Study of the Sympathetic Vasoconstrictor Nerves to the Vessels of the Dog

In anesthetized dogs, the vasoconstrictor nerves to the vessels of the hind limb left the spinal cord in the anterior spinal nerve roots from T-10 through L4 levels. Maximal vasoconstrictor responses occurred on stimulation of the T12, T-13, and L-l roots; none occurred on stimulation of roots caudal to L-4. The nerves first entered the lumbar paravertebral chain at or above L-l; the last point of entry was at the L-4, L-5 level. No fibers left the lumbar chain at L-l, L-2, and L-3 levels. The first point of exit was at L-4, and nerves continued to leave as far distal as S-l, the most caudal point examined. The maximal response to stimulation of the lumbar chain was at the L-4, L-5 level. With a single exception, the responses to electric stimulation of the anterior spinal nerve roots, lumbar chain, or sympathetic ganglia were confined to the vessels of the ipsilateral limb. In 22 dogs with unilateral sympathectomy (L-2 through L-7), changes in hind-limb vascular resistance were induced reflexly or by electric stimulation of the anterior spinal roots. The results indicated that sympathetic control of the resistance vessels of the hind limb was still absent 77 days after sympathectomy. ADDITIONAL