Amphetamine and conditioned 'anxiety'.

1. Rats pressed a bar for milk reward at a steady rate, but this baseline responding was suppressed in the presence of an auditory stimulus associated with electric shock (conditioned suppression). The effects of (+)-amphetamine sulphate on this conditioned suppression were studied in two experiments.2. (+)-Amphetamine sulphate (0.5, 1.0 or 2.0 mg/kg) reduced the baseline rate of responding and also reduced the conditioned suppression, i.e. responding in the presence of the auditory stimulus was partially restored. Both these effects were dose related.3. In a further experiment the effects of 1.0 mg/kg on two levels of conditioned suppression were studied. Regardless of its degree, (+)-amphetamine attenuated suppression.4. The results were compared to previous research which found that amphetamine increased baseline responding and exaggerated conditioned suppression. It was concluded that the conditioned suppression procedure should be used with caution as an animal model of anxiety in psychopharmacological investigations.