大鼠脑内甲硫氨酸脑啡肽(Met-Enk)和乙酰胆碱(ACh)的相互关系及其对电针镇痛作用的影响

<正> 脑啡肽和乙酰胆碱在针刺镇痛中的作用不少学者进行了研究,但是,它们在针刺镇痛作用中的相互关系尚不十分清楚。为了探讨大鼠脑内Met-Enk和ACh的相互关系及其对电针镇痛作用的影响,我们进行了本实验的研究。实验方法实验动物用成年健康的大白鼠,体重150～250克,雌雄兼用。第一部分:大鼠175只,随机分成二大

INVESTIGATIONS ON THE RELATIONSHIP BETWEEN METHIONINE--ENKEPHLIN (Met-Enk) AND ACETYLCHOLINE (ACh) IN BRAIN OF RATS,WITH THEIR INFLUENCE ON THE EFFECT OF ELECTROACUPUNCTURE ANALGESIA

A group of 311. rats weighing about 200g were used. The milliamperes required for vocalization in reponse to electrical stimulation at the rats tail was adopted as an indication of the value of pain threshold. Electroacupu- neture with the apparatus of G6805 model was applied at "Renzhong" and "Chenjiang" acupoints with a step-up intensity of 5-9-12v, sparse pulses and a frequency of 500Hz for 30 min. Met-Enk content in the brain was measured by radioimmunoassay. Acetylcholine content in the brain of animals electroacupunctured at "Zusanli" and "Huantiao" bilaterally was also estimated by bioassay, It was found: 1. There were much higher Met-Enk and the ACh contents in hypothalamus and caudate nucleus with simultaneous elevation of the pain threshold of rats (as compared with control P<0.01) in both intraventricular and the subcutaneous injection of saline plus acupuncture groups. It is elucidated that the increase of the Met-Enk and ACh contents in brain are correlated intimately with the analgesic effect of electroacupuncture. 2. Hemicholine injected intraventricularly (40μg/rat/4h) was used to block ACh synthesis. It resulted in a signficant decrease of both ACh(-39% and-64%, P<0.01) and of Met-Enk content (-19% and -29%, P<0.01) in the hypothalamus and caudate nucleus accompanied by an obvious lowering of pain threhold (-50% P<0.10). After subcutaneours injection of eserine (0.25mg/kg/20min), owing to the inhibition of cholinesterase activity, it made the ACh content increase by 32% (P<0.01) and 70% (P<0.01) in the hypothalamus and caudate nuclens respectively, and at the same time the Met-Enk content was elevated by 34% (P<0.01) and 27%(P<0.0) in the brain regions of rats with the pain threshold becoming apparently higher (+400% and +875%, P<0.001). This might denote that the factors affecting the transmitter of cholinergic nerve system could concidently exertan influence on that of enkephalinergic neurons. The decreasing of functional activity of cholinergic nerve would be accompanied by the lowering of fu- nction of this peptidergic neurons) that was responsible for the dropping of the pain threshold. Conversely, a reverse result would be obtained. 3. In the rats receiving intraventricular injection of Hemi-choline (40 ug/rat/4h) plus electroacupuncture for 30 min, the content of ACh in the hypothalamus and the caudate nucleus was further lowered (-66% and -73%, P<0.01) as compared with control group. But that of Met-Enk was increa- rently (+31% and +28%, P<0.01), and the absolute Met-Enk value of the valid increase was still greater than that of simple acupuncture group. It was suggested that when the synthesis of ACh was blocked, and when the utilization rate of ACh was significantly accelerated by electroneedling the function of enkephalinergic neurons could be further strengthened through the action of electroacupuncture. It turned out that the analgesic effect of electroacupuncture could not be completely inhibited by the intraventriculer injection of Hemicholine. The pain threshold of rats in this group was still higher than that of rats in the control group (+383%. P<0.01). when giving rats subcutaneous injection of eserine (0.25mg/kg) plus electroacupuncture for 20min, the contents of ACh and Met-Enk in the hypothalamus and caudate nucleus were much higgher than those in the rats of control groups (ACh: +31% and +75%, P<0.01, Met-Enk: +34% and +67%, P<0.01). The pain threshold was also obviously elevated (+775%, P<0.001) at the same time. The elevated range of pain threshold was obvi- ously higher than the increased ranges of Ach and Met-Enk in the brain. It may indicate that during the increase of Ach concentration by eserine administration plus electroacupuncture, the content of Met-Enk was also increased. Furthermore, these changes which would perhaps be associated extensively with other neurotransmitters in central nervous system, such as 5-Hydroxytryptamine, Noradrenaline and substance P etc. may further enha- nce the effect of acupuncture analgesis.