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Aging leads to progressive deterioration of physiological function and diminished responses to environmental stress. Organic and functional alterations are frequently observed in elderly subjects. Although chronic sleep loss is observed during senescence, little is known about the impact of insufficient sleep on cellular function in aging neurons. Disruption of neuronal calcium (Ca²⁺) signaling is related to impaired neuronal function and cell death. It has been hypothesized that sleep deprivation may compromise neuronal stability and induce cell death in young neurons; however, it is necessary to evaluate the impact of aging on this process. Therefore, the aim of this study was to evaluate the effects of chronic sleep restriction (CSR) on Ca²⁺ signaling and cell death in the hippocampus of young and aged animals. We found that glutamate and carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP) induced a greater elevation in cytosolic Ca²⁺ ([Ca²⁺](c)) in hippocampal slices from aged rats subjected to CSR compared to age-matched controls. Interestingly, aged-matched controls showed a reduced Ca²⁺ response to glutamate and FCCP, relative to both CSR and control young animals. Apoptotic nuclei were observed in aged rats from both treatment groups; however, the profile of apoptotic nuclei in aged CSR rats was highly variable. Bax and Bcl-2 protein expression did not change with aging in the CSR groups. Our study indicates that aging promotes changes in Ca²⁺ signaling, which may also be affected by CSR. These age-dependent changes in Ca²⁺ signaling may increase cellular vulnerability during CSR and contribute to Ca²⁺ signaling dysregulation, which may ultimately induce cell death.

This study was undertaken to evaluate the acute effects of single low doses of melatonin given to healthy volunteers in the evening. Six healthy male volunteers (age range 22-24 years) participated in this study, after signing an informed consent form. They received in a double-blind fashion placebo or 0.3 or 1.0 mg melatonin at three fixed times: 18:00, 20:00, and 21:00 hr. Polysomnographic recordings began immediately thereafter, with their being allowed to sleep. Prior to each experimental session and in the following morning, subjects completed a sleep quality questionnaire, the Profile of Mood States, the Stanford Sleepiness Scale, and underwent a visual reaction test. Significant decrease on sleep latencies was found following melatonin treatment at 18:00 and 20:00 hr. In addition, melatonin tended to improve sleep efficiency and to reduce intermittent wakefulness. However, at 21:00 hr, 0.3 mg melatonin increased latency to sleep onset and 1.0 mg melatonin had no effect on sleep variables. Furthermore, melatonin given at different times did not alter subjective sleepiness, mood, and reaction time in the following morning. The results from the present study support the notion that administration of low doses of melatonin, mimicking the nocturnal physiological concentration of this hormone may exert immediate sleep-inducing effects.

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