Fig. 1.

Lidocaine (4% w/v) or saline was microinjected bilaterally into the RVM of sham-operated male Sprague Dawley rats and of rats with L₅/L₆ SNL 3 and 6 d after nerve injury. Baseline responses to tactile and thermal stimuli were determined in sham-operated and SNL rats before injections (BL). Tactile hypersensitivity (A, C) and thermal hyperalgesia (B, D), indicated by significant decreases in the response thresholds, were measured at 10 min intervals for 60 min after each lidocaine or saline microinjection. Lidocaine did not reverse tactile hypersensitivity and thermal hyperalgesia on post-SNL day 3 (A, B) but was effective on day 6 (C, D). Behavioral responses were not altered by lidocaine in sham-operated rats or by saline in either group. *p ≤ 0.05 compared with pre-SNL values.