Hippocampus involves in learning and memory .Presence of opioid receptors reported in hippocampus . Effects of morphine on the neuronal and cognitive processes have suggested and paradoxical results have obtained .Stress influences on synaptic plasticity and memory in the hippocampus .Also, the hippocampus is enriched with receptors for corticosteroids .Previous studies suggest that acute stress and glucocorticoids modulate various phases of memory processing .Study of the effect of acute swimming forced stress on retention related to memory formed during ultra low to usual doses of morphine administration is the aim of this research. Adult male Wistar rats )200-250g (were divided into 2 categories )n=7 in each group :(1 -Acute stress groups )sham and acute stress (that were trained for 4 days without treatment in Morris Water Maze and were exposed to 5 minutes swimming forced stress half hour prior to the retention test on the 5th day .2 - Groups of repeated morphine accompanying with acute stress that morphine doses of )1μg/kg, 10μg/kg,100μg/kg, 1mg/kg and 10mg/kg (were injected intraperitonealy )i.p (.half hour prior to each training session for 4 constitutive days and animals were exposed to the acute stress on the 5th day .The latency and distance to reach the hidden platform was recorded on training days .On the 5th day, the time spent in target quadrant was recorded .On the 12th day, the test was the same as the 5th day without stress treatment for all groups. Difference between sham and acute stress groups on memory retention on the 5th and 12th days were not significant. In the category of repeated morphine accompanying with acute stress, only the morphine at the dose of 10mg/kg showed significant retention impairment on the 5th and 12th days. In acute stress group, impairment effects of acute stress on memory retention were not significant but in group of repeated morphine )10mg/kg (accompanying with acute stress, morphine facilitates impairment effects of stress .

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