Parasympathetic Rebound Following Stress In Four Rat Strains

Exposure to inescapable stress is accompanied by large and complex changes in autonomic nervous system functioning. Our knowledge however about genetic determinants of autonomic nervous system reactivity is still incomplete. For this purpose, we compared autonomic response to stress in four genetically defined rat strains: cholinergic hyperresponsive Flinders sensitive line rats and their control counterparts, Flinders resistant line rats; hypothalamo-pituitary-adrenal axis (HPA) hyperresponsive Fischer rats and HPA hyporesponsive Lewis rats. Autonomic function was estimated through vagal modulation of the heart by means of power spectrum analysis of a telemetrically obtained ECG signal. The ECG signal was recorded in freely moving rats before and following a 10 min forced swim procedure. Within 30 min of stress cessation the initial increase in power of low frequency spectrum component (LF, predominately sympathetic) was replaced by an increase in power of high frequency spectrum component (HF, parasympathetic). This shift in LF/HF power ratio indicates parasympathetic rebound following exposure to stress. This phenomenon was most pronounced in cholinergic hyperresponsive Flinders sensitive line rats and least pronounced in HPA hyporesponsive Lewis rats. This study demonstrates the use of power spectral analysis of heart rate variability in animal studies of stress-induced behaviors. Parasympathetic rebound may help explain genetically mediated differences in vulnerability to the occurrence of certain somatic manifestations of stress responses that are clearly vagally mediated such as bronchoconstriction and peristaltic contractions.