Ultradian rhythm
A biological rhythm is called ultradian in chronobiology (from the Latin ultra 'over' and this 'day') if its frequency is above that of a day, i.e. its period is shorter than 24 hours. This differs from the circadian rhythm with the approximate period length of a day and the infradian rhythm with a period length of more than one day.
Ultradian rhythms are observed in different cellular processes and different physiological functions such as heartbeat , breathing , hormone levels or sleep phases . In addition, they occur in cyclical behavior patterns and here especially when eating. Ultradian rhythms have great diversity, both in terms of period length - from hours to milliseconds - as well as in terms of processes and their functions. The ultradian rhythms, the duration of which does not exceed twelve hours, can repeat themselves more than once a day.
The tide- oriented, circatidal rhythms with a period of about 12.5 hours have a special position here .
Examples of regularly ultradian repeating events
Ultradian oscillations can be assumed for all biological systems and can be detected down to the cell or bacterial level. Typical examples of ultradian processes in the biological field are the action of the heart, breathing and the pulsatile release of hormones in animals and humans . Regularly repeating leaf movements in plants and the cell division rhythm in eukaryotes can also be included.
Important biochemical oscillations are also observed in yeast cell extracts in synchronous form. Synchronous ultradian rhythms occur here in glycolysis , with the allosteric enzyme phosphofructokinase playing a key role in this case. The striking accumulations of similar cell cycles in populations of ciliates and amoebas are based on stable ultradian and temperature-compensated mechanisms.
The time interval between individual food intake also corresponds to an ultradian rhythm in numerous animal species. Periodic processes such as rumination and coprophagia are observed particularly in herbivorous birds and mammals . Ultradian rhythms are very pronounced in many insectivors and rodents .
Another important example of ultradian rhythms is the alternation of the different sleep stages in a REM-Non-REM cycle . A cycle lasts about 1.5 hours and seems to be subject to endogenous control when it is free. A rhythmic ultradian change can also be observed with regard to general human performance over the course of the day (example “midday low”).
Chronobiological research in recent years has shown rhythmic biochemical processes at the cellular level as controlling mechanisms. The self-inhibiting biosynthesis of proteins, which is under the control of so-called CLOCK genes, is one of the molecular mechanisms in cells that function as an endogenous clock or internal clock . In some of these processes a temperature compensation could also be observed, so that the corresponding rhythmic process hardly or not at all depends on the temperature.
By lesion studies it was shown that for the emergence of ultradian the field of non rhythms suprachiasmatic nucleus is critical where in most mammals , the central controlling instance for circadian localized processes. For rhythms with a period of less than a day, another brain region caudal to the suprachiasmatic nucleus seems to play a role.
Circatidal rhythms
Similar to a circadian rhythm that structures the sequences of inner processes in such a way that they roughly correspond to the outer day-night cycle, living beings that prefer to live in the intertidal zone have a rhythm that is created with the help of endogenous "tidal oscillators “ Seeks to anticipate the times of high and low tide . In an area like the Wadden Sea , which regularly dries out at low tide and is then flooded again, this is beneficial for the vast majority of the species that live there. This tidal rhythm with circatidal rhythms of about 12.5 hours is based on the changing of the tides , the tides . After about twelve and a half hours, one low tide is followed by another at low tide.
Fiddler crabs ( Uca sp. ) Were also examined under this aspect . Under isolated conditions in the laboratory, they show two activity phases that are initially synchronized with the tides, but then increasingly less coincide with their dates and follow a free-running, stable rhythm. There is still no clarity about its biological clock as an internal clock and the external influences that act as a synchronizing timer . The mediating processes have also not been clarified; it is assumed that the upper pharyngeal ganglion overlying the esophagus plays a role in this connection.
In the meantime it has been shown in another crustacean , the speckled sea louse ( Eurydice pulchra ) , which occurs in the north-east Atlantic , that a different internal clock is responsible for its circatidal rhythm than its circadian rhythm. The same applies to the mangrove shrimp Apteronemobius asahinai , an insect that is less than one centimeter long , which is endemic to a group of islands in Southeast Asia ; when the optical praise is removed , the circadian rhythm is lost, but not the circatidal internal clock. The multi-bristled worm Platynereis dumerilii also has different internal clocks for the circatidal rhythm and for its circalunar rhythm .
Individual evidence
- ↑ Schulz, Dirlich and Zulley (Max Planck Institute for Psychiatry, Munich): Studies on the stability of ultradian rhythms in humans . In: drug research (= drug research) . Thieme Verlag, 1976, ISSN 0004-4172 , p. 1055-1058 ( uni-regensburg.de [PDF; accessed on June 11, 2015]).
- ↑ L. Zhang, M. Hastings, E. Green, E. Tauber, M. Sladek, S. Webster, C. Kyriacou, D. Wilcockson: Dissociation of Circadian and Circatidal Timekeeping in the Marine Crustacean Eurydice pulchra . In: Current Biology. Volume 23, No. 19, October 2013, pp. 1863–1873, doi: 10.1016 / j.cub.2013.08.038 , PMC 3793863 (free full text).
- ↑ Hiroki Takekata, Hideharu Numata, Sakiko Shiga: The Circatidal Rhythm Persists without the Optic Lobe in the Mangrove Cricket Apteronemobius asahinai . In: Journal of Biological Rhythms. Volume 29, No. 1, February 2014, doi: 10.1177 / 0748730413516309 , free access, accessed on January 11, 2017; ( PDF ).
- ^ Eliot Barford: Biological clocks defy circadian rhythms. In: Nature. September 2013, doi: 10.1038 / nature.2013.13833 , accessed on January 11, 2017