Systemic melatonin improves regeneration after facial nerve crush injury in a rat model

Melatonin, primarily secreted by the pineal gland, is a neuroendocrine hormone with multiple antioxidant and anti-apoptotic effects on neural tissues. The aim of the present study was to assess the regenerative potential of systemic melatonin treatment after facial nerve crush injury. Following the facial nerve injuries, 24 Sprague-Dawley rats were randomly divided into three groups as follows: (1) 20mg/kg melatonin, (2) 5mg/kg melatonin and (3) control. Rats were injected intraperitoneally daily for 28 days according to the study groups. Functional evaluations such as blinking reflex and whisking amplitude were evaluated weekly. At the end of the 28 days treatment period, electromyography (EMG) of facial nerves were performed and then buccal branches of facial nerves were harvested for histomorphometric analysis. Whisking amplitude was significantly higher in 5mg/kg and 20 mg/kg melatonin groups compared to the control group. Both treatment groups presented higher EMG amplitude and shorter duration values than the control group. Histomorphometric analysis revealed that the percentage of axons with optimum g-ratio was significantly lower in the control group. The mean axonal density was significantly higher in both melatonin treatment groups. Both supraphysiological doses of systemic melatonin treatment enhanced regeneration after facial nerve crush injury.