The Effect of Morphine Dependency on Spatial Learning and Memory in Male Rat

Opiates addiction is a phenomenon with complex physiological and social causes and consequences. The exact mechanisms of development of dependency and relapse remain unclear. Among the several possible mechanisms, the role of learning and memory in opiate dependency and relapse has received considerable attention in recent years. Therefore, in the current study the effect of morphine dependency induced by repeated subcutaneous injection of morphine on the above-mentioned parameters was examined. In this experimental study, animals in both dependent and withdrawal groups received morphine sulfate(10 mg/kg, s.c.) and normal saline was given to the control group. The administration of morphine sulfate and normal saline was done twice per day(8:00 AM & 8:00 PM) for 15 consecutive days. Dependent and control groups were observed from the 11th to 15th day but withdrawal animals were studied from the 16th to the 20th day. The animals were tested for four consecutive days(4 trials/day) to evaluate spatial learning process. During these 4 days(training days) the position of the hidden platform was unchanged. On the fifth day(probe trial) the platform was removed from maze to evaluate spatial memory process. The recorded spatial learning and memory parameters were subjected to ANOVA. The data showed that traveled times and distances to find the hidden platform, the mean of swimming speed on training days, and also the percentage of times and distances traveled in the target quarter in the probe trial stage were not statistically different among the studied groups. These findings clearly imply that morphine dependency induced by the current method has no significant effect on spatial learning and memory, which may result from a relative tolerance to morphine in dependent animals.