On Understanding Sleep

Scientists find what controls waking up and going to sleep.

The latest finding from an Indian-American circadian rhythms expert at Northwestern University is that he has discovered how an animal’s biological clock wakes it up in the morning and puts it to sleep at night.

In a study of brain circadian neurons that govern the daily sleep-wake cycle’s timing, doctor Ravi Allada and his team found that high sodium channel activity in these neurons during the day turn the cells on and ultimately awakening an animal, and high potassium channel activity at night turn them off, allowing them to sleep.

Investigating further, Allada was surprised to discover the same sleep-wake switch in both flies and mice.

Allada said that this oscillation mechanism appeared to be conserved across several hundred million years of evolution, adding that if it`s in the mouse, it was likely in humans, too.

The researchers call this a “bicycle” mechanism: two pedals that go up and down across a 24-hour day, conveying important time information to the neurons.

The researchers found the two pedals, a sodium current and potassium currents, active in both the simple fruit fly and the more complex mouse was unexpected. The balance between sodium and potassium currents controls the animal’s circadian rhythms.

Better understanding of this mechanism could lead to new drug targets to address sleep-wake trouble related to jet lag, shift work and other clock-induced problems. Eventually, it might be possible to reset a person’s internal clock to suit his or her situation.

What is amazing is finding the same mechanism for sleep-wake cycle control in an insect and a mammal. Mice are nocturnal, and flies are diurnal, or active during the day, but their sleep-wake cycles are controlled in the same way.

The balance between sodium and potassium currents controls the animal’s circadian rhythms.

Allada and their colleagues then wondered if such a process was present in an animal closer to humans.

They studied a small region of the mouse brain that controls the animal’s circadian rhythms, the suprachiasmatic nucleus, made up of 20,000 neurons and found the same mechanism there.

A properly functioning body clock adopts roughly the same 24-hour-cycle that dictates our alarm clocks and calendars, primarily because our circadian rhythms align with daily patterns of waning light and darkness.

Our internal clock controls the activity of sodium and potassium channels. Higher sodium channel activity result in more sodium currents (more sodium getting into the neurons), this excites the neurons and in turn wakes up the animal.

At night, sodium channel activity will be low (low sodium current, lower sodium getting into the cell), but potassium channel activity (more potassium currents) would be high. In this case, more potassium comes out of the cell, which silences (decreases the activity of the circadian neurons) and puts the animal to sleep.

Given that the biological clocks of mice and humans operate nearly identically, the same switch may very well control sleeping and waking in humans, too.


For more information please visit: www.northwestern.edu





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