Temperature determines the shift of thermal neutral zone and influences thermogenic capacity in striped hamsters

Abstract

The thermoneutral zone (TNZ) reflects the adaptation of mammals to their natural habitat. However, it remains unclear how TNZ shifts in response to variations in ambient temperature. To test the hypothesis that ambient temperature plays a key role in determining TNZ variations between seasons, we measured metabolic rate, body temperature, and cytochrome c oxidase (COX) activity of several visceral organs in striped hamsters (Cricetulus barabensis) either acclimated to semi‐natural conditions over a year, or subjected to a gradual decrease in mean temperature from 30 ± 1°C to −15 ± 1°C. The TNZ range in striped hamsters differed seasonally, with a wider TNZ and a lower lower‐critical temperature in winter compared to summer. The hamsters showed a considerable leftward shift of lower‐critical temperature from 30°C to 20°C after the ambient temperature of acclimation from 30°C down to −15°C, whereas the upper‐critical temperature of TNZ remained fixed at 32.5°C. The resting metabolic rate in thermoneutral zone (RMRt), nonshivering thermogenesis (NST), and COX activity of brown adipose tissue, liver, skeletal muscle, brain, and kidneys, increased significantly in hamsters acclimated at lower ambient temperatures. Following acute exposure to 5°C and −15°C, hamsters acclimated to 32.5°C had significantly lower maximal NST and lower serum thyroid tri‐iodothyronine (T3) levels compared to those kept at 23°C. These findings suggest that acclimation to the upper‐critical temperature of TNZ impairs the hamsters’ thermogenic capacity to cope with extreme cold temperature. Reduced ambient temperature was mainly responsible for the leftward shift of TNZ in striped hamsters, which reflects the adaptation to cold environments.

Fat accumulation in striped hamsters (Cricetulus barabensis) reflects the temperature of prior cold acclimation

“…The gross energy contents of the food and feces were determined using an oxygen bomb calorimeter (C2000, Germany), strictly according the instructions of the manufacturer. GEI, digestive energy intake (DEI) and digestibility were calculated as follows: GEI (kJ/d) = food intake (g/d) × dry matter content of the diet (%) × energy content of food (kJ/g); Gross energy of feces (GEF) (kJ/d) = dry mass of feces (g/d) × energy content of feces (kJ/g); DEI (kJ/d) = GEI − GEF; Digestibility (%) = DEI/GEI × 100% [ 43 – 45 ].…”

“…RMR was measured for 3 h in the chamber at 30 ± 0.5 °C (within the thermal neutral zone of this species), and the measurement of ambient temperature in the chamber was performed using a temperature probe (TSE system). The data were averaged and collected every 10 s by a computer connected analogue–digital converter (TSE system), and the continuous stable minimal recordings over 10 min were taken to calculate RMR [ 45 , 46 ].…”

The effects of ambient temperature and feeding regimens on cecum bacteria composition and circadian rhythm in growing rabbits

“…Seasonal Rotation caused by the Earth’s revolution are important regulators of the clock mechanism, integrating changes in the timing of light and ambient temperature ( Arendt, 2012 ). Environmental temperature changes are most pronounced during the turnover of seasons, causing a shift in the thermoneutral zone and changing the metabolic intensity for the animal SCN activity of the animals ( Liao et al, 2022 ). Daytime feeding in rodents alters the oscillatory rhythm of bile acids in the circulation ( Eggink et al, 2017 ), which subsequently interferes with the thermogenesis and thermoregulation of brown fat G protein-coupled bile acid receptor 1 (TGR5) ( Watanabe et al, 2006 ).…”