Premium
Pontine and Medullary Sources of Cardiac Vagal Tone
Author(s) -
Farmer David George Stephen,
Dutschmann Mathias,
Paton Julian F,
Pickering Anthony E,
McAllen Robin Michael
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1236.5
Subject(s) - medicine , vagal tone , brainstem , pons , heart rate , bradycardia , anesthesia , tachycardia , cardiology , vagus nerve , autonomic nervous system , blood pressure , stimulation
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=8). Cardiac vagal nerve activity continued, however, adopting a tonic discharge pattern with minor early‐inspiratory dips. In sympathetically disabled rats, transection of the brainstem at caudal pontine level had an effect on heart rate that varied between animals (bradycardia or tachycardia) (baseline: 205.6 ± 10.2, pontine transection: 233.9 ± 8.2, p = 0.1024; n=6). Subsequent bilateral inhibition of the nucleus tractus solitarii (NTS) in these animals produced tachycardia (261.5 ± 8.0 bpm, p=0.0020 vs. pontine transection). Atropine (0.1μg/ml) after either KF inhibition or pontine transection followed by NTS inhibition produced tachycardia, confirming that substantial cardiac vagal tone survived those procedures. We conclude that (a) postinspiration is integral to shaping of CVB discharge and to the generation of RSA; (b) a large component of cardiac vagal tone does not require connections to the pons and is independent of central respiratory drive; (c) part of that medullary component depends on neurons in the NTS. Support or Funding Information Supported by ARC