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NEUROHUMORAL CONTROL OF CIRCULATION AND HYPERTENSION

Interactions within the intrinsic cardiac nervous system contribute to chronotropic regulation

¹Department of Physiology, College of Medicine, and ²Center for Biomedical Engineering, University of Kentucky, Lexington, Kentucky 40536-0298; ³Department of Physiology, University of South Alabama, Mobile, Alabama 36688-0002; ⁴Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 4R2; and ⁵Department of Pharmacology, University of Montréal, Montréal, Quebec, Canada H3C 357; and ⁶Department of Pharmacology, East Tennessee State University, Johnson City, Tennessee 37614-0054

Submitted 3 April 2003 ; accepted in final form 1 July 2003

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 (PAGPx) attenuated vagally mediated bradycardia by 26%; it reduced heart rate slowing evoked by vagal stimulation superimposed on sympathetically mediated tachycardia by 36%. RAGP ablation (RAGPx) eliminated vagally mediated bradycardia, while retaining the vagally induced suppression of sympathetic-mediated tachycardia (-83%). After combined RAGPx and PAGPx, vagal stimulation still reduced sympathetic-mediated tachycardia (-47%). After RAGPx alone and after PAGPx alone, stimulation of the vagi still produced negative dromotropic effects, although these changes were attenuated compared with the intact state. Negative dromotropic responses to vagal stimulation were further attenuated after combined ablation, but parasympathetic inhibition of atrioventricular nodal conduction was still demonstrable in most animals. Finally, neither RAGPx nor PAGPx 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 sinoatrial node, are primarily located within the RAGP, prejunctional parasympathetic-sympathetic interactions regulating right atrial function also involve neurons within the PAGP.

intrinsic cardiac ganglia; sinoatrial node; inotropic; dromotropic

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