Abstract
Introduction Two basic properties summarize the biological effects of melatonin: the antioxidant properties and its activity as a marker of biological time. Both effects may counteract the deleterious consequences of aging. First, the cellular damage caused by free radicals has been claimed as a factor to explain many effects of aging. In addition, aged individuals suffer important perturbations in their sleep and biological rhythms. Both effects coincide with the practical suppression of melatonin secretion in aged individuals, a fact suggesting the therapeutic effectiveness of melatonin to revert the consequences of aging. The present study aims at recording the effects of melatonin administration to revert the effects of age in the sleep of rats. Materials and methods Wistar young and old rats (3 and 24 months, respectively, at the beginning of experiments) were used for the study. Two weeks before starting treatment, each animal was surgically implanted with two monopolar electrodes in the surface of the cortex for EEG recording and two bipolar EMG electrodes in the neck muscles for EMG. EOG electrodes were not used. Instead, REM sleep was identified by the presence of theta waves in the EEG and eye movements were monitorized through a closed video system. After recovery, the rats were housed individually and received ad libitum food. For drinking, old rats of the experimental group received melatonin dissolved in ethanol and then diluted in water in a proportion of 2%. The melatonin contents was calculated to provide an approximate daily dose of 1 mg/k bw during 30 days. The volume of consumed liquid was recorded every day and the proportions were corrected accordingly to maintain the desired dosage. Young and old control animals only received the 2% ethanol/water mixture. After 30 days of melatonin administration, the sleep of the rats was recorded during two hours (12:00–14:00). Samples of the recordings were selected corresponding to unambiguous waking, NREM and REM stages avoiding artifacts. The EEG recordings were submitted to Fourier analysis to obtain the power in the four typical frequency ranges. Results Aged control rats showed a significant reduction in delta and theta EEG power when compared to young controls. Melatonin administered to the experimental group reverted the changes, increasing delta and theta power during NREM and NREM, respectively. No significant changes were observed in waking. These results suggest the effectiveness of exogenous melatonin administration to correct the sleep perturbations observed in aged individuals. Conclusion Chronic low doses of melatonin improve the sleep quality in aging rats.
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