Dorsal Root Section Chronic Compression Model Small Cell Sympathetic Sensitized No - Cgmp - Pkg Signaling Pathways

Sympathetically maintained pain (SMP) is a commonly encountered chronicdisease in the clinic, which will be relieved by local anesthetics applying on thepainful region that dominated by sympathetic nerve. A feature of SMP is that thepain depends on the sympathetic nerve activity and/or the catecholamine level incirculation system, and thus was called sympathetic sensitization. In the cell level,the sympathetic sensitization exhibit an abnormal increase in neuronalexcitability after the stimulation on sympathetic nerve or an application ofnorepinephrine, which means either the decrease of strength of stimuli for anevoked action potential, or an increase of the number of ectopic spontaneousdischarges. The small DRG cells are traditionally supposed to transmit paininformation. The hyperexcitablity exists on small cells in neuropathic painsituation, but there’s no report about the sympathetic sensitization on the soma ofsmall cells, neither the signaling pathway involved in this sensitization. In thisstudy, the following questions would be investigated: First, whether thesympathetic sensitization exist on the small DRG cells after CCD? Second, whichsignaling pathway is involved in sympathetic sensitization if it displays on the small DRG cells after CCD.Aim: We designed the experiments according to this idea to reveal the signalingpathway and ion channel mechanisms of sympathetic sensitization on small DRGcells after a chronic compression of the dorsal root ganglion.Methods: Our experiment based on the CCD model on mouse and chose the C57mice as experiment object. We investigate sympathetic sensitization on injuredDRG small cells with behavior testing、patch clamp technologies. Also, variousdrug application were carried on to investigate the signaling pathway and ionchannel mechanisms involved in sympathetic sensitization.Results:1. Hyperalgesia appeared in CCD group.The PWT in the CCD group begin to descend, and was obvious lower than thatof control group at7d. The PWT declined to0.13g at7d comparing to that ofcontrol group, which was0.32g.2. Sympathetic sensitization on DRG small cells after CCD.On neurons with diameter of less than25μm, we recorded three typesreaction in response to NE, excitation、inhibition and suppress after excitation. InCCD group, there were58out of90examples which were excited by NE;fourteen out of90examples were suppressed by NE; sixteen examples with noreactions to NE; and the rest were excited first and later suppressed by NE. Andin control group, there were2out of10examples were excited by NE; two out of10examples were suppressed by NE; while other6examples with no reactions toNE.3. The antagonist of α2receptor can inhibit sympathetic sensitization.Yohimbine inhibited the excitation induced by NE on small cells after CCD,so the NE sensitization of DRG small neurons was mediated by α2receptor. 4. NO-cGMP-PKG signaling pathway involved in sympathetic sensitization.The agonist and antagonist of the NO-cGMP-PKG pathway were applied. Itwas found that NO donor-SNAP increased the excitation on sympatheticsensitization neurons, the number of spikes increased from8.36±1.08to11.72±1.26,(P>0.05)；ODQ, the inhibitor of cGMP, inhibited the excitation onsympathetic sensitization neurons, the number of spikes decreased from14.09±2.02to8.64±1.88(P<0.05); KT5823, which is the inhibitor of PKG,inhibited the excitation on sympathetic sensitization neurons, the number ofspikes decreased from15.56±2.07to9±0.75(P<0.05).Conclusion:1. The sympathetic sensitization exists on DRG small cells after CCD.2. NE excited neurons via α2receptor in sympathetic sensitization.3. NO-cGMP-PKG signaling pathway is involved in sympathetic sensitization. Presently, there are clear evidences that ectopic firing in injury nerve or DRGcould be a major contributor to the neuropathic pain. So lots of work has beendone to explore the ion components of ectopic discharge. But till now there wereno investigations referring to specific firing patterns which might mediatespecific pain feeling, such as hyperalgesia, allodynia and spontaneous pain. Thealteration of the ion currents were checked without clear index for neuron’sactivity which is correlated to a certain kind of pain signal, thus, it would influence the exploration of the current mechanism for pain signal.Aim: Based on the prediction that EB is the pain signal of mechanical allodynia,the ion components involved in EB production were explored and multipleconductances were considered in the production of EB.Methods: On the normal and CCD rats, the intact ganglion and patch clamptechnical were used to investigate the ion channel mechanisms of EB, as well asthe possible candidates for sympathetic sensitizationResults:α-DTX involved in EBα-DTX is the inhibitor of low threshold of potassium current and specificallysensitive to Kv1.1,1.2and1.6. DTX of1nM increased the excitability of DRGneuron and increased the duration of EB (n=5), spontaneous firing might appearon some previously silent neurons after the application of α-DTX (n＝2).Conclusions:IDTXcontributed to the modulation of EB appeared on the chronically compressedDRG Aβ neurons.