Administration of ovarian steroid hormones does not change the reward effectiveness of lateral hypothalamic stimulation in ovariectomized rats

The effect of two schedules of steroid hormone administration on the reward effectiveness of lateral hypothalamic stimulation was examined in ovariectomized Long-Evans female rats. In Experiment 1, estrogen and progesterone were administered on a 4-day schedule so as to mimic the hormonal profile of the estrous cycle; in Experiment 2, silastic implants of progesterone and estrogen were used to induce steroid hormone levels similar to those observed in mid- and late pregnancy. In both experiments, hormone administration was sufficient to induce characteristic behaviors: lordosis in Experiment 1 and a change in sucrose preference and body weight in Experiment 2. In contrast, hormone administration did not change the reward effectiveness of the electrical stimulation in either Experiment 1 or Experiment 2.