Role of CeA nitric oxide on expression of morphine reward behavior in the rat

Naloxone shows interaction with the morphine in expression of reward behaviors. L-arginine increases morphine induced conditioned place preference, whereas L-NAME decreases this process. In this project, effects of injections of L-arginine and L-NAME intra-CeA on morphine induced drug-seeking behaviorsincluding rearing, sniffing and compartment entering were investigated.

Animals (male Wistar rats weighing 200-250 g)were cannulated bilaterally by stereotaxis apparatus for the CeA coordinates and passed a recovery period lasting one week. Conditioned place preference was conducted using a five-day schedule of an unbiased procedure including three phases (pre-conditioning,conditioning, and test). Morphine was injected subcutaneously through the conditioning once a day. NO agents were intra-nucleus injected but the administration of naloxone was intraperitoneally 10 min prior to testing.

morphine (2.5-10 mg/kg s.c) induced a significant decrease in drug-seeking behaviors compared with the control group. Naloxone (0.1- 0.4 mg/kg i.p) potentiated the morphine-induced responses. When Larginine (0.3-3 μg/rat) injected intra–CeA before injection of naloxone (0.4 mg/kg) pre-testing showed a significant increase effect on the behaviors but injection of L-NAME (0.3-3 μg/rat) intra–CeA prior to Larginine (0.3 μg/rat) pre-testing blocked the response to L-arginine.

Naloxone, an opioid receptor agonist, competes with morphine in inducing the behaviors in the conditioning model and NO in the CeA shows interaction with morphine in expressing these effects. Present finding may confirm that there is an interaction between NO in the CeA and morphine in expressing the drug-seeking behaviors.