Effects of agmatine on neuronal nitric oxide synthase in hippocampus of morphine withdrawal rats

Aiguo WANG; Yuge JIANG; Longhe XU

ABSTRACT

BACKGROUND:

Agmatine can enhance the analgesic effect of morphine,and antagonize the tolerant and dependent effect of morphine.

OBJECTIVE:

To observe the effects of injecting agmatine on the neuronal nitric oxide synthase (nNOS) in hippocampus of morphine withdrawal rats.

DESIGN:

A randomized controlled experimental study.

SETTING:

Department of Anesthesiology, the General Hospital of Chinese PLA.MATERIALS All the experiments were carried out in the Department of anesthesiology, the General Hospital of Chinese PLA between April and July 2004. Eighteen healthy SD rats were randomly divided into saline control group (n=6), morphine group (n=6) and agmatine-treated group (n=6).

METHODS:

The rats in the saline control group were treated with subcutaneous injection of physiological saline (10 mg/kg), those in the morphine group were treated with 5-day preconditioning, subcutaneous injection of morphine of 10, 20, 30, 40 and 50 mg/kg respectively, twice a day, and those in the agmatine-treated group were treated with subcutaneous injection of agmatine (10 mg/kg) at 30 minutes before morphine was given, but at 6 hours later, before morphine was given for the last time, the rats in the morphine group and agmatine treated group were also given intraperitoneal injection of naloxone (5 mg/kg) to induce morphine withdrawal symptoms.The number of times of the morphine withdrawal symptoms (including physical signs of trembling like a wet dog, chewing, irrigating, drooling, diarrhoea, etc.) were recorded within 1 hour, and the reduction of body mass was calculated according to the different value of body mass before and after the withdrawal symptoms induced by naloxone. The rats were killed under anesthesia after praxiological detection, and then hippocampus was taken out and made into frozen sections, and the nNOS was detected with immunohistochemical staining. The CMIAS systemwas applied for imaging analysis, and the average value of the integral absorbance (A) values in 5visual sights for each section was taken as the integral A value of positive neuron.MAIN OUTCOME

MEASURES:

① The detected results of morphine withdrawal symptoms in each group; ② The changes of the nNOS expressions in hippocampus of rats in each group.

RESULTS:

All the 18 rats were involved in the analysis of results. ① The detected results of morphine withdrawal symptoms in each group The withdrawal symptoms of trembling like a wet dog, chewing, irrigating, drooling,diarrhoea and reduction of body mass in the agmatine treated group were all obviously lower than those in the morphine group [(2.0±1.3), (5.0±1.1);(0.3±0.4), (1.8±0.7); (3.2±1.2), (6.8±3.1); (0.2±0.4), (1.2±0.9); (2.7±2.1),(6.7±2.1); (6.0±3.0), (12.8±2.7) times, P ＜ 0.01], and close to those in the saline control group (P ＞ 0.05). ② The changes of the nNOS expressions in hippocampus of rats in each group The positive neurons of nNOS in hippocampus mainly distributed in CA1 region, the cytoplasm was stained buffy, and the round nuclei were stained pale purple by haematine. The immunofluorescent A value of positive neuron in the agmatine-treated group was significantly decreased as compared with that in the morphine group (24.32±8.31, 50.82±15.13, P＜ 0.01), and almost the same as that in the saline control group (24.32±8.31, 15.24±1.88, P ＞ 0.05).

CONCLUSION:

Agmatine can inhibit the morphine withdrawal syndrome and decrease the expression of nNOS in hippocampus CA1 region of morphine-withdrawal rats. Hippocampal nitric oxide pathway takes part in the inhibitory effect of agmatine on morphine withdrawal syndrome.