It has long been recognized that the incidence of disease In humans can show annual fluctuation. Meteorological conditions favor the spread of many infections during either the cold or hot or damp months. Centuries ago In France, the lack of vitamins in food during winter was a cause of visual Impairment

during early spring, described in Inhibitors,research,lifescience,medical poor people such as the French peasants. More recently, clinical and epidemiological studies have shown that given syndromes or disorders tend to occur more frequently at given astronomical times, for example myocardial Infarction during the very early hours of the morning.3 Although the role of astronomical Inhibitors,research,lifescience,medical time In the occurrence and the incidence of various disorders was recognized centuries ago, basic and medical research on biological clocks Is only recent. In the 18th century, the French

scientist Jean-Jacques Dortous de Malran (1678-1771) described a circadian rhythm In plant leaf movements that was independent of the Inhibitors,research,lifescience,medical lighting schedule. Then, In the early 20th century, studies on the capacity of the hon-eybee to remember the time of day when a given food was available led to the Idea of a memory of time. Inhibitors,research,lifescience,medical Whether this was more than a mere memory, and whether It reflected an endogenous production of time was then evaluated, leading to the discovery of biological clocks, a concept very different from that of memory of time. Biological clocks are defined by the fact that they Inhibitors,research,lifescience,medical generate a rhythm with cycles that exist Independently of any exogenous

cycles, such as the Influence from astronomical time (also named clock time or external light/dark cycle). Circadian promotion rhythms (circa means around or approximately Batimastat and dies means day) occur In activityrest cycles as well as In body temperature and In the secretion of many hormones, even when a subject lives without any external clues about time. This was clearly demonstrated by the French researcher Michel Slffre, who lived in an underground cave during 1962 and then In 1972. At the end of the first experiment, he believed that 43 days had passed rather than 60, and at the end of the second experiment, he believed that only 175 days had passed Instead of 205. He had had a few rest-activity cycles that extended up to 50 hours, of which he had remained unaware.