Effect of amphetamine dose on wheel-running functioning as reinforcement or operant behavior on a multiple schedule of reinforcement.

Does the effect of amphetamine on behavior (wheel running) differ depending on the functional role (operant, reinforcement) of that behavior? This study addressed this question using a multiple schedule of reinforcement in which wheel running served as reinforcement for lever pressing in one component and as operant behavior for sucrose reinforcement in the other component. Seven female Long-Evans rats were exposed to a multiple schedule in which pressing a lever on a variable ratio 10 schedule produced the opportunity to run for 15 revolutions in one component and running 15 revolutions produced a drop of 15% sucrose solution in the other component. Doses of 0.5, 1.0, and 2.0 mg/kg D-amphetamine were administered by intraperitoneal injection 20 min prior to a session. As amphetamine dose increased, wheel running decreased in both components - showing no evidence that the effect of the drug on wheel running depended on the function of wheel activity. Notably, lever pressing for wheel-running reinforcement also decreased with amphetamine dose. Drug dose increased the initiation of operant lever pressing, but not the initiation of operant wheel running. We propose that amphetamine dose had common effects on wheel running regardless of its function (reinforcement vs. operant) because wheel-running generates automatic reinforcement and the automatic-reinforcement value of wheel activity is modulated by drug dose.