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Pronounced Neuroplasticity in the Primary Visual Cortex of the Thirteen-lined Ground Squirrel During Hibernation
Hibernating animals can show neuroplasticity throughout the hibernation season. In ground squirrels, decreased dendritic arborization in the hippocampus, somatosensory cortex, and thalamus during deep hibernation (“torpor”) suggests that this neuroplasticity is a brain-wide phenomenon. However, the degree to which neuroplasticity occurs in the visual system is not clear. While transient retinal changes have been reported during torpor, neuroplasticity beyond the retina remains unknown. Here, we characterized hibernation-related neuroplasticity in the primary visual cortex (V1), the first cortical area to receive visual information, in the thirteen-lined ground squirrel (Ictidomys tridecemlineatus). We compared neuronal morphology in Golgi-stained samples from male and female hibernating or non-hibernating squirrels. For the hibernating squirrels, brain tissue was sampled during two different epochs: torpor and inter-torpor arousal. Dendritic arborization decreased during torpor in V1 layer 2/3 pyramidal neurons, manifesting as decreases in dendritic length, number, and complexity. These changes fully reversed during inter-torpor arousal, indicating that on average dendritic arbors grew by 0.75 mm (65%) over ∼1.5 hours. No morphological differences between hibernating and non-hibernating squirrels were apparent when compared 6 months after the hibernation season. We also found no neuroplastic changes in V1 layer 4 spiny stellate neurons, unlike in this cell type the somatosensory cortex. Together, this revealed, for the first time, hibernation-related neuroplasticity in V1 in support of a brain-wide mechanism but with area-specific differences. The speed and magnitude of this naturally occurring neuroplasticity could make ground squirrel V1 a powerful translational model system for conditions requiring neuroplasticity, such as recovery from stroke.
Significance Statement This study is the first demonstration of pronounced hibernation-related neuroplasticity in the primary visual cortex of ground squirrels. Layer 2/3 pyramidal neurons in the primary visual cortex (V1) reduced arborization during torpor. Within 1.5 hours after arousal from torpor, the arborization reversed to non-hibernation levels. The extent and speed of this naturally occurring neuroplasticity could make the relatively well-understood V1 of ground squirrels a powerful translational model system. Complementing insights on neuroplasticity in V1 during development, it has the potential to be leveraged for the study of treatment mechanisms and conditions requiring neuroplasticity, ranging from neurodegeneration to recovery after stroke.
Busseiron and the formation of a discipline in Japanese physics
The middle of the twentieth century was a period of significant scientific advancement, particularly in the realm of physics. Within this rapidly changing landscape, academic disciplines emerged and evolved to keep pace with scientific discoveries. The new subdiscipline of solid-state physics gained prominence in the United States, but it was later subsumed by the broader category of condensed matter physics.
In Japan, however, physics research since the 1940s has included a unique branch called Busseiron—a discipline concerning the study of matter that has no direct English equivalent but that has remained in use nonetheless.
A new article by Hiroto Kono in Isis: A Journal of the History of Science Society explores the historical formation of Busseiron and how it was shaped by its specific national context.
Consistency check casts doubt on evolving dark energy
Cosmologists have long struggled to determine whether the universe’s accelerating expansion is being driven by a simple cosmological constant, or whether dark energy’s influence is evolving over time. In a new analysis published in Physical Review D, Samsuzzaman Afroz and Suvodip Mukherjee at the Tata Institute of Fundamental Research, Mumbai, have identified a subtle impact on the inference of the nature of dark energy, due to a tiny mismatch between a fundamental cosmological distance relation and two key datasets used to measure the properties of dark energy.
The result casts fresh doubt on the robustness of the recent claims that dark energy could be evolving over time—perhaps bringing us a step closer to solving one of cosmology’s most enduring challenges.
Tritium-infused graphene could sharpen the hunt for neutrino mass
While neutrinos are some of the most abundant particles in the universe, they remain among the least understood. One of the biggest puzzles is their mass: although experiments have shown that neutrinos must have some mass, pinning down exactly how much has proven extraordinarily difficult.
Now, a team of physicists led by Valentina Tozzini of the Institute of Nanoscience in Pisa have published new theoretical calculations in Physical Review C, suggesting that tritium-infused graphene could give future experiments a decisive edge in measuring neutrino masses with unprecedented precision.
Chemists use sea sponge bacteria to create new molecules for drug discovery
Florida State University chemists have synthesized new molecules derived from bacteria found in a Pacific Ocean sea sponge, a breakthrough for the future of drug development, particularly for rare forms of cancer.
“Around 50% of approved drugs are either natural products or derivatives of natural products,” said Zackary Firestone, a fourth-year doctoral student in FSU’s Department of Chemistry and Biochemistry, and the study’s lead author. “Synthetic access to these molecules is important because it allows for easier procurement for biological testing as well as the making of new derivatives.”
The research team is the first to successfully synthesize two new marine natural products: tetradehydrohalicyclamine B and epi-tetradehydrohalicyclamine B. Both were isolated from bacteria that lives in symbiosis with Acanthostrongylophora ingens, a Pacific-dwelling sea sponge.
Migrating charges unlock hard-to-reach C-H bond edits in organic molecules
A team at the University of Vienna, led by chemist Nuno Maulide, has developed a new method for controlling chemical reactions in a more targeted and efficient manner. At the heart of this is the concept of “cation sampling”: specially selected groups (ketones), in a sense, function as molecular signposts for randomly migrating positive charges, enabling reactions to take place at sites on a molecule that were previously difficult to access. The method allows carbon-hydrogen bonds (C–H bonds) to be specifically modified. The study was published in the Journal of the American Chemical Society.
Organic molecules form the basis of almost all biological processes. They consist mainly of carbon and hydrogen—and hydrogen atoms in particular are very common in such molecules. “If you want to alter the properties of a molecule, you often have to specifically replace individual hydrogen atoms,” explains Philipp Spieß, a former Ph.D. student in the Maulide group and one of the study’s lead authors.
The precise modification of C–H bonds is therefore considered one of the key challenges of modern synthetic chemistry. It plays an important role in the development of new drugs, functional materials and more efficient chemical processes.
Visualizing sound: Scientists reveal hidden behaviors of sound waves
An international team of scientists has developed a new analysis of how sound waves behave, revealing surprising effects that have largely been overlooked for decades. In the new paper in Scientific Reports, which was led by researchers from City St George’s, University of London, the team explored how sound waves move through air and how those movements might be perceived visually.
Sound travels as a longitudinal wave, meaning air molecules vibrate back and forth rather than moving up and down like waves in a violin string. These vibrations are usually assumed to be smooth and regular, and as a physical phenomenon they form the basis of acoustics and some forms of seismic transmission. However, the new theoretical analysis of physical longitudinal wave motion reveals that the behavior of sound waves changes dramatically when they become stronger (i.e. above 160 dB at 10 kHz, which is similar to the noise level inside a high-pitched jet engine), and the prior assumptions are only true for moderate sounds.
Using computer simulations, the researchers—namely Professor Christopher Tyler and Professor Joshua Solomon at City St George’s and Professor Stuart M. Anstis from the University of California, San Diego—created animations where each dot represents an air molecule. Each dot moves back and forth in place, slightly out of step with its neighbors. This tiny delay between dots creates the appearance of a wave traveling through space as the dots move back and forth in place, just as sound does in real life.