Fig. 3. Effect of gabapentin on delayed hyperalgesia induced by subcutaneous administered fentanyl in uninjured rats when administered either before or after fentanyl injections. Four fentanyl (60 μg/kg) injections were performed every 15 min on the day of the test (D0). Intraperitoneal gabapentin (150 mg/kg) was administered either 30 min before the first subcutaneous fentanyl injection (n = 7) or 300 min after the last subcutaneous fentanyl injection (n = 7). The basal nociceptive threshold was evaluated after treatment for 5 h on D0and then daily for 5 days (D+1–D+5). Mean nociceptive thresholds (±SD) are expressed in grams. * P < 0.05 with the Newman-Keuls test when compared with the basal nociceptive threshold value. IP = intraperitoneal; SC = subcutaneous.