Neurophysiological Basis of Short-Chain Fatty Acid Action in Pain Modulation: Therapeutic Implications.

The gut microbiota influences both energy metabolism and central nervous system (CNS) functions. This influence is mediated by humoral factors, including various metabolites, neurotransmitters, cytokines, and hormones, in addition to neural pathways such as the vagus nerve. Notably, short-chain fatty acids (SCFAs)-comprising acetic, propionic, and butyric acids-merit specific attention. These compounds originate from the anaerobic fermentation of dietary fibers by the gut microbiota. Growing evidence indicates that SCFAs confer beneficial effects on diverse pain conditions. Although previous review articles have summarized animal studies suggesting the possibility that SCFAs can alleviate pathological pain, there are few reviews on the neurophysiological mechanisms by which SCFAs modulate the excitability of nociceptive neurons in the pain pathway under nociceptive and pathological conditions. Extending previous in vitro findings, our laboratory recently conducted in vivo neurophysiological studies using animal models to explore the pain-relieving properties of SCFAs. Our published results demonstrate two significant effects: (i) an intravenous anesthetic action against nociceptive pain and (ii) an anti-inflammatory contribution to chronic pain alleviation. This review synthesizes the current understanding of the mechanisms by which SCFAs modulate pain and explores their contribution to the attenuation of nociceptive and/or pathological pain. Furthermore, we discuss their prospective clinical application.