Specific Brain Cells Linked to Parkinson’s Disease

New research draws a conclusive link between Parkinson’s disease the deterioration of a subpopulation of neurons found within the substantia nigra, a brain region linked to motor control executive functioning.

Scientists have long known that Parkinson’s—a progressive, neurodegenerative condition that currently affects about 1 million people in the United States—is associated with a die-off of dopamine-making neurons in the substantia nigra, but multiple studies going back decades have shown that certain neurons in the area survive well into later stages of the disease. In a paper published yesterday (May 5) in Nature Neuroscience, scientists from the Broad Institute of Harvard MIT reveal why that is: there are ten different types of dopaminergic neurons in the substantia nigra, just one is linked to Parkinson’s.

“This seemed like an opportunity to . . . really clarify which kinds of cells are actually dying in Parkinson’s disease,” study coauthor Evan Macosko, a psychiatrist neuroscientist at the Broad Institute, tells Science News.

See “Study Links Flu to Increased Parkinson’s Risk a Decade Later”

In the study, scientists compared the neuronal diversity in two groups of people who had donated their brains to science: eight who didn’t have Parkinson’s ten who did. Using a technique called single-cell RNA sequencing, which can parse the gene expression activity of individual cells within a tissue sample, the team identified all ten types of neurons—each of which produced dopamine but had different gene expression profiles—in both populations found that there were fewer of only one type within the Parkinson’s group’s brains. That, New Scientist reports, suggests that only that type of neuron died while the Parkinson’s patients were still alive, is likely linked to the disease’s symptoms.

That specificity is “the strength of the paper,” Northwestern University Feinberg School of Medicine neuroscientist Raj Awatramani, who didn’t work on the study, tells New Scientist. He adds that the research “goes right to the core of the matter.”

See “Is It Time to Rethink Parkinson’s Pathology?”

The study authors tell Science News that they hope to replicate the work with a larger number of donor brains so that they can validate their findings perhaps identify other disease mechanisms. In the meantime, they say that their findings could lead to the development of new treatments for Parkinson’s that specifically target or replace the affected cells. Macosko says that stem cell researchers have already reached out, offering to find ways to generate the Parkinson’s-affected neurons.

See “Parkinson’s Patient Transplanted with Neurons Derived from iPSCs”

“If a particular subtype is more vulnerable in Parkinson’s disease, maybe that’s the one we should be trying to replace,” Awatramani tells New Scientist

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Corals Sea Anemones Turn Sunscreen into Toxins—Understanding How Could Help Save Coral Reefs

Sunscreen bottles are frequently labeled as “reef-friendly” “coral-safe.” These claims generally mean that the lotions replaced oxybenzone—a chemical that can harm corals—with something else. But are these other chemicals really safer for reefs than oxybenzone? 

Aiptasia anemones do so well in tanks that they’re considered pests in the saltwater aquarium trade.

This question led us, two environmental chemists, to team up with biologists who study sea anemones as a model for corals. Our goal was to uncover how sunscreen harms reefs so that we could better understwhich components in sunscreens are really “coral-safe.”

In our new study, published in Science, we found that when corals sea anemones absorb oxybenzone, their cells turn it into phototoxins, molecules that are harmless in the dark but become toxic under sunlight.

Protecting people, harming reefs

Sunlight is made of many different wavelengths of light. Longer wavelength—like visible light—are typically harmless. But light at shorter wavelengths—like ultraviolet light—can pass through the surface of skin damage DNA cells. Sunscreens, including oxybenzone, work by absorbing most of the UV light converting it into heat.

See “Bleached Corals ‘Sickest’ Scientists Have Ever Seen”

Coral reefs around the world have suffered in recent decades from warming oceans other stressors. Some scientists thought that sunscreens coming off of swimmers or from wastewater discharges could also be harming corals. They conducted lab experiments that showed that oxybenzone concentrations as low as 0.14 mg per liter of seawater can kill 50% of coral larvae in less than 24 hours. While most field samples typically have lower sunscreen concentrations, one popular snorkeling reef in the U.S. Virgin Islands had up to 1.4 mg oxybenzone per liter of seawater—more than 10 times the lethal dose for coral larvae.

Likely inspired by this research a number of other studies showing damage to marine life, Hawaii’s legislators voted in 2018 to ban oxybenzone another ingredient in sunscreens. Soon after, lawmakers in other places with coral reefs, like the Virgin Islands, Palau Aruba, implemented their own bans.

There is still an open debate whether the concentrations of oxybenzone in the environment are high enough to damage reefs. But everyone agrees that these chemicals can cause harm under certain conditions, so understanding their mechanism is important.

Sunscreen or toxin

While laboratory evidence had shown that sunscreen can harm corals, very little research had been done to understhow. Some studies suggested that oxybenzone mimics hormones, disrupting reproduction development. But another theory that our team found particularly intriguing was the possibility that the sunscreen behaved as a light-activated toxin in corals.

To test this, we used the sea anemones our colleagues breed as a model for corals. Sea anemones corals are closely related share a lot of biological processes, including a symbiotic relationship with algae that live within them. It is extremely difficult to perform experiments with corals under lab conditions, so anemones are typically much better for lab-based studies like ours.

We put 21 anemones in test tubes full of seawater under a lightbulb that emits the full spectrum of sunlight. We covered five of the anemones with a box made of acrylic that blocks the exact wavelengths of UV light that oxybenzone normally absorbs interacts with. Then we exposed all the anemones to 2 mg of oxybenzone per liter of seawater.

line of test tubes with anemones for testing oxybenzone toxicity

By putting sea anemones into test tubes with oxybenzone controlling what kinds of light they were exposed to, we could see whether the sunscreen was reacting to light.

The anemones under the acrylic box were our “dark” samples the ones outside of it our control “light” samples. Anemones, like corals, have a translucent surface, so if oxybenzone were acting as a phototoxin, the UV rays hitting the light group would trigger a chemical reaction kill the animals—while the dark group would survive.

We ran the experiment for 21 days. On Day Six, the first anemone in the light group died. By Day 17, all of them had died. By comparison, none of the five anemones in the dark group died during the entire three weeks.

Metabolism converts oxybenzone to phototoxins

We were surprised that a sunscreen was behaving as a phototoxin inside the anemones. We ran a chemical experiment on oxybenzone confirmed that, on its own, it behaves as a sunscreen not as a phototoxin. It’s only when the chemical was absorbed by anemones that it became dangerous under light.

Any time an organism absorbs a foreign substance, its cells try to get rid of the substance using various metabolic processes. Our experiments suggested that one of these processes was turning oxybenzone into a phototoxin.

To test this, we analyzed the chemicals that formed inside anemones after we exposed them to oxybenzone. We learned that our anemones had replaced part of oxybenzone’s chemical structure—a specific hydrogen atom on an alcohol group—with a sugar. Replacing hydrogen atoms on alcohol groups with sugars is something that plants animals commonly do to make chemicals less toxic more water soluble so they are easier to excrete.

chemical reaction turning oxybenzone into a phototoxin

When cells try to process oxybenzone, they replace part of an alcohol group (in red on the left) with a sugar (in red on the right) in doing so turn the sunscreen into a phototoxin.

But when you remove this alcohol group from oxybenzone, oxybenzone ceases to function as a sunscreen. Instead, it holds on to the energy it absorbs from UV light kicks off a series of rapid chemical reactions that damage cells. Rather than turning the sunscreen into a harmless, easy-to-excrete molecule, the anemones convert oxybenzone into a potent, sunlight-activated toxin.

When we ran similar experiments with mushroom corals, we found something surprising. Even though corals are much more vulnerable to stressors than sea anemones, they did not die from oxybenzone light exposure during our entire eight-day experiment. The coral made the same phototoxins from oxybenzone, but all of the toxins were stored in the symbiotic algae living in the coral. The algae seemed to absorb the phototoxic byproducts and, in doing so, likely protected their coral hosts.

Anemones in line to show how algae protects against oxybenzone-induced death

This photo series shows how darker-colored anemones on top with algae in them lived longer than the lighter-colored anemones on the bottom that did not have algae living in them.

Djordje Vuckovic Christian Renicke, CC BY-ND

We suspect that the corals would have died from the phototoxins if they did not have their algae. It is not possible to keep corals without algae alive in the lab, so we did some experiments on anemones without algae instead. These anemones died about two times faster had almost three times as many phototoxins in their cells compared than the same anemones with algae.

Coral bleaching, ‘reef-safe’ sunscreens, human safety

We believe there are a few important takeaways from our effort to better understhow oxybenzone harms corals.

First, coral bleaching events—in which the corals expel their algal symbionts because of high seawater temperatures or other stressors—likely leave corals particularly vulnerable to the toxic effects of sunscreens.

Second, it’s possible that oxybenzone could also be dangerous to other species. In our study, we found that human cells can also turn oxybenzone into a potential phototoxin. If this happens inside the body, where no light can reach, it’s not an issue. But if this occurs in the skin, where light can create toxins, it could be a problem. Previous studies have suggested that oxybenzone could pose health risks to people, some researchers have recently called for more research into its safety.

See “Sunscreen Ingredients Absorbed into Blood: Study”

Finally, the chemicals used in many alternative “reef-safe” sunscreens contain the same alcohol group as oxybenzone—so could potentially also be converted to phototoxins.

We hope that, taken together, our results will lead to safer sunscreens help inform efforts to protect reefs.

Djordje Vuckovic is PhD candidate in Civil Environmental Engineering at Stanford University Bill Mitch is a Professor of Civil Environmental Engineering at Stanford University.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Science Snapshot: Down but Not Out

Researchers catch release a vaquita in 2017, obtaining genetic information used in the current study.


Mother calf vaquita

Mother calf vaquitas. As the world’s smallest cetaceans, adults will only grow to be about 150 centimeters (just shy of 5 feet) long.

Paula Olson

Juvenile female vaquita in the water

A female juvenile vaquita was photographed in 2017. When fully grown, she’ll weigh around 55 kilograms (120 pounds).


For many animals, genetic diversity is crucial to survival because it affords the population some flexibility when encountering changes in the environment. Individuals may be lost, but variation helps protect whole populations from being wiped out in one fell swoop. Enter the vaquita (Phocoena sinus): the world’s smallest cetacean. These happy-looking porpoises, which occupy a small area in the Gulf of California, are critically endangered, with only 10 individuals estimated to remain in existence, giving conservationists doubts about the species’ survival due to genetic inbreeding.

A study published yesterday (May 5) in Science examined genomic data from archived vaquita tissue samples found that genetic diversity has been low yet stable among the animals for the last 1,000 years or so, indicating that the current lack of variation should not drive the species to extinction. The biggest threat to the vaquita’s continued existence is fishing, as they often become entangled in illegal gillnets. 

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The Unruh effect: Probing the structure of a vacuum

The impact of virtual particles on accelerating objects in a vacuum has never been observed, a new thought experiment aims to rectify this.

Is the vacuum of space truly empty? If quantum field theory is correct, then the answer is no. According to this theory — used to describe the physics of elementary particles or field quanta — vacuums are filled with continuously forming annihilating particles with observable manifestations; for example, they force structureless quarks to be confined within composite particles, like protons neutrons.

Moreover, the mathematical machinery of quantum field theory shows that even the number of stable particles that we see in the vacuum is never fixed but dependent on the motion of the observer — moving at a constant speed, then there are no observable particles, but at an accelerated rate, electromagnetic radiation will be observed, similar to the radiation of a heated body. The more rapid the acceleration, the higher the radiation temperature. This prediction of quantum field theory is called the Unruh effect.

The acceleration needed to observe Unruh radiation with modern photon detectors is about one quadrillion times bigger than the free fall acceleration at the Earth’s surface, making it very difficult to confirm experimentally.

In a new study, a team of physicists at MIT the University of Waterloo have perfected a classical thought experiment, paving the way for a possible future observation of Unruh radiation. The general idea is to rapidly accelerate an atom which, if the Unruh hypothesis is correct, would then “observe” the flow of electromagnetic field quanta — photons. Interaction with electromagnetic radiation can put an atom into an excited state in which its electrons occupy higher energy orbitals. If such an excitation of an accelerated atom could be found experimentally, this will confirm the existence of the Unruh effect.

As mentioned, the necessary acceleration is unattainable, to avoid this complication, the physicists suggested studying a stimulated Unruh effect by placing the atom into an electromagnetic field before accelerating it.

This idea is based on a famous effect put forth by Albert Einstein about a century ago where the more intense the electromagnetic field around an atom, the higher the probability that the atom will be excited. Due to this phenomenon, the acceleration required to excite the atom is much smaller than the acceleration required for the atom in a vacuum could maybe be achieved experimentally in the near future.

The problem here is that if an atom is placed in electromagnetic field, then there is a chance that it will be excited even without the Unruh effect, which makes it difficult to disentangle the contribution of the latter from that of the atom’s interaction with electromagnetic field.

However, if an atom’s acceleration is non-uniform, it is possible to completely suppress this competing effect, reducing the corresponding excitation probability to zero. What is even more important, by analyzing the interaction of the atom with electromagnetic field using quantum electrodynamics, the scientists found the exact law of atom’s motion, which guarantees this suppression.

In their paper, the researchers did not propose a specific experimental set up for testing the theoretical results they obtained, but the work on this problem is ongoing.

There is a very important application of the study, which relies on a mathematical similarity between the Unruh effect the Hawking radiation of black holes. If Hawking’s theory is correct, then the temperature radiation of a black hole are extremely small, as a result, there is almost no chance of detecting them, even with space-based telescopes. A study of the Unruh effect could be the only chance to understthis aspect of their bizarre physics.

Reference: Barbara Šoda, Vivishek Sudhir, Achim Kempf, Acceleration-Induced Effects in Stimulated Light-Matter Interactions, Phys. Rev. Lett. (2022). arXiv:2103.15838

Feature image: Fred Moon on Unsplash

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The Ocean’s Biggest Garbage Pile Is Full of Floating Life

There are several nonprofit organizations working to remove floating plastic from the Great Pacific Patch. The largest, the Ocean Cleanup Foundation in the Netherlands, developed a net specifically to collect concentrate marine debris as it is pulled across the sea’s surface by winds currents. Once the net is full, a ship takes its contents to lfor proper disposal.

Dr. Helm other scientists warn that such nets threaten sea life, including neuston. Although adjustments to the net’s design have been made to reduce bycatch, Dr. Helm believes any large-scale removal of plastic from the patch could pose a threat to its neuston inhabitants.

“When it comes to figuring out what to do about the plastic that’s already in the ocean, I think we need to be really careful,” she said. The results of her study “really emphasize the need to study the open ocean before we try to manipulate it, modify it, clean it up or extract minerals from it.”

Laurent Lebreton, an oceanographer with the Ocean Cleanup Foundation, disagreed with Dr. Helm.

“It’s too early to reach any conclusions on how we should react to that study,” he said. “You have to take into account the effects of plastic pollution on other species. We are collecting several tons of plastic every week with our system — plastic that is affecting the environment.”

Plastic in the ocean poses a threat to marine life, killing more than a million seabirds every year, as well as more than 100,000 marine mammals, according to UNESCO. Everything from fish to whales can become entangled, animals often mistake it for food end up starving to death with stomachs full of plastic.

Ocean plastics that don’t end up asphyxiating an albatross or entangling an elephant seal eventually break down into microplastics, which penetrate every branch of the food web are nearly impossible to remove from the environment.

One thing everyone agrees on is that we need to stop the flow of plastic into the ocean.

“We need to turn off the tap,” Mr. Lecomte said.

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