Fig. 6.
Local sympathectomy accelerates the resolution of paclitaxel-induced mechanical allodynia through anti-inflammatory transforming growth factor-β (TGF-β) signaling. (A) Schematic illustration of the experiment showing the timeline of the injections of paclitaxel (PAX), intrathecal injections of recombinant TGF-β protein or TGF-β + TGF-β receptor 1 inhibitor (TGF-βR1 inh.), and the behavioral assay that was carried out at 7 days after paclitaxel. (B) Reversal of paclitaxel-induced mechanical allodynia tested in ipsilateral hind paws in male mice after 3 h of treatment with different doses of recombinant TGF-β (n = 5 mice per group, one-way ANOVA showed significant difference between TGF-β and vehicle groups, Group: F4,20 = 14.02, P < 0.001; Tukey post hoc analysis revealed a significant difference at concentrations of 10 ng and 100 ng; *P < 0.05, *P < 0.001). (C) Time course of paclitaxel-induced mechanical allodynia showed that the antiallodynic effect of TGF-β was abolished by the intrathecal co-injection of the TGF-βR1 inhibitor (n = 5 male mice per group, two-way ANOVA showed significant difference between TGF-β and vehicle groups, Group × Time interaction: F8,48 = 5.63, P < 0.001; Bonferroni post hoc analysis revealed a significant difference between groups at 1 and 3 h; *P < 0.001). (D) Schematic illustration of the experiment showing the timeline of local microsympathectomy (mSYMPX), injections of paclitaxel (PAX), injections of TGF-βR1 inh., and the behavioral assay that was carried out at 7 days after paclitaxel. (E) TGF-βR1 inhibitor also reverses the antiallodynic effect of mSYMPX on paclitaxel-induced mechanical allodynia in mice (n = 5 male mice per group, two-way ANOVA showed significant difference between mSYMPX-SB431542 and vehicle groups, Group × Time interaction: F4,32 = 3.25, P = 0.024; Bonferroni post hoc analysis revealed a significant difference between groups at 1 h; *P < 0.05). (F) Sample traces of action potential firing in response to suprathreshold currents in small cells isolated after chemotherapy and mSYMPX, with TGFβ1R inhibitor (orange) or vehicle (green) present during the recording session. Shown is response to stimulus of 2.4 nA, which evoked maximum number of action potentials in the TGFβ1R inhibitor cell, and response to stimulus of 3.4 nA in the vehicle treated cell, where it was not possible to evoke more than one action potential. Scale bars = 25 msec, 50 mV. (G and H) Quantification of the TGF-βR1 inhibitor effect on the maximum number of action potentials evoked by suprathreshold currents in small-size dorsal root ganglia neurons (G) and large-size dorsal root ganglia neurons (H) isolated from mSYMPX mice treated with paclitaxel (n = 28–29 small neurons per group, or 41–43 large neurons per group; Mann–Whitney test, *P < 0.05 compared with vehicle). Additional electrophysiologic details can be found in Supplemental Digital Content, table 2 (https://links.lww.com/ALN/C297).