Figure 6.

Effects of chronic treatment of baclofen on the development of morphine sensitization. Four groups of rats were exposed to morphine and one group of rats was given saline for 4 consecutive days. For morphine group, saline or baclofen (1.25, 2.5, 5 mg/kg, s.c.) was concomitantly administered 15 min prior to the morphine injection. During a 3-day withdrawal period, rats in morphine group were still injected with saline or baclofen (1.25, 2.5, 5 mg/kg, s.c.) daily (b). On day 8, all five groups of animals were subjected to an acute challenge of morphine (3 mg/kg, s.c.). The locomotor activity was monitored for 3 h in the chambers. Each bar represents the total distance traveled for the 3 h test period. a: the saline/morphine group and morphine/saline group. Data are shown as means ± S.E.M (n = 8 per group). ^## P < 0.01 compared to saline/morphine group; ^* P < 0.05 and ^** P < 0.01 compared to morphine/saline group.