Effect of Altered Endogenous Melatonin Regulated by Conditional Light Exposure on Neural Reorganization by Regulation of ER Stress Response and Autophagy after Spinal Cord Injury

Abstract

Spinal cord injury causes unfolded protein response (UPR) to recover from endoplasmic reticulum (ER) stress. Melatonin is known to delay ER stress‐induced apoptosis. Furthermore, it has been suggested that melatonin‐mediated autophagy can induce neuroprotection.The purpose of this study was to elucidate the effect of endogenous melatonin on neural reorganization and locomotor recovery after spinal cord injury. To diversify the concentration of endogenous melatonin, differentiated light exposure time was needed. Thus, experimental animals were divided into 5 groups; group1 (12‐hr light/12‐hr dark), group2 (6‐hr light/18‐hr dark), group3 (24‐hr dark), group4 (18‐hr light/6‐hr dark), group5 (24‐hr light). 7 days after injury, animals were engaged in locomotor assessment.The BBB score of experimental animals was increased inversely proportional to light exposure time. Similarly, the more the rats were blocked from light, the more neural cells were reorganized. Furthermore, axonal sprouting showed a tendency to relatively increase in accordance with light blockade.In conclusion, UPR and autophagy might interact to play a neuroprotective role and, this effect is intensified by endogenous melatonin.Funding : 2012R1A1A2005089, 2013R1A2A2A01067169, KGM4611512, 2014R1A1A3051724