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

Abstract

The effect of two schedules of steroid honnone 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 honnonal profile of the estrous cycle; in Experiment 2, silastic implants of progesterone and estrogen were used to induce steroid honnone 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, honnone administration did not change the reward effectiveness of the electrical stimulation in either Experiment 1 or Experiment 2.In order to maintain homeostasis and satisfy reproductive imperatives, animals must select among a variety of goal objects available in the environment and then show the appropriate behaviors toward those goal objects. The requirements for particular goal objects change depending on the stage of the life cycle and contingencies imposed by the external environment.In female rats, changes in reproductive state dramatically alter choice of goal objects. Proceptivity toward males and the appropriate display of maternal behavior toward young both occur at clearly delineated phases of the reproductive cycle (e.g., see Feder, 1981;Numan, 1994). Overall food intake and nutrient choice have also been shown to vary across reproductive states: salt and carbohydrate intake change with estrus cycle stage (Danielsen & Buggy, 1980; Wurtman & Baum, 1980); pregnant female rats increase their intake of sodium and protein, and lactating females increase their intake of protein, fat, calcium, and sodium (Cohen

Effects of chronic morphine treatment on responding for intracranial stimulation in female versus male rats.

“…Although this hypothesis was not examined in the present study, sex differences in response to opioids may ultimately be explained by organizational or activational effects of gonadal hormones. Previous researchers have reported some (Bless, McGinnis, Mitchell, Hartwell, & Mitchell, 1997;Drewett & Herberg, 1975;Prescott, 1966) or no (Rao & Desiraju, 1990;Stratmann & Craft, 1997;Woodside, Renaudin, & Shizgal, 1996) ovarian hormone (or estrous cycle) modulation of responding for brain stimulation in female rats. We are aware of only one study in which the effects of androgens on responding for brain stimulation were examined; mostly negative effects were reported (Clark, Lindenfeld, & Gibbons, 1996).…”