Study On The Effect And Mechanism Of Warm Stimulation At Acupoints On Pain Induced By Lumbar Disc Herniation In Rats

Lumbar disc herniation(LDH)is a syndrome with backleg pain which is caused by irritating or compressing the adjacent spinal nerve roots because of herniation of the nucleus pulposus of the lumbar disc alone or together with the fibrous ring and cartilage endplates.As people’s working and living style change,the incidence of LDH is increasing due to sedentary and incorrect posture in younger people as well.As the effect of therapy is not satisfied,LDH brings great trouble for patients’ lives and work.Our previous study showed that the endogenous descending facilitation and descending inhibition of nociception were mediated by the mediodorsal nucleus(MD)and ventromedial nucleus(VM),respectively,and warm stimulation at 43℃ could alleviate pain by activating the endogenous descending inhibition alone.In this study,effects of 43℃ warm stimulation at different acupoints at the second lumbar plane on endogenous descending modulation of nociception were observed,and its thalamic P2X3 receptor-related mechanisms were explored by observing the bilateral mechanical/thermal stimulation induced paw withdrawal reflex in a rat model of lumbar disc herniation.Hopefully,it can provide new ideas for clinical treatment of lumbar disc herniation.Objective:1.To explore the changes in the endogenous descending modulation of nociception in a rat model of lumbar disc herniation.2.To explore the effects of 43℃ warm stimulation at different acupoints as Mingmen acupoint,Jiaji acupoint and Shenshu acupoint on the endogenous descending modulation of nociception in LDH rats.3.To explore the thalamic mechanisms associated with the effects of 43℃ warm stimulation at Jiaji acupoint and Shenshu acupoint on the endogenous descending modulation of nociception in LDH rats.Methods:1.Establishment of the rat model of lumbar disc herniation: Tails were severed in SD female rats,the autologous nucleus pulposus were extracted and prepared into a suspension.20μl suspension was injected epidurally into the interspace of the fourth and fifth lumbar vertebrae 7 days after tail severing.Mechanical paw withdrawal threshold and paw withdrawal thermal latency were measured bilaterally before and 1-21 days after tail severing.2.Therapeutic intervention: On the 10 th day after tail amputation,43℃ heating-needle stimulation was applied at unilateral Mingmen point,Jiaji point or Shenshu point for 45 minutes,mechanical paw withdrawal threshold and paw withdrawal thermal latency were observed 2-4h and 1-10 days following warm stimulation.3.To explore the mechanism: To explore the differences in the efficacy of 43℃ warm stimulation at Jiaji acupoint and Shenshu acupoint.(1)To explore whether bilateral increased mechanical paw withdrawal reflex threshold induced by heating-needle stimulation is related to changes in endogenous descending facilitation after heating-needle stimulaiton: 2% lidocaine was microinjected into the thalamic MD nucleus on the 10 th day after tail amputation in rats.30 minutes after injection of lidocaine,43℃ heating-needle stimulation was applied at Jiaji acupoint and Shenshu acupoint.Bilateral paw withdrawal reflexes induced by mechanical/thermal stimulation were evaluated 30 minutes after injection of lidocaine and 2-4h after heating-needle stimulation.(2)To investigate the thalamic mechanisms in heating-needle stimulation at different acupoints induced heat hypoalgesia: different doses of the P2X3 receptor antagonist A-317491 were microinjected into thalamic VM nucleus 1 day after heating-needle stimulation,bilateral paw withdrawal reflexes induced by mechanical/thermal stimulation were evaluated before,30 minutes and 1-4h after the administration of the drug.Results:1.Bilateral paw withdrawal mechanical threshold decreased significantly following tail amputation and gradually recovered at the seventh day.After epidural injection of autologous medullary suspension(20μl suspension+30μl 2% lidocaine),bilateral paw withdrawal mechanical threshold decreased significantly(P < 0.05),whereas no significant changes in bilateral paw withdrawal thermal latency were observed(P > 0.05).2.After 43℃ heating-needle stimulation at different acupoints for 45 minutes,bilateral paw withdrawal mechanical thresholds were significantly increased in all experimental groups,and bilateral paw withdrawal thermal latencies were significantly prolonged.The best efficacy in Jiaji acupoint group was observed and lasted for 7d,the efficacy in Shenshu acupoint group lasted for 2d,the efficacy of Mingmen acupoint lasted for only 1d(P < 0.05).3.Injection of 2% lidocaine into thalamic MD nucleus significantly depressed mechanical hyperalgesia in LDH rats(P < 0.05).30 minutes after injection of lidocaine/saline into the MD nucleus,43℃ 45 minutes heating-needle stimulation was applied at Jiaji acupoint,significant increased bilateral paw withdrawal mechanical thresholds were observed in LDH rats(P < 0.05).4.Heat hypoalgesia induced by heating-needle stimulation at Shenshu acupoint was reversed by intracerebral injection of low dose of P2X3 receptor antagonist A-317491 into thalamic VM nucleus(P < 0.05),whereas heat hypoalgesia induced by heating-needle stimulation at Jiaji acupoint was depressed by intracerebral injection of higher dose of P2X3 receptor antagonist A-317491 into thalamic VM nucleus(P < 0.05).Conclusion:1.The endogenous descending facilitation enhanced,while the descending inhibition was not affected in female LDH model rats.2.Warm stimulation of lumbar acupoints at 43°C could effectively relieve mechanical hyperalgesia and activate descending inhibition in LDH rats.43°C warm stimulation at Jiaji acupoint showed best efficacy in LDH treatment.3.The relief of mechanical hyperalgesia by warm stimulation at acupoints in LDH model rats was not due to the depression of descending facilitation.4.P2X3 receptors in thalamic VM nucleus are involved in descending inhibition induced by warm stimulation at acupoints.