Influence of the cerebrovascular sympathetic innervation on regional flow, autoregulation, and blood-brain barrier function.

Experiments have been done on rats, rabbits and baboons to elucidate the role of the cranial sympathetic nerves originating in the superior cervical ganglia in the regulation of local cerebral blood flow, including its autoregulation, and in blood-brain barrier functions. Flow was measured by the [14C] ethanol technique, thermoclearance, and xenon-133 clearance. Blood-brain barrier functions were studied by the extravasation of an Evan's blue-albumin complex and by calculation of brain uptake index for two compounds (noradrenaline and inulin). Electrical stimulation of the sympathetic nerves reduces regional flow to a degree that is related to the amount of local perivascular innervation. The breakthrough of autoregulation during induced systemic hypertension is prevented by bilateral stimulation of the superior cervical ganglia. Acute sympathectomy markedly enhances the vascular penetration both at normotension (tested by brain uptake index for noradrenaline and inulin) and rapidly induced hypertension (evidenced by extravasation of Evans' blue). This extravasation of Evans' blud during acute hypertension can be counteracted by sympathetic nerve stimulation. The results give further support for the view that the cranial sympathetic nerves afford an efficient control of the cerebrovascular bed.