Shigeki Watanabe of Johns Hopkins University School of Medicine, a familiar face at the Marine Biological Laboratory (MBL) as a faculty member and researcher, is hot on the trail of describing how glutamate signaling works in the brain to enable neuronal communication. In a paper last fall, Watanabe (along with several MBL Neurobiology course students) described how glutamate is released from neural synapses after the neuron fires. And today, Watanabe published a follow-up study in Nature Communications.

“With this paper, we uncover how signals are transmitted across synapses to turn on the switch for plasticity,” Watanabe says. “We demonstrate that glutamate is first released near AMPA-type glutamate receptors, to relay the signal from one neuron to the next, and then near NMDA-type receptors immediately after the first signal to activate the switch for synaptic plasticity.”

This new study was also partly conducted in the MBL Neurobiology course, where Watanabe is a faculty member. “It began in 2018 with (course students) Raul Ramos and Hanieh Falahati, and then we followed up in 2019 with Stephen Alexander Lee and Christine Prater. Shuo Li, the first author, was my teaching assistant for the Neurobiology course for both years,” Watanabe says. He will be returning to the MBL this summer to teach in the course — and discover more.

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Materials provided by Marine Biological Laboratory. Original written by Diana Kenney. Note: Content may be edited for style and length.

Now chemists at the U.S. Department of Energy’s Pacific Northwest National Laboratory have developed a simple and reliable method that holds promise for transforming how ultra-trace elements are separated and detected. Low levels of troublesome naturally occurring radioactive elements like uranium and thorium atoms are often tucked among valuable metals like gold and copper. It has been extraordinarily difficult, impractical, or even impossible, in some cases, to tease out how much is found in samples of ore mined across the globe.

Yet sourcing materials with very low levels of natural radiation is essential for certain types of sensitive instruments and detectors, like those searching for evidence of currently undetected particles that many physicists believe actually comprise most of the universe.

“We are really pushing the envelope on detection,” said chemist Khadouja Harouaka. “We want to measure very low levels of thorium and uranium in components that go into some of the most sensitive detectors in the world. It is particularly difficult to measure low levels of thorium and uranium in precious metals like the gold that goes into the electrical components of these detectors. With this new technique, we can overcome that challenge and achieve detection limits as low as 10 parts per trillion in gold.”

That’s like trying to find one four-leaf clover in about 100 thousand acres of clover?an area larger than New Orleans.

Colliding worlds of particles

The scientists locate their extraordinarily rare “four-leaf clover” atoms from the huge field of ordinary atoms by sending their samples through a series of isolation chambers. These chambers first filter and then collide the rare atoms with simple oxygen, creating a “tagged” molecule of a unique molecular weight that can then be separated by its size and charge.

The effect is like finding a way to tie a helium balloon to each target thorium or uranium atom so that it floats above the sea of gold sample and can be counted. In this case, the sophisticated counter is a mass spectrometer. The research is featured on the cover of the December 2020 issue of Journal of Analytical Atomic Spectrometry.

The central innovation is the collision cell chamber, where charged atoms of thorium and uranium react with oxygen, increasing their molecular weight and allowing them to separate from other overlapping signals that can disguise their presence.

“I had an aha moment,” said Greg Eiden, the original PNNL inventor of the patented collision cell, which is used to perform these reactions, thereby reducing unwanted interference in the instrument readout by a factor of a million. “It was this miracle chemistry that gets rid of the bad stuff you don’t want in your sample so you can see what you want to see.”

In the current study, Harouaka and her mentor Isaac Arnquist leveraged Eiden’s work to tease out the vanishingly small number of radioactive atoms that can nonetheless ruin sensitive electronic detection equipment. Among other uses, the innovation may allow chemists, led by senior chemist Eric Hoppe and his team at PNNL, to further hone the chemistry that produces the world’s purest electroformed copper. The copper forms a key component of sensitive physics detectors, including those used for international nuclear treaty verification.

Neutrino listening tour

Stanford physicist Giorgio Gratta helps lead a global quest to capture evidence for the fundamental building blocks of the universe. The nEXO experiment, now in the planning stages, is pushing the detection boundaries for evidence of these elusive particles, called Majorana Fermions. The signals they seek come from exceedingly rare events. To detect such an event, the experiments require exquisitely sensitive detectors that are free of stray radiation pings introduced through the materials that make up the detector. That includes the metals in the electronics required to record the exceedingly rare events that trigger detection.

“PNNL is a global leader in ultra-trace radiation detection,” said Gratta. “Their unique mix of innovation and application provide an important contribution that enables sensitive experiments like nEXO.”

Physicist Steve Elliott of Los Alamos National Laboratory emphasized the lengths to which researchers must go to ensure a scrupulously clean environment for rare particle detection.

“In experimental programs where even human fingerprints are too radioactive and must be avoided, techniques to measure ultra-low radioactive impurity levels are critical,” he said, adding that this method could provide an important way to source materials for another of the next generation of rare neutrino event detectors, called LEGEND, being planned for deployment in an underground location in Europe.

Cleaning semiconductors and quantum computers

Semiconductors, the basic building blocks of modern electronics, including integrated circuits, microchips, transistors, sensors and quantum computers are also sensitive to the presence of stray radiation. And the innovation cycle demands each generation pack more and more into ever tinier microchips.

“As the architecture gets smaller and smaller, radiation contamination is an ever-bigger issue that manufacturers have been working around by changing the architecture inside the chips,” said Hoppe. “But there’s only so far you can go with that, and you really start to become limited by the purity of some of those materials. The industry has set targets for itself that right now it can’t achieve, so having a measurement technique like this could make some of those targets achievable.”

More broadly, Eiden added, “in the big world of the periodic table there’s probably applications for any element that you care about. And what Eric, Khadouja and Isaac are going after here is analyzing any trace impurity in any ultra-pure material.”

Landscapes around the world are increasingly affected by rapid urbanization, deforestation and similar developments driven by human activity. So far, data collection has largely focused on measuring properties of the land — such as agriculture, urbanization, forestland, crops, or elevation. Other impacts from people are usually lumped together in categories such as population density, or distance from settlements or roads. The researchers propose that it is not merely the presence, absence, or number of people, but what the people are actually doing which affects wildlife movement. In fact, a range of psychological and socioeconomic factors can play a part in ‘anthropogenic resistance’. Some examples of these factors include hunting, poaching or supplementary feeding.

For their study, the researchers looked at three case studies in detail: wolves in Washington State; leopards in Iran; and large carnivores in central India. The same concept can be applied to other species: for example the Eurasian lynx, which are returning to their historical ranges; or roe deer who use croplands for both shelter and food but reduce their presence during the hunting season. In some parts of the world, cultural and religious beliefs can result in the tolerance of large carnivores, such as tigers and lions, despite substantial livestock losses and threats to human life. The researchers considered effects from beliefs, values and traditions to wildlife in different areas. The authors claim these nuanced differences in human behaviour strongly determine where wildlife may move and persist in a landscape.

Professor Niko Balkenhol, from Wildlife Sciences at the University of Göttingen, explains, “Anthropogenic resistance is also relevant to the BearConnect project, which aims to understand the factors that determine connectivity in European populations of the brown bear. Bears are capable of moving across huge distances, as shown by bear JJ1, better known as ‘Bruno’, who travelled from the Italian Trento region all the way to Bavaria, where he was shot. It is important to note that, although Bruno was able to cross the physical landscape, he was stopped by the severe ‘anthropogenic resistance’ provided by humans who could not tolerate his behaviour.”

“Our paper shows that ‘anthropogenic resistance’ is an important piece of the puzzle for connectivity-planning to ensure the functionality of corridors for wildlife and people,” says Dr Trishna Dutta, senior author of the study, also from Wildlife Sciences at the University of Göttingen. Dutta goes on to say: “It reveals that there are advantages for social and natural scientists to collaborate in understanding the effects of ‘anthropogenic resistance’ in future studies.”

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Materials provided by University of Göttingen. Note: Content may be edited for style and length.

But an exhaustive review of some of the shell bead record led the UC Santa Barbara professor emerita of anthropology to an astonishing conclusion: The hunter-gatherers centered on the Southcentral Coast of Santa Barbara were using highly worked shells as currency as long as 2,000 years ago.

“If the Chumash were using beads as money 2,000 years ago,” Gamble said, “this changes our thinking of hunter-gatherers and sociopolitical and economic complexity. This may be the first example of the use of money anywhere in the Americas at this time.”

Although Gamble has been studying California’s indigenous people since the late 1970s, the inspiration for her research on shell bead money came from far afield: the University of Tübingen in Germany. At a symposium there some years ago, most of the presenters discussed coins and other non-shell forms of money. Some, she said, were surprised by the assumptions of California archaeologists about what constituted money.

Intrigued, she reviewed the definitions and identifications of money in California and questioned some of the long-held beliefs. Her research led to “The origin and use of shell bead money in California” in the Journal of Anthropological Archaeology.

Gamble argues that archaeologists should use four criteria in assessing whether beads were used for currency versus adornment: Shell beads used as currency should be more labor-intensive than those for decorative purposes; highly standardized beads are likely currency; bigger, eye-catching beads were more likely used as decoration; and currency beads are widely distributed.

“I then compared the shell beads that had been accepted as a money bead for over 40 years by California archaeologists to another type that was widely distributed,” she said. “For example, tens of thousands were found with just one individual up in the San Francisco Bay Area. This bead type, known as a saucer bead, was produced south of Point Conception and probably on the northern [Santa Barbara] Channel Islands, according to multiple sources of data, at least most, if not all of them.

“These earlier beads were just as standardized, if not more so, than those that came 1,000 years later,” Gamble continued. “They also were traded throughout California and beyond. Through sleuthing, measurements and comparison of standardizations among the different bead types, it became clear that these were probably money beads and occurred much earlier than we previously thought.”

As Gamble notes, shell beads have been used for over 10,000 years in California, and there is extensive evidence for the production of some of these beads, especially those common in the last 3,000 to 4,000 years, on the northern Channel Islands. The evidence includes shell bead-making tools, such as drills, and massive amounts of shell bits — detritus — that littered the surface of archaeological sites on the islands.

In addition, specialists have noted that the isotopic signature of the shell beads found in the San Francisco Bay Area indicate that the shells are from south of Point Conception.

“We know that right around early European contact,” Gamble said, “the California Indians were trading for many types of goods, including perishable foods. The use of shell beads no doubt greatly facilitated this wide network of exchange.”

Gamble’s research not only resets the origins of money in the Americas, it calls into question what constitutes “sophisticated” societies in prehistory. Because the Chumash were non-agriculturists — hunter-gatherers — it was long held that they wouldn’t need money, even though early Spanish colonizers marveled at extensive Chumash trading networks and commerce.

Recent research on money in Europe during the Bronze Age suggests it was used there some 3,500 years ago. For Gamble, that and the Chumash example are significant because they challenge a persistent perspective among economists and some archaeologists that so-called “primitive” societies could not have had “commercial” economies.

“Both the terms ‘complex’ and ‘primitive’ are highly charged, but it is difficult to address this subject without avoiding those terms,” she said. “In the case of both the Chumash and the Bronze Age example, standardization is a key in terms of identifying money. My article on the origin of money in California is not only pushing the date for the use of money back 1,000 years in California, and possibly the Americas, it provides evidence that money was used by non-state level societies, commonly identified as ‘civilizations.’ “