juvenile social play behavior to female typical levels, but do not affect female juvenile play behavior.MeCP2 is important in organizing hormone-related behaviors and sex differences in the developing rat amygdala.MeCP2 appears to regulate arginine vasopressin (AVP) and androgen receptor (AR) production in male rats but not in females.