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Does Location Matter? Comparing Motor Neuron Survival in Cranial vs. Spinal Nerves Following Traumatic Injury
Julia Chrisbacher
2, Jordan Marx
*2, Njima Schläpfer
1, Remy Liechti
1, Jonathan Leckenby
11Division of Plastic & Reconstructive Surgery, University of Rochester Medical Center, Rochester, NY; 2University of Rochester School of Medicine & Dentistry, Rochester, NY
BACKGROUND: Peripheral nerve injuries can result in chronic pain and long-term functional deficits. While peripheral nerves regenerate more effectively than those in the central nervous system, recovery often remains incomplete. Prior studies report differing motor neuron (MN) survival rates in brainstem and spinal MNs, but no direct comparison exists. To address this, we investigated differences in MN survival between brainstem and spinal nerves following transection and repair in a mouse model.
METHODS: 8-week-old C57BL/6J mice were assigned to control (n=10), 30d (n=5), 60d (n=5), and 90d (n=5) groups. Animals underwent ipsilateral transection and repair of the facial and sciatic nerves. Retrograde labeling was performed at 30, 60, or 90 days post-injury. Tissue was harvested to quantify MN survival in the facial motor nucleus and spinal ventral horn. MN counts were analyzed using Welch's ANOVA with Dunnett's correction, and normalized survival rates were compared via two-way ANOVA with Tukey's test.
RESULTS: Control MN counts were 1400 (±188.6) in the facial nucleus and 516 (±42.3) in the spinal cord. In the facial nucleus, the percent of surviving facial MNs was not significantly different at 30 days, approached significance by day 60 (84.6%±1.8, p=0.075), and became significant by day 90 (82.7%±4.9, p=0.036). Similarly, in the spinal cord, the percentage of surviving sciatic nerve MNs was not significantly different at 30 days but became significant by days 60 (79.5%±6.8, p=0.012) and 90 (81.1%±11.7, p=0.022). No significant differences in survival rates were observed between facial and sciatic MNs at any time point.
CONCLUSION: Facial and sciatic MNs showed progressive loss that stabilized between 60 and 90 days post-injury, with similarities in survival rates across time points. These findings suggest comparable vulnerability of brainstem and spinal MNs despite anatomical differences. The mechanisms underlying survival and regeneration remain unclear, and further study may inform the development of targeted therapies to optimize outcomes in nerve repair.
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