Effects of corticosterone on submissiveness in mice: Some temporal and theoretical considerations

Two experiments were conducted to examine directly the effects of corticosterone on submissiveness in mice. A repeated testing paradigm was used in both of these studies, in order to begin to identify whether corticosterone's effects on submissiveness are of the “baseline” or the “feedback” variety. Experiment 1 examined the dose-response relationship between levels of corticosterone administered over a three week period and levels of submissiveness. This study showed that only a very high dosage (350 μg/day) increased submissiveness during an initial test, but that lower dosages increased submissiveness during a second submission test. Thus, the combination of corticosterone treatment and a prior experience of defeat is a more powerful facilitator of submissiveness than is either a prior defeat alone or corticosterone treatment alone. Experiment 2 examined the effects on submissiveness of a single treatment with corticosterone either before an initial test, before a second submission test, before both tests, or before neither test. This study showed that corticosterone did not affect submissiveness during the test which followed its application, but corticosterone treatment before the first test did increase submissiveness as measured during the second test. Thus, again, coupling corticosterone treatment with an initial experience of defeat increased future submissiveness. The findings of these two experiments show, first, that the duration of corticosterone treatment is not important to its effects on submissiveness. Second, these findings suggest that corticosterone affects submissiveness in what has been called a feedback way and may not operate at all on submissiveness in a baseline way.