Figure 7. Inflammation-induced plasticity in mechanical sensitivity revealed by GCaMP3 in vivo.
(A–C) Diverse changes in sensitivity to mechanical stimuli (indicated by black bar under GCaMP3 trace) were revealed when comparing GCaMP3 responses before (Ai–Ci, gray trace in each panel) and 30 min after (Aii–Cii, colored trace in each panel) 'inflammatory soup' (IS). These changes are summarized for increased and decreased responses and silent afferents in the graph on the right of each panel. Scale bar, 20 μm; 1 s, 10 ΔF/F0. Data are represented as mean ± SEM. *p<0.05, **p<0.01, ***p<0.001. (A) Example of an afferent with increased sensitivity to mechanical stimuli after IS (Ai–Aii; white arrowheads). Black asterisk indicates afferent with increased mechanical sensitivity post-IS within the same visual field. Average post-IS responses were significantly increased only at 500 mN (highest force tested). (B) Example of an afferent with decreased sensitivity to mechanical stimuli after IS (Bi–Bii; white arrowheads). Average post-IS responses were significantly decreased at 500 mN. (C) Cells that exhibited GCaMP3 signal in response to mechanical stimuli after IS were categorized as 'silent' afferents (Ci–Cii; example cell indicated by white arrowheads). (D) Summarized results of the proportions of each type of IS-induced change in sensitivity due to vehicle (left; n=6 mice; n=83 cells) and IS (right; n=5 mice; n=47 cells). Compared to changes seen after vehicle, there were significantly more cells that displayed increased and decreased sensitivity to mechanical stimuli. Further, IS caused entirely new sensitivity in a subset of afferents ('silent' afferents), which was never observed in vehicle-injected controls. NC, no change; D, decreased; I, increased; SA, silent afferent.