Nerves projecting from the intrinsic cardiac ganglia of the pulmonary veins modulate sinoatrial node pacemaker function

Abstract

Rationale: Autonomic nerves from sinoatrial node (SAN) ganglia are known to regulate SAN function. However, it is unclear whether remote pulmonary vein ganglia (PVG) also modulate SAN pacemaker rhythm. Objective: To investigate whether in the mouse heart PVG modulate SAN function. Methods and Results: In hearts from 45 C57BL and 7 Connexin40+/GFP mice, we used tyrosine-hydroxylase (TH) and choline-acetyltransferase (ChAT) immunofluorescence labeling to characterize adrenergic and cholinergic elements, repectively, within the PVG and SAN. PVG project postganglionic nerves to the SAN. TH and ChAT stained nerves, enter the SAN as an extensive, dense mesh-like neural network. Neurons in PVG are biphenotypic, containing ChAT and TH positive neurons. In Langendorff-perfused hearts, we compared effects of electrical stimulation of PVG, posterior (PRCVG) and anterior right vena cava ganglia (ARCVG) using 200-2000 ms trains of pulses (300μs, 0.2-0.6mA, 200Hz). Sympathetic and/or parasympathetic blockade was achieved using 0.5μM propranolol and 1μM atropine, respectively. Epicardial optical mapping of SAN activation was performed before, during and after ganglion stimulation. PVG stimulation increased the P-P interval by 36±9%; PRCVG stimulation increased the P-P interval by 42±11%. ARCVG stimulation produced no change. Propranolol perfusion increased the PVG stimulation effect to 43±13%. Atropine caused a 5±6% decrease. In optical mapping experiments of whole hearts and isolated atrial preparations, PVG stimulation shifted the origin of SAN discharges to varying locations. Conclusions: PVG contain cholinergic, adrenergic and biphenotipic neurons whose axons project across the right atrium to richly innervate the SAN region and contribute significantly to regulation of SAN function.