Stimulation of an intracranial trigeminally-innervated structure selectively increases cerebral blood flow

The cranial circulation, both extracerebral and cerebral, is innervated by fibers from the trigeminal nerve. This system is known as the trigeminovascular system. The large venous sinuses and dura mater are pain-sensitive and are innervated primarily by branches of the ophthalmic division of the trigeminal nerve. Studies were conducted in the alpha-chloralose anaesthetised cat to examine bulk carotid and cerebral blood flow responses to electrical stimulation of the trigeminal ganglion and superior sagittal sinus. Bulk carotid blood flow was measured using an ultrasonic flow probe and meter applied to the common carotid artery while cerebral blood flow was measured using laser Doppler flowmetry. Vascular resistance was calculated using simultaneously collected blood pressure data. Stimulation of the trigeminal ganglion resulted in a frequency-dependent reduction in both bulk carotid and cerebral vascular resistance. The mean maximal reduction was 39 +/- 5% at 20/s for the carotid bed and 37 +/- 6% at 20/s for the cerebral circulation. Stimulation of the superior sagittal sinus resulted in a frequency-dependent reduction in resistance that involved the cerebral circulation with little effect on bulk carotid resistance. The mean maximum reduction was 37 +/- 6% at 20/s for the cerebral circulation and 11 +/- 3% at 2/s for bulk carotid resistance. The more focused effects of superior sagittal sinus suggest a highly organised somatotopic arrangement of the trigeminal innervation of the cranial circulation. Such a physiological schema fits the known anatomy as reflected by the differential peptidergic innervation from the trigeminovascular system to cranial vessels and may be important in understanding the pathophysiology of migraine, cluster headache and subarachnoid haemorrhage.