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Cognitive impairment is very prevalent in schizophrenia and is currently undertreated in most patients. Attentional deficit is one of the hallmark symptoms of schizophrenia. Antipsychotic drugs, which can be quite effective in combating hallucinations are often ineffective in reducing cognitive impairment and can potentiate cognitive impairment. Previously, we found that the antipsychotic drug clozapine impaired, while nicotine improved, the accuracy of rats performing a visual signal detection attentional task in normal rats. For the current study, in a model of cognitive impairment of schizophrenia with the NMDA antagonist dizocilpine (0.05 mg/kg), we examined the effects of clozapine and nicotine on significantly impaired attentional hit accuracy. This dizocilpine-induced impairment was significantly (p<0.05) reversed by either clozapine (1.25 mg/kg) or nicotine (0.025 mg/kg). Interestingly, when clozapine and nicotine were given together, they blocked each other's beneficial effects. When the effective doses of 1.25 mg/kg clozapine and 0.025 mg/kg nicotine were given together the combination no longer significantly reversed the dizocilpine-induced hit-accuracy impairment. Given that the great majority of people with schizophrenia smoke, the potential beneficial effects of clozapine on attentional function may be largely blocked by self-administered nicotine. In addition, there are promising results concerning the development of nicotinic treatments to reverse cognitive deficits including attentional impairment. This is supported in the current study by the reversal of the dizocilpine-induced attentional impairment by nicotine. However, in schizophrenia the efficacy of nicotinic treatments may be limited by co-treatment with antipsychotic drugs like clozapine. It will be important to determine which of the complex effects of clozapine and nicotine are key in reversing attentional impairment and how they block each other's effects for the development of therapy to combat the attentional impairment of schizophrenia.

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