en Experimental research article Experimental research article <p>  The involvement of nitric oxide (NO) in the reinforcing properties of opiate reward was studied by examining the effect of a NO precursor (L-arginine) and a NO synthase inhibitor (L-NAME) on the rate of intravenous self-administration of morphine. This experiment was investigated in male albino Sprague Dawley rats (300 ± 50 g). At doses of 5 and 10 mg/kg (i.p.), L-arginine decreased morphine self- administration significantly, while 20 and 60 mg/kg doses were not significantly effective. In addition, L-arginine per se induced self-administration behavior. At doses of 0.75, 1.25, 2.5, and 5 mg/kg (i.p.), L-NAME had no effect on self-administration, whereas injection of 5 mg/kg 60 minutes before the test did increase self-administration significantly. We may therefore conclude that NO is involved in the VTA-mesolimbic pathway, and it can be involved in the psychological dependence to morphine. </p> Morphine; Self-administration; L-arginine; L-NAME; Reward 33 39 http://ppj.phypha.ir/browse.php?a_code=A-10-19-1&slc_lang=en&sid=1 Mohsen Foadodini 320031947532846001716 320031947532846001716 No Hasan Firooz-Abadi 320031947532846001717 320031947532846001717 No Ali Khosh Baten 320031947532846001718 320031947532846001718 Yes Alireza Asgari 320031947532846001719 320031947532846001719 No Hedayat Sahraei 320031947532846001720 320031947532846001720 No Hasan Ghoshooni 320031947532846001721 320031947532846001721 No