Bacteria and viruses ejected from the ocean

Researchers determined what bacterial taxa are most prone to being ejected into the air from breaking waves after simulating ocean conditions at this facility at Scripps Institution of Oceanography at UC San Diego.

Certain types of bacteria and viruses are readily ejected into the atmosphere when waves break while other taxa are less likely to be transported by sea spray into the air, researchers reported May 22.

An interdisciplinary team of scientists from Scripps Institution of Oceanography, the University of California San Diego, and the J. Craig Venter Institute (JCVI) reached this conclusion after replicating a phytoplankton bloom in a unique ocean-atmosphere wave facility developed by scientists in the National Science Foundation-funded Center for Aerosol Impacts on Chemistry of the Environment (CAICE) on the Scripps campus. They found that bacteria and viruses coated by waxy substances or lipids appear in greater quantity and are enriched in sea spray aerosols. According to researchers, the results suggest that the water-repellent properties of the surfaces of these microbes are what make them more likely to be cast out of the ocean as waves break at the sea surface.

The team in the National Science Foundation-funded study included chemists, oceanographers, microbiologists, geneticists, and pediatric medicine specialists who are attempting to understand how far potentially infectious bacteria and viruses can travel and if those that pose the greatest risks to public health are among those most likely to escape the ocean. In previous studies, individual members of the team have characterized sea spray aerosols, which form when waves break and bubbles burst at the ocean surface.

"Some of the bacteria we detected have been found on skin as well as in your gut, so they could be affecting your health -- at this point, no one really knows the health effects of breathing in ocean microbes," said Kim Prather, who has a joint appointment at UC San Diego's Scripps Institution of Oceanography and the Department of Chemistry and Biochemistry. "We are trying to understand sources of environmental microbes using the unique ocean-atmosphere facilities we have developed here at Scripps. By breaking waves in fresh seawater in an isolated wave channel, UC San Diego is the only place in the world that can directly measure the microbes transferred from the ocean to the atmosphere."

Prather's research group has previously shown how microbes have a nearly worldwide reach, able to travel tens of thousands of kilometers on the wind, sometimes re-entering the ocean and re-emerging from it along the journey. As they do, their chemical attributes, their ability to infect, and their effects on cloud formation and precipitation can evolve.

"In CAICE, we realized that many of the chemical components found in the aerosols are derived from living microorganisms in the ocean, so one of our first goals was to find out which ones are present in the water and then understand which of them are able to hitch a ride on the aerosol particles," said Michael Burkart, a researcher at the Department of Chemistry and Biochemistry at UC San Diego.

The study tapped into techniques developed in the Earth Microbiome Project, which was founded by co-author Rob Knight and others in 2010 to sample as many microbial communities as possible to understand the ecology of microbes and their interactions with humans.

"In the Earth Microbiome Project a key challenge is to model microbes across the planet," said Knight, a UC San Diego professor of pediatrics and computer science and engineering with the UC San Diego Center for Microbiome Innovation. "The ocean spray results provide a completely new and unexpected mechanism for dispersal that we will have to take into account for a full understanding of Earth's microbial biosphere."

The researchers conducted the experiment by establishing blooms of phytoplankton over a 34-day period. They did this inside an ocean-atmosphere facility housed at the Hydraulics Laboratory at Scripps Oceanography. After several days, the replicated ocean, which scientists call a mesocosm, began emitting into the air bacterial taxa such as Actinobacteria and Corynebacteria. Viruses contained in the aerosols that became airborne were few relative to bacteria, but the strains that were detected in the air such as Herpesvirales had a similar kind of water repelling surface that enables them to be transferred from the ocean to the atmosphere.

The potential human health effects of the ocean microbes most often found in the sea spray aerosols will now begin to be studied by the team at UC San Diego. There is little known about the health effects -- good or bad -- of breathing ocean air enriched in microbes and other biological material. The researchers reported the presence of strains not often found in seawater such as Legionella and an avian strain of E. coli, which they said could be evidence of contamination in certain coastal waters. Knowledge of which pathogens occurring in pollution runoff become aerosolized could help improve the understanding of human exposure pathways for those living near the coast.

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A first look at the earliest decisions that shape a human embryo

Researchers have identified a small cluster of cells in the human embryo that dictates the fate of other embryonic cells -- an 'organizer' of developmental activity.

The factors that shape the destiny of a cell, like that of a fully formed person, remain something of a mystery. Why, for example, does one stem cell in a human embryo become a neuron rather than a muscle cell? And why does another decide to build cartilage rather than cardiac tissue?

New research by a team of Rockefeller scientists under the direction of Ali H. Brivanlou illuminates the molecular circuitry that determines a cell's fate. Their work, which appears in the journal Nature, establishes a new platform for studying the earliest stages of human development and could lead to novel treatments for a wide range of ailments.

Organizational genius

Scientists already knew that embryonic stem cells can differentiate into any of the body's specialized cell types: bone and brain, lung and liver.

They also knew that special groups of cells found in amphibian and fish embryos play an executive role in shaping early developmental structures. These groups, called "organizers," emit molecular signals that direct other cells to grow and develop in specific ways. When an organizer is transplanted from one embryo to another, it spurs its new host to produce a secondary spinal column and central nervous system, complete with spinal cord and brain.

Due to the ethical guidelines that limit experimentation on human embryos, however, they did not know if a similar organizer existed in humans.

To see if it might, Brivanlou and his team performed a series of experiments involving artificial human embryos: tiny clusters of cells, roughly one millimeter across, grown in the lab from human embryonic stem cells. Though a far cry from their natural counterparts, these artificial simulacra nonetheless contain many of the cells and tissues that are present in genuine human embryos, and can be used as experimental stand-ins for the real thing.

Previous studies revealed that three different signaling pathways drive early embryonic development in animals such as mice and frogs. By activating those pathways in artificial human embryos confined to Petri dishes, Brivanlou and his colleagues showed that the same molecular signals can also drive development in human cells. When given those signals in the correct sequence, the artificial embryos even generated their own organizers.

There is a difference between what cells can do in a Petri dish, however, and what they will do inside a real embryo.

To validate their initial findings, the researchers therefore grafted artificial human embryos onto genuine chicken embryos -- but not before they had tagged the human cells with a fluorescent marker that allowed them to precisely track the cells under a microscope. What happened next astonished them.

Division of labor

Transplanting cells from one species to another is not necessarily easy: the team's previous attempts at combining artificial human embryos with genuine mouse embryos proved exceedingly difficult, and no one had ever successfully grafted human embryonic cells onto an early bird embryo.

Yet as soon as they were introduced to their avian hosts, the human cells began laying the groundwork for a secondary spinal column and nervous system -- an act that clearly announced the presence of a true human organizer.

"To my amazement, the graft not only survived, but actually gave rise to these beautifully organized structures," Brivanlou says.

He was even more surprised by the provenance of those structures. For while the progenitors of the cartilage and bone tissue that would eventually comprise a second spinal column were composed entirely of human cells, the beginnings of the nervous tissue that would ultimately form its accompanying spinal cord and brain were composed exclusively of chick cells.

According to Brivanlou, the fact that human cells are capable of building new structures in the embryo of a bird -- an animal more closely related to the dinosaurs than to us -- demonstrates that the ability of animal cells to choose a particular fate has been conserved over hundreds of millions of years of evolution.

But the fact that those same human cells were able to instruct chick cells to become nervous tissue also indicates that the molecules involved in cellular communication -- the actual signals that cells send to one another to influence their fate -- have been conserved for just as long.

"Once you transplant the human organizer into a chicken embryo, the language it uses to instruct the bird cells to establish the brain and nervous system is exactly the same as the one used by amphibians and fish," Brivanlou says.

Moving forward by looking back

Understanding how undifferentiated stem cells become a particular kind of tissue is essential to regenerative medicine, which relies on stem-cell based technologies to heal and rejuvenate failing tissues, or even replace them with freshly grown ones.

In addition, the chick-based grafting method invented by Brivanlou and his team represents a powerful new tool for studying the earliest stages of development in human beings -- a tool they are already using in other studies. By providing a window onto normal cell differentiation and tissue formation, their approach should help scientists understand when and how things can go awry during the first moments of life.

That, in turn, could lead to new ways of preventing miscarriages and birth defects, as well as new treatments for diseases ranging from cancer to diabetes.

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Mars rocks may harbor signs of life from 4 billion years ago

The Jezero Crater delta, a well-preserved ancient river delta on Mars.

Iron-rich rocks near ancient lake sites on Mars could hold vital clues that show life once existed there, research suggests.

These rocks -- which formed in lake beds -- are the best place to seek fossil evidence of life from billions of years ago, researchers say.

A new study that sheds light on where fossils might be preserved could aid the search for traces of tiny creatures -- known as microbes -- on Mars, which it is thought may have supported primitive life forms around four billion years ago.

A team of scientists has determined that sedimentary rocks made of compacted mud or clay are the most likely to contain fossils. These rocks are rich in iron and a mineral called silica, which helps preserve fossils.

They formed during the Noachian and Hesperian Periods of Martian history between three and four billion years ago. At that time, the planet's surface was abundant in water, which could have supported life.

The rocks are much better preserved than those of the same age on Earth, researchers say. This is because Mars is not subject to plate tectonics -- the movement of huge rocky slabs that form the crust of some planets -- which over time can destroy rocks and fossils inside them.

The team reviewed studies of fossils on Earth and assessed the results of lab experiments replicating Martian conditions to identify the most promising sites on the planet to explore for traces of ancient life.

Their findings could help inform NASA's next rover mission to the Red Planet, which will focus on searching for evidence of past life. The US space agency's Mars 2020 rover will collect rock samples to be returned to Earth for analysis by a future mission.

A similar mission led by the European Space Agency is also planned in coming years.

The latest study of Mars rocks -- led by a researcher from the University of Edinburgh -- could aid in the selection of landing sites for both missions. It could also help to identify the best places to gather rock samples.

The study, published in Journal of Geophysical Research, also involved researchers at NASA's Jet Propulsion Laboratory, Brown University, California Institute of Technology, Massachusetts Institute of Technology and Yale University in the US.

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Scientists introduce cosmochemical model for Pluto formation

Ralph Instrument Pluto Maps. New Horizons not only showed humanity what Pluto looks like, but also provided information on the composition of Pluto’s atmosphere and surface. These maps — assembled using data from the Ralph instrument — indicate regions rich in methane (CH4), nitrogen (N2), carbon monoxide (CO) and water (H2O) ices. Sputnik Planitia shows an especially strong signature of nitrogen near the equator. SwRI scientists combined these data with Rosetta’s comet 67P data to develop a proposed “giant comet” model for Pluto formation.

Southwest Research Institute scientists integrated NASA's New Horizons discoveries with data from ESA's Rosetta mission to develop a new theory about how Pluto may have formed at the edge of our solar system.

"We've developed what we call 'the giant comet' cosmochemical model of Pluto formation," said Dr. Christopher Glein of SwRI's Space Science and Engineering Division. The research is described in a paper published online today in Icarus. At the heart of the research is the nitrogen-rich ice in Sputnik Planitia, a large glacier that forms the left lobe of the bright Tombaugh Regio feature on Pluto's surface. "We found an intriguing consistency between the estimated amount of nitrogen inside the glacier and the amount that would be expected if Pluto was formed by the agglomeration of roughly a billion comets or other Kuiper Belt objects similar in chemical composition to 67P, the comet explored by Rosetta."

In addition to the comet model, scientists also investigated a solar model, with Pluto forming from very cold ices that would have had a chemical composition that more closely matches that of the Sun.

Scientists needed to understand not only the nitrogen present at Pluto now -- in its atmosphere and in glaciers -- but also how much of the volatile element potentially could have leaked out of the atmosphere and into space over the eons. They then needed to reconcile the proportion of carbon monoxide to nitrogen to get a more complete picture. Ultimately, the low abundance of carbon monoxide at Pluto points to burial in surface ices or to destruction from liquid water.

"Our research suggests that Pluto's initial chemical makeup, inherited from cometary building blocks, was chemically modified by liquid water, perhaps even in a subsurface ocean," Glein said. However, the solar model also satisfies some constraints. While the research pointed to some interesting possibilities, many questions remain to be answered.

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Cold production of new seafloor

This is the area of investigation at the Cayman Trough in the Caribbean.

A mountain range with a total length of 65,000 kilometers runs through all the oceans. It marks the boundaries of tectonic plates. Through the gap between the plates material from the Earth's interior emerges, forming new seafloor, building up the submarine mountains and spreading the plates apart. Very often, these mid-ocean ridges are described as a huge, elongated volcano. But this image is only partly correct, because the material forming the new seafloor is not always magmatic. At some spreading centres material from the Earth's mantle reaches the surface without being melted. The proportion of seabed formed this has been previously unknown.

Scientists from the Universities of Kiel (Germany), Austin (Texas, USA) and Durham (Great Britain) have now published data in the international journal Nature Geoscience that, for the first time, allow a detailed estimation on how much seafloor is formed by mantle material without magmatic processes. "This phenomenon occurs especially where the seabed spreads at paces of less than two centimeters per year," explains Prof. Dr. Ingo Grevemeyer from the GEOMAR Helmholtz Centre for Ocean Research Kiel, lead author of the study.

One of these zones is located in the Cayman Trough south of the island of Grand Cayman in the Caribbean. In 2015, the researchers used the German research vessel METEOR to investigate the seafloor seismically, i.e. by using sound waves. Sound signals sent through different rocks or sediment layers, are being reflected and refracted in different ways by each layer. Rock, which has been melted and solidified on the seabed, has a different signature in the seismic signal than rock from the Earth's mantle, which has not been melted.

But scientists had a problem so far: The contact with the seawater changes the mantle rocks. "After this process called serpentinisation mantle rocks are barely distinguishable from magmatic rocks in seismic data," says Professor Grevemeyer. Until now, mantle rock on the seabed could only be detected by taking samples directly from the seafloor and analyzing them in the laboratory. "But that way you only get information about a tiny spot. A large-scale or even in-depth information on the composition of the seabed cannot be achieved," says Grevemeyer.

However, during the expedition in 2015, the team not only used the energy of ordinary sound waves -- it also detected so-called shear waves, which occur only in solid materials. They could be recorded very clearly thanks to a clever selection of measuring points.

From the ratio of the speed of both types of waves, the scientists were able to differentiate mantle material from magmatic material. "So we could prove for the first time with seismic methods that up to 25 percent of the young ocean floor is not magmatic at the ultra-slow spreading centre in the Cayman trough," says Ingo Grevemeyer.

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Using the K computer, scientists predict exotic 'di-Omega' particle

Based on complex simulations of quantum chromodynamics performed using the K computer, one of the most powerful computers in the world, the HAL QCD Collaboration, made up of scientists from the RIKEN Nishina Center for Accelerator-based Science and the RIKEN Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) program, together with colleagues from a number of universities, have predicted a new type of "dibaryon" -- a particle that contains six quarks instead of the usual three. Studying how these elements form could help scientists understand the interactions among elementary particles in extreme environments such as the interiors of neutron stars or the early universe moments after the Big Bang.

Particles known as "baryons" -- principally protons and neutrons -- are composed of three quarks bound tightly together, with their charge depending on the "color" of the quarks that make them up. A dibaryon is essentially a system with two baryons. There is one known dibaryon in nature -- deuteron, a deuterium (or heavy-hydrogen) nucleus that contains a proton and a neutron that are very lightly bound. Scientists have long wondered whether there could be other types of dibaryons. Despite searches, no other dibaryon has been found.

The group, in work published in Physical Review Letters, has now used powerful theoretical and computational tools to predict the existence of a "most strange" dibaryon, made up of two "Omega baryons" that contain three strange quarks each. They named it "di-Omega." The group also suggested a way to look for these strange particles through experiments with heavy ion collisions planned in Europe and Japan.

The finding was made possible by a fortuitous combination of three elements: better methods for making QCD calculations, better simulation algorithms, and more powerful supercomputers.

The first essential element was a new theoretical framework called the "time-dependent HAL QCD method": It allows researchers to extract the force acting between baryons from the large volume of numerical data obtained using the K computer.

The second element was a new computational method, the unified contraction algorithm, which allows much more efficient calculation of a system with a large number of quarks.

The third element was the advent of powerful supercomputers. According to Shinya Gongyo from the RIKEN Nishina Center, "We were very lucky to have been able to use the K computer to perform the calculations. It allowed fast calculations with a huge number of variables. Still, it took almost three years for us to reach our conclusion on the di-Omega."

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Hot cars can hit deadly temperatures fast

How hot is a car after one hour in the sun or shade?

A lot can happen at 160 degrees Fahrenheit: Eggs fry, salmonella bacteria dies, and human skin will suffer third-degree burns. If a car is parked in the sun on a hot summer day, its dashboard can hit 160 degrees in about an hour. One hour is also about how long it can take for a young child trapped in a car to suffer heat injury or even die from hyperthermia.

Researchers from Arizona State University and the University of California at San Diego School of Medicine have completed a study to compare how different types of cars warm up on hot days when exposed to different amounts of shade and sunlight for different periods of time. The research team also took into account how these differences would affect the body temperature of a hypothetical 2-year-old child left in a vehicle on a hot day. Their study was published May 24 in the journal Temperature.

"Our study not only quantifies temperature differences inside vehicles parked in the shade and the sun, but it also makes clear that even parking a vehicle in the shade can be lethal to a small child," said Nancy Selover, an Arizona State climatologist and research professor in ASU's School of Geographical Sciences and Urban Planning.

From January through May 2018, six children have died after being left in hot cars in the United States. That number will go up. Annually in the U.S., an average of 37 children left in hot cars die from complications of hyperthermia -- when the body warms to above 104 degrees and cannot cool down. More than 50 percent of cases of a child dying in a hot car involve a parent or caregiver who forgot the child in the car.

The findings

Researchers used six vehicles for the study: Two identical silver mid-size sedans, two identical silver economy cars, and two identical silver minivans. During three hot summer days with temperatures in the 100s in Tempe, Arizona, researchers moved the cars from sunlight to shade for different periods of time throughout the day. Researchers measured interior air temperature and surface temperatures throughout different parts of the day.

"These tests replicated what might happen during a shopping trip," Selover said. "We wanted to know what the interior of each vehicle would be like after one hour, about the amount of time it would take to get groceries. I knew the temperatures would be hot, but I was surprised by the surface temperatures."

For vehicles parked in the sun during the simulated shopping trip, the average cabin temperature hit 116 degrees in one hour. Dash boards averaged 157 degrees, steering wheels 127 degrees, and seats 123 degrees in one hour.

For vehicles parked in the shade, interior temperatures were closer to 100 degrees after one hour. Dash boards averaged 118 degrees, steering wheels 107 degrees and seats 105 degrees after one hour.

The different types of vehicles tested warmed up at different rates, with the economy car warming faster than the mid-size sedan and minivan.

"We've all gone back to our cars on hot days and have been barely able to touch the steering wheel," Selover said. "But, imagine what that would be like to a child trapped in a car seat. And once you introduce a person into these hot cars, they are exhaling humidity into the air. When there is more humidity in the air, a person can't cool down by sweating because sweat won't evaporate as quickly."

Hyperthermia

A person's age, weight, existing health problems and other factors, including clothing, will affect how and when heat becomes deadly. Scientists can't predict exactly when a child will suffer a heatstroke, but most cases involve a child's core body temperature rising above 104 degrees for an extended period.

In the study, the researchers used data to model a hypothetical 2-year old boy's body temperature. The team found that a child trapped in a car in the study's conditions could reach that temperature in about an hour if a car is parked in the sun, and just under two hours if the car is parked in the shade.

"We hope these findings can be leveraged for the awareness and prevention of pediatric vehicular heatstroke and the creation and adoption of in-vehicle technology to alert parents of forgotten children," said Jennifer Vanos, lead study author and assistant professor of climate and human health at U.C. San Diego.

Hyperthermia and heatstroke effects happen along a continuum, Vanos said. Internal injuries can begin at temperatures below 104 degrees, and some heatstroke survivors live with brain and organ damage.

Why memories fail

Forgetting a child in the car can happen to anyone, said Gene Brewer, an ASU associate professor of psychology. Brewer, who was not involved in the heat study, researches memory processes, and has testified as an expert witness in a court case involving a parent whose child died in a hot car.

"Often these stories involve a distracted parent," he said. "Memory failures are remarkably powerful, and they happen to everyone. There is no difference between gender, class, personality, race or other traits. Functionally, there isn't much of a difference between forgetting your keys and forgetting your child in the car."

Most people spend a lot of time on routine behaviors, doing the same activities over and over without thinking about them. For example, driving the same route to work, taking the children to daycare on Tuesdays and Thursdays, or leaving car keys in the same spot every day. When new information comes into those routines, such as a parent's daycare drop-off day suddenly changing or an emergency phone call from a boss on the way to work, that's when memory failures can occur.

"These cognitive failures have nothing to do with the child," Brewer said. "The cognitive failure happens because someone's mind has gone to a new place, and their routine has been disrupted. They are suddenly thinking about new things, and that leads to forgetfulness. Nobody in this world has an infallible memory."

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Land rising above the sea 2.4 billion years ago changed planet Earth

A conceptual rendering suggests how Earth's land elevations and oceans may have appeared during the assembly of Kenorland, left, and later, right, after the Great Oxygenation Event. A University of Oregon-led study has potentially narrowed the window on when significant amounts of land emerged from under the ocean's surface.

Chemical signatures in shale, the Earth's most common sedimentary rock, point to a rapid rise of land above the ocean 2.4 billion years ago that possibly triggered dramatic changes in climate and life.

In a study published in the May 24 issue of the journal Nature, researchers report that shale sampled from around the world contains archival quality evidence of almost imperceptible traces of rainwater that caused weathering of land from as old as 3.5 billion years ago.

Notable changes in the ratios of oxygen 17 and 18 with more common oxygen 16, said lead author Ilya Bindeman, a geologist at the University of Oregon, allowed researchers to read the chemical history in the rocks.

In doing so, they established when newly surfaced crust was exposed to weathering by chemical and physical processes, and, more broadly, when the modern hydrologic process of moisture distillation during transport over large continents started.

The evidence is from analyses of three oxygen isotopes, particularly the rare but stable oxygen 17, in 278 shale samples drawn from outcrops and drill holes from every continent and spanning 3.7 billion years of Earth's history. The analyses were done in Bindeman's Stable Isotope Laboratory.

Based on his own previous modeling and other studies, Bindeman said, total landmass on the planet 2.4 billion years ago may have reached about two-thirds of what is observed today. However, the emergence of the new land happened abruptly, in parallel with large-scale changes in mantle dynamics.

Isotopic changes recorded in the shale samples at that time also coincides with the hypothesized timing of land collisions that formed Earth's first supercontinent, Kenorland, and high-mountain ranges and plateaus.

"Crust needs to be thick to stick out of water," Bindeman said. "The thickness depends on its amount and also on thermal regulation and the viscosity of the mantle. When the Earth was hot and the mantle was soft, large, tall mountains could not be supported. Our data indicate that this changed exponentially 2.4 billion years ago. The cooler mantle was able to support large swaths of land above sea level."

Temperatures on the surface when the new land emerged from the sea would have likely been hotter than today by several tens of degrees, he said.

The study found a stepwise change in triple-isotopes of oxygen around that time frame. That, the scientists said, resolves previous arguments for a gradual or stepwise emergence of land between 1.1 and 3.5 billion years ago. At 2.4 billion years ago, Bindeman said, the newly emerged land began to consume carbon dioxide from the atmosphere amid chemical weathering.

The timing also coincides with the transition from the Archean Eon, when simple prokaryotic life forms, archaea and bacteria, thrived in water, to the Proterozoic Eon, when eukaryotes, such as algae, plants and fungi, emerged.

"In this study, we looked at how weathering proceeded over 3.5 billion years," Bindeman said. "Land rising from water changes the albedo of the planet. Initially, Earth would have been dark blue with some white clouds when viewed from space. Early continents added to reflection. Today we have dark continents because of lots of vegetation."

Exposure of the new land to weathering, he said, may have set off a sink of greenhouse gases such carbon dioxide, disrupting the radiative balance of the Earth that generated a series of glacial episodes between 2.4 billion and 2.2 billion years ago. That, he said, may have spawned the Great Oxygenation Event in which atmospheric changes brought significant amounts of free oxygen into the air. Rocks were oxidized and became red. Archean rocks are gray.

In the absence of much land, he said, photons from the sun interacted with water and heated it. A bright surface, provided by emerging land, would reflect sunlight back into space, creating additional torque on radiative-greenhouse balance and a change in climate.

"What we speculate is that once large continents emerged, light would be reflected back into space and initiate runaway glaciation," Bindeman said. "Earth would have seen its first snowfall."

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People with family history of alcoholism release more dopamine in expectation of alcohol

People with a family history of alcohol use disorder (AUD) release more dopamine in the brain's main reward center in response to the expectation of alcohol than people diagnosed with the disorder, or healthy people without any family history of AUD, reports a new study in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging.

"This exaggerated reward center stimulation by expectation of alcohol may put the [individuals with family history] at greater risk of alcohol use disorder, and could be a risk factor in itself," said first author Lawrence Kegeles, MD, PhD, of Columbia University.

The study examined a range of risk for AUD, including 34 healthy participants with no family history of AUD, 16 healthy participants with a family history of the disorder (referred to as the family-history positive, or FHP, group), and 15 participants diagnosed with AUD. Dr. Kegeles and colleagues used PET brain scanning to measure the amount of dopamine release in areas of the brain important for reward and addiction. The participants underwent the brain scans after receiving either an alcohol drink -- a cocktail of vodka, tonic, and cranberry -- or a placebo drink without the vodka. Although the participants didn't know the order in which they would receive the drinks, if they received the placebo drink first they were cued into expecting the alcohol drink next.

All three groups had similar dopamine release-levels in response to the alcohol, suggesting that alcohol-induced dopamine release is normal in AUD. However, "we found that the FHP participants had a much more pronounced response to the placebo drink than the other groups, indicating that expectation of alcohol caused the FHP group to release more reward center dopamine," said Dr. Kegeles. The release of dopamine into the reward center is thought to reinforce alcohol consumption and possibly contribute to risk of AUD.

"This research finding exemplifies how advances in imaging brain chemistry using PET scanning can provide new insights into how differences in brain function in people with a family history of alcoholism can explain their own potential for addiction," said Cameron Carter, MD, Editor of Biological Psychiatry: Cognitive Neuroscience and Neuroimaging.

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When the dinosaurs died, so did forests -- and tree-dwelling birds

The asteroid impact that eliminated non-avian dinosaurs destroyed global forests. Here, a hyopothetical surviving bird lineage -- small-bodied and specialized for a ground-dwelling lifestyle--flees a burning forest in the aftermath of the asteroid strike.

Sixty-six million years ago, the world burned. An asteroid crashed to Earth with a force one million times larger than the largest atomic bomb, causing the extinction of the dinosaurs. But dinosaurs weren't the only ones that got hit hard -- in a new study, scientists learned that the planet's forests were decimated, leading to the extinction of tree-dwelling birds.

"Looking at the fossil record, at plants and birds, there are multiple lines of evidence suggesting that the forest canopies collapsed," says Regan Dunn, a paleontologist at the Field Museum in Chicago and a co-author on the study in Current Biology. "Perching birds went extinct because there were no more perches."

"We drew on a variety of approaches to stitch this story together," said Daniel Field, the paper's lead author, of the Milner Centre for Evolution at the University of Bath. "We concluded that the temporary elimination of forests in the aftermath of the asteroid impact explains why arboreal birds failed to survive across this extinction event. The ancestors of modern arboreal birds did not move into the trees until forests had recovered from the extinction-causing asteroid."

The project's pollen expert, Antoine Bercovici of the Smithsonian Institution and the Denver Museum of Nature and Science, helped determine that the world's forests were destroyed by looking at microscopic fossils of pollen and spores. Dunn explains, "After a disaster like a forest fire or a volcanic eruption, the first plants to come back are the fastest colonizers -- especially ferns." That's because ferns don't sprout from seeds, but from spores, which are much smaller -- just a single cell. "Spores are minuscule, the size of a grain of pollen, so they're easily dispersed. They get picked up by the wind and go further than seeds can, and all they need to grow is a wet spot."

"The spores are tiny -- you could fit four across a single strand of your hair," says Dunn. "To see them, we take a sample of rock from the time frame just after the collision and dissolve it in acid. Then we purify it so that all that remains is the organic debris, like pollen, spores and little leaf bits, then we look at them under a microscope."

Immediately after the asteroid hit, the fossil record shows the charcoal remains of burnt trees, and then, tons of fern spores. An abundance of fern spores in the fossil record often comes on the heels of a natural disaster that destroyed larger plants like trees.

"Our study examined the fossil record from New Zealand, Japan, Europe and North America, which showed there was a mass deforestation across the globe at the end of the Cretaceous period," says co-author Bercovici.

And with no more trees, the scientists found, tree-dwelling birds went extinct. The birds that did survive were ground-dwellers -- birds whose fossilized remains show longer, sturdier legs like we see in modern ground birds like kiwis and emus. The Cretaceous equivalent of robins and sparrows, with delicate little legs made for perching on tree branches, had no place to live.

"Today, birds are the most diverse and globally widespread group of terrestrial vertebrate animals -- there are nearly 11,000 living species," says Field. "Only a handful of ancestral bird lineages succeeded in surviving the mass extinction event 66 million years ago, and all of today's amazing living bird diversity can be traced to these ancient survivors."

And while fossil animals like dinosaurs and birds often get more love than fossil plants, Dunn says that plants are critical to understanding life on earth. "Plants are everything, plants are the context in which all terrestrial life evolves and survives. They're primary producers, they make energy available to all life forms by capturing it from the sun -- we can't do that."

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