ADMINISTRATION OF OVARIAN-STEROID HORMONES DOES NOT CHANGE THE REWARDEFFECTIVENESS OF LATERAL HYPOTHALAMIC-STIMULATION IN OVARIECTOMIZED RATS

The effect of two schedules of steroid hormone administration on the r eward effectiveness of lateral hypothalamic stimulation was examined i n 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 impl ants of progesterone and estrogen were used to induce steroid hormone levels similar to those observed in mid- and late pregnancy. In both e xperiments, hormone administration was sufficient to induce characteri stic behaviors: lordosis in Experiment 1 and a change in sucrose prefe rence and body weight in Experiment 2. In contrast, hormone administra tion did not change the reward effectiveness of the electrical stimula tion in either Experiment 1 or Experiment 2.