Cholinergic cerebral vasodilatation: lack of involvement of cranial parasympathetic nerves.

Cerebral blood flow (CBF) was estimated by measurement of internal carotid blood flow (ICBF) and sagittal sinus blood flow (SSBF) in mechanically ventilated rabbits under 70% N2O/30% O2. Electrical stimulation of cranial nerves III, VII, IX, or X, with stimulus parameters adequate to excite other visceromotor outflows of these nerves, failed to elicit change in CBF. Combined bilateral section of nerves VII, VIII, IX, X, and XI had no effect on the reactivity of CBF to CO2, nor did the sectioning of these nerves affect the increases in CBF induced by physostigmine. Division of the sinus and aortic nerves and of the vagi in the neck failed to change CO2 reactivity, even though normocapnic CBF was reduced. Pentobarbital blocked the increase in CBF produced by physostigmine, but had no effect on that produced by pilocarpine. The results indicate that cranial parasympathetic nerves do not contain cerebral vasodilator fibers, and that they are not the source of acetylcholine which is presumably involved in CBF regulation.