In humans, there are large individual differences in the levels of vagal modulation of resting heart rate (HR). High levels are a recognized index of cardiac health, whereas low levels are considered an important risk factor for cardiovascular morbidity and mortality. Several factors are thought to contribute significantly to this inter-individual variability. While regular physical exercise seems to induce an increase in resting vagal tone, chronic life stress, and psychosocial factors such as negative moods and personality traits appear associated with vagal withdrawal. Preclinical research has been attempting to clarify such relationships and to provide insights into the neurobiological mechanisms underlying vagal tone impairment/enhancement. This paper focuses on rat studies that have explored the effects of stress, psychosocial factors and physical exercise on vagal modulation of resting HR. Results are discussed with regard to: (i) individual differences in resting vagal tone, cardiac stress reactivity and arrhythmia vulnerability; (ii) elucidation of the neurobiological determinants of resting vagal tone.
Keywords: anxiety; arrhythmias; autonomic nervous system; depression; exercise; heart rate variability; rat; stress.