A drawing of an L2 pyramidal neuron in the auditory cortex of a mouse brain rendered with Neurolucida. Biocytin-labeled neurons were visualized using the avidin:biotinylated horseradish peroxidase complex. Neurons were completely reconstructed in 3D with Neurolucida using an up-right Zeiss microscope with an oil immersion x100/1.4 numerical aperture objective.
Sensory stimuli are all around us. Street traffic zooms by. A neighbor waves “hello.” A co-worker taps away at his keyboard. Each sight, sound, and motion ignite action within our brains. But even without all these stimuli, the brain is always active.
Known as “spontaneous activity,” the activity happening inside the brain in the absence of direct stimuli follows a pattern of up and down states that scientists say is essential for processing sensory signals. Spontaneous activity may also be involved in memory.
Scientists from the Brain Research Center at the Third Military Medical University (Chongqing, China), the Center for Integrated Protein Science, SyNergy Cluster, and the Institute of Neuroscience at the Technical University of Munich (Germany) are working on figuring out how the activity occurring in the brain during “spontaneous activity” compares with what goes on during periods of sensory stimuli. Specifically, they’re looking at calcium signaling – an important element in synaptic activity during periods of both sensory stimuli and spontaneous activity, that helps neurons transmit information to other parts of the brain and body.
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Life’s little pleasures often elude those suffering from depression, including rats, who show little interest in sugar water after experiencing stress. This behavior leads scientists to speculate that the illness might be characterized by a defect in the brain’s neural reward circuit.
Recent research focuses on a key element of this circuit – the nucleus accumbens (NAc), part of the brain region known as the ventral striatum, which is thought to regulate motivation and reward processing. In a new study of stress-induced depression in rats, researchers at the University of Minho in Braga, Portugal saw morphological changes in the dendrites of medium spiny neurons in the NAc, alongside disturbances in gene expression in this region. They also saw these changes reversed after administering antidepressants.
By using Neurolucida Explorer to analyze 3D reconstructions of medium spiny neurons generated with Neurolucida, the researchers observed longer than normal dendrites and greater spine density in the depressed rats. According to the paper, these findings contrast with studies of the hippocampus and prefrontal cortex, where chronic stress leads to shorter dendrites.
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Scientists hypothesize that seizures occur because brain cells fire in places they’re not supposed to. Dentate granule cells (DGCs), a type of neuron born throughout adulthood, sometimes migrate into a different region of the dentate gyrus, a part of the hippocampus. These abnormal newborn cells sprout axons called “mossy fibers” that form connections with neighboring DGCs in the inner molecular layer, causing synaptic changes that wouldn’t normally occur in healthy brains.
Much research has been done on this phenomenon, but neuroscientists still struggle to understand what exactly its relationship is with epilepsy.
A new study by researchers at the Cincinnati Children’s Hospital Medical Center validates hypotheses about the role of abnormal DGCs in epilepsy. In their study of a transgenic mouse model of temporal lobe epilepsy (TLE), the scientists observed a relationship between the presence of deviant DGCs and seizure frequency.
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Learning a new dance routine or how to ride a bike is possible because of Cerebellar Granule Cells (GCs) according to Galliano and colleagues in The Netherlands. To find out more about the role of these abundant brain cells, and why we have so many of them, the scientists silenced most of the GCs in a group of mutant mice. They found the rodents could balance and run as well as they ever did, but when it came to learning new activities involving motor function, the mice had a harder time.
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What does it take to survive that tumultuous time called adolescence? Good friends, exercise, and new brain cells.
Scientists at Michigan State University found evidence of neurogenesis in the brains of adolescent hamsters, according to a study published last month in PNAS. The new cells, which became integrated into neural circuits in adulthood, were discovered in the amygdala and connected limbic regions – areas associated with social learning and mating behavior.
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Courtesy of Thomas Marissal, INMED (France)
There’s a lot to be said for being in the right place at the right time. For a neuron, emerging at a certain place within the brain destines it for a particular function. A new study posits that, for a group of cells in the hippocampus, it’s not only where a neuron is born, but also when it is born, that defines the specific roles it will play. The study, conducted by researchers at the Mediterranean Institute of Neurobiology (INMED, France) and affiliated institutions, identifies a new population of cells in the hippocampus.
The cells identified are “a sub-population of early-generated glutamatergic neurons that impacts network dynamics when stimulated in the juvenile hippocampus,” according to the paper.
“These cells first operate as assemblies, in the developing hippocampus, and later become powerful single units capable of triggering network synchronization in the absence of fast GABAergic transmission,” Marissal et al. say.
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A monkey spots a mango and part of its brain lights up. The action takes place in the inferior temporal cortex, part of the brain that’s essential to object recognition. Using retrograde tracing and anatomical imaging, scientists at the National Institute of Neuroscience, and the RIKEN Brain Science Institute in Japan identified two interwoven, yet distinct, systems within the region’s complex circuitry.
“Our anatomical findings provide evidence for a recurrent network of at least two parallel systems,” the authors say in their paper published last December in Scientific Reports.
One system may send information about an object’s visual characteristics rapidly from one part of the inferotemporal cortex to the other, while the second system might work on a more local level, possibly helping to “compute multipart shape configurations,” the authors hypothesize.
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Revving engines, blasting sirens, the drummer next door. Despite the myriad sensory stimuli going on around us at any given moment, humans have the ability to stay focused on the task at hand. This skill is due to a part of the brain known as the neocortex, a six-layer structure whose intricate wiring is largely a mystery. But researchers at the University of Virginia just took a big step toward a broader understanding of how this region works. They discovered two never-before-identified circuits in the rat sensorimotor cortex that help explain how the brain filters information.
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At first, all appears normal with the infant’s development. But one day, around her first birthday, she stops making eye contact, her babbling comes to an end, she wrings her hands, and holds her breath. The child will likely survive into adulthood, but with Rett syndrome, she will lead a life with severe disabilities.
The symptoms of this autism-related disorder are complex, and treatments are not available. At the Case Western Reserve University School of Medicine, in Cleveland, Dr. David Katz and his team of neuroscientists are researching the rare genetic disorder, which affects one in 10,000 mostly female children. Their recent study, published in the Journal of Neuroscience, describes a map of brain dysfunction in a mouse model of Rett syndrome, as well as a promising treatment with the drug ketamine.
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Image adapted from “Neurovascular proximity in the diaphragm muscle of adult mice,” published with permission from Dr. S. Segal
A 3D model of a mouse diaphragm appears on the monitor. Blood vessels branch out from entry points around the muscle’s periphery, engaging in a graceful choreography with the nerve fibers that radiate from its center.
Could these two networks work together to ensure healthy blood and oxygen flow to the muscle? Or do they exist independently of each other, house mates living side by side within the confines of the diaphragm? Dr. Diego Correa and Dr. Steven Segal set out to test the hypothesis that the motor innervation and blood supply of the diaphragm muscle are physically associated.
“We used Neurolucida to map entire arteriolar networks together with entire motor nerve networks of the diaphragm muscle in adult mice,” explained Dr. Segal in an email.
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