L-NAME REVERSES MORPHINE-INDUCED SPATIAL MEMORY CONSOLIDATION IMPAIRMENT

Abstract

Memory impairment is among the early and debilitating features of Alzheimer's disease. Memory is considered to have different phases: acquisition, consolidation and retrieval. The major structure involving in learning and memory is the hippocampus. Morris water maze is a test assessing spatial memory as a hippocampal function. Morphine is reported to disrupt spatial memory consolidation phase. It has been shown that there is a relationship between morphine and nitric oxide (NO). NO is synthesized when L-Arginine is transformed to L-citrullin via nitric oxide synthase (NOS) activity. Morphine is assumed to activate nNOS in CNS by affecting μ receptors; which leads to production of NO. This study was aimed to assess if NO is involved in spatial memory consolidation impairment. 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 L-NAME (3mg/kg/ip) on memory consolidation impairment induced by morphine (10mg/kg/SQ), Morphine was injected immediately after training. In the groups receiving L-NAME, it was administered simultaneously with morphine. The results showed that post-training administration of L-NAME reversed the deteriorating effects of morphine on memory consolidation. This was due to the observation that trained rats spent more percentage of time in target zone at probe trial compared with the rats given morphine alone. As co-administration of L-NAME and morphine prevents morphine effect on memory consolidation, it seems that NO plays a role in morphine inducing memory consolidation defect. This study might indicate that morphine disrupts memory consolidation process in a NO dependent manner. This helps us in knowing more about neuromodulators and their roles in learning and memory.