How does Dihydroergotamine (DHE) work in Migraine Treatment?

A) DHE is a 5-HT1D receptor agonist.

Mechanisms mediated by 5-HT(1B/1D) receptors (triptans) include vasoconstriction of painfully dilated cerebral blood vessels, inhibition of the release of vasoactive neuropeptides by trigeminal nerves, and inhibition of nociceptive neurotransmission.

These collective mechanisms activated  by DHE relieve Migraine Headache.