The Expression And Role Of Peripheral ProBDNF In Inflammatory Pain Induced By Formalin

Objective To Explore the expression of proBDNF(pro-Brain Derived Neurotrophic Factor) in the plantar tissue of mice in biphasic pain model induced by intraplantar subcutaneous injection of formalin, and the effect of exogenous proBDNF antibody and anti-proBDNF protein on formalin induced inflammatory pain.Methods In this study, we use the normal adult male kunming mice as the research object. Firstly we establish acute inflammatory pain model with intraplantar subcutaneous injection of1%or5%formalin(5ul) into right hindpaw of male mice in the experimental group, and saline(5ul) in the control group. Then we observe the spontaneous pian behavior in1hour after injection of formalin with5minutes as a observation unit, and detect the mechanical hyperalgesia with electric Von frey and thermal hyperalgesia with thermal hyperalgesia dolorimeter. To explor the role of proBDNF on formalin induced inflammatory pian, we detect the effect of intraperitoneal injection of anti-proBDNF antibody30min before formalin injection on formalin induced spontaneous pain. Otherwise, we detect the mechanical and thermal pain threshold at1st,3rd and5th hour after intraplantar subcutaneous injection of2or4pmol proBDNF protein, and then observe the effect of proBDNF protein on light concentration formalin induced spontaneous pain with intraplantar subcutaneous injection of0.05%formalin at5th hour after injection of proBDNF protein.Results the expression of proBDNF in the plantar skin tissue of mice after injection of formalin Bothe intraplantar subcutaneous injection of1%or5%concentration formalin can induce biphase spontaneous pain in mice(p<0.001, p<0.01). Immunohistochemisty result shows that, the expression of proBDNF in plantar skin tissue of the mice was up-regulated at15min after injection of formalin (p<0.01), and sustained to3hour after injection.The effect of intrap intraperitoneal injection of anti-proBDNF antibody on formalin induced biphase spontaneous pain Intraperitoneal injection of anti-proBDNF antibody can alleviate the second phase spontaneous pain of mice induced by intraplantar subcutaneous injection of whether1%or5%formalin:the spontaneous pain induced by1%formalin in20-30min after injection of formalin was significantly alleviated(P<0.01%), and the spontaneous pain induced by5%formalin was significantly alleviated in15-20min(P<0.05%) and20-30min(P<0.01%) after injecdtion of formalin; however, there were no significant differences in the first phase spontaneous pain of both group compared with the control group.The effect of intraplantar subcutaneous injection of proBDNF on the mechanical hyperalgesia, thermal hyperalgesia and spontaneous pain induced light concentration formalin PWT of the injected paw in mice at all time point after intraplantar subcutaneous injection of2pmol or4pmol proBDNF protein was reduced compared with the base values, and the difference was statistically significant; otherwise, PWT of the injected paw after intraplantar subcutaneous injection of2pmol or4pmol proBDNF protein was also reduced compared with that in the control group. Intraplantar subcutaneous injection of light concentration formalin in mice can only induce the first phase spontaneous pain, but intraplantar subcutaneous injection of proBDNF protein can induce the second phase spontaneous pain after injection of light concentration formalin and the licking time was significantly increased(P<0.001), however there was no second spontaneous pain in intraplantar subcutaneous injection of BDNF protein and the control group. But there were no significant differences in licking time of the first phase of all groups, which suggests intraplantar subcutaneous injection of WT proBDNF protein and BDNF protein have no effect on the first phase spontaneous pain.Conclusion The expression of ProBDNF in plantar skin tissue was up-regulated by intraplantar subcutaneous injection of formalin in mice; intraperitoneal injection of anti-proBDNF antibody can significantly alleviate the second phase spontaneous pain induced by formalin; however intraplantar subcutaneous injection of proBDNF protein can significantly reduce PWT and PWL of the mice, and meanwhile induce the second phase spontaneous pain after injection of light concentration formalin. These suggest that proBDNF may can involve in regulating pain as a peripheric inflammatory mediator, and anti-proBDNF antibody may be a new target for the treatment of inflammatory pain.