A novel mouse model of contralateral C7 transfer via the pretracheal route: A feasibility study

Background: Contralateral seventh cervical nerve transfer (contralateral C7 transfer) is a novel treatment for patients with spastic paralysis, including stroke and traumatic brain injury. However, little is known on changes in plasticity that occur in the intact hemisphere after C7 transfer. An appropriate surgical model is required.

New method: We described in detail the anatomy of the C7 in a mouse model. We designed a pretracheal route by excising the contralateral C6 lamina ventralis, and the largest nerve defect necessary for direct neurorrhaphy was compared with defect lengths in a prespinal route. To test feasibility, we performed in-vivo surgery and assessed nerve regeneration by immunofluorescence, histology, electrophysiology, and behavioral examinations.

Results: Two types of branching were found in the anterior and posterior divisions of C7, both of which were significantly larger than the sural nerve. The length of the nerve defect was drastically reduced after contralateral C6 lamina ventralis excision. Direct tension-free neurorrhaphy was achieved in 66.7% of mice. The expression of neurofilament in the distal segment of the regenerated C7 increased. Histological examination revealed remyelination. Behavioral tests and electrophysiology tests showed functional recovery in a traumatic brain injury mouse.

Comparison with existing methods: This is the first direct tension-free neurorrhaphy mouse model of contralateral C7 transfer which shortened the time of nerve regeneration; previous models have used nerve grafting.

Conclusions: This paper describes a simple, reproducible, and effective mouse model of contralateral C7 transfer for studying brain plasticity and exploring potential new therapies after unilateral cerebral injury.