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Abstract

Background: One of the debilitating signs of Alzheimer�s disease is the loss of memory. Then, there has been always an interest to know the neurotransmitters, which mediate memory in order to assess their involvement in such neurodegenerative disorders. Opioid receptors are a group of G protein-coupled receptors, which are widely distributed in the brain and memoryrelated structures such as hippocampus. In 1799, Friedrich Serturner discovered the major active ingredient of opium, which he named morphine and today is used as a pharmacological tool to assess opioid receptors role. Memory is considered to have different phases: acquisition, consolidation and retrieval. Hippocampus is the major structure involving in learning and memory. Morris water maze is a golden test assessing spatial memory which is a hippocampal function. As the opioid receptors exist in the hippocampus there was always an interest to assess the effect of opioids on learning and memory. Most of the research, however; has focused on chronic opioids usage than acute usage of them; therefore the effect of acute administration of morphine on memory consolidation in Morris water maze has not been elucidated yet. This research was aimed to assess the role of morphine on water maze memory consolidation. Methods: Adult male Sprague-Dawely rats weighing 230-270 g were trained in a single session consisting of 8 trials. The probe test was done 24 hours later to assess memory retention. To assess the effect of morphine (10mg/kg/SQ) on consolidation phase, it was injected immediately after training. In another group naloxone was used to examine if the effect was exerted by morphine was directly related to opioid receptors. Results: The results showed that post-training administration of morphine deteriorates learning as the trained rats spent less percentage of time in target zone at probe trial. In addition, co-administration of naloxone and morphine prevented morphine effect on memory consolidation showing that morphine induces memory consolidation defect via opioid receptors. Conclusions: This study might indicate that acute over activation of opioid receptors disrupts memory consolidation processes, which helps us in knowing more about neurotransmitters and their role in learning and memory.

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