en Pain and addiction Neurophysiology/Pharmacology Experimental research article Experimental research article Abstract: ِIntroduction: The effect of morphine dependency on learning and spatial memory is controversial. So in this study effect of co-administeration of nitric oxide (NO) and morphine in CA3 of hippocampus on learning and spatial memory in morphine dependent rats was investigated. Methods: After anaesthetization of male rats, cannulae implanted bilaterally in CA3 of hippocampus. After recovery period (7 days), morphine dependency induced then animals divided in 6 groups that received 1μl saline (Sham), L-Arginine, L-Name and morphine individually and L-Arginine with morphine or L-Name with morphine individually. Morphine dependency was induced by subcutaneous injection of morphine(10mg/kg first day and 20mg/kg for four days). Last dose of morphine(20mg/kg) was injected daily to maintain morphine dependency during test period (5 days) in morris water maze Results: Results showed that L-Name decreased learning in morphine dependent rats although was ineffective on retention of memory. Morphine did not affect learning and spatial memory. Co-administeration of L-Arginine and morphine not only improved the effect of morphine on learning and memory but also promote the effect of L-Arginine on learning and spatial memory. Conclusion: Thus co-administeration of NO and morphine in morphine dependent rats can improve learning and spatial memory differently from using them individually. Keywords:Learning,SpatialMemory,Morphinedependency,Hippocampus,NO 293 299 http://ppj.phypha.ir/browse.php?a_code=A-10-102-2&slc_lang=en&sid=1 Mahshid Hoseinzadeh Hosseinzadehmahshid@yahoo.com 320031947532846003369 320031947532846003369 No Iran Pouraboli pouraboli_i@mail.uk.ac.ir 320031947532846003370 320031947532846003370 Yes Mehdi Abbasnejad mabbas@mail.uk.ac.ir 320031947532846003371 320031947532846003371 No Batool Pouraboli 320031947532846003372 320031947532846003372 No