Effects Of Morphine On Action Potential Of Peripheral Nerve Trunks And Its Conduction Velocity Of Rat

Objective Morphine is a representative of the opium antalgesic which mainly acts on the central nervous system. Some clinical studies have shown recently that morphine can bring about antinociceptic effect by combining with opioid receptors out of CNS [1,2]. The activition of opioid receptors directly and indirectly inhibit transmitter release of primary esthesioneure, which may be the important mechanism that opioid receptors educe analgesia effects in peripheral nervous system. This study assessed the effect of morphine , lidocaine and naloxone in action potential (AP) and conduction velocity of peripheral nerve in rats so as to investigate the local effect mechanisms of morphine and the synergistic action with local anesthetic.Methods 63 active and healthy wister rats with an average weight of 350g, offered by animal department of Shandong University School of Medicine, were randomized into seven groups: Group with normal saline, Groups with morphine of 0.1, 0.2, 0.3g/L respectively, Group with 0.02g/ L naloxone, Group with 0.25% lidocaine, Group with the mixed solution of 0.2g/L morphine and 0.25% lidocaine. Under room temperature of 20℃±3 ℃ and examined animal skin temperature of 34 ℃, the sciatic nerves were dissociated with traditional method. They were soaked in the 37 ℃ solutions of morphine, naloxone, lidocaine of above different concentration, andwere kept insulating, wet and warm with liquid paraffin and saline in 37 ℃ water bath. Stimulating electrode and leading electrode were put on distally extremity and proximum extremity of sciatic nerve respectively. The effects of nervus sensorius after soaked into the above solutions on amplitude, upward slope, downward slope of AP and conduction velocity of sciatic nerve were examined.Results1 .Comparing groups socked into morphine solution of different concentration for 40mins with group soaked into normal saline, amplitude of sciatic nerve action potential and conduction velocity decreased and even disappeared, its upward and downward slope extended (P<0.01). These effects showed dose-dependent. The change of amplitude of the AP was more obvious than the change of upward and downward slope.2.Naloxone can turnover the above decaying effect and can recover the amplitude, upward slope, downward slope of the AP and conduction velocity.3.After soaked into 0.2g/L morphine and 0.25% lidocaine respectively, amplitude of the AP and conduction velocity of sciatic nerve decreased (PO.Ol). Contrasting group soaked into mixed solution of morphine and lidocaine with group only soaked into lidocaine solution, the disappearing time of AP shortened and the recovering time of AP extended.ConclusionMorphine of opioid antalgesic can suppress action potential and conduction velocity of peripheral nerve trunk of mammalia animal rats. Naloxone presents exciting effect, which can turnover the depressive effect of the former. Morphine can shorten the effect-appearing time and postpone the action time of local anaesthetic.Besides the effect of centre mediated anti-nociceptive stimulus, results of this study have proved the existence of periphery anti-nociceptive stimulus and peripheral receptor system mediated analgesia mechanism of opioid antalgesic, which provides the theoretical foundation for rationality of the periphery administration route.