Pontine and Medullary Sources of Cardiac Vagal Tone

Abstract

Cardiac vagal tone is a major determinant of health. Here, we investigate the origins of cardiac vagal tone in the working heart‐brainstem preparation (WHBP). The WHBP shows ongoing activity in the cardiac vagal branch (CVB) and a normal pattern of respiratory sinus arrhythmia (RSA). Ongoing activity in the CVB peaks in late inspiration/postinspiration, correlating with the nadir of heart rate. Bilateral inhibition of the pontine Kölliker‐Fuse nucleus (KF) with isoguvacine (GABAA receptor agonist; 10 mM, 50–70nl) abolished RSA at the same time as removing postinspiratory phrenic activity. Mean heart rate rose modestly (baseline: 245.0 ± 9.2 bpm; KF isoguvacine: 270.6 ± 10.0 bpm; p=0.0370; n=..