After bilateral cervical sympathectomy (n = 9), carotid chemoreceptor reflex stimulation induced significantly different (P less than 0.01) effects on cerebral blood flow, which rose by 42 +/- 8%, and cerebral vascular resistance, which did not change.
To determine whether the difference in effect was due to the sympathectomy or merely to the repetition of the stimulus, another group of dogs (sham; n = 6) that had intact sympathetic nerves were studied a second time. In "sham" dogs, the repeat response to carotid chemoreceptor stimulation also induced significantly different effects from those in dogs with sympathectomy.
Am J Physiol Heart Circ Physiol 238: H594-H598, 1980;
http://ajpheart.physiology.org/cgi/content/abstract/238/4/H594