Vulnerability to arrhythmias during social stress in rats with different sympathovagal balance

Abstract

An increased activity of the sympathetic nervous system is an important factor in the genesis of ventricular arrhythmias. Changes in average R-R interval, R-R interval variability (indirect measure of sympathovagal balance), occurrence of arrhythmias, and plasma norepinephrine concentrations were measured during a social stress episode (defeat) in two strains of rats, Wistar and wild type, which were supposed to differ in their autonomic stress responsiveness. Electrocardiograms were telemetrically recorded, and blood samples were withdrawn through jugular vein catheters from healthy, freely moving animals. R-R interval variability was estimated by the following time-domain parameters: the standard deviation of the mean R-R interval, the coefficient of variance, and the root mean square of successive differences in R-R interval. Average R-R interval and R-R interval variability measures, as well as plasma norepinephrine concentrations, indicated a higher sympathetic tone, a larger sympathetic responsiveness, and a lower parasympathetic antagonism after sympathetic activation in wild-type animals, which also showed a much higher incidence of arrhythmias (ventricular premature beats), compared with Wistar rats. These two strains might represent a valuable experimental model for studying the mechanisms (cellular/electrophysiological) responsible for the susceptibility to arrhythmias in healthy individuals exposed to stressful situations.

Social Isolation Disrupts Autonomic Regulation of the Heart and Influences Negative Affective Behaviors

“…Further, HR was significantly changed (but RSA was not) following 2 weeks of isolation, suggesting a predominant sympathetic mechanism may underlie HR changes early during isolation whereas both sympathetic and vagal mechanisms may regulate cardiac responses during longer isolation periods and behavioral tasks. Consistent with this conclusion are findings that both sympathetic and parasympathetic mechanisms mediate ventricular arrhythmias during the resident-intruder paradigm in rats (50) The present findings are extended by the examination of relations among affective behaviors and basal and resident-intruder-induced cardiac variables after isolation. As expected, a greater degree of anhedonia (lower sucrose intake) and a greater degree of anxiogenic behavior (more time in the open arms of the elevated plus maze) both were related to higher HR and lower SDNN index following isolation and during the resident-intruder paradigm, and to lower RSA amplitude following 4 weeks of isolation.…”

“…Animals were anesthetized with ketamine and xylazine (67 mg/kg and 13.33 mg/kg, respectively, sc; NLS Animal Health, Owings Mills, MD). Transmitter implantation was similar to procedures described elsewhere (50,51). Animals were housed for 5 days in custom-designed divided cages (40) to permit adequate healing of suture wounds, and then were returned to the home cages (with the sibling) to recover for an additional 5-7 days.…”

Long-lasting bradypnea induced by repeated social defeat

“…Wild-type Groningen male rats (Rattus norvegicus, WTG strain), originally bred at the University of Groningen (The Netherlands) under conventionally clean conditions (40), weighing 400 -500 g, served as resident rats, in confrontation encounters. The same WTG rats were used for all successive series of experiments.…”

Mind-Body Medicine in Chronic Heart Failure

“…A wide range of stressors have been shown to be associated with sudden death. 5,8,9 In general, interventions that interrupt release of intracardiac but not circulating norepinephrine prevent stressinduced sudden death.…”

“…ECG recordings obtained in some rat models of stress show that sudden death is mediated by profound bradycardia progressing to asystole. 5,6,8 This suggests that extreme stress may produce an "autonomic storm" characterized by excessive activation of both the sympathetic and parasympathetic nervous systems. Such malignant parasympathetic activity has been shown to play a role in human disease.…”