Silent Nociceptive Neurons Are Involved In Acupoint Sensitization In A Chronic Colitis Model

ObjectiveColitis rats were used as research objects to observe :chronic colitis induced acupoint nociceptive sensitization and silent neuron phenomenon;The distribution and "arousal" characteristics of CHRNA3-labeled silent neurons under physiological and pathological conditions;Whether the acupoint hyperpathia and visceral pain sensitization induced by the colitis model are related to the activation of silent neurons;Whether the central sensitization of spinal dorsal horn induced by the colitis model is related to the "arousal" of silent neurons.MethodsIn this study,SD rats were used as experimental object,and the chronic colitis model was made by TNBS+50% ethanol.The experiment was mainly carried out on the 7th day after the model,which was divided into two parts:Experiment 1: Thirty-four male SD rats were randomly divided into normal(n=4),control,model and model+U0126 group(n=10).The distribution of Evans blue exudate points on the body surface of rats was observed and compared with the distribution of acupoints commonly used in the treatment of intestinal diseases to analyze its distribution.To observe the distribution of silent neurons in the peripheral tissues of rats and lay the foundation for experiment 2.Experiment 2:Thirty male SD rats in clean grade were randomly divided into control,model and model+U0126 group(n=10).The activation of DRG and SDH in silenced injury neurons was observed by immunofluorescence assay.To evaluate the role of silent injury neurons in pain-related behavioral responses induced by visceral inflammation,VMR was used to observe visceral pain sensitivity.Plantar mechanical referral pain was measured with hand-held Von Frey,caudosacral mechanical referral pain was measured with electronic Von Frey,and plantar thermal referral pain was measured with thermal radiometer.ResultsExperiment 1: TNBS+50% ethanol could cause significant colon inflammation.EB leaking dots were found in the sacrococcygeal skin which the same innervation segment of the colon.After injecting U0126,the inflammatory lesions of colon tissue were reduced and the EB leaking dots also reduced.We found CHRNA3+ labeled silent nociceptor were distributed in the sacrococcygeal skin,colon,DRG and the superficial layer of the spinal dorsal horn.The nociceptor were mainly classified as class C nociceptive neurons,which could activated by NGF and converted into mechanical responsivity.Experiment 2:In DRG,silent nociceptor can be activated by visceral inflammatory.In spinal dorsal horn,it could cause central sensitization in colon-related innervation segments.U0126 could block the activation of silent nociceptor in DRG and reduced SDH central sensitization.Silent nociceptor participate in mechanical referred pain sensitivity of visceral dilation,sacrococcygeal and plantar induced by experimental colitis in rats,except plantar heat referred pain.ConclusionThe silent nociceptor are participate in the formation of body surface and viscera hyperpathia induced by experimental colitis in rats,and the neural mechanism of acupoint sensitization is related to the active of silent nociceptor.