MATERNAL AGGRESSION AS A MODEL FOR ACUTE SOCIAL STRESS IN THE RAT - ABEHAVIORAL-ELECTROCARDIOGRAPHIC STUDY

Maternal aggression of lactating rats was used to induce acute social stress in a resident-intruder paradigm. Behavioral and electrocardiogr aphic responses of male intruders were simultaneously recorded. Cardia c electrical activity was measured by means of a telemetry system whic h ensured preservation of intruders' behavioral repertoire. Behavioral response to maternal attack was evaluated in terms of percent time sp ent in passive/submissive (pis) and active/non-submissive (a/ns) patte rns. This allowed us to classify the intruders as submissive, non-subm issive, and intermediates. During the test, a significant decrease of average R-R interval (R-R) compared to baseline conditions and the occ urrence of arrythmias of different nature were found. Ventricular arrh ythmias, including premature ventricular beats and ventricular tachyca rdias, were present in all the intruders while R-R fluctuations and II degree atrioventricular (A-V) blocks only appeared in submissive and intermediate rats. Most ventricular arrhythmias occurred within the up per range of heart rate and were preceded by periods of low R-R variab ility. These electrocardiographic events were temporally associated wi th a/ns behavioral patterns and were related to an increased prevalenc e of sympathetic activity. On the other hand, R-R fluctuations and II degree A-V blocks preceded by high R-R variability were synchronized w ith p/s behavior and were ascribed to a predominant inhibitory effect of vagal activation which becomes more pronounced as the level of symp athetic activity increases. (C) 1995 Wiley Liss, Inc.