Effects of ovariectomy and hormone replacement of DRL behavior in the rat

Fifty-two female rats were sham-operated or ovariectomized. Groups of ovariectomized animals were sham-implanted or implanted with estradiol, progesterone or a combination of estrogen and progesterone. Assays were conducted to determine serum hormone concentrations. Animals were trained on a DRL-20 schedule for 30 days. During DRL, ovariectomized animals showed an increased response rate relative to intact animals. However, DRL performance data indicated ovariectomized rats did not differ significantly from intact female rats or hormone replacement groups on measures of DRL efficiency or on the number of earned reinforcers.