Fig. 3. The effect of chronic gabapentin treatment on electrical-evoked and natural-evoked responses of wide-dynamic-range (WDR) superficial dorsal horn (SDH) neurones in MRMT-1 injected rats. SDH WDR neurones in MRMT-1 injected rats (n = 13 cells) show significantly (  P < 0.05) increased electrical-evoked responses (input, A-beta fiber, C-fiber, postdischarge) and natural-evoked responses (nonnoxious brush) compared with sham-operated rats (n = 9 cells).  14 Electrophysiological characterization of WDR SDH neurones in MRMT-1 injected rats having had chronic gabapentin treatment (twice-daily subcutaneous injections of gabapentin 30 mg/kg on postoperative days 11–14 with a single injection on day 15) on the final day of treatment (n = 10 cells) showed a significant reduction (  P < 0.05) in electrical-evoked (input, C-fiber) and brush-evoked responses compared with MRMT-1 injected rats receiving no drug treatment. The A-beta and postdischarge evoked responses to electrical stimuli were reduced such that there was no longer a significant difference to the degree of response of neurones in sham-operated rats. Characterization of WDR SDH neurones in MRMT-1 injected rats 2 days after cessation of gabapentin treatment (postoperative day 18, n = 16 cells) revealed that the electrical-evoked and natural-evoked responses had returned to the same degree as in MRMT-1 injected rats receiving no drug treatment. The input and C-fiber evoked responses were significantly increased (  P < 0.05) compared with the responses at day 15 (final day of gabapentin treatment).