Cold-acclimation-induced non-shivering thermogenesis in birds is associated with upregulation of avian UCP but not with innate uncoupling or altered ATP efficiency

Abstract

) were obtained from a commercial stockbreeder (Eclosion Grimaud-lacorbière, Roussay, France). Birds were fed ad libitum with commercial mash (Moulin Guenard, 645000MI, Vonnas, France) and had free access to water. From the age of 10 days, ducklings were caged for Accepted 7 April 2010 SUMMARY Despite their lack of brown adipose tissue, some bird species develop regulatory non-shivering thermogenesis (NST) of skeletal muscle origin in response to cold acclimation. Mechanisms involved in avian NST are still unclear but may involve reduced energetic coupling in skeletal muscle mitochondria through the expression of an avian homologue of mammalian uncoupling proteins. The aim of this work was to investigate whether the expression of avian uncoupling protein (avUCP) would correlate with the capacity for cold-induced muscle NST. Various levels of cold acclimation were obtained by rearing 1-week-old ducklings (Cairina moschata) for 4 weeks at three different ambient temperatures (25°C, 11°C or 4°C). Muscle NST was measured by simultaneous recordings of metabolic rate and electromyographic activity (gastrocnemius muscle) at ambient temperatures (T a ) ranging from 27°C to -5°C. The expression of avUCP gene and mitochondrial bioenergetics were also determined in gastrocnemius muscle. Results showed that muscle NST capacity depends on the T a at which ducklings were acclimated, i.e. the lower the rearing temperature, the higher the capacity for NST. This increased metabolic heat production occurred in parallel with an upregulation of avUCP, which was not associated with a change in mitochondrial membrane conductance. The intensity of mitochondrial oxidative phosphorylation also increased in proportion with the harshness of cold, while the efficiency of ATP generation was equally effective in all three acclimation temperatures. In the absence of mitochondrial uncoupling, these data indicate a clear link between avUCP expression and the capacity of ducklings to adjust their muscular aerobic activity to cold exposure.

Mitochondrial oxidative energy metabolism in guanethidine-induced sympathectomized ducklings

“…Altogether these data suggest that the sympathetic nervous system (norepinephrine) may modulate facultative thermogenesis in birds. This idea is also in line with recently published data suggesting that the beta-adrenergic system would be involved in regulating the expression of avian uncoupling protein (Joubert et al 2010(Joubert et al , 2011, a mitochondrial protein that has been linked to the intensity of regulatory thermogenesis in cold-acclimated ducklings (Teulier et al 2010). Whether guanethidine-treated ducklings displayed a lower expression of avian UCP is currently not known but deserves further study.…”

Novel energy-saving strategies to multiple stressors in birds: the ultradian regulation of body temperature

“…Six were assigned randomly to each of the two acclimation temperature groups. The ages of the ducklings at the beginning of the trial was five weeks and had been housed at their acclimation temperatures since 10 days of age: TN ducklings were housed at 258C and CA ducklings were housed at 58C following similar published protocols [30]. Ducklings varied in mass throughout the experiments, although at the outset of the measurement period the 12 ducklings chosen for the measurements were sizematched such that both acclimation groups had an average starting mass of approximately 1 kg.…”

“…The 0.5 value in the equation above is included to account for the fact that absolute temperature differences include both the decreases in T b as well as the increases over time, which would be symmetrical over a 24-h period in a homeothermic animal. These values were normalized to previously measured basal metabolic heat production (5 W kg 21 and 8 W kg 21 for 258C and 58C acclimated ducklings; [30,31]). …”

“…The metabolic costs associated with the periodic rises in T b were typically higher in cold-acclimated ducklings, but declined more profoundly during fasting. The metabolic costs are not insubstantial; when expressed as a portion of basal metabolic rate [30] are between 7 and 11%.…”

Alteration of mitochondrial efficiency affects oxidative balance, development and growth in frog (Rana temporaria) tadpoles

“…The mitochondrial oxidative phosphorylation efficiency was determined from the rate of ATP synthesis and oxygen consumption of isolated tadpole mitochondria (3mgml -1 ) respiring on succinate (5mmoll -1 plus 5mmoll -1 rotenone) in the respiratory medium supplemented with an ADP-regenerating system consisting of 1.5Uml -1 hexokinase, 20mmoll -1 glucose and two different concentrations of ) as previously described (Rigoulet et al, 1998;Nogueira et al, 2001;Clerc et al, 2007;Salin et al, 2010;Teulier et al, 2010).…”