Differentiation of endogenous neural stem cells in adult versus neonatal rats after brachial plexus root avulsion injury☆

An experimental model of brachial plexus root avulsion injury of cervical dorsal C(5-6) was established in adult and neonatal rats. Real-time PCR showed that the levels of brain-derived neurotrophic factor, nerve growth factor and neurotrophin-3 in adult rats increased rapidly 1 day after brachial plexus root avulsion injury, and then gradually decreased to normal levels by 21 days. In neonatal rats, levels of the three neurotrophic factors were decreased on the first day after injury, and then gradually increased from the seventh day and remained at high levels for an extended period of time. We observed that greater neural plasticity contributed to better functional recovery in neonatal rats after brachial plexus root avulsion injury compared with adult rats. Moreover, immunohistochemical staining showed that the number of bromodeoxyuridine/nestin-positive cells increased significantly in the spinal cords of the adult rats compared with neonatal rats after brachial plexus root avulsion injury. In addition, the number of bromodeoxyuridine/glial fibrillary acidic protein-positive cells in adult rats was significantly higher than in neonatal rats 14 and 35 days after brachial plexus injury. Bromodeoxyuridine/β-tubulin-positive cells were not found in either adult or neonatal rats. These results indicate that neural stem cells differentiate mainly into astrocytes after brachial plexus root avulsion injury. Furthermore, the degree of neural stem cell differentiation in neonatal rats was lower than in adult rats.