TAC1 and cyclic hematopoiesis: First, both in CH and MH patients, the trigeminovascular system plays a key role in the unilateral distribution of pain, as the activation of this system leads to the release of neuropeptides (calcitonin gene-related peptide (CGRP), nitric oxide synthase, pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38), substance P, and neurokinin A) from the sensory nerve terminals of the trigeminal nerve [12].