Abstract
In previous work, we found opioid receptors in the spinal cord of the afferent pathway from the acupuncture point to the pituitary gland in acpuncture analgesia (AA) caused by low frequency stimulation of the acupuncture point. Non-acupuncture point stimulation-produced analgesia (NAA) caused by non-acupuncture point stimulation after lesioning of the analgesia inhibitory system, was not naloxone reversible, but was dexamethasone reversible. Association of mu, delta and kapper, subtypes of opioid receptors in AA and NAA were investigated. Pain threshold was measured by tail-flick latency (TFL) . Drug was applied intraperitoneally or intrathecally through inserted cannule into the subarachonid space. AA was abolished by intrathecally applied antiserum of methionine-enkephalin (Met-Enk), but not by leucine-enkephalin (Leu-Enk) nor dynorphin (Dyn) . On the other hand, NAA was abolished by antiserum of Dyn, but not by antiserum of Met-Enk nor Leu-Enk. Intraperitoneal kapper receptor antagonist Mr2266 (5mg/kg) antagonized NAA. The kapper receptor agonist, U50-488H (5mg/kg) produced analgesia in animals in which the analgasia inhibitor system was lesioned and this was antagonized by dexamethasone as in NAA. Potentials evoked in the lateral part of the periaqueductal central gray (L-PAG) by stimulation of the non-acupuncture point were abolished 15 minutes after application of Mr2266 and recoverd 60 minutes after, whereas those evoked in the dorsal PAG by stimulation of the acupuncture point were not influenced by Mr2266. From these results, immunoreactive Met-Enk might be associated in AA, with transmission through opioid receptors of the acupuncture afferent pathway in the spinal cord, and Dyn might have smilar characteristics in NAA.
