Thoracic Spinal Cord and Cervical Vagosympathetic Neuromodulation Obtund Nodose Sensory Transduction of Myocardial Ischemia

Background Autonomic regulation therapy involving either vagus nerve stimulation (VNS) or spinal cord stimulation (SCS) represents emerging bioelectronic therapies for heart disease. The objective of this study was to determine if VNS and/or SCS modulate primary cardiac afferent sensory transduction of the ischemic myocardium. Methods Using extracellular recordings in 19 anesthetized canines, of 88 neurons evaluated, 36 ventricular-related nodose ganglia sensory neurons were identified by their functional activity responses to epicardial touch, chemical activation of their sensory neurites (epicardial veratridine) and great vessel (descending aorta or inferior vena cava) occlusion. Neural responses to 1 min left anterior descending (LAD) coronary artery occlusion (CAO) were then evaluated. These interventions were then studied following either: i) SCS [T1-T3 spinal level; 50 Hz, 90% motor threshold] or ii) cervical VNS [15–20 Hz; 1.2 × threshold]. Results LAD occlusion activated 66% of identified nodose ventricular sensory neurons (0.33 ± 0.08–0.79 ± 0.20 Hz; baseline to CAO; p < 0.002). Basal activity of cardiac-related nodose neurons was differentially reduced by VNS (0.31 ± 0.11 to 0.05 ± 0.02 Hz; p < 0.05) as compared to SCS (0.36 ± 0.12 to 0.28 ± 0.14, p = 0.59), with their activity response to transient LAD CAO being suppressed by either SCS (0.85 ± 0.39–0.11 ± 0.04 Hz; p < 0.03) or VNS (0.75 ± 0.27–0.12 ± 0.05 Hz; p < 0.04). VNS did not alter evoked neural responses of cardiac-related nodose neurons to great vessel occlusion. Conclusions Both VNS and SCS obtund ventricular ischemia induced enhancement of nodose afferent neuronal inputs to the medulla.