Sleep-wake cycle disorders, circadian rhythms

We have emphasized the fact that the progression of mental diseases, especially major depression, is associated with significant disturbances in the circadian rhythms of autonomous functions, especially sleep-wake cycles and hormone release. These rhythms are naturally occurring but are distorted in affective disorders. The most clear distortions are often seen in the ultradian components in specific phases of the circadian cycle, e.g. in the morning peak of cortisol release or in the REM to nonREM transition during the sleep state. 

The sleep-wake cycle is under the circadian control of oscillators and can be disrupted by misalignment between an individual s biological clock and external demands on the sleep cycle. Circadian rhythm sleep disorders usually present with either insomnia or hypersomnia, depending on the individual s performance requirements. Two commonly occurring circadian rhythm sleep disorders are jet lag and shift work sleep problems. 

Melatonin has been used to regulate the sleep-wake cycle and is used often to treat insomnia. It is not recommended during pregnancy and breast-feeding becanse of a lack of information abont its safety. Lower doses of melatonin (e.g., 0.1-1 mg at bedtime) are effective in initiating sleep higher doses may not improve the hypnotic effect. The rednction in daytime snnUght, which increases melatonin secretion, may exacerbate PMS in the winter this type of seasonal mood disorder may respond to phototherapy. Early sleep deprivation also may help to correct circadian rhythm disturbances in PMDD. ... 

In humans, circadian rhythms governed by the SCN affect a large number of physiological functions, including the sleep-wake cycle and nutrition (Moore-Ede et al, 1982 Touitou Haus, 1992). Moreover, a variety of hormone levels (Van Cauter Aschoff, 1989) or enzyme activities display circadian patterns. Circadian rhythms, accordingly, play important roles in both health and disease (Moore-Ede, Czeisler Richardson, 1983). Clinical applications of circadian rhythm research include the use of light to treat maladaptation to night work (Czeisler et al, 1990), jet lag, or seasonal affective disorder (Lewy et al, 1987). 

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