BUFFENSTEIN, R.*; WOODLEY, R.: Thermogenic responses to cold acclimation in naked mole-rats; evidence for central constraints limiting metabolism.

Naked mole-rats (Heterocephalus glaber) are hairless rodents that exhibit an unusual endothermic yet poikilothermic mode of thermoregulation. We questioned why this may be the case and how these animals respond to cold acclimation (CA). Specifically we asked if central or peripheral constraints influenced their mode of thermoregulation and whether or not thermogenic capacity and activity would be augmented with CA. Animals were housed at either 30°C (Control) or at 25°C (CA). These ambient temperatures (Tas) were specifically chosen, for when naked mole-rats are housed at 30°C, resting metabolic rate (RMR) peaks at 25°C and is four times greater than that at 30°C. This response to acute changes in Ta induces a greater response than shown by mice at 5°C. We measured changes in responses to acute Tas, as well as norepinephrine (NE) induced non-shivering thermogenesis and biochemical changes in brown adipose tissue mitochondrial activity and capacity. CA did not elicit an increase in NST capacity. Similarly GDP binding was unaltered. Mitochondrial proton conductance, an indicator of BAT thermogenic activity was however enhanced in the CA group and corresponded to the 50% increase in BMR and elevated thyroxine concentrations. Unchanged thermoregulatory capacity together with the high NST responses regardless of Ta, imply that thermogenesis in naked mole-rats is maximally primed and that it must be constrained by central limits, presumably to the oxygen delivery and transport systems.