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1 Physiology, University of Kentucky, College of Medicine, Lexington, KY, USA; Center for Biomedical Engineering, University of Kentucky, Lexington, KY, USA
2 Center for Biomedical Engineering, University of Kentucky, Lexington, KY, USA
3 Physiology, University of South Alabama, Mobile, AL, USA
4 Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada
5 Pharmacology, University of Montreal, Montreal, Quebec, Canada
6 Pharmacology, East Tennessee State University, Johnson City, TN, Algeria
* To whom correspondence should be addressed. E-mail: randall{at}uky.edu.
The objective of this study was to determine how neurons within the right atrial ganglionated plexus (RAGP) and posterior atrial ganglionated plexus (PAGP) interact to modulate right atrial chronotropic, dromotropic and inotropic function, particularly with respect to their extracardiac vagal and sympathetic efferent neuronal inputs. Surgical ablation of the PAGP attenuated vagally-mediated bradycardia by 26%; it reduced HR slowing evoked by vagal stimulation superimposed upon sympathetically-mediated tachycardia by 36%. RAGP ablation eliminated vagally-mediated bradycardia, while retaining the vagally induced suppression of sympathetic-mediated tachycardia (-83%). Following combined RAGP and PAGP ablation, vagal stimulation still reduced sympathetic-mediated tachycardia (-47%). After RAGPx alone, and after PAGPx alone, stimulation of the vagi still produced negative dromotropic effects, though these changes were attenuated compared to the intact state. Negative dromotropic responses to vagal stimulation were further attenuated after combined ablation, but parasympathetic inhibition of AV-nodal conduction was still demonstrable in most animals. Finally, neither RAGP nor PAGP ablation altered autonomic regulation of right atrial inotropic function. These data indicate that multiple aggregates of neurons within the intrinsic cardiac nervous system are involved in sinoatrial nodal regulation. Whereas parasympathetic efferent neurons regulating the right atrium, including the SA node, are primarily located within the RAGP, prejunctional parasympathetic-sympathetic interactions regulating right atrial function also involve neurons within the PAGP.
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