Dose effects on heart rate conditioning when pentobarbital is the CS and amphetamine is the US

If sodium pentobarbital is injected into rats 30 min prior to d-amphetamine sulphate on four or five occasions, there is a learned effect of pentobarbital on heart rate. The conditioned response is a higher heart rate than found in rats with a control history of exposure to the same drugs. In Experiment 1, when the pentobarbital dose was 32 mg/kg throughout, this effect was obtained with amphetamine doses of 2, 4, 8, or 16 mg/kg. In Experiment 2, when the amphetamine dose was 12 mg/kg throughout, pentobarbital doses of 16 and 32 mg/kg yielded conditioning, while 8 mg/kg yielded equivocal results.