An Analysis of Time-Dependent Changes of Neurotrophic Factors (BDNF, CNTF) in Traumatic Facial Nerve Injury of a Nerve-Cut and Nerve-Crush Model in Rats

Abstract

To investigate neurotrophic changes in the injured facial nerve in rats. Time-dependent follow-up of brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor (CNTF) concentrations in a standardized nerve-cut and nerve-crush trauma model could present valuable information about estimation of the extent of the injury. Ninety Wistar rats were grouped into permanent (transection: nerve-cut) and transient (compression: nerve-crush) nerve injury and analyzed for neurotrophic changes at Week 1 and after 1, 3, and 6 months. Ten undissected rats served as controls. Permanent injury was accomplished with a 5-mm transection. To model transient injury, the facial nerve was pressed by vascular clamps for 40 minutes. Rat BDNF and CNTF enzyme-linked immunosorbent assay kits were used to perform histochemical analysis of blood samples. Measurements were compared with variance analysis and Student's t tests. BDNF levels in nerve-injured preparations from both groups at consecutive intervals were not significant from those of controls, except for transient increases in the first week. When BDNF levels in nerve-cut and nerve-crush groups were compared at each interval separately, differences were insignificant (p > 0.05). CNTF levels at consecutive intervals were significant from that of control rats in both groups. When CN0054F levels in nerve-cut and nerve-crush groups were compared at each interval separately, differences were significant (p = 0.023, p = 0.001, p = 0.043, and p = 0.023). Elevated levels of BDNF in the first week after nerve injury do not differentiate the severity of the facial nerve injury. However, diminished CNTF levels in the nerve-crush group were significant when compared with that of nerve-cut group. This finding suggests the possibility that CNTF levels can distinguish whether the facial nerve is interrupted after trauma. Further experimental studies should investigate the indicative role of CNTF levels as a marker of nerve disruption in the clinical setting.