Role of nitric oxide in nucleus raphe magnus in pain regulation and electroacupuncture analgesia in rats

Bilan HUANG; Zongping TU; Liangzhu YU

ABSTRACT

BACKGROUND:

L-arginine (L-Arg) is the precursor of endogenous nitric oxide (NO), which joins the pain regulation of peripheral myeloid level and above.

OBJECTIVE:

To study the role and mechanism of NO in nucleus raphe magnus (NRM) in pain regulation and electroacupuncture analgesia.

DESIGN:

A random control experiment on rats.

SETTING:

Physiology Department of Medical College of Xianning College.MATERIALS The experiment was done during May 2002 to March 2003in the Physiology Department of Medical College of Xianning College. The 63 Wistar rats were randomized into 7 groups with 9 in each. ①. Five groups for the experiment of L-Arg dose-effect relationship Normal saline group and L-Arg 1, 2, 4, 8 mmol groups. ②. Two groups for the experiment of relationship between L-Arg and electroacupuncture analgesia Normal saline + electroacupuncture group and L-Arg + electroacupuncture group.

METHODS:

①Experiment of L-Arg dose-effect relationship Normal saline group was injected normal saline. L-Arg 1, 2, 4, 8 mmol groups were injected L-Arg 1, 2, 4, 8 mmol respectively. The volume was all 1.5 μL.Then, the hot water (50±0.5) ℃ was used to stimulate the tail once every 10 minutes to cause tail flick for testing the pain threshold. The observation was carried out continuously for 90 minutes. ②. Experiment of relationship between L-Arg and electroacupuncture analgesia The two groups were injected normal saline and L-Arg 8 mmol respectively. The volume was all 1.5 μL. Ten minutes later, Zusanli (ST 36) of both posterior legs of rats were punctured with electric stimulation. The frequency was 4-16 Hz, and the intensity in an increasing order of 1, 2, 3V given 10 minutes of each. The electroacupuncture was totally 30 minutes, during which, testing the pain threshold 3 times. After needling, the pain threshold was still tested once every 10 minutes, till 90 minutes after injecting L-Arg.MAIN OUTCOME

MEASURES:

Pain threshold at different time points.

RESULTS:

The 63 rats entered the result analysis. ① The pain threshold of L-Arg 1 mmol group at all time points was lower than that of the normal saline group, but without statistical significance (P ＞ 0.05). The pain threshold of L-Arg 2, 4, 8 mmol groups was much lower than that of the normal saline group at all time points (P ＜ 0.001), and the effect was lasting to 80 minutes after injecting L-Arg, and with the increase of L-Arg density, the amplitude of pain threshold lowering was increased. ② The pain threshold of L-Arg + electroacupuncture group was much lower than that of the normal saline + electroacupuncture group at the time points of 20-50 minutes (P ＜ 0.01).

CONCLUSION:

① The L-Arg injection to NRM can lower the pain threshold and there is a dose-dependent effect in it. ② The electroacupuncture can raise the pain threshold, and the L-Arg injection can weaken the effect of electroacupuncture analgesia. ③ NO in NRM joins in the pathological and physiological processes of pain and electroacupuncture analgesia. Its increase can lower the pain threshold greatly.