Itching is not the only sensation to arise from unique neurons. A team at the California Institute of Technology has identified neurons that transmit the pleasurable sensations of massage, at least in mice. The cells responded to gentle rubbing but not to pinching or poking. Activation of the cells requires “a pressure component,” says lead investigator David Anderson, a neuroscientist at Caltech, “much like you would apply if you were stroking your cat.”
The team first identified the mysterious cells several years ago by an unusual protein on their surface called MrgprB4—closely related to the receptor expressed by the newly identified itch cells. The rare sensory cells make up only about 2 percent of the body's peripheral neurons that respond to external stimuli, but they seem to cover about half the skin's surface with large, branching nerve endings. Whereas sensory neurons that transmit pain have been intensely studied, this is the first demonstration in live animals of a sensory cell that gives pleasure. After the scientists activated those neurons with a designer drug, the mice came to favor the place where they received the drug, according to the paper published January 31 in Nature.