Pathogenesis Study Of Neuropathic Pain Based On Spinal Glycine Receptor

Neuropathic pain(NP)is a chronic pain arising from peripheral or central nervous system injures.This pathological pain is very difficult to cure,and it has brought great and persistent pain to the patient.Up to now,there are still no drugs or surgical programs has emerged that can completely cure the NP.Numerous studies have reported that NP is associated with the upregulation or downregulation of various neurotransmitters and neuromodulators.For example,NP can result in the abnormal expression of various neurotransmitters in the nervous system,such as endogenous opioid peptides,glutamate,and y-aminobutyric acid(GABA),which could be utilized for development of therapeutic treatments.New drugs and interventions targeting these neurotransmitters and their receptors may provide new possibilities for more efficient clinical treatment of NP.In recent years,a large number of studies have found that cannabinoids have a good therapeutic effect on various inflammatory pains and neuropathic pain,and elucidated this therapeutic effect is achieved by targeting glycine receptor α3(GlyRα3)of the α3 subtype in the spinal cord dorsal horn(SCDH).In addition to GlyRα3,a large number of GlyRals were distributed in SCDH.Studies have shown that cannabinoids can also enhance the function of GlyRαl in the SCDH to treat inflammatory pain.However,the function and expression level of GlyRα1 in NP have not been investigated in detail.Meanwhile,whether cannabinoids can target these GlyRals to treat NP remains unclear.The Spared nerve injury model(SNI)is a common animal model of neuropathic pain clinically.The SNI model of NP was established by ligating and transecting the common peroneal and sural nerves of C57BL/6J mice.The von Frey test was used to assess the degree of pain in the hind limbs of mice in this model.In addition,we also measured the function and protein expression level of GlyRal distributed in the SCDH by means of in vitro spinal cord slice electrophysiological recording and Western Blotting.The results indicate that neuronal excitability in SCDH was significantly increased in NP,and the increased neuronal activity of SNI mice was positively associated with pain withdrawal thresholds in the mice.We also recorded exogenous glycine activated current(IGly)and endogenous Miniature inhibitory postsynaptic currents(mIPSCs)in SCDH neurons of Sham and SNI groups using electrophysiological recording.The results showed that the frequency and amplitude of IGly and mIPSCs recorded in the SNI group were significantly higher than those in the sham group,suggesting that the function of GlyRal in the spinal dorsal horn was enhanced.The dose-response curves of glycine were also recorded.The results showed that although the glycine-induced IGly was significantly increased in the SNI group,the glycine dose-response curve did not change,indicating that the affinity of the glycine receptor and its ligand did not change,suggesting that the protein expression level of GlyRal may change.Then we analyzed the expression level of GlyRal by Western Blotting.The results showed that the expression level of GlyRal in the SCDH of SNI group was significantly higher than that of Sham group,indicating that the upregulation of GlyRαl function of glycine receptor may be due to the increased protein expression.By intrathecal injection of a specific inhibitor of calcium/calmodulindependent protein kinase Ⅱ/Ⅳ(CaMKⅡ/Ⅳ)and cyclic AMP response binding protein(CREB)phosphorylation,we found that the activation of CAMKⅡ/Ⅳ-CREB signaling transduction pathway is closely related to the up-regulation protein expression level of GlyRα1.Finally,intraperitoneal or intrathecal injection of a novel non-psychoactive cannabidiol Dehydroxylcannabidiol(DH-CBD)showed that it could further enhance spinal GlyRα1 function and inhibit SNI-induced hyperexcitation of spinal neurons.Ultimately,neuropathic pain in mice in the SNI group was alleviated in this way.In conclusion,we found that spinal GlyRal may be a key element in the intrinsic compensatory mechanism for NP,which is one of the effective targets for the treatment of NP.As a non-psychoactive cannabinoid specifically targeting the synthesis of GlyRα1 receptors,DH-CBD can effectively alleviate neuro-injurious neuralgia to a certain extent,and provides a new therapeutic strategy for the clinical treatment of NP.