Autonomic nervous system control of the cerebral circulation.

The classic view of cerebrovascular physiology has been that blood flow and cerebral metabolism are tightly coupled under the influence of substances, such as H(+), adenosine, nitric oxide, and K(+), which ensure a rapid and matched supply of blood. In part driven by the use of cerebral blood flow measurements in functional brain imaging, it has become clear that astrocytes also play a role in modulating functionally associated changes in cerebral blood flow. The concept of neural control or neurogenically mediated changes in cerebral blood flow is relatively newer, although the presence of such nerves was probably identified anatomically more than 500 years ago. The autonomic innervation of the cranial circulation has both a sympathetic component that arises predominantly from the superior cervical ganglion and a cranial parasympathetic component that traverses the pterygopalatine (sphenopalatine) and otic ganglion. Neuropeptide transmitters such as neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), and pituitary adenylate cyclase-activating peptide (PACAP), helodermin, and helospectin have each been identified in components of the system. Clinical problems such as migraine, cluster headache, and stroke likely involve the autonomic innervation of the cerebral circulation in terms of disorder expression and ultimately with an eye to novel therapies.