Gut–Brain Crosstalk and the Central Mechanisms of Orofacial Pain

Accumulated evidence has demonstrated that the gut microbiome can contribute to pain modulation through the microbiome–gut–brain axis. Various relevant microbiome metabolites in the gut are involved in the regulation of pain signaling in the central nervous system. In this review, we summarize recent advances in gut–brain interactions by which the microbiome metabolites modulate pain, with a focus on orofacial pain, and we further discuss the role of gut–brain crosstalk in the central mechanisms of orofacial pain whereby the gut microbiome modulates orofacial pain via the vagus nerve-mediated direct pathway and the gut metabolites/molecules-mediated indirect pathway. The direct and indirect pathways both contribute to the central regulation of orofacial pain through different brain structures (such as the nucleus tractus solitarius and the parabrachial nucleus) and signaling transmission across the blood-brain barrier, respectively. Understanding the gut microbiome-regulated pain mechanisms in the brain could help us to develop non-opioid novel therapies for orofacial pain.