Circadian shift

Ding, J. M., Chen, D., Weber, E. T. et al. (1994). Resetting the biological clock mediation of nocturnal circadian shifts by glutamate and NO. Science 266, 1713-17. 

There are two concerns about the effects of shift rotation and night work disruption of "circadian rhythms" and sociological costs, that is, effects on the worker s family life. 

The practical implications of this experiment are that when evaluating the effects of shift work due to circadian effects, the type of task being carried out by the worker must be taken into account. For example, skill-based tasks would be expected to exhibit the performance changes characteristic of low memory load tasks, whereas performance variations in knowledge-based tasks would be expected to follow the pattern of high memory load tasks. Performance on rule-based tasks may depend on the degree of frequency of use of the rules, which in turn may determine the memory load. If these results were confirmed by further process plant studies, it would have implications for when different types of operation (involving different levels of memory load) should be scheduled to reduce circadian rhythm effects and minimize errors. 

Studies by Smith et al. (1982), Folkard et al. (1979), and Colquhoim et al. (1969), have investigated the disruption of circadian rhythms caused by having to be awake and work at imusual hours and by having to sleep during daytime. With respect to the sociological effects, studies by Kasl (1974) and Kahn (1974) concluded that fixed afternoon and night shifts lead to lower levels of social satisfaction because it becomes difficult to participate in family activities. 

Monk, T. H., Embrey, D. E. (1981). A Field Study of Circadian Rhythms in Actual and Interpolated Task Performance. In A. Reinberg, N. Vieux, P. Andlauer (Eds.), Night and Shift Work Biological and Social Aspects. Oxford, UK Pergamon Press. 

The most common CRDs include jet lag, shift-work sleep disruption, delayed sleep-phase disorder, and advanced sleep-phase disorder. Jet lag occurs when a person travels across time zones, and the external environmental time is mismatched with the internal circadian clock. Delayed and advanced sleep-phase disorders occur when bed and wake times are delayed or advanced (by 3 or more hours) compared with socially prescribed bed and wake times. 

Steenhard B., Besharse J. (2000). Phase shifting the retinal circadian clock xPer2 mRNS induction by light and dopamine. J. Neurosci 20, 8572-7. 

Meijer, J. H., van der Zee, E. A. Dietz, M. (1988). Glutamate phase shifts circadian activity rhythms in hamsters. Neurosci. Lett. 86, 177-83. 

A role for the 5-HT7 receptor in the regulation of circadian rhythms has been implicated. As discussed above, 5-HT has been known for some time to induce phase shifts in behavioral circadian rhythms and modulate neuronal activity in the suprachiasmatic nucleus, the likely site of the mammalian circadian clock. The pharmacological characteristics of the effect of 5-HT on circadian rhythms are consistent with 5-HT7 receptor. Moreover, mRNA for the 5-HT7 receptor is found in the suprachiasmatic nucleus. There is also increasing evidence that the 5-HT7 receptor may play a role in psychiatric disorders. The regional distribution of 5-HT7 receptors in brain includes limbic areas and cortex. Atypical antipsychotics, such as clozapine and risperidone, and some antidepressants display high affinity for this receptor. In the periphery, 5-HT7 receptors havebeenshown to mediate relaxation of vascular smooth muscle. 

Breathing-related sleep disorder Circadian rhythm sleep disorder Delayed sleep phase type Jet lag type Shift work type Unspecified type... 

The results obtained with the model for the mammalian circadian clock provide cues for circadian-rhythm-related sleep disorders in humans [117]. Thus permanent phase shifts in LD conditions could account for (a) the familial advanced sleep phase syndrome (FASPS) associated with PER hypopho-sphorylation [118, 119] and (b) the delayed sleep phase syndrome, which is also related to PER [120]. People affected by FASPS fall asleep around 7 30 p.m. and awake around 4 30 a.m. The duration of sleep is thus normal, but the phase is advanced by several hours. Moreover, the autonomous period measured for circadian rhythms in constant conditions is shorter [121]. The model shows that a decrease in the activity of the kinase responsible for PER phosphorylation is indeed accompanied by a reduction of the circadian period in continuous darkness and by a phase advance upon entrainment of the rhythm by the LD cycle [114]. 

Another common perturbation of the circadian clock is the jet lag, which results from an abmpt shift in the phase of the LD cycle to which the rhythm is naturally entrained. The molecular bases of the jet lag are currently being investigated [124]. The model for the circadian clock is being used to probe the various ways by which the clock returns to the limit cycle trajectory after a sudden shift in the phase of the LD cycle. 

M. Nagano, A. Adachi, K. Nakahama, T. Nakamura, M. Tamada, E. Meyer-Bemstein, A. Sehgal, and Y. Shigeyoshi, An abrupt shift in the day/night cycle causes desynchrony in the mammalian circadian center. J. Neurosci. 23, 6141-6151 (2003). 

The final category is termed the sleep-wake schedule disorders. These are seen in people who get their days and nights turned around. The most common examples are shift workers and travelers with jet lag. Additionally, in the elderly, especially those with dementia, a malfunction in the circadian biological rhythm that regulates sleep can leave them awake and alert at night but drowsy and sleeping during the day. 

Van Gelder Again, how these different pigments play into the different output pathways is not clear. For example, in the pupillary light responsiveness we see a marked diminution in pupillary response comparing wild-type to rd rd mice. We see no diminution in phase-shifting response for entrainment in these animals. This means that, for pupillary responses, 90% of the response is driven by the outer retina, whereas for circadian responses it may be that none or only a small fraction is normally mediated by the outer retina. 

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