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Anesthetics used for local and regional anesthesia block pain signals from pain-sensing (nociceptive) neurons. However, they also affect the function of other sensory neurons and (in the case of regional anesthesia) of autonomic neurons and motor neurons as well. They do so because current anesthetics easily diffuse through the lipid membranes of all types of neurons.
Recently, nociceptive neurons have been found to have unique ion channels, called TRPV1 channels, that open in response to a few stimuli, including the irritating molecule capsaicin (the substance that makes chili peppers “hot”). A team from Harvard Medical School combined a lidocaine derivative called QX-314, which cannot pass through lipid membranes on its own, with capsaicin…