Considering the essential role of CGRP in the pathophysiology of migraine (a common CPP) [56] and the correlation of its expression with HFS-induced chronic pain [6], we also quantitatively examined the expression of CGRP in the LF-PENS model and the possible mechanism of 2R, 6R-HNK’s effect. The gene discussed is CALCA; the disease is migraine disorder.