Neuronal re-juvenilization in the nucleus ambiguus after vagal nerve injury

Nestin is an intermediate filament expressed in immature cells in the CNS including neural stem/progenitor cells, reactive astrocytes and immature neurons in lesser amounts after injury. Nestin expression in the nucleus ambiguus following vagal nerve injury was studied using nestin-EGFP transgenic rats. We confirmed that EGFP immunoreactivity was evident at 6 h to 8 days in ipsilateral nucleus ambiguus after nerve transection. Properties of these cells were examined immunohistochemically. These EGFP-immunoreactive cells were immunoreactive for Tuj1 and Hu, and exhibited ChAT activity. However, no immunoreactivity for GFAP or CNPase was observed. In normal development, the level of KCC2 expression is known to increase with maturation of neurons. In our study, decreased KCC2 expression was observed in nestin-EGFP-positive cells within the nucleus ambiguus on the lesioned side compared with the contralateral side. These EGFP-immunoreactive cells were immunonegative for BrdU. This is the first study to demonstrate the expression of a neural stem/progenitor cell-enriched marker, Nestin, in the nucleus ambiguus after vagal nerve injury. The present findings suggest that mature motoneurons are an origin of these Nestin-positive cells, which are induced after injury. Mature neurons in the nucleus ambiguus may thus have the potential to juvenilize after vagal/recurrent laryngeal nerve injury.