In traditional folk medicine, Xanthoxylum plants are referred to as 'toothache trees' because their anesthetic or counter-irritant properties render them useful in the treatment of pain. Psychophysical studies have identified hydroxy-α-sanshool as the compound most responsible for the unique tingling and buzzing sensations produced by Szechuan peppercorns or other Xanthoxylum preparations. Although it is generally agreed that sanshool elicits its effects by activating somatosensory neurons, the underlying cellular and molecular mechanisms remain a matter of debate. Here we show that hydroxy-α-sanshool excites two types of sensory neurons, including small-diameter unmyelinated cells that respond to capsaicin (but not mustard oil) as well as large-diameter myelinated neurons that express the neurotrophin receptor TrkC. We found that hydroxy-α-sanshool excites neurons through a unique mechanism involving inhibition of pH- and anesthetic-sensitive two-pore potassium channels (KCNK3, KCNK9 and KCNK18), providing a framework for understanding the unique and complex psychophysical sensations associated with the Szechuan pepper experience.
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We are grateful to S. Yost (University of California, San Francisco) and D. Kim (Rosalind Franklin University) for providing KCNK6 and KCNK16 cDNAs, respectively; H. Haeberle and E. Lumpkin (University of California, San Francisco, and Baylor College of Medicine) for TrkC-GFP mice; A. Tzingounis and A. Priel for helpful discussion; and J. Poblete for expert technical assistance. This work was supported by grants from the NIH (D.J. and R.A.N.), a Burroughs Welcome Fund Career Award in Biomedical Sciences (D.M.B.) and an NSF Graduate Research Fellowship (A.D.M.).
Supplementary Figures 1–6 and Supplementary Tables 1 and 2 (PDF 1834 kb)
Both wild type and TRPV1/TRPA1 double mutant mice display aversion to sanshool. The first segment shows a TRPV1/TRPA1 double mutant mouse drinking saccharine-containing water (vehicle). The second segment shows the same mouse drinking saccharine-containing water laced with sanshool (1 mM). Behavior did not differ from that of wild type littermates. The third segment shows the same TRPV1/TRPA1 double mutant mouse drinking saccharine-containing water laced with capsaicin (1 μM) and mustard oil (100 μM). As expected, no aversive response was observed. In contrast, the final segment shows robust aversion by a wild type littermate after briefly sampling saccharine-containing water laced with capsaicin (1 μM) and mustard oil (100 μM). Quantification of these behaviors is shown in Fig. 3d. (MOV 16637 kb)
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Bautista, D., Sigal, Y., Milstein, A. et al. Pungent agents from Szechuan peppers excite sensory neurons by inhibiting two-pore potassium channels. Nat Neurosci 11, 772–779 (2008). https://doi.org/10.1038/nn.2143
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