Effects Of α-2 Receptor And 5-HT3 Receptor On Synaptic Transmission And Pain Perception In The Spinal Dorsal Horn Of 6-OHDA Rats

Objective:Pain is one of the main non-motor symptoms of Parkinson’s disease(PD).The incidence of pain in PD can be as high as 40%-85%and its pathogenesis is not clear.Preliminary studies in our laboratory have shown that 6-OHDA rats perform hyperalgesia and increased neuronal excitability in the spinal dorsal horn,and inhibition of 5-HT3 receptor in the spinal dorsal horn can alleviate hyperalgesia and reduce neuronal excitability in the spinal dorsal horn in 6-OHDA rats.The aim of present study was to research effects of α-2 receptor and 5-HT3 receptor on synaptic transmission and pain perception in the spinal dorsal horn of 6-OHDA rats.Methods:The PD rat model was induced by microinjection of 6-OHDA in the substantia nigra pars compacta by means of brain stereotaxic injection.Three weeks after modeling,the motor ability of 6-OHDA rats was detected by rotarod test and open field test,striatal tyrosine hydroxylase expression was detected by western blotting method;The mechanical threshold and thermal threshold of 6-OHDA rats were detected by von frey test and radiant heat test.Four weeks after modeling,intrathecal injection ofα-2 receptor agonist clonidine(30 mg/kg).von frey method and radiant heat method were used to detect mechanical pain threshold and thermal pain threshold at different time points after administration of clonidine.Whole-cell patch-clamp recording of spinal cord slices was used to detect changes in synaptic transmission in dorsal horn neurons of 6-OHDA rats,changes of neural excitability in spinal dorsal horn before and after perfusion administration of α-2 receptor agonist clonidine and changes of synaptic transmission in spinal dorsal horn before and after perfusion administration of α-2 receptor agonist clonidine(10 μmol/L)and 5-HT3 receptor antagonist ondansetron(20μmol/L).Results:A rat model of PD induced by microinjection of 6-OHDA into bilateral substantia nigra pars compacta performs mechanical hyperalgesia and thermal hyperalgesia.Behavioral results showed that intrathecal injection of α-2 receptor agonist clonidine can significantly relieve mechanical and thermal hyperalgesia in 6-OHDA rats.Current-clamp results showed that the frequency of action potentials and the resting potentials of neurons in the spinal dorsal horn of 6-OHDA rats increased.Perfusion administration of α-2 receptor agonist clonidine can reduce the action potential frequency and increase rheobase of spinal dorsal horn neurons in L4-L6 segment of 6-OHDA rats.Voltage clamp results showed the excitatory synaptic transmission(sEPSCs)in the L4-L6 spinal dorsal horn region of the 6-OHDA rats was enhanced,but the inhibitory synaptic transmission(sIPSCs)did not change significantly,compared with the rats in the Sham group.Perfusion administration of α-2 receptor agonist clonidine can significantly reduce the frequency of sEPSCs in the dorsal horn of spinal cord in 6-OHDA rats,but has no significant effect on the amplitude of sEPSCs;Perfusion administration of the α-2 receptor agonist clonidine can significantly increase the amplitude of sIPSCs in the spinal dorsal horn of 6-OHDA rats,but has no significant effect on the frequency of sIPSCs.Perfusion administration of 5-HT3 receptor antagonist ondansetron can significantly reduce the amplitude of sEPSCs in the spinal dorsal horn of 6-OHDA rats,but has no significant effect on the frequency of sEPSCs;Perfusion administration of the 5-HT3 receptor antagonist ondansetron can significantly reduce the frequency of sIPSCs in the spinal dorsal horn of 6-OHDA rats,but has no significant effect on the amplitude of sIPSCs.Perfusion administration of 5-HT3 receptor antagonists can reverse the increase in the amplitude of sIPSCs in the dorsal horn of spinal cord caused by administration of clonidine.Conclusion:Our study showed that excitatory synaptic transmission was enhanced in spinal dorsal horn neurons in 6-OHDA rats,but inhibitory synaptic transmission was unchanged.Agitation of α-2 receptor reduces the excitability of spinal dorsal horn neurons in 6-OHDA rats by inhibiting presynaptic excitatory synaptic transmission and enhancing inhibitory synaptic transmission,while inhibiting 5-HT3 receptor inhibits postsynaptic excitatory synaptic transmission,reducing the excitability of spinal dorsal horn neurons in 6-OHDA rats,thereby alleviating pain sensitivity in 6-OHDA rats.