Acquisition of a Morris water maze task is impaired during early but not late withdrawal from morphine

Behavioral changes in male Sprague-Dawley rats during early and late withdrawal from morphine were investigated. Morphine-treated subjects (M) were implanted (SC) with osmotic pumps containing 2.0 ml of a 159 mg/ml morphine sulfate solution while control subjects (C) received sham implants. Implants were removed after 7 days. M subjects exhibited a significant decrease in body weight during withdrawal that recovered by 21 days after pump removal. Beginning 1 or 21 days following pump removal, subjects were tested for 8 days in a Morris water maze (MWM) task. M subjects trained in the MWM during early withdrawal exhibited significantly longer escape latencies than C subjects. However, during sequential probe trials, the same subjects exhibited a significant preference for the target quadrant of the maze and executed accurate searches for the escape platform. Though these subjects failed to locate the platform as efficiently as controls during training trials, they learned the location of the escape platform. M rats trained during late withdrawal exhibited no deficits in any measure of MWM performance relative to C subjects. The data suggest that a variety of processes involved in the acquisition and performance of the MWM task are differentially affected during early withdrawal from morphine. Copyright (C) 1996 Elsevier Science Inc.