Functional Studies of Right Cardiac Sympathetic Nerves and Ganglia in the Dog 1

Abstract

Many studies have provided detailed descriptions of the variations of sympathetic innervation of the dog heart (1-5), but only a few studies have been done to determine the locations of synaptic connections between pre and postganglionic fibers within this cardiac sympathetic system. Although most investigators have freely assumed that the stellate ganglia are the principal sites of ganglionic transmission in most animals, our previous studies indicate that the major site of synapse for sympathetic cardiac fibers in the dog occurs within the caudal cervical ganglia and not the stellates (6-8). On the other hand, Aiken and Reit (9) have shown a species difference; in the cat, these cardiac sympathetic synapses do predominate in the stellates.

The present experiments were designed to study under precise conditions the pathways taken by sympathetic nerves to the right side of the dog's heart in order to quantify and better define the functional distribution of pre and postganglionic chronotropic and inotropic fibers within the various pathways.

Methods. Open-chest experiments were done on 11 adult mongrel dogs of both sexes weighing 13-32 kg. The animals were anesthetized with sodium pentobarbital (30 mg/kg) given intravenously. Blood pressure was monitored from the descending aorta with a Statham pressure transducer, and heart rate was recorded by a tachograph. Contractile force was measured with a Walton strain gauge arch sutured to the anterior surface of the right ventricle. The myocardial fibers between the feet of the arch were stretched to such an extent that the maximum active tension was recorded during contraction.

In order to eliminate reflex effects on the heart, the cardiac nerves were decentralized in all experiments. Both vagosympathetic trunks were isolated and cut in the upper cervical region. The left stellate ganglion was removed, and the right stellate was decentralized by sectioning the right thoracic sympathetic trunk at T-5 and all communicating rami from C-6 to T-5.