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Aiden Davis
Aiden Davis

Acclimation High Quality


Detectable BAT volume and NST increased significantly upon the cold acclimation period. A significant relation is found between NST and BAT activity. (A) Individual data on BAT activity. Left panel: detectable BAT volume (cc); middle panel: glucose uptake rate (μmol/min/100 g); right panel: NST (%). Please note that detectable BAT volume is an overestimation of true active BAT volume. (B) Relation between NST and BAT. Left panel: NST expressed as percentage and BAT activity as SUV mean; right panel: NST expressed as percentage and BAT activity as SUV max. (C) [18F]FDG-PET images of the upper body after cold exposure in a female (top) and a male subject (bottom), before (pre) and after (post) cold acclimation. Main BAT locations are indicated with black arrows; additionally, paravertebral BAT is activated. (D) Transversal CT (top) and PET/CT fusion (bottom) slice of the supraclavicular region demonstrating [18F]FDG-uptake in BAT locations (white arrows) after cold exposure, both before and after the cold acclimation period.




acclimation



A higher sensation and thermal comfort and lower self-reported shivering were reported on day 10 as compared with day 3. The iAUC decreased with 57%, 72%, and 61% for sensation, thermal comfort, and self-reported shivering respectively (P


Previously we have shown a positive relation between changes in SM mitochondrial uncoupling and the increase in 24-hour energy expenditure after 3 days of mild cold exposure (19, 35). In this study, we could not confirm a relation between changes in NST and SM uncoupling as assessed in permeabilized muscle fibers. Also, a more in-depth analysis of mitochondrial respiration in isolated mitochondria did not reveal changes in mitochondrial uncoupling. Although the type (continuous vs. intermittent) and duration (3 vs. 10 days) of cold exposure may contribute to this discrepancy in results, the present study shows that changes in mitochondrial uncoupling capacity in SM did not relate to the increased NST after cold acclimation in humans.


From cell culture studies, it is now well established that there are 2 distinct types of BAT cells, one derived from myf5-positive lineage (36), called the classical BAT cells, and myf5-negative, called inducible BAT, or beige or brite cells (22, 23). Based on cell-specific markers and on UCP1 (characteristic of both BAT and beige/brite cells), this study did not show browning of abdominal subcutaneous WAT upon cold acclimation. Possible increases in beige/brite cells may have been under the detection level, or browning in deeper depots (visceral, deeper subcutaneous) may have occurred. Unfortunately, we are unable to take WAT biopsies from these areas in our lean, healthy subjects. Furthermore, it remains possible that a longer cold stimulation period may result in a more general browning of human WAT.


MAP during thermoneutrality was reduced after cold acclimation, and a stronger reduction in skin perfusion upon acute cold exposure at the hand was found. The latter may indicate that next to a metabolic response to cold acclimation (increase in NST), also an insulative response has occurred. Together, these physiological adaptations are in line with the change in subjective reporting on cold sensation, as subjects judged the environment warmer, felt more comfortable in the cold, and reported less shivering, indicating that cold was better tolerated. These changes in comfort also indicate that daily mild cold exposure might be a feasible therapy against the obesity pandemic. Earlier studies have shown that temporal exposures to 17C are acceptable for both adults and the elderly (37). Introducing indoor temperature variations in dwellings and offices may therefore activate BAT and NST and thus impose a healthier indoor environment.


In recent years, it has been shown that humans have active brown adipose tissue (BAT) depots, raising the question of whether activation and recruitment of BAT can be a target to counterbalance the current obesity pandemic. Here, we show that a 10-day cold acclimation protocol in humans increases BAT activity in parallel with an increase in nonshivering thermogenesis (NST). No sex differences in BAT presence and activity were found either before or after cold acclimation. Respiration measurements in permeabilized fibers and isolated mitochondria revealed no significant contribution of skeletal muscle mitochondrial uncoupling to the increased NST. Based on cell-specific markers and on uncoupling protein-1 (characteristic of both BAT and beige/brite cells), this study did not show "browning" of abdominal subcutaneous white adipose tissue upon cold acclimation. The observed physiological acclimation is in line with the subjective changes in temperature sensation; upon cold acclimation, the subjects judged the environment warmer, felt more comfortable in the cold, and reported less shivering. The combined results suggest that a variable indoor environment with frequent cold exposures might be an acceptable and economic manner to increase energy expenditure and may contribute to counteracting the current obesity epidemic.


It is also important to note that factors affecting these changes determine the extent to which adaptations occur. For example, acclimation in hot and dry environments has been shown to be different from that in hot and humid environments (a greater sweat rate increase has been seen in the latter case). Acclimation is also known to depend on volume of exercise, intensity, duration and maintenance of an elevated internal body temperature during exercise.


Acclimatization or acclimatisation (also called acclimation or acclimatation) is the process in which an individual organism adjusts to a change in its environment (such as a change in altitude, temperature, humidity, photoperiod, or pH), allowing it to maintain fitness across a range of environmental conditions. Acclimatization occurs in a short period of time (hours to weeks), and within the organism's lifetime (compared to adaptation, which is evolution, taking place over many generations). This may be a discrete occurrence (for example, when mountaineers acclimate to high altitude over hours or days) or may instead represent part of a periodic cycle, such as a mammal shedding heavy winter fur in favor of a lighter summer coat. Organisms can adjust their morphological, behavioral, physical, and/or biochemical traits in response to changes in their environment.[1] While the capacity to acclimate to novel environments has been well documented in thousands of species, researchers still know very little about how and why organisms acclimate the way that they do.


While the capacity for acclimatization has been documented in thousands of species, researchers still know very little about how and why organisms acclimate in the way that they do. Since researchers first began to study acclimation, the overwhelming hypothesis has been that all acclimation serves to enhance the performance of the organism. This idea has come to be known as the beneficial acclimation hypothesis. Despite such widespread support for the beneficial acclimation hypothesis, not all studies show that acclimation always serves to enhance performance (See beneficial acclimation hypothesis). One of the major objections to the beneficial acclimation hypothesis is that it assumes that there are no costs associated with acclimation.[11] However, there are likely to be costs associated with acclimation. These include the cost of sensing the environmental conditions and regulating responses, producing structures required for plasticity (such as the energetic costs in expressing heat shock proteins), and genetic costs (such as linkage of plasticity-related genes with harmful genes).[12]


The degree to which organisms are able to acclimate is dictated by their phenotypic plasticity or the ability of an organism to change certain traits. Recent research in the study of acclimation capacity has focused more heavily on the evolution of phenotypic plasticity rather than acclimation responses. Scientists believe that when they understand more about how organisms evolved the capacity to acclimate, they will better understand acclimation.


The Guide for the Care and Use of Laboratory Animals and the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching recommend a period of stabilization and acclimation for newly arrived animals. This document provides standard recommendations to PIs regarding appropriate acclimation times for animals following transport prior to their use in experiments.


Researchers are strongly encouraged to ascertain how physiologic changes associated with transport may affect the specific research to be conducted as well as the length of time necessary for confounding physiologic changes to normalize. Longer periods for acclimation, conditioning, and/or training of animals may be required for specific protocols based on individual research needs.


Guidelines listed below are for minimum recommended periods of stabilization and acclimation and vary with species. They are applicable to animals acquired from approved vendors and of known health status. Information on approved vendors for each species can be obtained from DLAR. Longer periods of acclimation may be warranted based on mode and length of transport, source, or other considerations relevant to the health of the animal as determined by the veterinarian. NHP (non-human primate) species require longer acclimation, quarantine and special procedures. These recommendations do not apply to non-human primates and the DLAR veterinary staff should be contacted for information on the current requirements for these species. 041b061a72


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