Stereological assessment of the total number of hypoglossal neurons after repeated crush injuries to the hypoglossal nerve in adult rats.

Objective: Retrograde neuronal cell death does not occur in mature motoneurons following the axonal injury of peripheral nerves. However, a previous study suggested that retrograde neuronal cell death does occur in adult rats after the creation of double lesions on the hypoglossal (XII) nerve based on a substantial decrease in the number of XII neurons. Using stereological methods, we examined neuronal apoptosis in XII neurons and the total number of XII neurons following repeated crush injuries to the XII nerve. Methods: The right XII nerve of adult rats was crushed three times at one-week intervals with a brain aneurysm clip. At 4weeks after the final crush, the total numbers of XII neurons on the injured right and uninjured left sides were estimated stereologically. Results: After repeated crush injuries, no apoptosis was evident in XII neurons as indicated by immunostaining for cleaved caspase-3. Moreover, immunohistochemistry for the vesicular acetylcholine transporter revealed axonal elongation in the tongue 4weeks after repeated crush injuries. At 4weeks, the total numbers of XII neurons were 7800290 on the injured right side and 8000 +/- 230 on the uninjured left side, and no significant difference was evident between the injured and uninjured sides. Conclusion: Neuronal cell death does not occur in XII neurons and the total number of XII neurons does not decrease after repeated crush injuries of the XII nerve in adult rats.