Beneficial effects of endogenous and exogenous melatonin on neural reconstruction and functional recovery in an animal model of spinal cord injury

: The purpose of this study was to investigate the beneficial effects of endogenous and exogenous melatonin on functional recovery in an animal model of spinal cord injury (SCI). Eight‐week‐old male Sprague‐Dawley (SD, 250–260 g) rats were used for contusion SCI surgery. All experimental groups were maintained under one of the following conditions: 12/12‐hr light/dark (L/D) or 24:0‐hr constant light (LL). Melatonin (10 mg/kg) was injected subcutaneously for 4 wk, twice daily (07:00, 19:00). Locomotor recovery, inducible nitric oxide synthase (iNOS), glial fibrillary acidic protein gene expression, and muscle atrophy‐related genes, including muscle atrophy F‐box (MAFbx) and muscle‐specific ring‐finger protein 1 (MuRF1) gene expression were evaluated. Furthermore, autophagic signaling such as Beclin‐1 and LC3 protein expression was examined in the spinal cord and in skeletal muscle. The melatonin treatment resulted in increased hind‐limb motor function and decreased iNOS mRNA expression in the L/D condition compared with the LL condition (P