Fig. 2. Withdrawal threshold to von Frey filament application to animals before spinal nerve ligation (time before 0) and after injection, at time 0 of intrathecal DPCPX, 10 μg alone or in doses of 3–10 μg with 2.5 μg ( left ) or 5 μg ( right ) morphine. DPCPX alone did not affect withdrawal threshold, morphine significantly increased withdrawal threshold, and DPCPX reduced the effect of morphine. Each symbol represents the mean ± SE of six to eight rats.