OBJECTIVETo explore if induced nitric oxide in the spinal cord mediates withdrawal syndrome in morphine-dependent rats.

METHODSMale SD rats weighing 200-250 g were employed in the present study. To set up morphine dependence model, rats were subcutaneously injected with morphine (twice a day, for 5 d). The dose of morphine was 10 mg/kg in the first day and was increased by 10 mg/kg each day. On day 6, 4 h after the injection of morphine (50 mg/kg), morphine withdrawal syndrome was precipitated by an injection of naloxone (4 mg/kg, ip). Inducible nitric oxide synthase (iNOS) inhibitors aminoguanidine (AG) was intrathecally injected 30 min before the administration of naloxone. All the rats were divided into four groups: control group, dependence group, withdrawal group, AG group. Morphine withdrawal score, touch evoked agitation scores (TEA scores), immunohistochemical and Western blot technique were used to evaluate morphine withdrawal response and the expression of iNOS in the spinal cord.

RESULTSIntrathecal injection of iNOS inhibitors AG could alleviate morphine withdrawal symptoms. Morphine withdrawal scores and touch evoked agitation scores in AG group were significantly lower than that of withdrawal group (P < 0.05). iNOS positive neurons in dorsal horn of AG group were significantly lower than that of withdrawal group (P < 0.05). Level of iNOS protein in spinal cord of AG group was significantly lower than that of withdrawal group (P < 0.05).

CONCLUSIONInduced nitric oxide in the spinal cord may mediate withdrawal syndrome in morphine-dependent rats.