Figure 1: Ascending and descending pathways of the endogenous pain modulation system mediating visceral pain sensation in the brain-gut axis. Picture quoted from Zhang et al., Anesthesiology (2014) [11] and Moloney et al., Front Psychiatry (2015) [17]. RVM: rostral ventromedial medulla; MD: mediodorsal thalamic nucleus; PFC: prefrontal cortex; ACC: anterior cingulate cortex; DR: dorsal raphe nucleus; DMH: dorsomedial hypothalamic nucleus; AVP: arginine vasopressin; CNF: corticotropin releasing factor; GFAP: glial fibrillary acidic protein; WDR: wide dynamic range neurons; BK: bradykinin; PG: prostaglandins; β-EP: β-endorphin; (−): inhibition of cell discharge; NTS: nucleus of the solitary tract; TNF-α: tumor necrosis factor-α; NK1R: neuropeptide K 1R; SP: substance P; ENK: enkephalin.