Extensive neuronal cell death following intracranial transection of the facial nerve in the adult rat

The aim of the present study is to examine the neuronal degeneration and th e glial response following intracranial transection of the facial nerve clo se to the brainstem and furthermore to compare the results with a distal ne rve injury, The facial nerve was cut either intracranially in the posterior cranial fossa or further distally, where it passes the parotid gland, in a dult rats. Intracranial axotomy caused a massive loss of neuronal profiles, Only 26.8 +/- 11.3% of facial motor neuronal profiles were found ipsilater al to the nerve injury when compared to the contralateral side, following i ntracranial axotomy, This was statistically significant in comparison to th e distal injury (72.4 +/- 9.5%), 4 weeks post-lesion, Reactive microglial c ells expressed ED1 immunoreactivity following the intracranial axotomy but not following the distal nerve injury. In conclusion, there was a large dis crepancy in neuronal degeneration as well as presence of phagocytic (ED1 po sitive) microglia between the two lesions. The intracranial lesion model us ed in the present study generates a massive neuronal cell death and should therefore be a useful tool for studies on proximal cranial nerve injuries a nd in particular mechanisms causing cell death, which may occur following, for example, head trauma. (C) 1999 Elsevier Science Inc.