Hypoglossal nerve injury with long nerve resection leading to slow motoneuron death

Crush injury to peripheral nerves in adult animals is considered not to trigger retrograde neuronal cell death; however, several studies reported neuronal cell death following severe injuries including nerve transection, resection, or avulsion. However, the rate of neuronal cell death varied among studies. In this study, we evaluated the outcomes of very severe nerve injury by long nerve resection in adult rats. Right hypoglossal (XII) nerve was exposed, and a 9-mm section was resected. At 4, 8, and 12 weeks after the resection, the number of XII neurons were counted in from the rostral to caudal sections. The number of XII neurons in the injured right side was reduced after the XII nerve resection compared with the uninjured left side. The mean rates of surviving neurons at 4, 8, and 12 weeks after the nerve resection were 83.5 %, 73.9 %, and 61.1 %, respectively, which were significantly lower than those of the control. The number of XII neurons after extensive XII nerve resection declined gradually over a relatively long time period, revealing that extensive nerve resection led to slow cell death of the injured neurons.