Fig. 5.

Treatment with 6β-naltrexol does not alter BK-induced functional competence of MOR or DOR in vivo. Rats received injections (intraplantar, 50 µl) of either vehicle (VEH) or 6β-naltrexol (6βNTX; 4 μg) at 85, 65, and 45 minutes before injection (intraplantar, 50 µl) of vehicle (VEH) or bradykinin (BK, 25 µg) 15 minutes later, rats received intraplantar injection with PGE₂ (0.3 µg) and either DAMGO (8 µg) or DPDPE (20 µg). Paw withdrawal latency (PWL) in response to a thermal stimulus applied to the ventral surface of the hind paw was measured in duplicate before (baseline) and at 5-minute intervals after the PGE₂/opioid injection for 20 minutes. Data are expressed as the change in PWL from baseline responses and represent the mean ± S.E.M. of 4–8 rats per group. **P < 0.01, ***P < 0.001 compared with VEH/VEH pretreatment group.