| Neuropathic pain is a rapid,intense,long-lasting pain syndrome that occurs after inflammation,trauma,and drug damage to the peripheral or central nerves,usually manifested as hyperalgesia,spontaneous pain,and ectopic pain,and the pain site is often far away from the injury area.Different,related to emotional and psychological factors,the pathogenesis is still unclear,and the current conventional treatment is not effective.Clinically,according to statistics,the incidence of neuropathic pain is about 6.9-10%.A large number of medical resources are devoted to the treatment of neuropathic pain every year,but the clinical pain relief is not satisfactory because the underlying mechanism is not fully understood.At present,there is a broad consensus that peripheral and central sensitization play an important role in the development of neuropathic pain,among which central sensitization is particularly important.Cut off pain transmission.A large number of studies have been conducted on small molecule peptides such as nerve growth factor(TGF),tumor necrosis factor(TNF),neurotrophin(NT-4),glial-derived neurotrophic factor(GDNF)and BDNF5,as well as substance P.Some progress has been made,but the exact mechanism of pain transmission remains unclear.In recent years,the role of BDNF in the nervous system has been gradually discovered and reported,and it plays an important role in neuronal survival and glial cell activation,thereby participating in the development and maintenance of neuropathic pain.Brain-derived neurotrophic factor(BDNF),a member of the neurotrophic factor family,is synthesized in small and medium-sized dorsal root ganglion neurons,and then transported anterogradely to primary afferent fibers in the superficial dorsal horn of the spinal cord,which not only promotes Neuronal growth and differentiation,and also act as neuromodulators to regulate neuronal excitability and synaptic plasticity.A large number of experiments have confirmed that traumatic brachial plexus injury,including brachial plexus avulsion injury,greatly increases the release of BDNF at the level of the spinal cord near the injury.The evidence confirms that BDNF knockout rats and the application of anti-BDNF antibodies can significantly alleviate neuropathic pain behaviors.BDNF acts through its high-affinity receptor-TRKB(tyrosine kinase B)-promoting receptor autophosphorylation,and we hypothesized that upon activation,BDNF-TrkB binding may maintain high intracellular CI by downregulating KCC2,thereby inhibiting neuronal excitation However,it has been reported that the BDNF-TRKB-KCC2 pathway plays an important role in nicotine withdrawal-induced inflammatory neuralgia,and whether it also plays a role in neuropathic pain after traumatic brachial plexus avulsion is unclear.In this study,a rat model of neuropathic pain after lower trunk brachial plexus avulsion was established to observe the effect of TRKB-specific antibody K-252 a on the expressions of BDNF,TRKB and KCC2,and to explore the role of BDNF-TRKB-KCC2 pathway in neuropathic pain.and its mechanism,aiming to provide a potential therapeutic target for neuropathic pain.Part One Establishment and behavioral evaluation of a neuropathic pain model induced by avulsion of the lower trunk of the brachial plexus in SD rats via anterior cervical approach and behavioral assessmentsMethods: Thirty adult male SD rats were divided into control group(n=10),sham operation group(n=10)and avulsion group(n=10).Rats were anesthetized by intraperitoneal injection of 1% phenobarbital(100 mg/kg).The brachial plexus is exposed through a parallel clavicle incision,from the sternum to the axillary region.The pectoralis major muscle was removed,leaving the cephalic vein intact.By locating the subclavian blood vessels,the upper,middle,and lower trunks of the brachial plexus were separated and exposed.After careful identification and confirmation,the lower trunks were separated.Grasp the lower trunk with forceps and pull it from the root near the spinal cord.The leakage of cerebrospinal fluid and the dorsal root ganglion during the operation are the signs of root avulsion.In the avulsion group,the inferior trunk of the brachial plexus was avulsed;in the control group,no treatment was performed;in the sham operation group,only incision was performed to expose and separate the trunks of the brachial plexus without damaging the nerve.The thresholds of mechanical pain withdraw,cold ectopic pain and thermal pain withdraw of the hind paws of the three groups of rats were detected on the 0th day before the operation,and on the 1st,3rd,7th,10 th,14th,and 21 st days after the operation.Results: There was no statistical difference in the mechanical pain evoked thresholds between the three groups on the 0th day before surgery.At1,3,7,10,14,and 21 days after the operation,the avulsion group rats showed atrophy of the front paw,decreased mechanical withdraw threshold of the hind paw,and increased cold ectopic pain score,but the thermal pain withdraw threshold was increased.There was no difference among the groups,and the daily activities of the rats in each group were not restricted.There were significant differences in hindpaw withdraw threshold and cold touch ectopic pain score between the avulsion group and the control group and the sham operation group(P<0.05).There was no significant difference in hindpaw withdrawal threshold and cold touch ectopic pain score between the control group and the sham-operated group(P>0.05).There was no difference in the thermal pain withdraw threshold among the three groups at each time point(P>0.05).Summary: The neuropathic pain model induced by avulsion of the inferior trunk of the brachial plexus through the anterior cervical approach is simple in operation,less surgical complications,less intraoperative bleeding,and low in mortality.Significant but no apparent thermal hyperalgesia occurred,and pain indicators remained unchanged until 21 days after surgery.Part Two The second part of the spinal cord histomorphological study of the model of neuropathic pain induced by avulsion of the lower trunk of the brachial plexus in SD rats through anterior cervical approach Histomorphological studiesMethod: Grouping is the same as the first part.On the 7th and 21 st days after the operation,the rats were overdose with 1% phenobarbital(200 mg/kg)anesthesia,and then the fresh spinal cord tissue of the C5-T1 segment of the avulsion side was collected to detect the expression of GFAP/BDNF by immunohistochemistry.Western Blot method was used to detect the expression of BDNF.Results: 7 and 21 days after operation,no abnormal expression was found in the spinal cord of the rats in the control group and the sham-operated group;the expression of GFAP/BDNF in the superficial layer of the dorsal horn of the C5-T1 spinal cord segment on the avulsion side of the avulsion group was detected by immunohistochemistry.Compared with the control group,there was a statistically significant difference(P<0.05).The expression of BDNF in the C5-T1 spinal cord segment on the avulsion side of the rats was significantly increased by Western Blot,which was significantly different from that of the control group(P<0.05).There was no significant difference in the expression of each protein between the control group and the sham-operated group.(P>0.05).Summary: The expression of neuralgia marker BDNF/GFAP in a neuropathic pain model induced by avulsion of the inferior trunk of the brachial plexus through the anterior cervical route was significantly increased.Academic performance is consistent.Part Three Uses K252 a to block the BDNF-TrkB-KCC2 pathway on the effect and mechanism of brachial plexus avulsion-induced neuropathic pain The therapeutic effect and mechanism of neuropathic pain.Methods: Forty adult SD male rats were divided into control group(n=10),sham operation group(n=10),avulsion group(n=10)and K252 a treatment group(n=10).In the K252 a group,5u L of K252 a was intrathecally injected into the C7-C8 segment every day for three consecutive days after avulsion.Behavioral examinations(mechanical hyperalgesia,cold allodynia,and thermal hyperalgesia)were performed on the four groups of rats before operation and at 1,3,7,10,14,and 21 days after operation.On the 7th and21 st days after the operation,the rats were sacrificed by excessive intraperitoneal anesthesia with phenobarbital(200 mg/kg),and then the spinal cord tissue of the C5-T1 segment of the avulsion side was collected,and the expression of GFAP/BDNF/TrkB was detected by immunohistochemistry.,Western Blot method to detect the expression of BDNF/TrkB/KCC2.Results: No abnormal expression was found in the spinal cord of the rats in the control group and the sham-operated group at 7 and 21 days after operation.Immunohistochemical detection of GFAP/BDNF/ The expression of TrkB was significantly increased compared with the control group and the sham-operated group(P<0.05).The expression of GFAP/BDNF/TrkB in the spinal cord of the K252 a treatment group was significantly decreased,which was statistically significant compared with the avulsion group.There was no significant difference compared with the control group and the sham-operated group.The expression of BDNF/TrkB in the C5-T1 spinal cord segment of the avulsion side of the rats was significantly increased,and the expression of KCC2 was significantly decreased,and there were significant differences compared with the control group and the sham-operated group(P<0.05).BDNF/TrkB in the K252 a treatment group was significantly decreased to the level close to that in the control group,and the difference was statistically significant compared with the avulsion group(P0.05),and no difference compared with the control group and the sham operation group(P>0.05).The expression of KCC2 was significantly increased and was significantly different from the avulsion group(P<0.05).There was no statistical difference in the expression of each protein between the control group and the sham operation group(P >0.05).Summary: The BDNF-TrkB-KCC2 pathway plays an important role in neuropathic pain transmission and is an important pathway for neuropathic pain transmission.Blocking this pathway with K252 a can significantly reduce neuropathic pain,providing a new approach for the treatment of neuropathic pain. |
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