Cardiac vagal preganglionic fibers in neonatal rats: a comparison with cervical vagal components.

Origins of cardiac innervation were determined by injection of horseradish peroxidase (HRP) into the myocardium of rats. Bilaterally labeled efferent cells in the brainstem were found in the rostral nucleus ambiguus (NA) with fewer cells in the dorsal motor nucleus (DMN). No afferent labeling was seen. In young rats, but not in adults, there was labeling in the ventral horn of the cervical spinal cord. A unilateral vagotomy prior to the HRP injection resulted in labeled cells in the brainstem contralateral to the vagotomy while cells in the spinal cord remained bilateral. Thus the label in these spinal cord cells may represent HRP uptake by fibers of passage. These results were compared to the afferent and efferent vagal components of the entire cervical vagus nerve.