Figure 2.

Repeated cocaine injections produce behavioral sensitization in a subset of rats. A, B, Locomotor activity data for all animals receiving repeated cocaine and saline injections; sum of two independent trials for both A and B (4 trials total). After behavioral testing was completed, rats from trials shown in A were killed for biochemical analysis 1 d after the last cocaine injection. Rats from trials shown in B were used for biochemical analysis 21 d after the last cocaine injection. C, Cocaine-treated rats from A were divided into sensitized and nonsensitized subgroups (see Materials and Methods for criteria), and locomotor activity data were reanalyzed. D, Cocaine-treated rats from B were divided into sensitized and nonsensitized subgroups, and locomotor activity data were reanalyzed. All data are expressed as mean ± SEM total beam breaks. ^**p < 0.01; ^*p < 0.05 for comparison between beam breaks on day 1 versus day 7.