Disruption of selective attention by apomorphine, but not amphetamine, in the mongolian gerbil

Abstract

To test the hypothesis that apomorphine, but not amphetamine, disrupts selective attention to a novel stimulus, gerbils were exposed to a novel object for one 60-s trial following an injection of 0, 1, 3, or 6 mg/kg d-amphetamine base, or 0, 0.1, 0.3, 1, 3, or 10 mg/kg apomorphine HClSC. They were tested the next day for habituation to the stimulus. As a control, half of each group of gerbils were injected but not exposed to the object on day 1. All non-exposed gerbils and all exposed gerbils that received amphetamine showed a decrement in investigation, indicative of habituation, on day 2. Furthermore, a gradient of responding during dishabituation was obtained from gerbils given d-amphetamine (1 mg/kg) which was dependent on the distance a novel object was moved, indicating a perception of location as occurs in normal gerbils. In contrast, those exposed gerbils that received 1 mg/kg or more of apomorphine did not show habituation on day 2. That the disruption of habituation by apomorphine was due to a failure of input rather than of retrieving the information was demonstrated in an experiment in which two groups of gerbils were habituated to a novel object prior to injection with apomorphine (1 mg/kg) or saline. Both groups continued to show habituation on subsequent trials and increased responding when the object was moved. Thus, the motor capabilities necessary for investigation were functional. When gerbils that received apomorphine were pretreated with the dopamine receptor blocker pimozide, habituation occurred on day 2, suggesting that the disruption of habituation was mediated by dopamine. On the other hand, the depressant effect of large doses of apomorphine on initial investigation was not blocked completely by pimozide.