Distribution of cardiac sympathetic afferent fibers in the guinea pig heart labeled by anterograde transport of wheat germ agglutinin-horseradish peroxidase.

Anterogradely transported wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was used to selectively label the distribution within the guinea pig heart of cardiac sympathetic afferent fibers whose cell bodies lie in the dorsal root ganglia (DRGs) of C6, C8, T1-3. The majority of fibers were seen in the posterior atrial wall, the pulmonary arterial walls, and along the major branches of the coronary arteries. Labeled fibers were also found in the parietal pericardium and associated with the atrioventricular and aortic valves. The labeling pattern was dependent upon segmental level: the most general labeling followed upper thoracic DRG injection, while labeled fibers associated with the coronary arteries were nearly absent after lower cervical DRG injection. Comparison of heart labeling among chemically sympathectomized and untreated animals demonstrated no difference in the distribution of frequency of WGA-HRP labeled fibers, indicating the specificity of this technique. The present findings indicate that the spinal sensory innervation of the heart has its major origins in the uppermost thoracic dorsal root ganglia and has a highly selective regional distribution. The implications of these findings in relation to cardiac autonomic dysfunction and pain are discussed.