Neonatal 6-hydroxydopamine lesion of forebrain norepinephrine does not eliminate critical period for behavioral effects of gonadal hormone manipulation.

Newborn rats were injected s.c. with 6-hydroxydopamine to deplete forebrain norepinephrine (NE) or with the vehicle. The males were then castrated at 4 days and the females injected with testosterone at 5 days of age. Both sexes were tested for female-like sexual responsiveness to a stud male at 6 months of age. The loss of forebrain NE did not prevent the feminization of the males due to castration or the masculinization of the females due to testosterone. This result contraindicates a general permissive-requisite role for forebrain NE for the mammalian brain's plasticity during its critical periods.