HCRT and Cluster headache: The role of orexins in noradrenergic activation, shown by innervation and stimulation of the locus coeruleus in rats, monkeys and cats (Hagan et al., 1999; Horvath et al., 1999; Diano et al., 2003), may implicate changes in blood flow in cluster headache, although this evidence is not conclusive (Cohen and Goadsby, 2004).