Response to an itch-producing substance in cat. I. Cutaneous receptor populations with myelinated axons.

The purpose of this study was to determine which myelinated cutaneous receptor populations in cat are responsive to a stimulus (cowhage) that produces unambiguous pruritus in human subjects. Initial experiments using electrocutaneous stimuli demonstrated that fibers conducting as slowly as 1.5 m/s could be recorded from small fascicles of cutaneous nerves. Multiunit recordings from fascicles and nerve filaments revealed small, but significant changes in nerve firing following application of cowhage. A sample of all known myelinated receptor populations showed that each gave a response that was less than its response to adequate intensities of mechanical stimulation (n = 118). It was concluded that the slight changes in multunit discharge induced by cowhage could be accounted for by changes in mechanoreceptor behavior and hence there was no evidence to support the possibility that an unknown population of myelinated sensory fibers exists that signals pruritus. The possibility that itch is signaled by coactivation of myelinated mechanoreceptive and C-polymodal nociceptive neurons was discussed.