Fig. 1

Schematic overview of the microneurography setup and single-fiber responses. A A tungsten recording needle (white flag) was inserted into C-fiber fascicles of the superficial peroneal nerve and a reference electrode (blue flag) needle into the skin nearby. A pair of needles was inserted into the previously located innervation territory (gray circle) for intracutaneous stimulation of the recorded C-fibers at a low repetition rate (0.25 Hz). Intracutaneous microinjections of pruritogens were applied in the receptive field of the recorded fibers (gray circle). B The latencies of electrically induced action potentials (0.25 Hz) for one CM (triangles) and one CMi (diamonds) fiber are depicted. The CM-fiber shows activation (dotted black arrow) by mechanical (first gray bar) and chemical stimulation in the form of a sudden increase in latency of the electrically induced action potentials, whereas the CMi-fiber does not respond to the mechanical stimuli. Note the regular activation periods in the CM-fiber due to chemical activation with long intervening breaks indicating a “slow bursting pattern”. Only activation periods that occurred in the time frame after the syringe was removed (gray bar) were also counted as such. The cumulative latency shift was assessed as the sum of all individual activation periods of one C-fiber