The Change Of Action Potential In Inflammatory Pain Model Rat DRG Neurons

Objective: To explore the change of action potential in the periphery dorsal root ganglia( DRG) of the inflammation pain model rat.Methods: 1)experimental groups and model :16 Sprague Dawley rats are randomly divided into two groups.Formalin group(n=8): Injecting 100 μl of 5% formalin into the palm of the right hind leg.Noraml saline group(n=8):Injection the same saline into the right hind leg palm. By using Abbott and other methods [4] immediately record the cumulative paw licking time in every 5 minutes of 1 hour. 2) Record Ing the action potention(AP): By using the current clamp technique to record the action potential(action in acute isolated rat L5 lumbar 6 dorsal root ganglion neurons,namely statisticsly comperare the rest potential(RP),the action potential threshold(APT),the peak of action potential( APP),the half duration of action potential(APD50).Result: 1) behavior changes of model rats: after subcutaneous injection of formal into right hind foot,rats immediately occured the spontaneous pain behavior such as swelling, lift, turn claw action bumps limbs, lameness, and licking, biting of the injected foot. Obviously there were two phases of the whole process of reactions: the first stage occurs immediately after injection, last about 5 min; 10 min after the interim period, beginning the second phase of the pain, which lasted about 40 min. And not enough action injected normal, there were no licking, leg, limping and other acts in the normal group. 2) neuronal resting potential(RP) record: Formalin group DRG neurons resting potential(RP) was-52.55 ± 1.15 m V(n = 8), the normal control group of animals resting potential(RP) is-53.17 ± 2.52 m V(n = 7), the difference was not statistically significant(P> 0.05). 3) neuronal action potential( AP) threshold(APT) records: show ed that formalin group DRG neurons action potential threshold(APT) was-25.31 ± 0.47 m V(n = 8), normal animals in the control group DRG neurons action potential threshold(APT) was-20.36 ± 0.46 m V(n = 7), the difference was statistically significant(P <0.01).4) neuronal action potential(AP) peak(APP): Formalin group of small and medium DRG neurons AP peak(APP) was 72.43 ± 1.60 m V(n = 8), normal animals in the control group of small and medium DRG neurons AP Peak(APP) was 85.96 ± 5.51 m V(n = 7), the difference was statistically significant(P <0.01).5) neuronal action potential half-peak time(APD50): Formalin rat DRG neurons action potential half-peak time( APD50) was 6.40 ± 0.21 ms(n = 8), and rat DRG normal animals in the control group neuronal action potential half-peak time( APD50) was 6.04 ± 0.95 ms(n = 7), the difference was not statistically significant( P> 0.05).Conclusion: Inflammatory pain is due to the increaing of the excitability of primary sensory neurons.