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 performance 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, but 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 signalling the non-reinforcement of the target. The interval between the feature and the target was varied in the non-reinforced trials following pretreatment with subcutaneous saline, D-amphetamine (0.5 mg/kg) or ketamine (5 mg/kg). The main behaviour measured was visits to the place of food delivery during target presentation. Under saline, the response frequency during the target was lowest when the interval between the feature and the target exactly matched the interval used during training. Either shortening or lengthening the interval enhanced responding. Neither D-amphetamine nor ketamine disturbed this temporal pattern, although D-amphetamine and ketamine non-specifically increased and decreased response frequencies, respectively, in all the trial types. The results are discussed in the framework of the amphetamine and ketamine models of schizophrenia.