Identification of peripheral neural circuits that regulate heart rate using optogenetic and viral vector strategies

Abstract

Heart rate is under the precise control of the autonomic nervous system. However, the wiring of peripheral neural circuits that regulate heart rate is poorly understood. Here, we develop a clearing-imaging-analysis pipeline to visualize innervation of intact hearts in 3D and employed a multi-technique approach to map parasympathetic and sympathetic neural circuits that control heart rate in mice. We identify cholinergic neurons and noradrenergic neurons in an intrinsic cardiac ganglion and the stellate ganglia, respectively, that project to the sinoatrial node. We also report that the heart rate response to optogenetic versus electrical stimulation of the vagus nerve displays different temporal characteristics and that vagal afferents enhance parasympathetic and reduce sympathetic tone to the heart via central mechanisms. Our findings provide new insights into neural regulation of heart rate, and our methodology to study cardiac circuits can be readily used to interrogate neural control of other visceral organs.

Quantitative estimation of nerve fiber engagement by vagus nerve stimulation using physiological markers

“…We found that B-fiber activation by VNS is related to HR drop (Fig. 4B, E), in agreement with findings in other animal studies [37,38,47]. Indeed, the vagus innervates the sinoatrial and the atrioventricular nodes, with negative chronotropic and dromotropic effects, respectively [48e50].…”

“…3B and C) may contribute to the cardio-inhibitory effect of VNS beyond maximum activation of Bfibers. Bradycardia can indeed be induced by selective stimulation of efferent C-fibers [52,53], whereas activation of afferent fibers, probably A-and C-type, can decrease HR by centrally enhancing parasympathetic efferent outflow and reducing sympathetic efferent outflow [47]. Finally, optogenetic activation of vagal A-and C-type afferent fibers caused bradycardia [31].…”

Selective Modulation of Heart and Respiration by Optical Control of Vagus Nerve Axons Innervating the Heart

“…Heart rate and ECG parameters were analyzed in response to vagal photostimulation in ChAT-ChR2 transgenic mice (expressing the ChR2 opsin in cholinergic, and thus parasympathetic axons). With 473nm illumination at the left cervical vagus nerve, as expected 44,45 , heart rate was reduced substantially from baseline during stimulation and returned to baseline following the stimulus (-54%, p=8.1e-37) (Figure 2A). The Q-T interval also decreased significantly (-43%, p=8.0e-26), along with P-wave amplitude (-26%, p=4.3e-9) and T-wave amplitude (-13%, p=2.1e-13), while the P-R interval increased during stimulation (+5%, p=9.2e-12)(Figure2A&B).…”

Novel target identification using single cell sequencing and electrophysiology of cardiac sympathetic neurons in disease

“…The stellate ganglia, which contain the cell bodies of sympathetic neurons that predominantly innervate the heart 1 , are of considerable interest to cardiovascular research 2 . Surgical removal of these ganglia is being used with great success clinically to treat life threatening ventricular arrhythmias associated with structural heart disease and some inherited arrhythmia syndromes 2,3 .…”