Figure 6

Activation of C-fibres by IBA. Raster plot of latencies and identification of single action potentials. A: Raster plot of latencies in the C-fiber range corresponding to several C fibers during baseline stimulation (0.25 Hz), pause (0 Hz, open bar) and tetanus (2 Hz, filled bar). Different fibers with particular activity-dependent profiles can be observed. B: Modified raster plot from A with extraction of 3 units of interest at latencies of 175, 215 and 220 ms during the period just before the 2 Hz stimulation (a, in red, CV = 0.45; b, in blue, CV = 0.32 m/s; c, in grey, CV = 0.31 m/s; CV: conduction velocity), for a better visualization. These three units displayed appreciable slowing (>2%) following the pause (open bar), and slowed more than 50% during the 2 Hz tetanus (units b and c slow beyond the 300 ms latency limit of the recorded signal), indicating they were Type 1B mechano-insensitive C-nociceptors [40]. Injection of IBA (1%, 2 μl) s.c. induced persistent ongoing discharges in all three mechano-insensitive C-nociceptors, giving rise to jittery baselines with a "saw-tooth" profile, lasting many minutes (>30 min for unit a). Onset of action was different for the three units (marked with a colored asterisk).