Effects of the nonselective adenosine antagonist caffeine in combination with 0.1 mg/kg haloperidol. (A) Mean (±S.E.M.) number of lever presses after treatment with vehicle or haloperidol plus various doses of caffeine are shown. (B) Mean (±S.E.M.) intake of lab chow (in grams) after treatment with vehicle or haloperidol plus various doses of caffeine are shown. Veh/Veh (vehicle plus vehicle), HP/Veh (0.1 mg/kg haloperidol plus vehicle), HP/CAF 5.0 (0.1 mg/kg haloperidol plus 5.0 mg/kg caffeine), HP/CAF 10.0 (0.1 mg/kg haloperidol plus 10.0 mg/kg caffeine), HP/CAF 20.0 (0.1 mg/kg haloperidol plus 20.0 mg/kg caffeine). #p < 0.01, haloperidol different from vehicle/vehicle, planned comparison; *p < 0.05, different from vehicle plus haloperidol, planned comparison.