TLR4 and irritable bowel syndrome: Modulation of the Kynurenine (l-kyn) pathway (KP) may provide common triggers for migraine and FGIDs involving of TLR, aryl hydrocarbon receptor (AhR), and MyD88 activation; Meanwhile, TLR4 signaling was observed to initiate and maintain migraine-like behavior through mouse MyD88, and KP metabolites detected downstream of TLR activation may be a marker of IBS.