Relative Effects of Fighting on Bound and Unbound Corticosterone in Mice ∗

Abstract

Summary

Circulating corticosterone is almost entirely zinc-precipitable in isolated C57BL/6J (adult male) mice. Mice maintained in isolation except for daily 15-minute exposures to trained fighting mice show a profound increase in circulating corticosterone which is entirely traceable to increases in unbound (non-zinc-precipitable) hormone following fighter-exposure. Mice exposed to the first defeat by a fighter were characterized by more than 24 hours of elevated unbound corticosterone with no alteration in that fraction bound to protein. Adaptation to the experimental situation is rapid since, by the fourth exposure to a fighter, the elevation of unbound hormone lasts less than 3 hours; again, with no change in the level of protein-bound corticosterone.