Effects of psychostimulant withdrawal on latent inhibition of conditioned active avoidance and prepulse inhibition of the acoustic startle response

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Chronic intermittent administration of amphetamine and cocaine can precipitate psychotic episodes in humans and produce persistent behavioral changes (i.e. increased locomotion, stereotypy) in the rat. The psychostimulant sensitization model of psychosis holds that the repeated administration of drugs such as amphetamine and cocaine induces long-lasting neuroadaptations and behavioral outcomes in animals that parallel aspects of the schizophrenic condition. In the present study, we attempted to validate this model further by examining the effects of short-term withdrawal from repeated administration of cocaine and amphetamine on performance in two animal behavioral models of cognitive deficits found in schizophrenia: latent inhibition and prepulse inhibition. Reductions in both of these behavioral phenomena have been reported in schizophrenic patients and in acutely amphetamine-treated rats. Animals were tested after 4 days of withdrawal from 5 days of daily systemic 20 mg/kg cocaine or 1.5 mg/kg amphetamine injections for either latent inhibition of two-way active avoidance acquisition or prepulse inhibition of an acoustic startle response. Our results indicate that, rather than reducing the expression of these behaviors, withdrawal from either cocaine or amphetamine enhanced the expression of latent inhibition of the active avoidance response while having no effect on prepulse inhibition of acoustic startle. These data indicate that although the sensitized response to amphetamine and cocaine administration may model some aspects of schizophrenic psychosis, behaviors exhibited by sensitized animals in the absence of an acute drug challenge are not consistent with models of the positive symptoms of schizophrenia.