Do cholinergic neurons directly innervate nasal blood vessels?

The main aim of this work was to provide additional evidence that cholinergic neurons can induce nasal vasodilation by inhibiting norepinephrine release, not by a direct action on nasal blood vessels. We induced a degeneration of the nasal sympathetic neurons in order to observe the effects of electrical stimulation of the cholinergic neurons on nasal blood vessels. Electrical stimulation had no measurable effect. One interpretation of this result is that cholinergic fibers control vasomotor tone by inhibiting the output of the sympathetic neurons, i.e., they have a presynaptic influence. However, it should be stressed that the data were obtained from in vitro experiments, which may not reflect the true in vivo processes. Additional evidence was obtained to demonstrate that electrical stimulation of the in vitro nasal tissue causes contraction by the release of norepinephrine from remnants of sympathetic nerve fibers remaining in the tissue. Also, there is no evidence of transganglionic degeneration in the cervical sympathetic nerve.