Fig. 1.

Cumulative record of events (A) and calculated level of cocaine at the time of each event (B) in representative FR1 cocaine self-administration session. Each symbol represents an event. The injections were two initial self-administeredloading doses (3 μmol/kg), then rats self-administered two unit doses (0.3 (75 injections) then 3 μmol/kg (15 injections)). All lever presses on the active lever are also shown. After access to cocaine was terminated, active lever presses had no consequence but were recorded until lever pressing stopped.