针刺穴位所引起的镇痛作用是通过机体内因实现的一种生理性镇痛。大量研究资料证明针刺是通过神经

特别是中枢神经系统发挥镇痛作用的。近十几年来发现脑内存在有内在的镇痛系统。此系统涉及到脑室周围和导水管周围灰质以及一些其他结构并通过最后的驿站延脑的下行抑制In recent years

many investigators have demonstrated that there is an intrinsic analgesic system in the brain

which centres around the periventricular and periaqueductal gray matter. It could activate the neuron of the nucleus raphe magnus (NRM)

a descending inhibitory system

which in turn blocks the trasmission of nociceptive information in the dorsal horn

and then the analgesia is produced. The analgesic action of opiate and the focal brain stimulation are both involved in this intrinsic analgesic system. The aim of the present work is to see whether the electro-acupuncture canactivate the neuron of the NRM and inhibit its response of pain. Experiments were carried out on 74 male rats. The spontaneous discharge of single unit of NRM was recorded extracellularly with glass microelectrode. The frequency of the spontaneous discharge was different

most of which was 0.5 20/sec and some 20～50/sec. 1. The response of the spontaneous discharge of the NRM cells upon the electro stimulation of the major splanchnic nerve: observations upon 239 neurons with train impulses for 50-100msec. revealed that the intensity of the stimulation was about 20v

the frequency 100/sec

and duration of each impulse 0.5 msec. The firing rate of 155 neurons were increased and 45 decreased by the stimulation. The former were called excitatory type neurons

and the latter inhibitory.8 neurons were inhibited first and then followed by excitatory response

and the other seven were reversal and 24 neurons had no response. We consider that the excitatory type neurons may be raphespinal cells and they may play a negative feedback control role on the input of pain information into the dorsal horn. 2. The effect of electro-acupuncture of Zusanli point for 5 minutes on the spontaneous discharge of NRM units and the response of pain stimulation: In the 38 neurons of NRM investigated

28 neurons were excitatory. Of the 28 cells

spontaneous discharge was activated upon 18 cases

inhidited in one case

activated at the beginning and then inhibited in one case

and 8 were unaffected by electro-acupuncture. Seven neurons were inhibitory. Of these 7 inhibitory neurons

the firing rate of 3 cells were increased

one was gained first and followed by reduction and three had no response. One cell

which was excited first and followed by inhibitory response upon pain stimulation

was activated. The 2 units

which did not response on pain atimulation

were ineffctive upon electro-acupuncture. The effect of electro-acupuncture on the pain response was observed upon 33 of the 38 units

which consisted of 23 excitatory neurons

7 inhibitory neurons and 3 inefficient neurons. Of these 23 excitatory neurons

the pain response of 15 units

which were activated by electro-acupuncture

were decreased

except one being enhanced and another haveing no change. The pain response of 7 units

whose spontaneous discharge was not affected by electro-acupuncture

exhibited no influence upon 4 and increasedupon 3. The pain response of one unit

whose spontaneous discharge was decreased by electro acupuncture

was increasedby electro-acupuncture. Upon the 7 inhibitory neurons

three had activation of spontaneous discharge and their pain response was inhibited by electro acupuncture.Three had no change of spontaneous discharge upon activation and their pain response was not affected by electo-acupuncture. That one whose spontaneous dischargee was excitatory at first and then inhibitory showed elevation of pain response caused by electro acupuncture. The firing rate and response to pain were not affected by electro-acupuncture upon the 2 units

which were indifferent to pain stimulation. The results showed that the spontaneous discharge of NRM neurons could be activated and the pain response inhibited by electro-acupuncture. It is suggested

that analgesia of electro-acupuncture may be produced by activa ting the intrinsic analgesic system.