Regulation Mechanism Of 5-HT3 Receptor On Pain In Parkinson’s Disease Rat Model At Spinal Dorsal Horn

Background:Parkinson’s disease(PD)is an age-related neurodegenerative disease,which is affected by environmental and genetic factors,with high incidence,complex pathogenesis and concomitant occurrence of non-motor symptoms.Pain is one of the common non-motor symptoms in PD patients,which seriously affects their quality of life,although the specific pathogenesis is not clear.We used a 6-OHDA induced PD rat model,explored the mechanism of 5-HT3 receptors involved in the occurrence of pain in PD at the spinal cord.We found a new view to provide a theoretical basis for the treatment of clinical PD pain.Materials and methods:The bilateral substantia nigra densification was used as the registration site,and the 6-OHDA induced PD rat model was injected with brain stereotactic apparatus.Three weeks later,the rotarod test and open-field experiments were conducted to determine the motor ability of the Sham group and the 6-OHDA group Western blot was used to detect the protein levels of TH in striatum and 5-HTA receptor and 5-HT1A receptor in L4-L6 segment of spinal cord.The expression of TH-positive neurons in the substantia nigra was detected by immunofluorescence technique.The mechanical pain threshold and thermal pain threshold of Sham group and 6-OHDA group were determined by using the electronic Von Frey test and the tail flick test.Isoflurane was used to anesthetize the rats,and the pain threshold was determined by intrathecal injection of the 5-HT3 receptor antagonist Ondansetron or the agonist M-CPBG at 15 min,30 min,45 min,60 min,90 min and 120 min respectively.Whole-cell patch clamp method was used to record the cell electrical activity in the dorsal horn of the spinal cord of L4-L6 at the age of 4-6 weeks,and the changes of electrophysiology-related indicators such as action potential frequency,action potential,threshold and membrane resistance were analyzed.Results:Three weeks later,the rotarod test results showed that the rod stay time of rats in the 6-OHDA group was significantly lower than that in the Sham group,indicating that the motor ability of rats in the 6-OHDA group was impaired.The open-field results showed that the total movement distance and average speed of the 6-OHDA group were not significantly different from that of the Sham group,indicating that the voluntary movement ability of the rats was not affected.Immunofluorescence results showed that dopaminergic neurons in the dense part of the substantia nigra were lost,and Western blot results showed that the protein expression of TH was significantly reduced by 50-70%,indicating the success of modeling.There was no significant difference in the protein expression of 5-HT3A and 5-HT1A in the spinal dorsal horn.The results of Von Frey and tail flick test showed that the mechanical pain threshold and thermal pain threshold of the 6-OHDA rats were significantly lower than that of the Sham group,indicating that the 6-OHDA rats had hypersensitivity.Intrathecal injection of 5-HT3 receptor antagonist Ondansetron(100 μg)can effectively decrease hypersensitivity of 6-OHDA rats,while the agonist M-CPBG(100 μg)has no significant change hypersensitivity in the of rats.The electrophysiological results showed that the excitability of spinal dorsal horn neurons in the 6-OHDA group increased significantly,the action potential threshold decreased significantly,and the membrane resistance did not change significantly compared with that in the Sham group.After infusion of 5-HT3 receptor antagonist Ondansetron(10 μmol/L),the excitability of spinal dorsal horn neurons in the 6-OHDA group was significantly reduced,the threshold value of action potential was increased,the maximum frequency was significantly reduced,and there was no significant change in half-width.The excitability of spinal dorsal horn neurons in the 6-OHDA group was not affected by the agonist M-CPBG(10 μmol/L).The 5-HT1 receptor antagonist WAY-100635(10 μmol/L)had no significant effect on the excitability of spinal dorsal horn neurons in 6-OHDA rats.conclusions:In the spinal dorsal horn,the 5-HT3 receptor rather than the 5-HT1 receptor,may be involved in hypersensitivity in the 6-OHDA rat PD model by increasing receptor sensitivity.Inhibition of 5-HT3 receptor can improve pain sensitivity in PD model rats induced by 6-OHDA.