Fig. 2.

The mean (± S.E.M.) number of 90° movements per 5 min interval in control animals (○, open circles; N = 42) and animals tested after 3 days (□, open squares; N = 20), 7 days (△, open triangles; N = 18), or 28 days (◆, closed diamonds; N = 20) of withdrawal from escalating-dose amphetamine treatment. The first eight intervals represent basal activity. The animals received an injection of saline at the time indicated by the first arrow and then were left undisturbed for 12 intervals (1 h), at which time they received an injection of 0.5 mg/kg of amphetamine (second arrow). There were significant group differences in the response to amphetamine (two-way ANOVA with repeated measures on one factor, effect of treatment group, F = 5.47, P < 0.002; effect of time, F = 74.8, P < 0.0001; group by time interaction, F = 2.11, P < 0,0001). Subsequent factorial one-way ANOVAs (followed by Fisher’s PLSD tests if significant) at each point in time after amphetamine administration revealed that the group tested after 28 days of withdrawal differed from the other three groups at the times indicated by asterisks. The control, 3 day, and 7 day withdrawal groups did not differ from one another at any point in time. * 28 days differs from control, 3 day, and 7 day groups, P < 0.05, † 28 days differs from control and 3 day groups.