Ganglionic distribution of afferent neurons innervating the canine heart and cardiopulmonary nerves

The ganglionic distribution of the perikarya of afferent axons in cardiopulmonary nerves or the heart was studied in 64 dogs by injecting horseradish peroxidase into physiologically identified cardiopulmonary nerves or different regions of the heart. In 6 additional dogs, horseradish peroxidase was injected into the aortic arch, pericardial sac, left ventricular cavity or the skin. After injections into cardiopulmonary nerves, retrogradely labeled perikarya were found in the ipsilateral nodose ganglion and the ipsilateral C₇-T₇ dorsal root ganglia. After injections into different regions of the heart, retrogradely labeled neurons were found in the nodose ganglia bilaterally and in the C₆-T₆ dorsal root ganglia bilaterally. Many more retrogradely labeled neurons were found in the nodose ganglia in comparison to the dorsal root ganglia. The largest numbers of retrogradely labeled perikarya in the dorsal root ganglia occurred in the T₂-₄ ganglia following nerve or heart injections. Following injections into specific regions of the heart or individual physiologically identified cardiopulmonary nerves, regional distributions of labeled neurons could not be identified within or among ganglia with respect to the structures injected. Perikarya in dorsal root ganglia which were labeled after heart injections ranged in area from 436-3280 μm² (X = 1279 ± 51 S.E.M.) while after skin injections labeled perikarya ranged in area from 224-5701 μm² (X = 1631 ± 104 S.E.M.). The results show that the afferent innervation of the canine heart is provided by neurons located throughout the nodose ganglia and to a lesser degree in the C₆-T₆ dorsal root ganglia bilaterally. The bilateral distribution of cardiac afferent neurons raises questions regarding mechanisms underlying unilateral symptoms frequently associated with heart disease.