Effect And Mechanism Of Tropisetron On Chronic Neuropathic Pain In Rats By Activating α7nAChR

ObjectiveTo explore the effects and mechanism of intrathecal injection of tropisetron(Tro)on chronic neuropathic pain induced in rats after nerve injury by activating alpha 7 nicotinic acetylcholine receptor(α7n ACh R).MethodsSPF male healthy adult SD rats,weighing 180-220 g,were provided by the Experimental Animal Center of Hubei University of Medicine.According to the random numerical table method,the rats with successful SNI model and spared nerve injury(SNI)were randomly divided into Sham group,SNI group,Tro group,α7n ACh R antagonist Methyllycaconitine citrate group(MLA group)and MLA + Tro group.In the Sham group,only the sciatic nerve and its branches were exposed and dissociated,and the sural nerve was not damaged.SNI group,Tro group,MLA+Tro group and MLA group were all operated on SNI model.The dose-effect curve was drawn by observing the paw mechanical withdrawal threshold(PMWT)1 hour after intrathecal injection of different doses(1 μg,3 μg,10 μg,30 μg,100 μg,300 μg)Tro to determine the maximum analgesic effect(Emax)and 95% effective dose(ED95)of Tro.The time and peak of drug effect were determined by observing the PWMT and paw withdrawal thermal latency(PWTL)at different time after intrathecal injection(H0.5,H1,H2,H4,H8).And the dose of MLA also was determined.The subsequent experiments based on the obtained drug doses and effect times.After the pain behavior measurement was completed on the 14 th day after operation,the same volume(10 μL)of drugs were injected intrathecally with microsyringes: Tro group was injected with tropisetron,MLA group was injected with MLA,and MLA+Tro group was injected with tropisetron 1 hour after MLA injection.ELISA was used to detect the expression levels of Interleukin-6(IL-6),Interleukin-1β(IL-1β)and tumor necrosis factor-α(TNF-α)in spinal cord tissue of rats in each group,and immunofluorescence staining and Western blot was used to observe the distribution and expression of α7n ACh R in spinal cord of rats in each group.The protein phosphorylated expressions of p38mitogen-activated protein kinase(p-p38MAPK)and c AMP-response element binding protein(CREB)in spinal cord of rats in each group were detected by Western blot.Results1.SNI induces mechanical stimulation hyperalgesia and thermal stimulation hyperalgesia in rats;2.The maximum effect(Emax)and 95% effective dose(ED95)of Tro were73.64% and 17.47μg respectively.Tro significantly reduced mechanical hyperalgesia and thermal allodynia,and the effects peaked at about 1 hour and0.5 hour and remained within 2 hours and 1 hour,respectively;3.SNI significantly increased the levels of inflammatory cytokines(IL-6,IL-1β and TNF-α)of spinal cord,but significantly decreased the contents of IL-6,IL-1β and TNF-α in Tro group;4.Compared with the Sham group,the expression level of α7n ACh R in the spinal cord of rats in the SNI group was significantly decreased,while 1 h after intrathecal injection of Tro the expression of α7n ACh R was not significantly increased compared with that in the SNI group;5.10μg α7n ACh R antagonist MLA abolished partially the analgesic effect of Tro;6.α7n ACh R antagonist MLA inhibited partially the anti-inflammatory action of Tro;7.Tro can down-regulate the phosphorylation of p38 MAPK and CREB in the spinal cord of rats after SNI surgery,and MLA can reverse the effect of Tro.ConclusionsIntrathecal injection of Tro can alleviate neuroinflammation and chronic neuropathic pain in rats after peripheral nerve injury.The mechanism of its action may be through the activation of α7n ACh R inhibits the activation of p38MAPK-CREB signaling pathway and the release of inflammatory factors,finally lead to the relief of pain.