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Sleep and Biological Rhythms in 2015

2015; Springer Science+Business Media; Volume: 13; Issue: 1 Linguagem: Inglês

10.1111/sbr.12104

1479-8425

Murat Aksu,

Sleep and Wakefulness Research

First of all I would like to welcome you to Istanbul for the World Sleep meeting this year and the Asian Sleep Research Society meeting in 2016. Sleep is a crucial part of life. Not just because life slows down during sleep, but also because many functions of living creatures require sleep. Even in the very early periods of medical science, it was thought that sleep was the recovery of body and brain. In the first half of the 20th century, it was known that sleep was necessary for some endocrine functions like growth hormone secretion. Now we know clearly that sleep is the most important time for memory consolidation, some immune reactions and endocrine functions. Sleep is very complex and a component of a large circadian pattern. In fact, we live on a planet that has only one energy source – the sun – and all living creatures can reach that source for only half of their lives. Therefore, all of those living creatures need to produce a mechanism that keeps and regulates the energy they have captured during the daytime. The circadian rhythm is involved in that procedure. As I mentioned before, sleep is only a part of that big circadian rhythm procedure. Circadian rhythm was first recognized in the 19th century in plants, then in fungi and protozoa and finally in mammals. Circadian rhythm regulates all of the endocrine and autonomic functions of the central nervous system. In fact, the central nervous system regulates all of the visceral functions via circadian rhythm. Therefore, the hypothesis ‘slow wave sleep causes growth hormone secretion’ is not correct. Instead, growth hormone secretion and slow wave sleep are created during the same time of the circadian rhythm. We believe it is important to understand sleep disorders and circadian rhythm from that perspective. If the human circadian clock regulates all of the functions of the body, then disorders of day and night should be different. That is why sleep disorders are so unique, and why their mechanisms and treatments are so hard to understand. If sleep disorders appear only in sleep and mostly at night, it is almost impossible to understand them without understanding the circadian pattern of the brain and body. Restless legs syndrome (RLS or Willis-Ekbom disease), obstructive sleep apnea syndrome, and narcolepsy are only a few examples of these sleep disorders. Willis-Ekbom disease, which I still prefer to call a syndrome rather than a disease, has a characteristic circadian pattern. It is possible that the circadian pattern is involved in dopamine synthesis. However, we already know that some other neurotransmitters like glutamine play a role in RLS. The circadian pattern of RLS could be related to many other circadian patterns and to understand those coherences, it is necessary to solve the puzzle of the pathogenesis of RLS. It is also interesting to know the changes of tonic activity in the upper airway muscles in sleep and in the evening. This will show us new horizons to solve the problem of sleep apnea. I believe the near future will bring new opportunities in the treatment of sleep disorders. Fully understanding the sleep-wake cycle and the circadian rhythm may be the fundamental goal of sleep medicine. I hope to see you in Istanbul for the World Sleep and Asian Sleep Research Society Meetings, and wish for a wonderful and productive 2015 for sleep medicine.