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Radiation Syndromes and Their Modifications
Published in Kedar N. Prasad, Handbook of RADIOBIOLOGY, 2020
Certain mammals, such as ground squirrels and doormice, undergo hibernation. When these animals are irradiated in the hibernating state, the expression of radiation damage is considerably delayed; but as soon as the animals are allowed to wake up, the symptoms of radiation injury develop just as in the nonhibernating controls. Thus, survival time in hibernating animals after irradiation is increased, but the absolute survival is unaffected.
Candidate Substances, Research Background, and Biological Roles
Published in Shojiro Inoué, Biology of Sleep Substances, 2020
Mammalian hibernation is closely connected with sleep.133 For example, hibernation of golden-mantled squirrels is characterized by a continuation of SWS at moderate temperatures.134 Daily shallow torpor with a lowering of body temperature and metabolism can be observable even in nonhibernating animals like fasting doves135 and small-sized marsupials.136,137 However, since the biological function of sleep may not be identical to that of sleep, no further discussion will be focused on the hibernation inducers.
Summary and Development of a New Approach to Senescence
Published in Nate F. Cardarelli, The Thymus in Health and Senescence, 2019
Circulating lymphocytes, serum complement immunoglobulin, and thymosin levels, as well as other elements of the immune system display circadian rhythmicity. Some have asserted that the thymus is a biological clock, though evidence is rather scanty. Thymus transplants from normal mice to one strain of dwarf mice will extend lifetime from around 4 months to 6 months. The thymus gland involutes during hibernation, then rejuvenates just before arousal, thus following a circannual rhythm. Interestingly, even though one would suppose that the immune system would lose capability as the thymus involutes, the appearance and growth of malignant tumors, and metastasis are much lower during hibernation.153 The differences between subjects and controls prevented from hibernation appear too great to be merely a matter of reduced metabolic rate. Hibernating species, such as the bat, show a much longer life-span (20 years) as compared with related nonhibernators (e.g., 2 to 3 years for mice and rats). Morphology of the pineal also changes during hibernation, and melatonin levels decrease substantially. It has been suggested that the pineal pacemaker in the hamster is arrested in the day phase of the cycle during hibernation.
Influences of ovarian hormones on physiological responses to cold in women
Published in Temperature, 2022
Andrew M. Greenfield, Nisha Charkoudian, Billie K. Alba
The existence and functional nature of BAT has long captivated the scientific community since its discovery in the 16th century [55]. Remarkably, this brown, multilocular tissue has inspired multiple resurgences in concerted research efforts for over four centuries. Early observations in hibernating rodents found BAT to be highly thermogenic, defending against decreases in core temperature and serving as a mechanism for energy homeostasis [56]. Given the significantly larger body surface area (BSA)-to-mass ratio of rodents relative to humans, it could be speculated a greater reliance on BAT thermogenesis would be expected and beneficial to survival. While abundant in small mammals, BAT in humans was thought to exist only in newborns, with atrophy occurring throughout infancy and minimal levels soon after [57]. This diminution of BAT raised speculation that its purpose was physiologically inconsequential in adult humans. Nonetheless, the potential for anti-obesity therapeutics (e.g., potential for burning extra calories without exercise) remained a significant and perpetuating impetus for the continuation of BAT research in rodents [58].
Genetic identification of preoptic neurons that regulate body temperature in mice
Published in Temperature, 2022
Natalia L. S. Machado, Clifford B. Saper
Recent studies have also focused on the long duration of the hypothermic and hypometabolic state induced by the MnPO neurons, and compared this to daily torpor (regulated periods of several hours of hypothermia to about 31° C and reduced activity when energy stores are low in a cool environment) or even hibernation (a controlled hypothermic state where core temperature is regulated below 31°C and there is reduced spontaneous activity lasting for many hours or days) [28,29]. Takahashi and colleagues used hM3Dq and CNO to activate MnPO neurons that express the pyroglutamylated RFamide peptide (QRFP) and found a fall in body temperature to about 24°C which lasted for 2–3 days [30] in mice, which is much longer than the 2–4 hour half-life of CNO. This state was also associated with a slowed heart rate and respiration, which is seen in torpor or during hibernation.
Chlorpromazine and promethazine reduces Brain injury through RIP1-RIP3 regulated activation of NLRP3 inflammasome following ischemic stroke
Published in Neurological Research, 2021
Qian Jiang, Mélissa Wills, Xiaokun Geng, Yuchuan Ding
Hibernation is a unique physiologic process that is seen in various mammalian species [14] in which metabolic rates are lowered to decrease body temperatures by up to 2.9°C [17]. Many studies suggest that this state of reduced metabolic ability plays an important role in neuroprotection as it confers a greater tolerance to hypoxic and hypoglycemic states, and thereby is proposed to be of neuroprotective value during cerebral ischemia [10]. Furthermore, the post-stroke inflammatory response, which is involved in ischemic stroke pathogenesis, has also been shown to be attenuated in hibernating animals [18]. Indeed, the typical inflammatory response of euthermic brain tissue, such as microglia activation and leukocytopenia, both were suppressed in hibernating animals when compared to their non-hibernating counterparts [19].