Alterations in core body temperature, locomotor activity, and corticosterone following acute and repeated social defeat of male NMRI mice

Repeated social defeat of male NMRI mice, coupled with the stress of continuously living opposite a dominant animal, induces a citalopram-reversible increase in anxiety. The experiments reported in the present paper were performed in an attempt to further validate this paradigm by studying the effects of acute and repeated social defeat on corticosterone and the circadian rhythms of core body temperature and locomotor activity, measured by telemetry. Acute social defeat induced a large (controls: 37.14 +/- 0.29 degreesC; subordinates: 39.79 +/- 0.33 degreesC) increase in core body temperature and corticosterone (controls: 30.14 +/- 2.70 ng/ml; subordinates: 89.62 +/- 9.25 ng/ml). Repeated social defeat (24 defeats) induced a chronic elevation in core body temperature across 24-h (controls: 36.62 +/- 0.04 degreesC; subordinates: 37.11 +/- 0.16 degreesC) in subordinate animals and a very large increase in corticosterone (controls: 28.60 +/- 1.27 ng/ml; subordinates: 441.52 +/- 8.86 ng/ml). These results illustrate that the chronic social defeat procedure described in this paper induces a state of chronic stress in the subordinate animals. Further studies are warranted to ascertain if the chronic hyperthermia and increases in corticosterone observed in the subordinate animals could be attenuated by chronic antidepressant treatment, thus further extending the predictive validity of this model. (C) 2001 Elsevier Science Inc. All rights reserved.