HDAC9 and Parkinson disease: Given that sodium butyrate, an HDAC inhibitor diminishes CCI-induced TNF-α release and pain (167), it can be surmised that PD-induced gut SCFAs can raise circulating cytokine levels (i.e., TNF-α) and promote sensory hypersensitivities by increasing the immunomodulatory action of HDAC in leukocytes Finally, SCFA were found to sensitize GPR41-expressing lumbar and vagal neurons (Figure 3B) (168).