Interactions within the ICN

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Various lines of evidence indicate that peripheral sites that are separate from the end effectors contribute to mediating sympathetic-parasympathetic interactions for the control of regional cardiac function. Stimulating parasympathetic and/or sympathetic efferent projections to the heart can activate subpopulations of intrinsic cardiac neurons (20, 21, 53). These extrinsic autonomic projections converge on separate aggregates of intrinsic cardiac neurons, each of which exhibits preferential control over regional cardiac function (4, 96). As shown in Fig. 3, with respect to control of chronotropic function, surgical disruption of the right atrial ganglionated plexus eliminates direct vagal projections to the sinoatrial node

FIGURE 2 Schematic of proposed neural interactions occurring within the intrathoracic autonomic ganglia and between these peripheral networks and the central nervous system. Within the intrinsic cardiac ganglia are included sympathetic (Sympath) and parasympathetic (Parasym) efferent neurons, local circuit neurons (LCN), and afferent neurons. Contained within the extracardiac intrathoracic ganglia are sympathetic efferent neurons, local circuit neurons, and afferent neurons. These intrinsic cardiac and extracardiac networks form separate and distinct nested feedback loops that act in concert with CNS feedback loops involving the spinal cord and medulla to regulate cardiac function on a beat-to-beat basis. These nerve networks are also influenced by circulating humoral factors, including catecholamines (catechol) and angiotensin II (ANG II). Aff., afferent; DRG, dorsal root ganglia; Gs, stimulatory guanine nucleotide-binding protein; Gi, inhibitory guanine nucleotide-binding protein; AC, adenylate cyclase; ^-adrenergic receptor; M2, muscarinic receptor.

FIGURE 2 Schematic of proposed neural interactions occurring within the intrathoracic autonomic ganglia and between these peripheral networks and the central nervous system. Within the intrinsic cardiac ganglia are included sympathetic (Sympath) and parasympathetic (Parasym) efferent neurons, local circuit neurons (LCN), and afferent neurons. Contained within the extracardiac intrathoracic ganglia are sympathetic efferent neurons, local circuit neurons, and afferent neurons. These intrinsic cardiac and extracardiac networks form separate and distinct nested feedback loops that act in concert with CNS feedback loops involving the spinal cord and medulla to regulate cardiac function on a beat-to-beat basis. These nerve networks are also influenced by circulating humoral factors, including catecholamines (catechol) and angiotensin II (ANG II). Aff., afferent; DRG, dorsal root ganglia; Gs, stimulatory guanine nucleotide-binding protein; Gi, inhibitory guanine nucleotide-binding protein; AC, adenylate cyclase; ^-adrenergic receptor; M2, muscarinic receptor.

4 Hz Sympathetic Stim.

12 Hz PS Stim.

c 200 H

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