Chronic melatonin administration mitigates behavioral dysfunction induced by γ-irradiation

Abstract

Melatonin, a ‘hormone of darkness,’ has been reported to play a role in a wide variety of physiological responses including reproduction, circadian homeostasis, sleep, retinal neuromodulation, and vasomotor responses. Our recent studies reported a prophylactic effect of exogenous melatonin against radiation-induced neurocognitive changes. However, there is no reported evidence for a mitigating effect of chronic melatonin administration against radiation-induced behavioral alterations. In the present study, C57BL/6 mice were given either whole day chronic melatonin administration (CMA) or chronic night-time melatonin administration (CNMA) by a low dose of melatonin in drinking water for a period of 2weeks and 1month following exposure to 6Gy of γ-radiation. Various behavioral endpoints, such as locomotor activities, gross behavioral traits, basal anxiety level, and depressive tendencies were scored at different time points. Radiation exposure significantly impaired gross behavioral traits as observed in the open field exploratory paradigms and forced swim test. Both the CMA and CNMA significantly ameliorated the radiation-induced changes in exploratory tendencies, risk-taking behavior and gross behavior traits, such as rearing and grooming. Melatonin administration afforded anxiolytic function against radiation in terms of center exploration tendencies. The radiation-induced augmentation of immobility time in the forced swim test, indices of depression-like behavior was also inhibited by chronic melatonin administration. The results demonstrated the mitigating effect of chronic melatonin administration on radiation-induced affective disorders in mice.