AJP - Regulatory, Integrative and Comparative Physiology, Vol 260, Issue 1 255-R262, Copyright © 1991 by American Physiological Society
Characteristics of facial nerve-elicited cerebral vasodilatation determined using laser Doppler flowmetry
P. J. Goadsby
Department of Neurology, Prince Henry Hospital, Sydney, Australia.
Cerebral cortical perfusion was monitored continuously with laser Doppler
flowmetry and quantitative measurements of cerebral blood flow performed
with the freely diffusible tracer 4-iodo[N-methyl-14C]antipyrine in the
alpha-chloralose-anesthetized cat. The facial nerve was isolated from the
brain stem via a posterior fossa craniotomy and electrically stimulated at
frequencies of 1, 2, 5, 10, and 20 s-1. A stimulus-locked
frequency-dependent increase in cerebral perfusion was seen in the parietal
cortex; the mean maximum increase was 91 +/- 22% at 20 s-1. This compared
with an absolute flow of 116 +/- 3 ml.100 g-1.min-1 at the same site. In
addition, the response was associated with a marked increase in cerebral
venous O2 content indicating that it is a primary neurogenic dilator
response. This response could be blocked by hexamethonium but not by
atropine and was thus mediated by an autonomic ganglion but not by the
classical muscarinic postsynaptic receptor. Sectioning of the facial nerve
did not alter cerebrovascular reactivity to hypercapnia. These data confirm
the vasodilator effect of activation of the facial nerve and document its
mediation through an intermediate parasympathetic ganglion. Consistent with
previous data, the facial nerve does not appear to play a role in
hypercapnic cerebral vasodilatation. Furthermore, this study highlights the
usefulness of laser Doppler flowmetry in the cerebral circulation and in
particular in the setting where repeated measures are required, such as in
pharmacological studies.
