Organization of the sympathetic postganglionic innervation of the rat heart

Abstract

The origins and organization of cardiac sympathetic postganglionic nerves in the rat were identified in the present investigation. The retrograde tracer, Diamidino Yellow, was injected into the right or left ventricles to label somata in the sympathetic chain. Analysis of all sympathetic ganglia from superior cervical ganglion through the 10th thoracic ganglion indicated that the postganglionic innervation of the rat cardiac ventricles originates bilaterally. The majority of these somata were located in the middle and inferior cervical ganglia (middle cervical-stellate ganglion complex) (approximately 92% of all labelled cells), with lesser contributions from the superior cervical and 4th through 6th thoracic ganglia. To confirm and further quantitate these findings, the middle cervical-stellate ganglion complex was removed (MC-S ganglionectomy) bilaterally or ipsilaterally from the left or right sides, and regional cardiac norepinephrine concentration (left and right atrial appendages and left and right ventricles) was analysed 7 or 28 days later. At both times after bilateral MC-S ganglionectomy, regional cardiac norepinephrine was reduced by 89% to 100%, indicating the removal of almost all cardiac noradrenergic cells of origin and possibly fibers of passage. The results of unilateral MC-S ganglionectomy experiments indicated that the atrial appendages and the left ventricle receive bilateral innervation from the middle cervical-stellate ganglion complex. However, the left middle cervical-stellate ganglion complex appears to contribute a majority of the norepinephrine to the right ventricle. Furthermore, between 7 and 28 days after contralateral MC-S ganglionectomy, atrial appendages, but not ventricles, display significant recovery of norepinephrine content. The present data demonstrate: (1) a bilateral locus of origin of cardiac sympathetic postganglionic neurons, limited longitudinally to cervical through mid-thoracic ganglia, and (2) the ability of the cardiac postganglionic innervation to regenerate after partial denervation. These results demonstrate anatomical evidence for significant bilateral integration of cardiac sympathetic activity at the level of the sympathetic ganglion in the rat.