EFFECTS OF CAFFEINE, THEOPHYLLINE AND THEOBROMINE ON SCHEDULED CONTROLLED RESPONDING IN RATS

1 Rats were trained to respond under a variable interval 30 s (VI 30) schedule of food reinforcement. 2 Caffeine (0.32–32 mg/kg), theophylline (1.0–56 mg/kg) and theobromine (10–320 mg/kg) in general produced dose‐related decreases in operant responding. At relatively low doses, caffeine (1.0 mg/kg) and theophylline (3.2 mg/kg) produced slight but nonsignificant increases in VI 30 responding. 3 The rank order of potency for producing decreases in responding was caffeine > theophylline > theobromine. 4 Daily caffeine injections (32 mg/kg, i.p.) resulted in the development of caffeine tolerance. This tolerance was characterized by a 6 fold shift to the right in the caffeine dose‐effect curve Saline substitution for the 32.0 mg/kg caffeine maintenance dose resulted in a substantial decrease in responding.