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Cumulative records from a representative animal in the 1.5 mg/kg/inj group illustrating an increased rate of cocaine intake under a PR schedule after 14 days of continuous d-amphetamine treatment. Each drug infusion (i.e., breakpoint) is represented by a diagonal inflection. PRE: 1.5 mg/kg/inj test session from the initial dose-response curve. POST: 1.5 mg/kg/inj test session from the post-treatment dose-response curve.
