FEB 05, 2017 8:49 AM PST

Microscopy Shows the Importance of Sleep to Brain Cell Health

WRITTEN BY: Carmen Leitch

It's not surprising to learn that scientists have found additional evidence that sleep is critical to the health of nerve cells in the brain; they use that down time to perform a sort of recalibration. Images captured with an electron microscope show that the area where nerve cells meet, synapses, are enlarged during the day when we are active, and then get around 20 percent smaller during sleep; space is generated for growth and new learning the next day. Drs. Chiara Cirelli and Giulio Tononi of the Wisconsin Center for Sleep and Consciousness have published their findings in Science.

3-D reconstructions of electron microscope images of tree branch-like dendrites. At the end of the branches are cup-like structures called the spines, and in the tips of the spines are synapses. / Credit: Wisconsin Center for Sleep and Consciousness

The researchers have generated visual evidence supporting their "synaptic homeostasis hypothesis" (SHY), it suggests that sleep is a necessary price for the dynamic, plastic nature of human brains, which can thus continue to learn new things and generate new memories. Repeated activation of a synapse causes it to gain strength and grow, believed to be crucial for memory and learning. SHY posits that such growth must be balances in order to avoid saturating synapses, which could wipe out neural signaling, and memories. Because sleep is a time of relative mental rest, it is thought that would be the most opportune time for recalibration or normalization of synapses.

Cirelli and Tononi knew that as synapses grow in strength they grow in size, and the reverse is also true. As such it was thought that SHY could be tested by directly measuring the actual size of a synapse during sleeping and resting states. A powerful tool was needed - three-dimensional electron microscopy.

Drs. Cirelli, foreground, and Tononi, right, study an image of a mouse brain taken by a scanning electron microscope, left. Thousands of these images were analyzed for the study published this week in the journal Science. / Credit: John Maniaci/UW Health

It took a team of scientists utilizing a mouse model over four years, photographing and reconstructing 6,920 synapses from parts of the cerebral cortex, and determining the sizes of each one. The researchers performing the work did not know what samples they were working on so any chance of bias was removed from the work. The change in the size of individual synapses could be measured. A synapse would be captured, and after six to eight hours of sleep that same synapse would again be imaged. Comparisons of those sizes indicated that the sleepy synapses were about 18 percent smaller than daytime synapses. That difference, which was proportional to synapse size, occurred in both regions of the cerebral cortex that were assayed.

It seemed the largest of the synapses did not undergo this shift in size, suggesting to the researchers that these biggest synapses are associated with the most fundamental and stable memories. 

"This shows, in unequivocal ultrastructural terms, that the balance of synaptic size and strength is upset by wake and restored by sleep," commented Cirelli. "It is remarkable that the vast majority of synapses in the cortex undergo such a large change in size over just a few hours of wake and sleep.

"Extrapolating from mice to humans, our findings mean that every night trillions of synapses in our cortex could get slimmer by nearly 20 percent," explained Tononi. 

The study comes along with research from Richard Huagnir and colleagues, published in PNAS that also confirmed how sleep is essential to brain cell health. That work identified molecular players involved in SHY and the scale down that occurs during sleep.

Check out a video featuring one of the study investigators, Dr. Tononi, speaking on a panel discussion at MIT on consciousness and intelligence.

 

Sources: AAAS/Eurekalert! via University of Wisconsin-MadisonScience

About the Author
  • Experienced research scientist and technical expert with authorships on over 30 peer-reviewed publications, traveler to over 70 countries, published photographer and internationally-exhibited painter, volunteer trained in disaster-response, CPR and DV counseling.
You May Also Like
AUG 03, 2021
Genetics & Genomics
Aging Cells May Lose Control of Where an mRNA Sequence Starts
AUG 03, 2021
Aging Cells May Lose Control of Where an mRNA Sequence Starts
When a gene is active, it's transcribed from DNA to RNA, and a specific sequence in the genetic code acts like a sig ...
AUG 05, 2021
Clinical & Molecular DX
Gene Markers in Mothers Point to the Risk of Preterm Birth
AUG 05, 2021
Gene Markers in Mothers Point to the Risk of Preterm Birth
Preterm births—when the baby is born fewer than 37 weeks gestational age—are very common. Experts estimate o ...
AUG 09, 2021
Genetics & Genomics
Middle Eastern Data Fills in Some Knowledge Gaps on Human Genetics
AUG 09, 2021
Middle Eastern Data Fills in Some Knowledge Gaps on Human Genetics
Although the human genome has basically the same genes from one person to the next, there is a huge amount of variation ...
AUG 13, 2021
Cell & Molecular Biology
Taking Aim at the Sugar Coat of the SARS-CoV-2 Spike Protein
AUG 13, 2021
Taking Aim at the Sugar Coat of the SARS-CoV-2 Spike Protein
We've learned a lot about the virus that causes COVID-19, SARS-CoV-2, in the past year and a half. Researchers know the ...
AUG 19, 2021
Cardiology
How Gut Microbes May Link a High-Fat Diet and Heart Disease
AUG 19, 2021
How Gut Microbes May Link a High-Fat Diet and Heart Disease
Cardiovascular disease is the leading cause of death around the world. Atherosclerosis is known to be a major contributo ...
SEP 14, 2021
Health & Medicine
Graphene-Oxide Based Nanotechnology and Immunology-An Exciting Partnership
SEP 14, 2021
Graphene-Oxide Based Nanotechnology and Immunology-An Exciting Partnership
As treatments and infection control practices surrounding COVID-19 continue to evolve, nanotechnological solutions are b ...
Loading Comments...