Acute social stress and cardiac electrical activity in rats

This paper summarizes the results of experiments aimed at describing electrocardiographic responses to different acute social stressors in healthy male rats. Electrocardiograms were telemetrically recorded during maternal aggression, social defeat, and psychosocial stimulation, as obtained using the classical resident-intruder paradigm. Autonomic input to the heart was indirectly evaluated by means of heart rate variability measures and plasma catecholamine level determinations. Social stressors produced changes in cardiac electrical activity that were markedly higher than those observed in nonsocial challenging conditions such as novelty and restraint. Defeat, which produced the highest catecholaminergic responses, was the most potent as a social aversive experience in inducing heart rate accelerations and arrhythmias, particularly when applied to a wild-type strain of rats. The far most frequent arrhythmic events were ventricular and supraventricular premature beats, either as isolated events or grouped. Ventricular premature beats usually occurred immediately after attacks and in association with higher heart rate values and lower heart rate variability scores. The relationships between the type of stressor used (either social or nonsocial), the different contributions of the emotional and physical components of stress response, the resulting modulation of autonomic control over cardiac electrical activity, and the incidence of arrhythmic events are discussed. Aggr. Behav. 24:287–296, 1998.