Fig. 4.
Male Sprague Dawley rats received intrathecal infusions of saline or of DAMGO (1 nmol · μl−1 · hr−1) for 7 d. Antinociceptive tolerance after chronic infusion of DAMGO was accompanied by tactile allodynia, indicated by a significant (*p ≤ 0.05; Student's t test;n = 10) decrease in paw withdrawal thresholds to probing with von Frey filaments on the sixth day of infusion. The acute intrathecal injection of 200 μg of antiserum to dynorphin A(1–17) on day 7 blocked tactile allodynia when given 20 min before testing in DAMGO-tolerant rats (n = 10). DYN A/S, Dynorphin antiserum.