Influence of cerebrovascular parasympathetic nerves on resting cerebral blood flow, spontaneous vasomotion, autoregulation, hypercapnic vasodilation and sympathetic vasoconstriction.

Activation of perivascular parasympathetic nerves enhances cerebral blood flow. In the present experiments, functional aspects of this flow regulating capacity were investigated. It was found that parasympathetic nerve stimulation does not facilitate the normalization of the cerebral blood flow reduced by sympathetic stimulation. In contrast, activation of sympathetic nerves may contribute to a rapid normalization of the cerebral blood flow increased by parasympathetic stimulation. The lower limit of cerebral autoregulation is shifted towards higher blood pressures in parasympathetically denervated rats. Parasympathetic nerves do not influence hypercapnic cerebral vasodilatation, but CO2 influence the effect of parasympathetic stimulation on cerebral blood flow. We conclude that activity in parasympathetic nerves does not contribute to cerebral vasomotion.