THE EFFECTS OF ALPHA-2 AGONIST, MEDETOMIDINE AND ITS ANTAGONIST, ATIPAMEZOLE ON REACTION AND MOVEMENT TIMES IN A VISUAL CHOICE-REACTION TIME TASK IN MONKEYS

Alpha-2 adrenoceptor agonists have been shown to improve the working m emory task performance of aged monkeys, Suggestions offered to explain this finding include improved short-term memory processing, slight se dation, and decreased distractiveness. Although sedation is evident at high doses, it may also contribute to the working memory task perform ance at low doses. The aim of the present work was to find out whether the positive effects of an alpha-2 agonist, medetomidine, on working memory performance could be explained by its sedative effects, This wa s accomplished by measuring the reaction and movement times of monkeys performing a visual choice reaction time task under the influence of medetomidine or its antagonist atipamezole. In the task a trial began with the monkey holding a central pad. After a short period one of two lateral light emitting diodes was turned on for 300 ms and the monkey s were trained to release the central bar and touch either of the bars , situated below the diodes, depending on the location of the stimulus , The reaction and movement times were significantly longer than on sa line control only at the highest dose of medetomidine (10.0 mu g/kg). At the lowest dose of atipamezole (0.01 mg/kg), the reaction times wer e significantly shorter than on saline control, The results of this st udy demonstrate that low doses of medetomidine, which have earlier bee n shown to improve working memory performance, do not induce sedation as measured by reaction and movement times, (C) 1997 Elsevier Science Inc.