Figure 1.

Effect of acute morphine challenge dose (10 mg kg⁻¹ s.c.) on the locomotor activity of mice withdrawn for 3 days from 5 day repeated morphine treatment and pretreated with idazoxan (1 mg kg⁻¹ i.p., 30 min before morphine challenge). Each point gives the mean±s.e.mean cumulative locomotor activity counts of groups of three mice and represent the following treatments: (A) repeated saline+acute saline+acute saline (n=10 groups of three mice); (B) repeated saline+acute saline+acute morphine (n=10); (C) repeated saline+acute idazoxan+acute saline (n=5); (D) repeated saline+acute idazoxan+acute morphine (n=5); (E) repeated morphine+acute saline+acute saline (n=10); (F) repeated morphine+ acute saline+acute morphine (n=10); (G) repeated morphine+acute idazoxan+acute saline (n=5); (H) repeated morphine+acute idazoxan+acute morphine (n=5). Statistical significances: effect of acute morphine treatment: ^**P<0.01, ^***P<0.001 as compared with corresponding group given acute saline (B vs A, F vs E, H vs G); effect of idazoxan pretreatment: ⁺P<0.05 as compared with corresponding group given acute saline (H vs F); effect of repeated morphine treatment: °P<0.05 as compared with corresponding repeated saline group (H vs D) (repeated measures ANOVA).