ABSTRACT
Figure 1 The upper panel shows instantaneous discharge frequency of a mechanoand heat-insensitive C-fiber (CMiHi) in the superficial peroneal nerve following histamine iontophoresis (marked as open circles in the diagram). The unit was not spontaneously active before histamine application, but continued to fire for about 15 min further (not shown in the diagram).The lower panel shows average itch magnitude ratings of a group of 21 healthy volunteers after an identical histamine stimulus. Ratings at lOs intervals on a visual analog scale (VAS) with the end points "no itch" and "unbearable itch." Bars: standard error of means. (From Ref. 4.)
Figure 2 Relative proportion of mechano-responsive and mechano-insensitive unmyelinated nociceptors in human skin nerves. About 20% of the nociceptors are mechano-insensitive. "Itch" units are found only among these mechano-insensitive fibers and comprise about 5% of all nociceptors.
