Bulbo-cortical pathways and their possible relevance to migraine and epilepsy

Facilitation of the visual evoked response from the reticular formation in the cat has been shown to depend on nicotinic cholinergic receptors distinct from the muscarinic cholinergic receptors responsible for the arousal reaction. An increase in the amplitude of visual evoked responses in migraineurs does not therefore imply any change in reticulocortical activity of relevance to epilepsy. Stimulation of locus ceruleus and nucleus raphe dorsalis exerted comparatively minor effects on the visual evoked response and did not alter the discharge rate of cortical neurons in the resting state. It is concluded that the changes in cerebral blood flow previously reported to result from stimulation of these monoaminergic brainstem nuclei, which resemble those observed in migraine, must be exerted directly on the cortical microcirculation and not simply follow the metabolic demand of cortical neurons. There is thus a place in the management of migraine for pharmaceutical agents acting on cerebral vessels even if the neural hypothesis for the mechanism of migraine proves to be correct.