We report on in vivo temperature measurements performed in mice at two specific sites of interest in the animal body over a period of several hours. In particular, the aim of this work was to monitor mouse metabolism during cold exposure, and to record possible temperature differences between the body temperature measured in the abdomen and the temperature of the brown adipose tissue (BAT) situated in the interscapular area. This approach is of biological interest as it may help unravelling the question whether biochemical activation of BAT is associated with local increase in metabolic heat production. For that purpose, miniaturized thermistor sensors have been accurately calibrated and implanted in the BAT and in the abdominal tissue of mice. After 1 week of recovery from surgery, mice were exposed to cold (6 °C) for a maximum duration of 6 h and the temperature was acquired continuously from the two sensors. Control measurements with a conventional rectal probe confirmed good performance of both sensors. Moreover, two different mouse phenotypes could be identified, distinguishable in terms of their metabolic resistance to cold exposure. This difference was analyzed from the thermal point of view by computational simulations. Our simple physical model of the mouse body allowed to reproduce the global evolution of hypothermia and also to explain qualitatively the temperature difference between abdomen and BAT locations. While with our approach, we have demonstrated the importance and feasibility of localized temperature measurements on mice, further optimization of this technique may help better identify local metabolism variations.
A straightforward and general way for monitoring chemical reactions is via their thermal signature. Such approach requires however an experimental setup with a high thermal stability that simultaneously allows time-resolved heat detection with high sensitivity. We present a nanocalorimetric platform for accurate thermochemical studies of (bio-)chemical reactions in a miniaturized format (tens of microliter volume), characterized by a fast thermalization time to a preset temperature (< 30 minutes), an excellent base temperature stability (± 1 mK) and a fast sensing response time (few seconds). The platform is built around a commercial thermopile-based sensor chip, on which an open-well reservoir holding the sample is directly positioned. The sample is, prior to the experiment, pipetted into the reservoir, in which small aliquots of reagents are injected subsequently and sequentially via thermalized microfluidic conducts. The design of the platform is optimized by means of numerical simulations. Via thermoelectric calibration using a resistive heater positioned either on the sensor chip or in the reservoir, we obtain a maximum power sensitivity of 2.7 V/W and a heat limit of detection of 70 nW. The excellent functionality of the platform is demonstrated by measuring the reaction enthalpy of 1-propanol in water and the rate constant k and enthalpy change of the oxidation reaction of glucose catalyzed by glucose oxidase, showing good agreement with literature data. Our versatile platform may be applied to many thermochemical studies, including thermodynamic analysis and kinetic reaction analysis, and its ease of use will allow implementation of many different experimental protocols.
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