W. Tornatzky et Ka. Miczek, LONG-TERM IMPAIRMENT OF AUTONOMIC CIRCADIAN-RHYTHMS AFTER BRIEF INTERMITTENT SOCIAL STRESS, Physiology & behavior, 53(5), 1993, pp. 983-993
This experiment was designed to examine the short- and long-term behav
ioral, cardiovascular, and thermoregulatory responses to brief intermi
ttent agonistic confrontations in rats. The experimental procedure inv
olves resident-intruder confrontations consisting of a 10-min period d
uring which both animals are separated in the home cage of the residen
t, followed by a brief physical encounter leading to defeat of the int
ruder and a 10-min period, when the intruder was alone in the home cag
e of the resident. These 30-min-long confrontations were repeated on 5
consecutive days. Before the first confrontation with a resident, an
intruder rat's telemetered heart rate and core temperature show a stab
le circadian rhythm that is entrained by the light cycle. Acutely, the
confrontations produce immediate and large tachycardia and hypertherm
ia in intruders. A decrease in amplitude of the circadian rhythms for
heart rate and core temperature, as detected by cosinor analysis, pers
ists for at least 10 days after the last of five daily brief confronta
tions with the resident. The defensive upright posture is nearly absen
t during the first exploration of the resident's home cage, but is dis
played by the intruder for one-third of the available time before and
after the fifth defeat. Intermittent brief social stress is sufficient
to induce profound changes in defensive behavior and long-lasting dep
ression of circadian rhythmicity that persist for weeks.