Cells of origin of sympathetic pre‐ and postganglionic cardioacceleratory fibers in the pigeon

The pre‐ and postganglionic cardioacceleratory innervation is described in the pigeon. The peripheral course of the postganglionic cardiac nerves has been determined using microdissection and electrical stimulation. Using these techniques and retrograde degeneration methods, the distribution within the sympathetic ganglia of the cells of origin of these fibers has been localized to the three right caudal cervical ganglia (12, 13 and 14). It has also been shown on the basis of electrical stimulation combined with selective ablation of the right sympathetic chain that cardioaccelerator preganglionic fibers probably arise from the most caudal cervical segment of the spinal cord (14), always arise from the upper two thoracic segments (15 and 16), and occasionally arise from a mid‐thoracic segment (17). The left sympathetic chain was shown to have an inconsistent influence on heart rate. On the basis of retrograde degeneration, the cells of origin of sympathetic preganglionic fibers have been localized to a welldefined cell column dorsal to the central canal (column of Terni).