Figure 1.

Alcohol consumption enhances methamphetamine (MA) self‐administration on a fixed ratio 1 (FR1) schedule of reinforcement. (a) Timeline illustrating the schedule of combining the 24‐hour two‐bottle choice procedure, daily 2‐hour self‐administration sessions and extinction sessions. (b) Average number of MA infusions (± SEM; 0.1 mg/kg/100 µl infusion) for each session of self‐administration under a FR1 and fixed ratio 5 (FR5) schedule of reinforcement. Alcohol consuming animals (n = 31) had significantly greater number of infusions during a FR1 schedule of reinforcement compared with water consuming animals (n = 16). However, this effect was not evident when MA self‐administration was conducted with an FR5 schedule of reinforcement. (c) Average number of drug‐paired and inactive lever responses (± SEM) for each session of self‐administration under a FR1 and FR5 schedule of reinforcement. Active, drug‐paired lever responses were greater than inactive lever responses, but no group effects were observed between the water and alcohol consumption groups. (d) Average number of MA infusions and total drug‐paired lever responses on the progressive ratio (PR) schedule of reinforcement. No significant group effects were observed over the three sessions of PR schedule testing. (e) There were no differences in the average number of active and inactive lever presses during extinction between alcohol and water consuming animals. *Significant from water‐drinking control (p < 0.05)