Locomotor activity testing

Drug-induced hyperlocomotion was measured using Med Associates activity chambers as previously described [19]. For the majority of experiments, activity testing was performed with prior habituation wherein, on day 1, mice were placed in the chamber for 30 min to acclimate to the testing environment. Two days later, mice were again habituated for 30 min, injected with sterile saline (0.9% NaCl) or 0.01% dimethyl sulfoxide (DMSO) in saline (fluoxetine only) and activity was recorded for 60 or 120 (RTI-113 only) min post-injection. On the final day of testing, mice received drug injections following an initial 30 min habitation and activity was again monitored for 60 or 120 (RTI-113 only) min post-injection. Habituation was omitted for all testing with DAT Val559/SERT Met172 hybrid mice and their littermate controls, as well as for experiments with SDZ SER-082, a 5-HT_2C receptor (5-HT_2CR) antagonist. For studies with SDZ SER-082, the drug or saline was administered 30 min prior to cocaine injection and locomotor testing. The following drugs were obtained from the vendors noted, dissolved in sterile saline and administered as noted via intraperitoneal injection (i.p.): cocaine HCl, Sigma, St. Louis, MO (10, 30 mg/kg); methylphenidate HCl, Sigma (10 mg/kg); RTI-113 (2β-carbophenoxy-3β-(4-chlorophenyl)tropane), Research Triangle Institute, Research Triangle Park, NC (2 mg/kg); SDZ SER-082 fumarate, Tocris, Minneapolis, MN (0.5 mg/kg). Fluoxetine HCl was purchased from Sigma and dissolved in saline with 0.01% DMSO at 20 mg/kg.