Response to "do vasomotor nerves significantly regulate cerebral blood flow?".

There is no doubt that pial vessels have dense adrenergic and cholinergic innervation. Intracerebral vessels, however, have not been demonstrated to have cholinergic innervation and, although intracerebral vessels receive adrenergic innervation, the extent of innervation (i.e., the number of classical nerve terminals to cerebral vessels) is unclear. MJP indicates that adrenergic innervation of cerebral vessels is not homogeneous, with denser innervation of the carotid arterial system than of the vertebrobasilar vessels. Similarly, it is possible that there are variations in characteristics of adrenergic receptors in cerebral vessels. The extremely unusual features of adrenergic transmission in cerebral vessels (including dilator responses to field stimulation in vitro and constrictor responses that are not blocked by a-adrenergic blocking drugs) have been described primarily in the basilar artery. This pattern of regional differences in innervation and receptors suggests that sympathetic activation could reduce blood flow in the carotid but not vertebrobasilar distribution. Recent studies which indicate that intense physiological stimulation of sympathetic pathways during hypertension in cats produces constriction of vessels in the cerebrum, but not the brainstem or cerebellum, may provide support for this concept.