Fig 2.
Dorsal column conditioning stimulation (CS) of 1 Hz and 50 Hz frequencies changed Aα/β-fiber conduction property in nerve-injured rats. (A) Left: schematic diagram illustrating the experimental setup for recording antidromic sciatic compound action potentials (APs) evoked by graded test electrical stimulation (0.1–2.2 mA, 0.2 ms) applied at the L4 dorsal root in rats that received an L5 spinal nerve ligation (SNL). The CS (5 min, 50 and 1 kHz, 0.024 ms, biphasic pulse) was delivered to the ipsilateral dorsal column at T13–L1 level. Right: examples of different compound AP waveforms corresponding to Aα/β- and Aδ-fiber activation to increasing intensities of dorsal column CS and dorsal root test stimulation. The intensity for CS was calibrated by recording sciatic compound AP to graded dorsal column stimulation (0.01–2.0 mA, 0.024 ms, biphasic pulse): The intensity that resulted in the first detectable Aα/β waveform (Ab0), followed by the peak Aα/β waveform (Ab1, the highest Aα/β waveform intensity without inducing an Aδ waveform), to dorsal column stimulation was determined. (B) Examples of sciatic compound APs evoked by 0.2 and 0.4 mA dorsal root test stimulation before and after dorsal column CS (1 kHz, Ab1, 5 min) were shown. (C) In the off-line analysis, the areas under the Aα/β waveforms generated by graded dorsal root stimulation were measured to establish the stimulus–response (S–R) functions. The S–R functions were not changed after 50 Hz CS of Ab0 intensity, but were significantly depressed at 0–5 min after 50 Hz CS at Ab1 intensity. (D) The size of Aα/β waveform to the lower intensities of dorsal root stimulation (0.2–0.6 mA) was significantly decreased from the prestimulation baseline at 0–5 min after 1 kHz dorsal column CS of Ab0 intensity. The S–R function was significantly depressed by 1 kHz CS of Ab1 intensity. Data are expressed as mean, and error bars are not shown to improve clarity. *P < 0.05, **P < 0.01, ***P < 0.001 versus pre-CS baseline.