Fig. 3. Reversal of antiallodynic effects of intrathecal (i.t.) morphine by naloxone in the spared nerve injury model. Naloxone (5 mg/kg) was administered intraperitoneally 30 min after intrathecal morphine (1 μg) administration. Compared with normal saline (NS), naloxone significantly reversed the antiallodynic effects of intrathecal morphine. Behavioral tests were performed in the sural nerve–innervated hairy skin of the hind paw (*P < 0.05, **P < 0.01, ***P < 0.001 vs. normal saline).