Fig. 1.

Paradigm for behavioral testing. Due to breeding difficulties and lengths of experiments, some mice were used for multiple tests. Before surgery, some mice received operant conditioning for food reward. After catheter implantation, mice were used in one of four pathways. Animals assigned to Path A administered 0.5-mg/kg infusions for 10 days followed by 1.0-mg/kg infusions for 10 days, then underwent a progressive ratio test and were sacrificed for dissection. Those in Path B received the lower dose (0.25 mg/kg/infusion) after the first 10 days. Path C animals had 10 days of saline self-administration followed by cocaine. Animals in Path D had 10 days of saline self-administration and were then sacrificed and dissected to serve as molecular biology controls for the mice from Path A.