EFFECTS OF EARLY POSTNATAL SEX STEROIDS ON ACQUISITION AND EXTINCTION OF A CONTINUOUSLY REINFORCED LEVER-PRESSING RESPONSE

The effects of early postnatal dihydrotestosterone (DHT) and estradiol on the sexually dimorphic continuously reinforced lever-pressing response were investigated. 90-day-old male rats postnatally treated (during the first eight days of postnatal life) with cyproterone acetate (CA), tamoxifen (TX) or vehicle, and 90-day-old females treated with estradiol benzoate (EB). DHT or vehicle in the same postnatal period. were studied during the acquisition and extinction of the continuously reinforced lever-pressing response using a free-operant procedure. During acquisition. the control males made more responses per minute than the control females. and also reached the extinction criterion significantly sooner than the females. CA treatment impaired the male's performance at the levels of that shown by females. whereas TX treatment affected neither acquisition nor extinction. Inversely, in both experimental phases females treated with DHT performed like control females, whereas the acquisition and extinction performances of the EB-females were similar to those obtained in the control or TX male groups.