The Role Of NMDA Receptor In Intrathecal Morphine-induced Pruritus And Its Mechanisms

IntroductionIntrathecal opioids administration is a common practice for anesthesia.Meanwhile,many patients can appear pruritus on their head,face and chest skin and some of them even terminate analgesic treatment because of severe pruritus.The mechanism of morphine induced pruritus is still not clear and medicine used to relieve the pruritus can reduce the efficacy of morphine and also reduce the satisfaction.According to the research,?-opioid receptor(MOR)isoform MOR1 D expressed in spinal cord is the specific receptor mediating pruritus signaling transmission which promotes dimerization of MOR1 D and gastrin released peptide receptor(GRPR).The activation of GRPR signaling lead to occurrence of pruritus.The interaction between C terminal of MOR and NR1 subunit of N-methyl-D-aspartate receptors(NMDARs)mediated by histidine triad nucleotide-binding protein 1(HINT1)and protein phosphatase C(PKC)involves in opioids tolerance.Since the similarity between pain and pruritus,the interaction between NMDAR and MOR1 D may also participate morphine induced pruritus.In addition,glutamate is an important neurotransmitter which mediates pruritus signaling in spinal cord.NMDAR is the glutamate receptor and its activation may also have involved in morphine-induced pruritus.Therefore,the aim of this study is based on the morphine-induced pruritus animal model and to explore the role of NMDAR and spinal cord tissue will be taken to detect activation of NMDAR signaling protein to reveal the effect of NMDAR in morphine-induced pruritus.Method(1)C57BL / 6 male mice were randomly divided into Na?ve group,normal saline group,morphine group(0.1 ?g,0.25 ?g,0.5 ?g,1 ?g).The animal model was established by intrathecal injection.The degree of pruritus was observed by video of mice within 30 minutes after injection.The degree of morphine induced pruritus was evaluated by counting the number of scratching.(2)To explore the effects of NMDA receptor agonists on the behavior of pruritus in mice,C57BL/6 male mice were randomly divided into normal saline group,NMDA group(5 nmol,0.5 nmol,0.05 nmol,0.005 nmol).The effects of NMDA receptor agonists on the behavior of pruritus in mice was evaluated by counting the number of scratches in mice for 30 minutes.(3)To explore the effects of NMDA receptor agonists on morphine-induced pruritus,C57BL/6 male mice were randomly divided into normal saline group,morphine + NMDA group(morphine 0.25 ?g + NMDA 0.05 nmol;morphine 0.25 ?g + NMDA 0.005 nmol;morphine 0.1 ?g + NMDA 0.05 nmol;morphine 0.1?g + NMDA 0.005nmol).The effects of NMDA receptor agonists on morphine-induced pruritus were evaluated by counting the number of scratching in the mice in 30 minutes.(4)To explore the effects of NMDA receptor inhibitor on morphine-induced pruritus: C57BL/6 male mice were randomly divided into normal saline group,morphine + ifenprodil group(morphine 0.5 ?g + ifenprodil 0.1 ?g;morphine 0.5 ?g + ifenprodil 0.5 ?g).The effects of NMDA receptor inhibitors on the morphine-induced pruritus were evaluated by counting the number of scratches in mice within 30 minutes.(5)The spinal dorsal horn tissue was taken after 5 minutes of intrathecal injection of morphine 0.5 ?g.The expression of and the phosphorylation of the NMDA receptor activation pathway like NR2 B,CAMKII were analyzed by Western Blot.Results(1)After intrathecal injection of 0.5 ?g morphine,it was observed that the mice had significant scratching response.The number of scratches in mice within 30 min was significantly higher than that in the control group,and the most obvious scratching response was observed within 10 min after administration.After 10 min of administration,the number of scratching in mice was significantly reduced.The degree of morphine-induced pruritus is related to the dose of morphine.(2)Intrathecal injection of NMDA receptor agonists did not affect the behavior of pruritus in mice.Among Different concentrations of NMDA receptor agonists,5 nmol and 0.5 nmol NMDA can result in obvious psychiatric symptoms and 0.05 nmol,0.005 nmol NMDA didn't cause obvious psychiatric symptoms.(3)Combined application of morphine and NMDA receptor agonists,Intrathecal injection of NMDA can increase the number of scratching of mice thus increase the degree of morphine-induced pruritus which is significantly higher than morphine group.(4)Combined application of morphine and NMDA receptor inhibitor ifenprodil,intrathecal injection of morphine 0.5 ?g and ifenprodil 0.5 ?g can significantly relieve morphine-induced pruritus.(5)Compared with the control group,Western Blot showed that NMDA receptor activation pathway-related protein was significantly increased in the spinal dorsal horn of mice after 0.5 ?g of intrathecal morphine.Conclusion(1)Intrathecal morphine can cause skin pruritus in mice.(2)NMDA receptor agonists NMDA can increase the degree of morphine-induced pruritus.(3)NMDA receptor inhibitor ifenprodil can relieve the degree of morphine-induced pruritus.(4)The expression of NR2B?CAMKII in the spinal dorsal horn of mice were increased after intrathecal injection of morphine.The activation of NMDA receptor pathway was involved in morphine-induced pruritus.