Differential Chronotropic and Dromotropic Responses to Focal Stimulation of Cardiac Vagal Ganglia in the Rat

Abstract

Activity in vagal preganglionic motoneurones running to the heart provokes a generalized cardioinhibition producing a decrease not only in heart rate (chronotropy), but also in the rate of atrioventricular (AV) conduction (dromotropy), and in the force of myocardial contraction (inotropy). These effects are secondary to, and are contingent upon, excitation of ganglion cells located in clusters on the epicardium of the dorsum of the atria, closely apposed to the sites of entry of the major veins. There is evidence that in many of the larger mammalian species, the ganglion cells are clustered into discrete zones or 'fat pads' which project to different regions of the heart and selectively control cardiac function (Ardell & Randall, 1986; Randall et al. 1986a,b;Gatti et al. 1995Gatti et al. , 1997. Several recent studies have described the anatomy of the cardiac vagal ganglia in the rat (Pardini et al. 1987;Abrahamian et al. 1991;Klimaschewski et al. 1992;Burkholder et al. 1992;deSouza et al. 1996;Cheng et al. 1999;Cheng & Powley, 2000).Although the results of some of these studies suggest the existence of a functional topography (e.g. Pardini et al. 1987), there is little clear physiological or pharmacological evidence of this in the rat. In the only previous study of a possible functional organization of rat cardiac ganglia (Burkholder et al. 1992), a brief description is given of a partial selectivity revealed by differing responses to vagal stimulation following local infiltration of hexamethonium into identified fat pads.Data from preliminary experiments in this laboratory suggest that glutamate excitation of cardiac vagal preganglionic motoneurones from different regions of the rat nucleus ambiguus results in differential chronotropic and dromotropic effects (Sampaio et al. 2000). That this may result from a different termination pattern of preganglionic axons onto ganglion cells from different ganglionic clusters is supported by the finding of restricted ganglionic innervation from motoneurones labelled with anterograde Vagal cardioinhibition is exerted through a reduction not only in the heart rate but also in the rate of propagation of the cardiac action potential and in myocardial contractility. In several species, such effects can be produced independently by selective activation of ganglia in identified 'fat pads'. In this study we investigate differential control of heart rate and atrioventricular conduction by two ganglionic clusters in the rat, a species increasingly important in studies of cardiovascular control. Epicardial sites producing low-threshold changes in P-P and P-R interval of the ECG in an arterially perfused preparation were explored with concentric bipolar stimulating electrodes. Stimulation sites centred on two principal ganglia, the sinoatrial (SA) ganglion at the junction of the right superior vena cava and right atrium, and the atrioventricular (AV) ganglion at the junction of the inferior pulmonary veins and left atrium. Stimulation of the SA ganglion decreased heart rate in all ...

Reduced N‐Type Ca 2+ Channels in Atrioventricular Ganglion Neurons Are Involved in Ventricular Arrhythmogenesis

“…Cardiac vagal postganglionic neurons are located in the intracardiac ganglia. Rat intracardiac ganglia are divided into the sinoatrial ganglion and the AVG 24. The ventricular myocardium only receives the projection of nerve terminals from the AVG 25.…”

Discharge Patterns of Preganglionic Neurones with Axons in a Cardiac Vagal Branch in the Rat

“…In the past we have electrically stimulated this branch (Jones et al 1998), followed its anatomical route by microdissection (Izzo & Jones, 1994) and used anterograde tracing techniques to follow the path taken by preganglionic axons to atrial ganglion cells (Jones et al 1999). Other researchers have also demonstrated that this branch projects directly to atrial ganglia (Cheng et al 1999;Corbett et al 1999;Cheng & Powley 2000;Sampaio et al 2003). These atrial ganglia effect chronotropic and dromotropic changes when electrically stimulated (Sampaio et al 2003).…”

“…Other researchers have also demonstrated that this branch projects directly to atrial ganglia (Cheng et al 1999;Corbett et al 1999;Cheng & Powley 2000;Sampaio et al 2003). These atrial ganglia effect chronotropic and dromotropic changes when electrically stimulated (Sampaio et al 2003).…”

Developmental Changes in Electrophysiological Properties and Synaptic Transmission in Rat Intracardiac Ganglion Neurons

“…ICG neurons were visualized using differential interference contrast optics on a fixed-stage microscope. Recordings were normally made from the largest ganglion, located at the junction of the right superior vena cava and right atrium, which regulates the sinoatrial node (Sampaio et al 2003).…”