Dexmedetomidine Alleviates Neuropathic Pain Via The TRPC6-p38 MAPK Pathway In The Dorsal Root Ganglia Of Rats

Objective:Neuropathic pain is a chronic pain directly caused by injury or disease of the somatosensory nervous system.It is characterized by spontaneous pain,nociceptive hyperalgesia and sensory abnormalities.Due to the complex mechanism of neuropathic pain,it currently lacks effective treatment in the clinical work.Transient receptor potential cation 6(TRPC6)is a non-selective calcium channel protein that is sensitive to mechanical stimuli and injurious temperature stimuli.Dexmedetomidine(Dex)is an α2adrenergic receptor agonist with desirable analgesic effects.Both receptors regulate intracellular calcium ion levels to produce biological functions.However,the relationship between TRPC6 and Dex is currently unclear.We hypothesize that the analgesic effect of dexmedetomidine may be closely linked to the TRPC6 channel.The aim of this study was to investigate whether dexmedetomidine relieves neuropathic pain in rats by regulating the TRPC6 pathway in the dorsal root ganglion.Methods:Male SD rats were randomly divided into sham-saline(NS)group,chronic compressive injury(CCI)-NS group and CCI-Dex group.Each group was divided into 4subgroups according to time points.The changes of thermal retraction threshold(TWL)and mechanical retraction threshold(MWT)were recorded at different time periods.TRPC6 m RNA expression in the dorsal root ganglion was detected using q-PCR;Western blot was used to detect changes in the expression of TRPC6,Iba-1,p38 and other proteins;ELISA was used to detect the expression levels of inflammatory factors TNF-α and IL-1β in the dorsal root ganglion;immunofluorescence staining was used for localization analysis.Statistical analysis was performed using Graph Pad Prism 8.Results:(1)Dexmedetomidine relieved CCI-induced mechanical pain and thermal pain hypersensitivity.On the seventh postoperative day,the mechanical pain threshold was significantly reduced in the CCI-NS group,while there was a significant increase in the CCI-Dex group compared with the CCI-NS group.Meanwhile,on the seventh day after administration,the thermal pain thresholds of rats were significantly increased compared with the CCI-NS group.(2)Dexmedetomidine inhibited TRPC6 expression in CCI-induced DRG.After surgery,q-PCR results showed that TRPC6 m RNA expression increased with time,while in the CCI-Dex group,TRPC6 expression was inhibited.Similarly,the results of Western blot confirmed that dexmedetomidine could significantly inhibit the expression of TPPC6.Immunofluorescence confirmed that TRPC6 was mainly expressed in dorsal root ganglion neurons.It was also found that a large number of microglia proliferated around neurons in the CCI-NS group,while the proliferation of peripheral microglia was significantly reduced after continuous dexmedetomidine administration.(3)Continuous administration of dexmedetomidine significantly alleviated the levels of peripheral inflammatory factors.(4)Western blot results showed that p38 was not significantly different in the three groups,while phosphorylated p38 was significantly upregulated in the CCI group,and dexmedetomidine could inhibit the level of phosphorylated p38.Conclusion:The experimental results showed that dexmedetomidine could effectively alleviate mechanical and thermal pain hyperalgesia in CCI neuropathic pain model rats.The underlying mechanism may be closely related to the inhibition of TRPC6 expression in peripheral dorsal root ganglia,reduction of microglia proliferation,down-regulation of downstream p38 phosphorylation and alleviation of peripheral nerve inflammatory response.