Ultradian sleep rhythm

The ultradian sleep—wake and temperature rhythm produced by 3rd ventricle infusion of TGFa closely resembles the effect of a focal excitotoxic lesion of SPZ neurons (Lu et al 2001). This ultradian rhythm is normally suppressed by circadian control and is disinhibited when SPZ neurons fail to relay SCN circadian information to sleep—wake circuits. Our results indicate that chronic TGFa administration uncouples SPZ neurons from sleep-regulatory circuits and that SPZ neurons expressing the EGFR transmit circadian information from the SCN to sleep—wake centres, in addition to likely regulating circadian locomotor activity. 

Lavie P, Zomer J. Ultrashort sleep-waking schedule. II. Relationship between ultradian rhythms in sleepability and the REM-NONREM cycles and effects of the circadian phase. Electroencephalogr and Clin Neurophysiol 1984 57 35 -2. 

Many hormonal secretion processes also exhibit strong circadian components. This is true, for instance, for cortisol, antidiuretic hormone, and growth hormone. The secretion of growth hormone is markedly increased during the early periods of sleep, and the secretion of antidiuretic hormone also reflects the sleep-wake cycle. The mechanisms underlying these oscillations can often be traced back to cyclical variations in the activity of the central nervous system. At the same time, the circadian rhythm modulates the above-mentioned ultradian oscillations. 

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. 

Beyond the two-hour ultradian rhythms, our lives are also set to the circadian or diurnal rhythm of the daily cycle that regulates sleep and wakefulness. In fact, our biological clock is set not to a twenty-four-hour day but to one that lasts closer to twenty-five hours. Presumably that gap be-... 

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