AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 6 1193-R1199, Copyright © 1993 by American Physiological Society
Dorsal root afferent influences on tonic firing of renal and mesenteric sympathetic nerves in rats
R. B. Taylor and L. C. Weaver
John P. Robarts Research Institute, University of Western Ontario, London, Canada.
After spinal cord transection in cats and rats, the activity of many
sympathetic nerves is not entirely lost, and firing of other nerves
continues unabated or is increased. This study was done to evaluate the
importance of dorsal root afferent discharge on the generation of tonic
sympathetic activity in renal and mesenteric postganglionic nerves in
spinal rats and in rats with intact neuraxes. Sympathetic discharge was
recorded in anesthetized rats, and peripheral afferent influences were
eliminated by dorsal rhizotomy from T4 to L2. Activity of renal and
mesenteric nerves was well maintained after high cervical and thoracic (T4)
cord transections. Rhizotomy had no effect on sympathetic discharge in rats
with intact neuraxes but decreased renal nerve activity significantly
(-25%) in spinal rats. Because rhizotomy decreased mesenteric discharge in
only three of six spinal rats, mean mesenteric nerve discharge was not
decreased significantly. The decreased renal nerve discharge after dorsal
rhizotomy could not be attributed to input from any specific spinal
segment, and ipsilateral input was no greater than contralateral input.
After rhizotomy, both renal and mesenteric nerves had substantial
excitatory drive from the transected, deafferented spinal cord. These
findings demonstrate that dorsal root afferent influences on spinal neurons
can contribute to the generation of tonic discharge in some sympathetic
nerves in spinal animals.
