Effects Of Low Level Laser On The Expression Of TRPV4 And Pain Sensitivity In Rat DRG After Sustained Compression

BackgroudNeuropathic pain(NP)refers to the pain directly caused by the lesions or related diseases that affect the somatosensory system.The course of NP is repeated and hard to cure.It is a global health problem,involving 6.9%-10%of the global population.Radicular neuralgia caused by lumbar disc herniation is one of the most common neuropathic pain,usually accompanied by hypersensitivity and hyperalgesia.Central sensitization is an important pathogenesis of NP.The chronic compression of the dorsal root ganglia(CCD)model in rats can simulate the pathological changes of nerve compression,which has the advantages of simple operation and high success rate,and can trigger stable spontaneous and induced pain symptomsTransient receptor potential vanilloid 4(TRPV4)is a kind of non selective cation channel,which is widely distributed in nervous system,lung,kidney.testis,skin and other tissues.It can be activated by a variety of physical and chemical stimulation,such as hypotonic,mechanical deformation,high temperature,inflammatory medium(arachidonic acid),changes of intracellular and extracellular calcium concentration,so it can participate in many biological functions,such as nerve cell signal transmission,cell growth and regulation.Low level laser therapy(LLLT)is widely used in the field of physical medicine and rehabilitation.It has a good effect on pain treatment.especially musculoskeletal pain,and also has a certain effect on neuropathic pain.Low level laser therapy can accelerate the healing of injured tissue,reduce local inflammation and edema,restore local blood supply and inhibit local pain.Research objectiveTo observe the effect of low level laser on the pain sensitivity of CCD rats and the changes of TRPV4 expression and distribution in spinal dorsal horn,and to explore the mechanism of low-energy laser analgesia on CCD ratsResearch method1.Establishment of the rat model of sustained compression of dorsal root ganglionThirty six healthy male Wistar rats(each weighing 1 80-200g,purchased from the animal experimental center of Shandong University)were divided into blank group,CCD group and laser group.The L-bar with diameter of 0.63mm was inserted into L4/L5 intervertebral foramen of rats in CCD group and laser group.In the blank group,the operation steps were the same except that the steel bar was not inserted.2.Low level laser irradiation treatmentIn the laser group,810nm low level laser was given to the L4/L5 spinal cord segment through the skin on the 4th day after CCD.The output power was 150MW,10min/time,7 times in a row.The blank group and the CCD group were not given laser treatment,and the feeding conditions of the three groups were the same.3.Behavioral measurement-the threshold of claw retraction response to mechanical stimulation and the latency of hot claw retractionBefore and on the 4th,7th and 11th day after operation,the response threshold of mechanical stimulation and the incubation period of thermal contraction were measured,and the changes of mechanical pain threshold and thermal pain threshold were observed.4.Detection of TRPV4 protein expression and positive cell distribution in spinal dorsal hornOn the 11th day after the operation,the rats were killed and collected after the behavioral test.Western blot was used to detect the protein expression of TRPV4 in spinal dorsal horn of each group,and immunofluorescence was used to detect the distribution of TRPV4 positive cells in each group.Result1.Changes of mechanical pain and thermal pain threshold in rats after CCD operationCompared with the blank group,the mechanical pain threshold and thermal pain threshold in the CCD group decreased on the 4th,7th and 11th day after operation(P<0.01).Compared with CCD group,the mechanical pain threshold and thermal pain threshold of laser group were significantly higher on the 7th and 11th day after operation(P<0.01).2.Expression of TRPV4 protein and distribution of positive cells in spinal dorsal hornOn the 11th day,compared with the control group,the expression of TRPV4 in the dorsal horn of the spinal cord in the CCD group was significantly up-regulated(P<0.01),and the number of TRPV4 positive cells in the laser group was significantly down regulated(P<0.01),while the number of TRPV4 positive cells in the laser group was significantly down regulated(P<0.01).ConclusionLow level laser may alleviate the pain sensitivity caused by CCD by affecting the expression of TRPV4 protein in spinal dorsal horn.