Chronic cold acclimation increases thermogenic capacity, non-shivering thermogenesis and muscle citrate synthase activity in both wild-type and brown adipose tissue deficient mice.

The purpose of this study was to determine whether chronic cold exposure would increase the aerobic capacity of skeletal muscle in UCP-dta mice, a transgenic line lacking brown adipose tissue (BAT). Wild type and UCP-dta mice were acclimated to either warm (23 °C), or cold (4 °C) conditions. Cold increased muscle oxidative capacity nearly equivalently in wild-type and UCP-dta mice, but did not affect the respiratory function of isolated mitochondria. Summit metabolism ( ̇V O2summit) and norepinephrine-induced thermogenesis ( ̇V O2NST) were significantly lower in UCP-dta mice relative to wild-type mice regardless of temperature treatment, but both were significantly higher in cold relative to warm acclimated mice. BAT mass was significantly higher in the cold relative to warm acclimated wild-type mice, but not in cold acclimated UCP-dta mice. BAT citrate synthase activity was lower in transgenic animals regardless of acclimation temperature and BAT citrate synthase activity per depot was significantly higher only in the cold acclimated wild-type mice. Muscle citrate synthase activity was increased in both genotypes. As defects in muscle oxidative function have been observed with obesity and type 2 diabetes, these results suggest that chronic cold exposure is a useful intervention to drive skeletal muscle oxidative capacity in mouse models of obesity.

Chronic cold exposure increases skeletal muscle oxidative structure and function in Monodelphis domestica, a marsupial lacking brown adipose tissue.

Monodelphis domestica (Marsupialia: Didelphidae) was used as a model animal to investigate and compare muscle adaptation to exercise training and cold exposure. The experimental treatment consisted of four groups of animals: either warm or cold acclimation temperature and with or without endurance exercise training. Maximal aerobic capacity during a running VO2max test in the warm-exercised or cold-exposed (with or without exercise) groups was about 130 mL O(2)/kg/min, significantly higher than the warm-acclimated controls at 113.5 mL O(2)/kg/min. Similarly, during an acute cold challenge (VO2summit), maximal aerobic capacity was higher in these three experimental groups at approximately 95 mL O(2)/kg/min compared with 80.4 mL O(2)/kg/min in warm-acclimated controls. Respiratory exchange ratio was significantly lower (0.89-0.68), whereas relative heart mass (0.52%-0.73%) and whole-body muscle mitochondrial volume density (2.59 to 3.04 cm(3)) were significantly higher following cold exposure. Chronic cold exposure was a stronger stimulus than endurance exercise training for tissue-specific adaptations. Although chronic cold exposure and endurance exercise are distinct challenges, physiological adaptations to each overlap such that the capacities for aerobic performance in response to both cold exposure and running are increased by either or both treatments.

A transcutaneous wire interface for small mammals using an expanded PTFE patch.

The objective of this paper is to provide the reader with a method of surgical implantation of a transcutaneous wire interface for chronic instrumentation of small mammals, utilizing a non-bioreactive expanded polytetrafluoroethylene (ePTFE) material (W.L. Gore and Associates, Inc., Flagstaff, AZ). We describe the implant assembly, as well as details of the surgical implantation, which will facilitate successful data acquisition. EMG signal from the implant is of a high quality during both rest and activity of the animal and the signal quality is maintained up to at least 7 weeks post-implantation without any sign of infection or other adverse reaction. This represents an improvement in the viability of long-term physiological signal collection via a surgically implanted back plug.

Use of allometry in predicting anatomical and physiological parameters of mammals.

One challenge for veterinarians, animal facilities and research scientists is the making of physiological estimates appropriate to a variety of species for which data are often either completely lacking or are incomplete. Our intent in compiling the data in this paper is to provide the best possible database of normal physiological and anatomical values primarily (though not exclusively) for four common mammalian model species: mouse, rat, dog and man. In order to make those data as accessible and applicable as possible, we have presented the results of this study in the form of body-size dependent allometric equations in which some variable (Y) is expressed as a dependent function of body mass (M) in the power-law equation, Y = aM(b). By compiling these data, it is apparent that the resultant equations are quantitatively grouped (with similar slope or 'b' values). These emergent patterns provide insights into body-size dependent 'principles of design' that seem to dictate several aspects of design and function across species among all mammals. In general, the weights of most individual organs scale as a constant fraction of body mass (i.e. the body mass exponent, b approximately equal to 1.0). Biological rates (e.g. heart rate, respiratory rate) scale as b approximately equal to -1/4. Finally, volume-rates (the product of volume and rate) such as cardiac output, ventilation and oxygen uptake vary as b approximately equal to 3/4.

Cold exposure increases running VO(2max) and cost of transport in goats.

We inadvertently subjected a group of goats to 5 mo of cold exposure (mean minimum temperature less than -13 degrees C) during an experiment designed to examine the effects of training by daily running on one member of each sibling pair. During the three coldest months, the sedentary but cold-exposed goats experienced a 34% increase in maximal oxygen uptake (VO(2 max), P < 0.01) and a 29% increase in running speed at maximal (P < 0.05). When temperatures increased in the spring, both oxygen uptake and running speed decreased. We interpret these findings as evidence that cold is a sufficient stimulus to invoke the development of aerobic structures in muscle and that these structures subsequently can be utilized for the novel task of running. When the experiment was subsequently repeated without the cold exposure, running speed and VO(2 max) of trained animals increased less than in either group of cold-exposed animals. However, the cost of transport of these warm runners was lower than either group of cold-exposed animals (from 13-19%, P < 0. 0001). Thus, although aerobic capacity was increased with acclimation to severe winter weather, cold-acclimated goats operated with lower efficiency during locomotion.

The development of the ventilatory response to cold in very young rats.

To assess the range of functional responses of the ventilatory apparatus of developing rats and the degree to which ventilatory function is developed in advance of other functional characteristics, rat pups at five ages (between 4 and 20 days old) were exposed to temperatures of 28, 32 and 36 degrees C while in a flow through metabolic chamber modified to serve as a whole body plethysmograph. Ventilatory frequency, tidal volume and oxygen extraction 'efficiency' (EO2 = VO2/FEO2 x VI) were measured at each age and temperature. Mean breathing frequency at 4 days old was 2.56 breaths per second, decreasing to 1.99 at 20 days old. There was insignificant modification of breathing frequency with temperature. Four day old rat pups at 28 degrees C had mass specific tidal volumes of 0.017 ml/g, 142% of the value at 36 degrees C (0.012 ml/g). Twenty day old pups at 28 degrees C had mass specific tidal volumes of 0.027 ml/g, also 142% of the thermoneutral value (0.019 ml/g at 32 degrees C). At all ages, increases in tidal volumes were similar and increases in tidal volume were the only response to increased metabolic demand. Oxygen extraction 'efficiency' was about half that previously observed in adult rodents. These observations of ventilation during a cold challenge suggest that although structural development is not complete until much later, functional development is sufficient, either at birth or shortly thereafter.