Suppression of cortical spreading depression in migraine prophylaxis.

Topiramate, valproate, propranolol, amitriptyline, and methysergide have been widely prescribed for migraine prophylaxis, but their mechanism or site of action is uncertain. Cortical spreading depression (CSD) has been implicated in migraine and as a headache trigger and can be evoked in experimental animals by electrical or chemical stimulation. We hypothesized that migraine prophylactic agents suppress CSD as a common mechanism of action. Rats were treated either acutely or chronically over weeks and months, with one of the above migraine prophylactic drugs, vehicle, or D-propranolol, a clinically ineffective drug. The impact of treatment was determined on the frequency of evoked CSDs after topical potassium application or on the incremental cathodal stimulation threshold to evoke CSD. Chronic daily administration of migraine prophylactic drugs dose-dependently suppressed CSD frequency by 40 to 80% and increased the cathodal stimulation threshold, whereas acute treatment was ineffective. Longer treatment durations produced stronger CSD suppression. Chronic D-propranolol treatment did not differ from saline control. Our data suggest that CSD provides a common therapeutic target for widely prescribed migraine prophylactic drugs. Assessing CSD threshold may prove useful for developing new prophylactic drugs and improving upon existing ones.