Effects of acute D-amphetamine and ketamine on the performance of rats in a serial negative patterning procedure

This study assessed the effects of acute amphetamine and ketamine on the pe rformance of rats in a serial negative patterning procedure. A 5 s auditory target stimulus and a 5 s visual feature cue were each followed by food, b ut the target stimulus was not followed by food if preceded by the feature, There was a 5 s empty gap between feature termination and target onset in the latter, non-reinforced trials. Thus, the feature functioned as a cue si gnalling the non-reinforcement of the target. The interval between the feat ure and the target was varied in the non-reinforced trials following pretre atment with subcutaneous saline, D-amphetamine (0.5 mg/kg) or ketamine (5 m g/kg), The main behaviour measured was visits to the place of food delivery during target presentation, Under saline, the response frequency during th e target was lowest when the interval between the feature and the target ex actly matched the interval used during training. Either shortening or lengt hening the interval enhanced responding, Neither D-amphetamine nor ketamine disturbed this temporal pattern, although D-amphetamine and ketamine non-s pecifically increased and decreased response frequencies, respectively, in all the trial types. The results are discussed in the framework of the amph etamine and ketamine models of schizophrenia. (C) 2001 Lippincott Williams & Wilkins.