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Community => Recreation Commons => Our researchers have made a breakthrough! => Topic started by: gwillybj on October 07, 2014, 11:11:45 am

Title: When it Comes to Sleep, Timing is Everything
Post by: gwillybj on October 07, 2014, 11:11:45 am

The New York Times
Science
When it Comes to Sleep, Timing is Everything
By CLAIRE MALDARELLI
OCT. 6, 2014

(http://static01.nyt.com/images/2014/10/07/science/07sleep/07sleep-master675.jpg)
Michael Reynolds/European Pressphoto Agency

Whether it’s lying wide awake in the middle of the night or falling asleep at an international business meeting, many of us have experienced the funk of jet lag. New research has uncovered some of the mysteries behind how our cells work together to maintain one constant daily rhythm, offering the promise of defense against this disorienting travel companion.

Many organisms, including humans and fruit flies, have pacemaker neurons — specialized cells in the brain that have their own molecular clocks and oscillate in 24-hour cycles. But in order for an organism to regulate itself, all of these internal clocks must tick together to create one master clock.

While scientists understood how individual neurons set their own clock, they didn’t know how that master clock was set. Working with young fruit flies, whose neuronal system is simpler than adults with fewer cells and easier to study, the researchers found that two types of neurons, which they called dawn cells and dusk cells, maintain a continuous cycle. As the sun rises, special “timeless” proteins, as they’re called, help the dawn cells to first signal to each other and then signal to the dusk cells. Then as the sun sets, proteins help the dusk cells signal to each other and then signal back to the dawn cells. Each signal tells the cells to synchronize with each other. Together, these two distinct signals drive the daily sleep and wake cycle.

“This really shifts our view of these cells as super strong, independent oscillators to much more of a collective group working together to keep time,” said Justin Blau, a neurobiologist at New York University and co-author of the study.

Biologists hope that by understanding more about how the connections between these pacemaker neurons work, they can try to decrease the amount of time it takes for people traveling to new time zones to adjust. Dr. Blau thinks that by loosening the connection between both the dawn and dusk cells, individual pacemaker neurons may be able to reset their clocks faster and allow people to recover more quickly from jet lag. However, he emphasizes that this idea still requires a better understanding of the pathways that help the cells to communicate.

Erik Herzog, a biologist at Washington University in Saint Louis who was not involved in the study, said that our ability to synchronize to the dawn and dusk cycle is quite potent. “Only in the last 150 years have we been able to leave lights on at night,” he said. “We have not yet evolved to the challenge of crossing time zones really quickly.”

But Dr. Herzog is optimistic that the new study will help pave the way for future discovery. “The more we know about the neurons and the signals they use, the more clues we have about how to get these signals to perform better,” he said.

http://www.nytimes.com/2014/10/07/science/when-it-comes-to-sleep-timing-is-everything.html?ref=science (http://www.nytimes.com/2014/10/07/science/when-it-comes-to-sleep-timing-is-everything.html?ref=science)

Title: Re: When it Comes to Sleep, Timing is Everything
Post by: gwillybj on October 07, 2014, 11:17:12 am

The New York Times
Science | Matter
The Evolution of Sleep: 700 Million Years of Melatonin
Carl Zimmer
October 7, 2014

As much as we may try to deny it, Earth’s cycle of day and night rules our lives.

When the sun sets, the encroaching darkness sets off a chain of molecular events spreading from our eyes to our pineal gland, which oozes a hormone called melatonin into the brain. When the melatonin latches onto neurons, it alters their electrical rhythm, nudging the brain into the realm of sleep.

At dawn, sunlight snuffs out the melatonin, forcing the brain back to its wakeful pattern again.

We fight these cycles each time we stay up late reading our smartphones, suppressing our nightly dose of melatonin and waking up grumpy the next day. We fly across continents as if we could instantly reset our inner clocks. But our melatonin-driven sleep cycle lags behind, leaving us drowsy in the middle of the day.

Scientists have long wondered how this powerful cycle got its start. A new study on melatonin hints that it evolved some 700 million years ago. The authors of the study propose that our nightly slumbers evolved from the rise and fall of our tiny oceangoing ancestors, as they swam up to the surface of the sea at twilight and then sank in a sleepy fall through the night.

(http://static01.nyt.com/images/2014/10/02/science/02zimmer/02zimmer-articleLarge.jpg)
A highly-magnified view of young larva of the marine worm Platynereis dumerilii. Credit Harald Hausen

To explore the evolution of sleep, scientists at the European Molecular Biology Laboratory in Germany study the activity of genes involved in making melatonin and other sleep-related molecules. Over the past few years, they’ve compared the activity of these genes in vertebrates like us with their activity in a distantly related invertebrate — a marine worm called Platynereis dumerilii.

The scientists studied the worms at an early stage, when they were ball-shaped 2-day-old larvae. The ocean swarms with juvenile animals like these. Many of them spend their nights near the ocean surface, feeding on algae and other bits of food. Then they spend the day at lower depths, where they can hide from predators and the sun’s ultraviolet rays.

Maria Antonietta Tosches and her colleagues examined how different genes became active in the worm larvae. They discovered that some cells on the top of the larvae make light-catching proteins — the same ones we make in our eyes to switch melatonin production on and off. These same cells also switch on genes required to produce melatonin.

The scientists wondered if the worms were using this network of melatonin genes the way we do. To find out, Dr. Tosches and her colleagues tracked the activity of the genes over 24-hour periods.

They found that the worms didn’t produce melatonin all the time. Instead, they made it only at night, just as we do.

The scientists also found that this nightly surge of melatonin allowed the worms to move up and down in the ocean each day.

The worms travel by beating tiny hairs back and forth. During the day, they rise toward the surface of the ocean. By the time they get there, the sun has gotten so faint that the worms start making melatonin.

The hormone latches onto the neurons that control the beating hairs and cause them to produce a steady rhythm of electrical bursts. The bursts override the beating, causing the hairs to freeze and the worm to sink. When dawn comes, the worms lose their melatonin and start to swim upward again.

When it comes to melatonin, humans and worms are so similar that they can both get jet lag.

“If you take larvae in daytime and put them in darkness, they stay in their own daytime behavior,” Dr. Tosches said. The melatonin-driven cycle continues to determine how they swim. “They have a clock that’s controlling this,” she said.

That the melatonin network works so similarly in worms and humans suggests that it was what arose in their common ancestor. “It could have been the first form of sleeping,” said Detlev Arendt, a co-author of the new study.

David C. Plachetzki, an evolutionary biologist at the University of New Hampshire who was not involved in the study, called it “an exciting paper — it’s a very complete story.”

Still, he added that while the similarities between worms and humans were striking, there was more work to be done to confirm an evolutionary link. It would still be necessary to find melatonin playing a similar role in other animals.

“We just have this tantalizing hypothesis,” Dr. Plachetzki said. “But it’s a great hypothesis.”

The new study offers an intriguing idea for how our vertebrate ancestors adapted the melatonin genes as they evolved a complex brain.

Originally, the scientists argue, the day-night cycle was run by all-purpose cells that could catch light and make melatonin. But then the work was spread among specialized cells. The eyes now took care of capturing light, for example, while the pineal gland made melatonin.

The new study may also help explain how sleep cuts us off from the world. When we’re awake, signals from our eyes and other senses pass through the thalamus, a gateway in the brain. Melatonin shuts the thalamus down by causing its neurons to produce a regular rhythm of bursts. “They’re busy doing their own thing, so they can’t relay information to the rest of the brain,” Dr. Tosches said.

It may be no coincidence that in worms, melatonin also produces electrical rhythms that jam the normal signals of the day. We may sink into sleep the way our ancestors sank into the depths of the ocean.

A version of this article appears in print on October 7, 2014, on page D3 of the New York edition with the headline: 700 Million Years of Melatonin.

http://www.nytimes.com/2014/10/02/science/the-evolution-of-sleep-700-million-years-of-melatonin.html (http://www.nytimes.com/2014/10/02/science/the-evolution-of-sleep-700-million-years-of-melatonin.html)