reversal effect of intra-central amygdala microinjection of l-arginine on place aversion induced by naloxone in morphine conditioned rats

background: role of nitric oxide (no) on expression of morphine conditioning using a solely classic task has been proposed previously. in this work, the involvement of no on the expression of opioid-induced conditioning in the task paired with an injection of naloxone was investigated. methods: conditioning was established in adult male wistar rats (weighing 200-250 g) using an unbiased procedure. naloxone (0.05-0.4 mg/kg, i.p.), a selective antagonist of mu-opioid receptor, was administered once prior to morphine response testing. no agents were administered directly into the central amygdala (cea) prior to naloxone injection pre-testing. results: morphine (2.5-10 mg/kg, s.c.) produced a significant dose-dependent place preference in experimental animals. when naloxone (0.05-0.4 mg/kg, i.p.) was injected before testing of morphine (5 mg/kg, s.c.) response, the antagonist induced a significant aversion. this response was reversed due to injection of l-arginine (0.3-3 µg/rat), intra-cea prior to naloxone administration. however, pre-injection of l-name (intra-cea), an inhibitor of no production, blocked this effect. conclusion: the finding may reflect that no in the nucleus participates in morphine plus naloxone interaction.