Biological Rhythms: Concepts, molecular mechanisms and non-photic zeitgebers
Biological rhythms, chronobiology, non-photic zeitgebers, food entreinment oscillator
Geophysical characteristics of planet Earth movements in space, especially rotation along its own axis, creat two well-stablished environments: Day and night. Life in our plant evolved with this paradigm and adapted in a way it shows differences among those two situations, creating cyclic rhythms that repeat in a 24-hour cycle. Those are called circadian rhythms (From latin: circa = around; dies = day), which the most prominent one in animals is the sleep-awake cycle. Living organisms, “knowing” the day-night cycle, prepare themselves for these changes in a so-called predictive homeostasis, which is pivotal for their survival. All of that is possible because of a complex molecular mechanism that is highly dependent os daylight, that receive the termination zeitgeber, controlling the endogenous 24-hour internal clock. Although light is the main zeitgeber indicating central areas involved in rythmic control (suprachiasmatic nucleus in hypothalamus being the main site), other zeitgeber may influence the predictive homeostasis for controlling the activity of the animal organism. The main non-photic zeitgeber is feeding, in a so-called food-entrainment oscillator (FEO), which may strongly affect how the animal will behave in a circadian rhythm. Other zeitgebers includes temperature which has an infradian rhythm through seasons that can be quite important. More recently, thirst and water intake, which has long been shown to have an anticipatory component, has been implicated in a possible zeitgeber that could control the circadian change of animal organisms.