Hibernating animals enter a state of reduced metabolism and decreased body temperature called torpor that can continue for several days to several weeks in small mammals and several months in large mammals. Hibernation is found in a variety of species in several different orders. This behaviour is not restricted to specific geographical areas and it is not a feature of a particular evolutionary stage of development. It rather can be observed in rodents inhabiting the Arctic, where core body temperature can decrease to below the freezing point 
and in primates living in tropical regions. In small mammals torpor is interrupted regularly by arousal episodes, which are brief returns to normal levels of metabolic rate and body temperature. The biological relevance of these arousals is still not Pimozide understood. However, they are likely important for restoration of some physiological or neurological capacity or even be necessary to prevent damage. Mammalian hibernation is thought to be based on similar physiological mechanisms and a consequence of alternative regulation of general physiological programmes by the differential expression of existing genes. Hence, regulated hypometabolism may be supposed as a basal physiological function of mammals. These species were selected to determine whether tau Ginsenoside-Ro phosphorylation is a general, hibernation-related phenomenon and whether species that hibernate with different body temperatures and patterns show the same patterns of phosphorylation change. Arctic ground squirrels and black bears are obligate hibernators. Hibernation of these species is controlled by an endogenous circannual rhythm. Although referring to the same hibernation category, the physiological parameters of these species in torpor differ substantially. Under natural conditions the hibernation season of arctic ground squirrels starts in September and ends in April. The basic metabolic rate of a torpid animal is decreased to only 2% compared to euthermic conditions. With an extent of four to seven months the duration of the hibernation season of black bears is similar to that of arctic ground squirrels. However, hibernation of black bears is continuous, i.e. in contrast to arctic ground squirrels it is not interrupted by spontaneous arousals. They rather abide the entire hibernation season in a den without drinking, eating, urinating and defecating. All animal rates of metabolism are only slightly narrowed. The minimum metabolic rate of a hibernating bear is lowered to about 25% compared to non-hibernating resting state and body temperature usually declines to no lower than 30uC. Syrian hamsters are referred to as permissive hibernators, i.e. hibernation is an optional response to temporary non-optimal environmental conditions. Very little is known about the behaviour and physiology of wild Syrian hamsters. However, limited food supply, low ambient temperature and a reduced photoperiod may trigger animals to enter hibernation. Hence, these parameters are critical elements for the induction of hibernation in Syrian hamsters under laboratory conditions. Once entered into hibernation animals display a hibernation pattern similar to that of arctic ground squirrels. Torpor bouts alternate with spontaneous arousals were animals revert to euthermic state. Values of basic metabolic rate, body temperature and torpor bout duration differ depending on the experimental conditions. The body temperature decreases to a range of 1�C2uC above ambient temperature that in the most applied setups varies between 4uC and 8uC and basic metabolic rate may be reduced to about 2.5% when compared to euthermy. The interspecies comparison of hibernation-related tau phosphorylation was one major element of this study. Up to now hibernation related PHF-like tau phosphorylation was reported for European ground squirrels and recently for arctic ground squirrels. An increased phosphorylation of tau at the site S202/T205 in association with hibernation was also shown in Syrian hamsters. In the present work we comprehensively describe the formation of PHF�Clike tau phosphorylation during hibernation.