Differential effects on the internal and external carotid circulation of the monkey evoked by locus coeruleus...

Electrical stimulation at 1-200/s of the locus coeruleus in 12 Macaca nemestrina monkeys caused a frequency-dependent drop in vascular resistance in the extracerebral circulation which was twice as great on the side stimulated. Accompanying this dilatation of the extracerebral vasculature was a frequency-dependent rise in internal carotid vascular resistance, usually seen only on the side ipsilateral to stimulation. This constrictor response was maximal at low frequencies of stimulation and minimal at higher frequencies. Neither the dilator nor constrictor responses were affected by sectioning of the vagus nerve or sympathetic trunk in the neck. The simultaneous occurrence of intracranial vasoconstriction and extracranial vasodilatation has not been demonstrated previously, and bears a remarkable resemblance to the vascular changes of migraine.