Functional Expression Of Glycine Receptors In DRG Neurons Of Mice

Objective:Glycine receptors（Gly Rs）are one of the ligand-gated chloride channels composed of combinations of fourαsubunits and oneβsubunit.In the adult spinal cords,the majority of inhibitory glycinergic synaptic transmission requires the involvement of glycine receptorα1 subunit（Gly Rs-α1）.The reduced glycinergic inhibition is regarded as one of the key spinal mechanisms underlying pathological pain.However,the distribution and function of Gly Rs in the periphery remain unclear as yet.This study was designed to investigate the possible role of Gly Rs in the dorsal root ganglia（DRG）of mice in the modification of nociceptive transmission.Method:We examined the localization of Gly Rs-α1 in the DRGs of adult mice by performing immunohistochemistry.The biotinylation assays were conducted to observe the effects of peripheral inflammation on the expression of Gly Rs-α1 on the plasma membrane of DRG neurons.Behavioral tests were performed to study the influence of Gly Rs-selective agonists and antagonists on the painful responses.Results:（1）Gly Rs-α1 was detected in the DRG neurons,but not in the DRG astrocytes.（2）The DRG neurons expressing Gly Rs-α1 included the neurofilament200-positive（NF200⁺）myelinated neurons,calcitonin gene-related peptide-positive（CGRP⁺）peptidergic nociceptors and isolectin B4-positive（IB4⁺）non-peptidergic nociceptors.Gly Rs-α1 was also densely distributed in the sciatic nerves of mice.（3）Local injection of Gly Rs-selective antagonist strychnine（0.15-1.5 nmol）in L5 DRG of intact mice evoked mechanical allodynia,thermal hyperalgesia and cold allodynia in a dose-dependent manner.（4）Intraplantar injection of strychnine（0.15-1.5 nmol）in intact mice also evoked mechanical allodynia,thermal hyperalgesia and cold allodynia in a dose-dependent manner.（5）Neither intraganglionar nor intraplantar injection of strychnine（0.15-1.5 nmol）affect the motor function of mice.（6）The inflammatory pain caused by formalin correlated with the reduction of Gly Rs-α1expression on the plasma membrane of DRG neurons.Inhibition of protein kinase C（PKC）,but not c AMP–dependent protein kinase（PKA）,reversed the reduction of surface Gly Rs-α1 expression in the DRGs of inflamed mice.（7）Intraplantar injection of glycine（3 nmol）effectively alleviated the first-phase painful behaviors induced by formalin.（8）Intraplantar injection of another Gly Rs-α1 allosteric modulator Zn²⁺（20nmol）generated similar analgesic action.Conclusion:Functional Gly Rs was widely distributed in the periphery and activation of these Gly Rs effectively alleviated inflammatory pain.