Abstract
It was found previously that individual variation of the analgesia (AA) caused by 1 Hz stimulation of the Tsusanli point, the tibial muscle, is quite parallel to that of morphine analgesia (MA) caused by intraperitoneal application 0.5 mg/kg of morphine. It was suggested that such morphine analgesia might be caused by activation of the opiate receptor in the spinal cord of the acupuncture afferent pathway from the acupuncture point to the hypophysis since lesion of anterolateral tract abolished both AA and MA. Therefore, it was estimated that morphine has two actions in the spinal cord. ; one is the activation of the acupuncture afferent pathway and the other is the direct inhibition of the pain pathway. In present experiment, two morphine actions were examined by the dose reponse relationships appeared in the intraperitoneal, intrathecal or intracerebral application of morphine. Pain threshold was measured by tail flick latency of the rats. Intrathecal or intracerebral morphine was applied through catheter inserted to the spinal enlargement or to the 3rd ventricle. All rats were classified into responder or non-responder by presence or absence of the significant (p<0.05) increase of tail flick latency. The dose response relations of the intraperitonial and intrathecal morphine in the responder is different from those of the non-responder. The summated two dose-response relations in the responder were observed by intraperitoneal morphine of its maximums 0.5 mg/kg and above 10 mg/kg in the intraperitoneal morphine and 0.05 μg and above 10 μg in the intrathecal morphine, while single dose-response relation was observed in the non-responder by these morphine applications. The Scatchard plots of these dose-response relation, in which the relation between response per unit dose of morphine and response (%) were plotted, exibited two different lines in the responder, while single line in the non-responder. After lesion of the anterolateral tract or the dorsal part of the periaqueductal central gray, which are belonged to the acupuncture afferent pathway, the relation of the dose-response in the responder was resembled to that of the non-responder. The dose-response relation of the intracerebral morphine exhibited the simple one although that of the responder somewhat shifted to low dosed compared to that of the non-responder. It was concluded that morphine analgesia appearred only in the responder not in the non-responder was produced by activation of the opiate receptor in the acupuncture afferent pathway of the spainal cord.
