Abstract
It was found previously that the individual variations of analgesia caused by 1Hz stimulation of the tibial muscle (Tsusanli point) was quite parallel to that of analgesia caused by intra-peritoneal 0.5 mg/kg morphine and that both analgesia were abolished by the anterolateral tract lesion. Therefore it was suggested that individual variations of both analgesia might exist in the spinal cord transmission involved the opiate receptor in the acupuncture afferent pathway from the acupuncture point to the hypophysis. It was also found previously that the individual variations of both analgesia were abolished by D-phenylalanine which is known as the inhibitor of the enzyme for degradation of the endogenous morphine like factors. In present exprement, the individual variations of the analgesia were examined by the threshold and amplitude of the potential in the dorsal part of the periaqueductal central gray (D-PAG) evoked by the acupuncture point stimulation, since it was found previously that potential in the D-PAG was specially evoked by stimulation of the acupuncture point. Rats were classified into responder or non-responder by presence or absence of a significant (p<0.05) increase of the tail flick latency. Potentials in the D-PAG evoked by stimulation of the tibial muscle integrated 30 times. Evoked potential in the D-PAG caused by acupuncture point (tibial muscle) stimulation was abolished by intra-peritoneal 1 mg/kg naloxone, while that in the lateral part of the PAG caused by non-acupuncture point (abdominal muscles) was not influenced. The stimulus threshold to produce D-PAG evoked-potential is always about 1 volt lower in 0.05 msec rectangular pulse in the responder than in the non-responder. The amplitudes of the D-PAG evoked potential are always heigher in the responder for each stimulus strength than those in non-responder and did not reach to those in the responder. After treatment of intra-peritoneal 250 mg/kg DPA, the threshold strength to cause D-PAG evoked potential in the non-responder decreased to that of the responder and height of it in non-responder also increased to that of the responder. It was concluded that the individual variatons of effectiveness in acupuncture analgesia might be originated in the spinal transmission involved the opiate receptor and DPA act on this transmission to abolish individual variations.
