VIP and cyclic hematopoiesis: Moreover there is a clear increase of both trigeminal (CGRP) and parasympathetic (VIP) neuropeptides during CH attacks which is normalized when the pain was controlled in CH [19, 20], and it appears that activation of the VPAC1 and PAC1 receptors influences the TAR, the parasympathetic cranial outflow [17, 21].