Effect of ovarian hormones on conflict behavior.

We injected ovariectomized female rats with estrogen and progesterone. Some of the injection regimens used are known to induce estrus, while other do not. The effects of these treatments on operant behavior were evaluated. Operant behavior was maintained under a reinforcement schedule, one segment of which involved experimentally induced conflict. Such behaviors previously have been shown to be modified by anti-anxiety drugs. Those hormone treatments effective in inducing estrus had behavioral effects similar to the effects observed for established anti-anxiety agents. Hormone-injection regimens not capable of inducing estrus were without effect on operant behavior. Our findings suggest that the reproductive cycles of female rats are associated with behavioral changes which may be indicative of changing anxiety levels mediated in part by changing titers of ovarian hormones. We suggest that the evaluation of hormonal influences on operant behaviors sensitive to tranquilizers should be a useful model system for studying possible mechanisms underlying emotional changes associated with reproductive cycles.