Responses of the cerebral circulation to hypercapnia and hypoxia after 7th cranial nerve transection in baboons.

It has been proposed that the responses of the cerebral circulation to hypoxia, hypercapnia and hypotension may be partially mediated by an autonomic reflex with receptors in the carotid body or sinus serving as sensors and the efferent limbs being the 7th cranial nerves. Transection of the 7th cranial nerve has been reported to impair the cerebral circulatory response to isolated chemoreceptor stimulation by hypoxia and hypercapnia. To test this hypothesis we measured cerebral blood flow (CBF) by an intra-arterial 133Xe technique in 10 baboons during periods of induced hypoxia and hypercapnia, both before and after transection of the 7th cranial nerve, We found that the responses of CBF were unaltered by either unilateral or bilateral section of the nerve. Our results showing the preservation of normal CBF responses, following transection, suggest that neurogenic control of the cerebral circulation by an autonomic reflex involving the 7th nerve is unlikely.