Original Articles

Effect of electro-acupuncture on neurons of midbrain periaqueductal gray sensitive to morphine and 5-HT in rabbits

Jie-shi Cheng, Shu-pei Ou, Xiao-pin He


The spontaneous discharges of midbrain periaqueductal gray (PAG) neurons sensitive to morphine, etorphine and 5-HT were recorded by 7-barrel glass microelectrodes and examined by micro-iontophoresis in 106 units of 40 anesthelized rabbits. Morphine depressed 32/83 and excited 10/83 units, 5-HT depressed 21/92 and excited 31/92 units, whereas etorphine depressed 23/43 units but had no excitatory effects.
Electro-acupuncture was made on 84 out of these 106 units. Among the 84 units 24 were activated by electro-acupuncture, 31 depressed and 29 not significantly affected. Most neurons sensitive to morphine, etorphine or 5-HT responded to electro-acupuncture with an increase or decrease in the frequency of spontaneous discharges.
Most units in dorsal part of the PAG fired slowly with a frequency <20/s. The majority of them were depressed by morphine or etorphine, and were inhibited by electro-acupuncture. Most units fired with a frequency of >21/s were located in ventral region of the PAG. Among them the majority of the neurons sensitive to 5-HT were excitated by micro-iontophoresis of 5-HT and were activated by electro-acupuncture.
The inhibitory effect of electro-acupuncture upon the spontaneous discharges of the units in PAG was markedly reversed by naloxone in 6/7 units. But the activation effects of then eedling were not reversed by naloxone.
These results indicate that the inhibitory action of electro-acupuncture upon the neurons in the mesencephalic central gray is closely related to the activity of opiate receptors and the opioid substances. But the activation effect by needling may likely occur through other transmitters such as 5-HT.

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