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Growth Factor Expression in Mouse Lumbar Motor Neurons Following Sciatic Nerve Laceration and Electric Stimulation
Andree-Anne Roy, MD1, Anne-Marie Pion, MD1, Eric Beaumont, PhD2, Artur Kania, PhD3 and Jenny C. Lin, MD, PhD1
1Plastic Surgery, University of Montreal, Montreal, QC, Canada, 2Research Centre Sacre-Coeur Hospital, University of Montreal, Montreal, QC, Canada, 3Institut de recherches cliniques de Montreal, Montreal, QC, Canada
Purpose: Growth factors such as BDNF and its receptor, trkB, are involved in the regeneration of motor axons following axotomy. However, other growth factors and receptors such as Hepatocyte Growth Factor (HGF), Ciliary Neurotrophic Factor Receptor (CNTFR) and Cardiotrophin-like Cytokine (CLC) play a role in directing the growth of motor neurons during embryonic development. These factors might also be important in directing the regeneration of motor neurons following laceration, but this has not yet been studied. We aimed to identify the expression patterns of HGF, CNTFR and CLC following axotomy, with or without direct or transcutaneous electrical nerve stimulation in a mouse model. Methods: Sixty adult C57BL/6 mice were divided into 5 groups. The first group (control; n=12) had no surgery. The second group (n=12) underwent sciatic nerve laceration and immediate repair. The third group (n=12) had sham surgery. The fourth group (n=12) had sciatic nerve laceration, immediate repair, and application of direct electrical stimulation on the proximal end of the nerve for one hour at 20Hz. The fifth group had nerve laceration and immediate repair followed by transcutaneous electrical stimulation for one hour at 20Hz. Spinal cords were harvested at 1, 3, 7 and 14 days post-surgery. The expression patterns of BDNF, trkB, HGF, CNTFR and CLC were measured using in situ hybridization. Results: Our results showed an upregulation of BDNF and trkB expression in mouse spinal cords following sciatic nerve axotomy. This was seen to occur more quickly following electrical stimulation in both groups four and five. The expression pattern of HGF was altered in mouse spinal cords following sciatic nerve axotomy, becoming localized to the motor neuron pools. This altered expression pattern was also observed to happen in the electrical stimulation groups. CNTFR and CLC levels remained unchanged in all groups. Conclusions: The molecular mechanisms involved in the regeneration of peripheral nerves are not well described. Nerve regeneration following laceration may involve similar mechanisms as during axon outgrowth in development. In this project, we have shown that HGF, a growth factor involved in directing the outgrowth of motor axons in development, has an altered expression pattern following sciatic nerve laceration, suggesting that it may also play a role in directing motor nerve regeneration. Furthermore, electrical stimulation induced a more rapid change in the expression pattern of HGF, suggesting that it may also be involved in the upregulation of nerve regeneration following electrical stimulation.
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