Figure 1: Time-course of morphine-induced tolerance. Morphine was infused (2.5 mg/kg/d, i.p.) through an osmotic mini-pump during 16 days in rats submitted to SNL. A) Latency in response to thermal stimulation in rats submitted to SNL. B) Withdrawal threshold in response to mechanical stimulation applied to the paw of rats submitted to SNL(⌈). saline infusion or(∇) morphine infusion. Data represent the mean ± SEM (n=4). *P<0.05 versus day 0. #P<0.05 versus day 7.