The Mechanism Of β-Arrestin2 And BDNF In The Sensitization Of Pain

Pain is an extremely complex feeling accompanied by actual or potential tissue damage.Acute inflammatory pain is the protective mechanism of the body and achieves the purpose of cure through natural transformation.However,if the natural transformation process of acute pain is interrupted,it may develop into chronic pain.Inflammatory pain is a nociceptive pain that occurs when inflammation occurs due to trauma,bacterial or viral infection,and peripheral tissue damage caused by surgery.It is a key component of the body’s defense mechanism.Neuropathic pain,due to damage to the peripheral or central nervous system,is associated with abnormal tactile and thermal responses outside the injured area.In recent years,with the deepening of pain-related research,more and more molecules play an important role in the process.In this study,we investigated the role ofβ-arrestin2 in different types of pain and its duration at the central level,and the role of BDNF in the somatosensory system and sympathetic nervous system in pain sensitization at the peripheral level.Part I: The role of β-arrestin2 of inflammatory pain and neuropathic painObjective: To investigate the role of β-arrestin2(Arrb2)in the development of inflammatory pain and neuropathic pain by establishing different types of inflammatory pain models.Methods: 1.The acute inflammatory pain model induced by carrageenan and the chronic inflammatory pain model induced by Freudian’s complete adjuvant(CFA)were established in WT mice and transgenic mice,and the SNI neuropathic pain model was established.Mechanical paw withdrawal threshold(PWT)and thermal paw withdrawal latency(PWTL)were determined by von Frey filament method and hot plate method at different time points.2.Western Blot was used to observe the expression of β-arrestin2 in spinal cord lumbar enlargement in acute inflammatory pain and chronic inflammatory pain.3.The short-term and long-term PWT of mice after administration of μ receptor selective agonist(DAMGO)was measured by von Frey filament method by intrathecal administration at the lumbar spinal cord enlargement.Results:1.Knockdown of β-arrestin2 slowed down the recovery process of acute inflammatory pain,but promoted the recovery of chronic inflammatory pain.In the neuropathic pain model,knockdown of β-arrestin2 can reduce the degree of pain sensitivity in the early stage of neuropathic pain,but aggravate the pain sensitivity in the late stage of neuropathic pain.2.In the inflammatory pain model,WT mice and Arrb2-/-mice were given intrathecal DAMGO.The results showed that β-arrestin2 knockout did not play an obvious role in the early stage of acute pain,but could induce pain sensitivity similar to morphine tolerance in the later stage,while it could significantly improve the analgesic effect of μ receptor in the early and late stage of chronic pain.3.The expression of β-arrestin2 in spinal dorsal horn was significantly downregulated at 6 h and 24 h after chronic inflammatory pain was induced by plantar injection of CFA.Conclusion: β-arrestin2 plays different roles in different types of pain.Part II: BDNF regulates somatosensory-sympathetic interaction in DRG in neuropathic painObjective: To explore the mechanism of BDNF in peripheral receptors involved in the somatosensory-sympathetic interaction after BPAMethods: 1.BPA induced neuropathy model was established in WT mice.Mechanical paw withdrawal threshold(PWT)was measured by von Frey filament method at different time points,and sympathetic symptoms were analyzed by measuring body temperature,edema degree and Cat Walk.The expression changes of BDNF,Trk B,TH,α1-AR and α2-AR in DRG of mice after BPA were detected by Western Blot.2.BDNF knockout virus and control virus were injected into the DRG in the BPA group 20 days before modeling,and pain behavior,temperature,edema and Catwalk were detected 3 and 7 days after modeling,and the excitability of neurons in the DRG was evaluated by single cell patch clamp technique.3.Pain behavior,body temperature,and edema were detected 3 and 7 days after modeling,and then ANA-12,a Trk B inhibitor,and phentolamine,a non-selective α-ARs antagonist,were injected intraperitoneally for 5 consecutive days.Pain behavior,body temperature,edema,and Catwalk were detected.The excitability of neurons in the DRG was evaluated by single cell patch clamp technique.Results: 1.After BPA,the affected foot of mice showed obvious mechanical pain sensitivity,and this pain sensitivity state could be maintained until 28 days after the operation.Meanwhile,the affected forepaw showed symptoms such as hypothermia and edema.Western Blot results showed that the expressions of BDNF,Trk B,α1-AR and α2-AR in DRG of mice were increased after BPA,but there was no significant change in TH.2.Reduction of BDNF expression in DRG can reverse mechanical pain sensitivity,hypothermia and edema in BPA mice,with statistical differences compared with the control virus group.Single-cell patch-clamp results showed that decreasing BDNF expression increased the basal strength of cellular action potentials.3.After 5 days of intraperitoneal injection of ANA-12,a Trk B inhibitor,and phentolamine,a non-selective α-ARs antagonist,the mechanical hyperalgesia,hypothermia and edema of BPA mice were significantly reversed.Whole cell patch-clamp recording showed that the basal intensity and threshold of the action potential of the neurons increased significantly after ANA-12 administration.After administration of phentolamine,the basal intensity and threshold of neuronal action potentials were significantly increased and the amplitude was decreased,and both inhibitors reduced neuronal excitability.Conclusion: At the peripheral level,BDNF is a key molecule in BPA-induced somatosensory-sympathetic interaction in NP.