Electrophysiological Study on the Influence of the Morphine Microiontophoresis on Firing Activity of Neurons in Nuclei Related to Acupuncture Analgesia

Abstract

Background and Aim: Many nuclei such as periaqueductal central gray (PAG), raphe magnus nucleus (RMG) and gigantocellular reticular nucleus (Gi) are related in acupuncture analgesia. The aim of this study is to find the analgesic characteristics when dorsolateral periaqueductal gray (DLPAG), ventrolateral periaqueductal gray (VLPAG), RMG and Gi were individually stimulated in rat. Methods: Wistar rats (200~230g) were used in experiments. Rats were put in a small plastic box except the tail when the tail of a rat was stimulated by using radiant heat, tail flick latency (TFL), threshold of the painful response on account of the radiant heat was determined. The stimulus experiments were performed 3 to 5 days after inserting the electrodes. The current intensity for microiontophoresis is 30nA and time is 20s. Results: When DLPAG was locally stimulated in rats, the analgesia gradually appeared. Its characteristics resembled those of electroacupuncture at ST36 point. And then the analgesic effect appeared only in the period when VLPAG, RMG and Gi were individually stimulated in rats, but didn’t appear after cessation of stimulation. The rates of the excited neurons in the VLPAG, RMG and Gi were increased by microiontophoresis of morphine. Conclusion: There are mechanisms inhibiting the painful impulse in input of spinal cord by influence of endogenous morphine-type substance affecting neurons in VLPAG, RMG, and Gi among the mechanisms of electroacupuncture analgesia on ST36 point.