Temperature tunes circadian timing in some desert mammals | The Transmitter: Neuroscience News and Perspectives

These studies are starting to fill in a gap in the chronobiology literature, says Roberto Refinetti, professor of psychology at the University of New Orleans, who was not involved in any of the African mammal work but has done his own temperature studies in mice and ground squirrels.

“The amount of information about light synchronizing circadian rhythms is probably 1,000—if not 10,000, 100,000—times more than temperature,” Refinetti says. But researchers should examine all potential zeitgebers to gain a “full understanding of how animals will behave in nature.”

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Light also has a clear pathway to the brain. The suprachiasmatic nucleus, a region inside the hypothalamus, functions as the circadian clock. Neurons in the retina project directly to the suprachiasmatic nucleus, which “neuroanatomically makes it easy” to study, says Satchidananda Panda, professor of regulatory biology at the Salk Institute for Biological Studies. Panda was not involved in the desert studies but says he has recently begun circadian temperature experiments in mice.

The amount of information about light synchronizing circadian rhythms is probably 1000—if not 10,000, 100,000—times more than temperature.

But it’s likely that most mammals can tune in to ambient temperature changes and prioritize that as a zeitgeber when needed, Panda says. “Why not design a system that will sense both temperature and light?” he says. “The system has evolved to use all the sensory mechanisms to sense light and temperature to entrain the clock so that in the absence of one stimulus, maybe the other stimulus will work.”

This kind of flexibility holds true for mice living in less extreme biomes than the desert, for example. In a pair of studies in laboratory mice, Refinetti reported that temperature can entrain the circadian rhythm of locomotor activity, but not as effectively as light.

El Allali’s experiments clearly demonstrate that temperature can set circadian clocks in camels and goats but do not determine which signal is a stronger zeitgeber, says Shin Yamazaki, professor of neuroscience at the University of Texas Southwestern Medical Center. To find out, Yamazaki adds, the researchers could mismatch the light and temperature cues—low temperatures during the day and high temperatures at night—and see which wins out.

El Allali conducted a version of this experiment in the 2013 camel work. Under mismatched light and temperature cues, the ambient temperature entrained the body temperature of all seven camels tested but entrained the melatonin rhythm of only three. More dramatic temperature changes might entrain melatonin in more animals, El Allali says.

Moving forward, he wants to explore whether circadian adaptations are present in smaller desert mammals, such as two species of Egyptian jerboa. He is curious, he says, if the lifestyles of people who live in the desert—sleeping more during the day and staying active late into the night—are partly due to heat-driven clock changes.

“I mean, I’m a veterinarian. I could not do such studies in a human,” El Allali says, but it’s an open question for other researchers to explore.