Figure 1.

Unmyelinated (C) nociceptors terminate in outer SG. Examples from two C-polymodal nociceptors are shown in A–D and E. Note the well circumscribed arborizations in lamina IIo, evident at low- (D, arrow) and high- (E) power photomicrographs; in this and all subsequent figures, dotted lines indicate the ventral border of the SG, and midline is to the right. Stereotypical physiological properties are exemplified in A–C; cells exhibited broad somal spikes with long AHPs (A), relatively low mechanical thresholds (B), sensitivity to cooling (C), and robust activation by heat (data not shown). Bars under mechanically evoked responses (B) signify 0.35 mN (i), 1.3 mN (ii), and stimulation with a fine paintbrush (iii). Note that although these afferents habituated rapidly to repeated cooling, rebound responses after termination of cooling did not. Postnatal ages, CVs, and mechanical thresholds of afferents in A–D and E were 40 d, 0.7 m/s, and 0.76 mN and 32 d, 0.8 m/s, and 0.35 mN, respectively. Physiology calibration: A, 20 mV; B, C, 80 mV; A, 10 ms; B, 2 s; C, 20 s. Scale bars: D, 50 μm; E, 10 μm.