The Ups And Downs Of Hibernation-Like Daily Torpor

The key to the state of daily torpor, researchers have found, is reduced sensitivity to the fall of body temperature.

AsianScientist (Dec. 2, 2016) – Researchers at the RIKEN Center for Developmental Biology in Japan have determined that the largest factor that contributes to daily torpor, a hibernation-like state in animals, is reduced sensitivity of the thermoregulatory system. Their work was published in Scientific Reports.

Depending on environmental conditions and the availability of food, many animals can slow down their metabolism to save energy by way of seasonal hibernation, which can last weeks to months. Perhaps less well-known is a state called daily torpor, in which metabolism is dramatically reduced from several minutes to a few hours. The present study shows that during daily torpor, the body’s compensatory response to lowered temperature is much less than during normal active periods.

“While hibernation is associated with the winter season and cold temperatures, we were surprised to discover that instances of daily torpor could be induced at temperatures as high as 24°C, provided mice did not receive food for 24 hours,” noted first author Dr. Genshiro Sunagawa.

Many researchers believe that the mechanisms underlying hibernation and daily torpor overlap to some extent, but daily torpor in particular is still not well understood. Sunagawa and team leader Dr. Masayo Takahashi developed a system that can automatically record the metabolic activity and body temperature of mice and identify periods of daily torpor.

Scientists agree that three factors influence the regulation of body temperature during hibernation. The first is the ease with which the body loses heat, the second is the reference temperature, and the third is the sensitivity of temperature regulation. Similar to how a thermostat controls the air conditioning in your house, when body temperature gets too low, negative feedback tells the body to raise the temperature. However, if the sensitivity of the system is reduced, a similar drop in temperature will not trigger the response, and temperatures will continue to drop.

The authors speculate that the difference between daily torpor and hibernation is likely due to the speed at which the animals need to enter and come out of the different states. Because mice enter and come out of daily torpor within hours, the reference temperature cannot drop as much as it does in hibernation.

According to Sunagawa, these findings will help propel research in hypometabolism, because it shows that torpid animals share similar mechanisms with hibernators in heat production regulation.

The article can be found at: Sunagawa and Takahashi (2016) Hypometabolism During Daily Torpor in Mice is Dominated by Reduction in the Sensitivity of the Thermoregulatory System.


Source: RIKEN; Photo: Pixabay.
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