Figure 2.

Aging does not account for the decreased behavioral effects seen after repeated exposures to amphetamine. A, the percentage of animals exhibiting SWIP over a 10-minute treatment with control (open squares) or AMPH (open circles) is reported during the fourth exposure. Animals that received three consecutive exposures in control solution followed by one AMPH exposure (filled circles) exhibit higher levels of SWIP with respect to animals that were exposed four times to AMPH (*p < 0.001, 2-way ANOVA test). N represent the number of animals tested per group. B, the percentage of animals exhibiting SWIP after 10-minute treatment with AMPH during the 1^st, 2^nd, 3^rd and 4^th exposures are presented as bar graph. Values collected after the third and fourth exposure with AMPH were statistically different than values collected during the first and second exposure. Animals that were treated three times in control solution and one time with AMPH (gray bar) exhibited statistically higher levels of SWIP then animals treated four times with AMPH (∞p < 0.05, 1-way ANOVA test). But no difference was measured between animals treated one time with AMPH and those treated three times with control and one-time AMPH (compare white and gray bars). The number of animals tested per each group are as in B.