Rebound Depolarization Of Substantia Gelatinosa Neurons In Rat Spinal Dorsal Horn

Objective:Chronic pain is a public health problem to be solved urgently with high incidence,and neuropathic pain is intractable,so it brings heavy burden to patients and society.Studies have shown that rebound depolarization is mediated by hyperpolarization-activated cation current(Ih)and T type calcium current(IT),and it can regulate neuronal excitability,participate in modulation of pain local neural circuits.Substantia gelatinosa(SG)neurons,laminae II in spinal dorsal horn,have been identified as the “central gate”,and play a crucial role in the transmission and modulation of nociceptive information.However,there are no reports so far on the characteristics and modulation mechanism of the rebound depolarization of SG neurons in spinal dorsal horn.Therefore,we used electrophysiological techniques to explore the characteristics and regulation mechanism of rebound depolarization of SG neurons,further clarify pain modulation mechanism of spinal,and provide new ideas and scientific basis for the research and development of drugs to treat chronic pain.Methods:4-week-old male Sprague-Dawley rats(N=66),weight 90~100g,were randomly divided into three groups: PSNL group(N=22),sham operation group(N=22)and control group(N=22).The mechanical threshold of the PSNL group and the sham operation group of preoperative and on 3,7,10 and 14 days after operation was recorded by Von Frey.15 days after the operation,in vitro parasagittal spinal cord slices were prepared and the rats were sacrificed.The basic characteristic of electrophysiology and responses to hyperpolarization stimulation of the 3 groups SG neurons were recorded by whole cell patch clamp technique(n=102).The comparison of PSNL group(n=34),sham operation group(n=34)and control group(n=34)is made.Effects of hyperpolarization-activated cyclic nucleotide gated cation(HCN)channel blockers and T-type calcium channel blockers on rebound depolarization were studied.Results:1.The mechanical threshold of the PSNL group surgery side on 7~14 days after operation was significantly lower than that of the sham operation group and the control group.2.In the PSNL group,34 SG neurons were recorded,and 26 neurons had rebound depolarization.In the sham operation group,34 SG neurons were recorded,and 19 neurons had rebound depolarization.In the control group,34 SG neurons were recorded,and 17 neurons had rebound depolarization.More than half of the SG neurons had rebound depolarization,and the probability of rebound depolarization in the PSNL group was significantly higher than the other 2 groups.3.In the PSNL group,the action potential thresholds were lower than that of the other 2 groups.The Rin and the action potential frequency in the PSNL group were significantly higher than that in the other 2 groups when they were stimulated by110 pA to 150 pA current.4.HCN channel blockers CsCl and ZD7288 strongly increased the latency of rebound depolarization but had no obvious effect on the amplitude.On the other hand,T-type calcium channel blockers NiCl2 and mibefradil significantly decreased the amplitude of rebound depolarization but had no obvious effect on the latency.Conclusion:1.The probability of rebound depolarization,the Rin and action potential frequency of rats SG neurons after PSNL surgery significantly increase when they are stimulated by current,and the action potential thresholds decrease.Which increase neuronal excitability and lead to mechanical hyperalgesia,and it suggest that rebound depolarization of SG neurons may be involved in modulation of chronic pain.2.The latency of rebound depolarization of SG neurons is modulated by HCN channel,and the amplitude is modulated by T-type calcium channel.