en Experimental research article Experimental research article It has been shown that L-arginine like the abused drugs could release dopamine from meso-cortico-limbic system. The purpose of the present study was to compare the effect of L-arginine with morphine as a standard abuse drug in the induction of conditioned place preference (CPP) in rat. For this purpose, male Wistar rats (250-300 g) were used in the experiments. Five days after surgical cannulation in the ventral tegmental area (VTA), different doses of L-arginine, L-NAME or morphine were injected and conditioned biased method was preformed. The results showed that: 1. Intraperitoneal (i.p.) (0.1, 1 and 5 mg/kg) but not intra-VTA (i-VTA) (0.3, 0.1 and 3 µg/rat) injections of L-arginine induced CPP in a dose-dependent manner. Injection of 10 mg/kg (i.p.) and 2 µg/rat of morphine (i-VTA) also caused a significant CPP in rats. Both i.p. (0.1, 1 and 5 mg/kg) and i-VTA (0.3, 0.1 and µg/rat) injection of L-NAME did not produce any effect in the rats, but the drug at higher dose (5 mg/kg, i.p.) attenuated the CPP induced by L-arginine (5 mg/kg, i.p.) Administration of morphine (10 mg/kg, i.p.) on three consecutive days and, then with 3-day interval caused the occurrence of sensitization to morphine, so that injection of ineffective dose of morphine (0.5 mg/kg, i.p.) induced CPP in sensitized rats. However, when the procedure was repeated for L-arginine (5 mg/kg, i.p.), rats showed negative response to the ineffective dose of L-arginine (0.1 mg/kg, i.p.). Meanwhile, in rats that received L-arginine (5 mg/kg, i.p.) on training days, injection of the same dose L-arginine on the test day dramatically decreased the time spent in drug-paired side while injection of morphine (10 mg/kg, i.p.) on the test day to those rats which had received morphine (10 mg/kg, i.p.) on training days caused an increase in time spent in the drug-paired compartment. It could be concluded that i.p. injection of L-arginine causes significant CPP rats and this behavior was attenuated by nitric oxide synthase inhibitor, L-NAME. Furthermore, the site of action of the drug seems not to be VTA. On the other hand behaviors due to administration of L-arginine did not show some properties of abused drugs such as sensitization and state dependency. L-arginine; L-NAME; CPP; Drug reward; Ventral segmental area; Morphine 29 40 http://ppj.phypha.ir/browse.php?a_code=A-10-74-47&slc_lang=en&sid=1 Hedayat Sahraie 320031947532846002637 320031947532846002637 Yes Hasan Ghoshooni 320031947532846002638 320031947532846002638 No Gila Pirzadeh Jahromi 320031947532846002639 320031947532846002639 No Ali Reza Asgari 320031947532846002640 320031947532846002640 No Gholamreza Pourheydari 320031947532846002641 320031947532846002641 No Ali Khoshbaten 320031947532846002642 320031947532846002642 No