Fig. 8.

Sig-1R agonist increases neuronal excitability in sham surgery rats’ sensory neurons by inhibiting calcium influx at dorsal root ganglia. (A) (+)Pentazocine ((+)PTZ) elicits neuronal hyperexcitability in skin sham dorsal root ganglion (DRG) neurons. (Aa) (+)PTZ increases action potential (AP) generation during depolarizing stimulus trains (50 Hz for 2 s with 1 ms duration and 1.5 × threshold stimulus). Sample traces from whole-cell patch clamp show 21 APs before (+)PTZ application and 30 after. (Ab) Summary data show that (+)PTZ increases AP generation in naïve sensory neurons. (Ac) Summary data show that (+)PTZ does not affect the after hyperpolarization (AHP) amplitude. (Ad) Summary on the effect of (+)PTZ on the 50% duration of AHP. (Ae) Sample AP traces of vehicle- and (+)PTZ-treated DRG neurons were from intracellular recordings. The trace shows that (+)PTZ decreases 50% recovery of AHP duration when compared to vehicle control. AHP and duration of AHP until 50% recovery to baseline (red segment) were measured from intracellular recordings using intact DRGs and dorsal root stimulation. (B) (+)-Pentazocine inhibits K⁺-induced Ca²⁺ transient in dissociated skin-sham DRG neurons. By adding (+)PTZ (1–100 μM) to the bath solution (2 mM Ca²⁺), (+)PTZ time-dependently depresses activity-induced transient amplitude (traces). When compared with vehicle-treated cells, summary data (right panel) show that (+)PTZ dose-dependently diminishes (i.e., increased inhibition on Y-axis) K⁺-induced (50 mM for 3 s) Ca²⁺ transient amplitudes in skin sham DRG neurons. (C) (+)PTZ (100 μM) did not affect K⁺-induced transient Ca²⁺ amplitudes in injured neurons isolated from the spinal ligated 5th (SNL L5) DRG. In contrast, (+)PTZ administration inhibited K⁺-induced Ca²⁺ transient amplitudes in non-injured neighboring neurons from the 4th SNL L4 DRG. Note: K+-induced Ca²⁺ transient decreases in a time-dependent manner (left lower traces) in (+)PTZ-treated SNI L4 DRG neurons. Details of experimental procedures are described in the “Methods”. Data are means ± SEM; two-way ANOVA followed by Tukey’s test, Student’s t test or paired t test, *P < 0.05, **P < 0.01, ***P < 0.001