Abstract
Since acupuncture analgesia is abolished by lesion of periaqueduct central gray (PAG) or by treatment of naloxone and since the low frequency stimulation used for acupuncture analgesia is a kind of induction methods to induce animal hypnosis, the possibility of the involvement of PAG and of endogenous morphine like factor in acupuncture analgesia and a similarity of analgesia during animal hypnosis with the acupuncture anesthesia have been suggested. These proposed problems were investigated by recording single unit discharges of PAG and the center core of midbrain reticular formation (MRF) in unanesthetized and unrestricted 30 rabbits.
Spontaneous unit discharges of 89 PAG and MRF neurons which were selected not to responded to noxious stimuli were changed by induction methods to cause animal hypnosis such as inversion (INV.), pinching the base of the ear (P.E.) or acupuncture stimulation (A.S.) . Those changes were an increase or a decrease of firing rates of unit discharge which were observed in 28 and 63 neurons respectively in 126 such trials. 64% of these neurons were commonly responded in same direction by two or three procedures (INV., P.E. and A.S.) . In A.S., the changes of firing rates were induced after latent period and the induced changes lasted for long time after termination of stimulation (after-effect) . Unlike A.S., a latent period was lacking and after-effect was very slight in respondises to INV.. A majority of these neurons responding to INV., P.E. and A.S. were also responded in the same way to systemic application of morphine.
The data indicate that 1) the PAG is involved in the mechanism which causes acupuncture analgesia and analgesia during animal hypnosis ; 2) a morphine like substance is also involved in this mechanism and 3) the acupuncture stimulated state should be classified as animal hypnosis.
