Construction of a rat tibial neuroma transposition model and changes of neurotrophin expressions in the nervous system
Objective: To construct a rat tibial neuroma transposition (TNT) model, observe changes in expressions of neurotrophins (NTs) family[nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF)] in injured nerves, dorsal root ganglions (DRGs), and spinal cord, and investigate the effects of changes in NTs expression after peripheral nerve injury on the formation of neuroma and pain-related behavior. Methods: TNT model was built by transecting the tibial nerve and transposing it in upper lateral ankle subcutis through a transcutaneous channel. Neuroma pain and plantar mechanical paw withdrawal threshold (PWT) were measured with Von Frey filaments at different time points after TNT surgery. Rats were sacrificed and injured tibial nerves were harvested at the end of the experiment. The formation of neuroma at the broken end of tibial nerves was observed by fluorescent labeling of nerve fibers with Neurofilament-20. Animal models were built again. Rats were sacrificed and tibial nerves, DRGs, and spinal cords at injured side were collected on days 7, 21, 42 and 49.Changes in NGF and BDNF expressions in tibial nerves and DRGs were measured with ELISA kit. Changes in NGF and BDNF expressions in spinal cords were detected with Western blotting. Results: The rate and score of neuroma pain at day 7 after surgery significantly increased. The PWT level in lateral plantar skin started to decrease at day 3 after surgery. The neuroma pain and mechanical pain in lateral plantar skin lasted the whole experimental period, while the PWT level in middle plantar skin has no significant changes. The immunofluorescence staining revealed neuroma was formed at the broken end of injured nerves. ELISA results showed that in tibial nerves the NGF expression was increased, while the BDNF expression was increased at days 7 and 21 after surgery and then gradually decreased to normal level. The NGF expression in DRG was increased at days 7 and 21 and then gradually decreased to normal level, while the BDNF expression was increased at day 7 after surgery and gradually decreased to normal level. NGF and BDNF expressions in spinal cords were increased at different time points after surgery and lasted the whole experimental period. Conclusion: TNT can cause the formation of neuroma at the broken end of nerves and neuropathic pain in rats (neuroma pain and mechanical allodynia). NGF and BDNF may be associated with the occurrence and development of neuroma and neuropathic pain.
