Influence of chronic treatment with olanzapine, clozapine and scopolamine on performance of a learned 8-arm radial maze task in rats

Cognitive deficit is a significant symptom in schizophrenic patients. Use of atypical antipsychotics has been demonstrated to improve some cognitive functions in schizophrenics, as well as in patients with dementia. However, side effects like sedation and muscarinic antagonism induced by these drugs have detracted from this improvement. We are interested in determining the behavioural effect of acute and chronic treatments with olanzapine and clozapine, two atypical antipsychotics, in a paradigm of working memory, and the influence on behavioural response of possible motor effects during test performance. Unspecific muscarinic, antagonist scopolamine has been used for comparison. Male Wistar rats were trained on the 8-arm radial maze up to an accuracy level in choice of 80%. Distance travelled in the maze was also measured during test performance. Acute olanzapine, clozapine and scopolamine caused significant impairment of correct performance. Rats treated with olanzapine and clozapine presented a decrease in motor activity level at the same time. After the test at acute dosage, rats were chronically treated for 14 days with olanzapine, clozapine or scopolamine and 24 h after the last dose were again tested in the 8-arm radial maze. Under this procedure, chronic treatment with olanzapine, clozapine and scopolamine did not impair correct task performance and did not modify distance travelled. We concluded that the sedative effect masked a possible effect on working memory after acute administration of olanzapine and clozapine, whereas chronic treatment with olanzapine, clozapine and scopolamine did not adversely affect working memory performance. In the case of scopolamine, it suggests that chronic muscarinic antagonism does not induce memory impairment and for atypical antipsychotics, it suggests that chronic treatment induced a tolerance to acute motor effects of these drugs. (c) 2005 Elsevier Inc. All rights reserved.