REPEATED ACQUISITION OF A SPATIAL NAVIGATION TASK IN MICE - EFFECTS OF SPACING OF TRIALS AND OF UNILATERAL MIDDLE CEREBRAL-ARTERY OCCLUSION

The working memory version of the Morris water escape task, the repeat ed acquisition task, consists of trial pairs in which an animal is sta rted twice from the same start position. Animals have mastered this ta sk when they need less time to find the platform in the second of the two trials. In this study, study, male C57BL mice were trained on this task with massed, spaced, or spaced delay trials in which there was a 90-min delay between the first and second trials of a pair. The mice trained with spaced trials learned the repeated acquisition task, wher eas the mice trained with massed or spaced delay trials were not consi stently able to do so. When the mice had reached a stable baseline per formance, the middle cerebral artery (MCA) was occluded or the mice we re sham-operated. Then, the effects of the MCA occlusion (MCA-O) on th e performance in the repeated acquisition tasks were studied. MCA occl usion hardly affected the performance in this task, irrespective of th e spacing condition of the trials, although surgery per se seemed to h ave a transient disruptive effect. (C) 1998 Elsevier Science Inc.