Scientists Discover New “Rosehip” Neuron in Human Brain

Posted on September 19, 2018 by Celeste Sunderland

Neurolucida and Neurolucida Explorer Used for 3D Reconstruction and Quantitative Analysis

Researchers used Neurolucida to reconstruct a newly discovered type of neuron found only in the human brain, according to a study published in the journal Nature Neuroscience. Known as “rosehip” neurons because of the way they resemble a rose after its petals have fallen off, these cells feature compact, bushy axonal arborizations.

Found in the first layer of the cerebral cortex, a highly complex brain region that is thought to play an important role in consciousness, “rosehip neurons” have not been seen in mice or other laboratory animals, and scientists suggest that they may exist only in humans. Classified as inhibitory neurons, these brain cells form synapses with pyramidal neurons in layer 3 of the cerebral cortex, according to the study.

Led by Dr. Ed Lein, of the Allen Institute for Brain Science, and Dr. Gábor Tamás, a neuroscientist at the University of Szeged in Szeged, Hungary, the research team used Neurolucida to reconstruct rosehip neurons in 3D. Their reconstructions revealed that these cells display morphological characteristics that differ significantly from other types of cells found in this region of the brain.

Scientists used Neurolucida and Neurolucida Explorer to reconstruct and analyze a rosehip neuron. Image Credit: Tamas Lab, University of Szeged

Using Neurolucida Explorer to quantitatively analyze their cell reconstructions, the researchers observed similar numbers of primary dendrites in both rosehip neurons and basket cells, but fewer compared to neurogliaform cells. Meanwhile, they calculated similar total dendritic length and frequency of dendritic nodes in rosehip neurons and neurogliaform cells, but recorded differences in basket cells.

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Exercise changes astrocytes and eases symptoms of neurodegenerative disorders

Posted on February 16, 2017 by Kristin

Astrocytes (GFAP) in the dentate gyrus of a mouse hippocampus. Image courtesy of Dr. Ahmad Salehi, Stanford University.

It is well known that physical exercise eases the symptoms of neurodegenerative disorders like Alzheimer’s disease and helps to prevent their onset. Researchers at Stanford University are working on figuring out how it happens.

In their study, published in the journal Brain Structure and Function, scientists in Dr. Ahmad Salehi’s lab examined the effects of physical exercise on astrocytes in a region of the mouse brain that is critical for cognition – the dentate gyrus of the hippocampus. Previous studies have shown that an increase in the expression of brain-derived neurotrophic factor (Bdnf) occurs in this region after exercise (Philips, Salehi et al 2014). Bdnf is a protein that supports the survival of existing neurons and encourages new growth, playing an important role in cognitive function.

While the current study reconfirms that exercise generates increased levels of Bdnf (more than a fourfold increase in exercised mice versus non-exercised mice), it also describes several new findings including increased synaptic load in the dentate gyrus, alterations in the morphology of astrocytes, and changes in the orientation of astrocytic projections toward dentate granule cells.

The authors speculate that the changes they observed may be attributed to increased expression of a receptor called TrkB, which astrocytes express in response to increases in Bdnf levels. According to the paper, TrkB binds to Bdnf, activating the mechanisms behind neuronal development.

“Our study suggests that astrocytes actively respond and could indeed mediate the positive effects of physical exercise on the central nervous system and potentially counter degenerative processes during aging and neurodegenerative disorders,” (Fahimi, et al 2016).

The researchers used Neurolucida to determine the location, the extent, and orientation of astrocytic projections, finding a significant increase in the length of astrocytic projections in exercised mice.

“Neurolucida is one of the very few systems that combines complex morphometrical quantification with beautiful display of the results,” said Dr. Salehi, Clinical Professor, Department of Psychiatry and Behavioral Sciences at Stanford Medical School.

Since astrocytes help prevent excitotoxicity in the brain by removing excess glutamate from extracellular space, the researchers speculate that the increased length of astrocytic projections they observed in exercised mice could make this process more efficient.

Differences in the orientation of astrocytic projections were also reported, with the majority of projections of exercised mice directed toward the dentate granule cell layer – a region featuring increased levels of Bdnf release and synthesis after exercise.

The number of astrocytes in the molecular layer of the dentate gyrus in exercised and non-exercised mice was quantified with Stereo Investigator, however, there was no significant difference in astrocyte populations between the two groups.

“In summary, our study suggests that astrocytes constitute an important element in mediating the positive effects of physical exercise in the dentate gyrus of the hippocampus. Furthermore, it appears that physical exercise-induced release of Bdnf by the DG leads to a significant alteration in structure and function of astrocytes in protection against glutamate toxicity during aging and a number of neurodegenerative disorders,” (Fahimi et al 2016)

Fahimi, A., Baktir, M.A., Moghadam, S., Mojabi, F.S., Sumanth, K., McNerney, M.W., Ponnusamy, R., Salehi, A. Brain Struct Funct (2016). doi:10.1007/s00429-016-1308-8

Phillips, C., Baktir, M.A., Srivatsam, M., Salehi, A. Front. Cell. Neurosci., (2014) https://doi.org/10.3389/fncel.2014.00170

Scientists Observe Differences Between Brains of Stressed and Unstressed Rats After Fear Conditioning

Posted on July 6, 2016 by Celeste Sunderland

This figure illustrates the separate and combined effects of acute stress and fear conditioning/extinction on dendritic morphology of pyramidal neurons in the infralimbic region of medial prefrontal cortex. Each neuron shown is a composite made up of apical (blue) and basilar (orange) arbor near the mean of the group. The apical and basilar arbors of each composite are from different neurons. Image courtesy of Cara Wellman, PhD.

A soldier jumps at the sound of fireworks. Though there is no threat to his or her life, the blasts mimic the ones heard on the battlefield, and that fear response is not easy to forget. The process of shedding a fear response like this one is called fear extinction. Scientists think patients suffering from stress-sensitive psychopathologies, like Post-Traumatic Stress Disorder, aren’t able to suppress certain fear responses because of deficits in their brain circuitry induced by stress.

A recent study by researchers at Indiana University and the University of Haifa, in Israel, describes significant differences between the brains of stressed rats and unstressed rats.

Using Neurolucida to analyze neurons in the infralimbic cortex (IL) – a region of the brain associated with fear extinction – the research team found that stressed rats had shorter dendrites and less dendritic branching in pyramidal neurons of the IL. They also found that while stress had no affect on spine density, rats that underwent fear conditioning and extinction had decreased spine density on apical terminal branches, providing evidence that dendritic morphology in this region is sensitive to stress, while spine density may be a reflection of learning.

“Having helped colleagues set up procedures for neuron reconstructions and spine counts in labs that aren’t equipped with Neurolucida, I can tell you with complete confidence that my lab wouldn’t be nearly as productive without our Neurolucida system,” said Dr. Cara Wellman. “It makes mapping out regions of interest, identifying neurons for reconstruction, and reconstructions, and data analysis a simple and streamlined process. My students and I especially appreciate the Lucivid, which allows us to trace neurons while looking through the oculars – so much easier and clearer in my opinion than on a video monitor.”

To achieve their results, the researchers subjected rats to fear conditioning, where they learned to associate a certain tone with a footshock. Some of the rats were then exposed to an elevated platform in a brightly lit room for 30 minutes (stressed) while others returned to their home cages (unstressed). Next came extinction sessions. In a test to see if they would be able to shed the fear response associated with the stimulus, rats were placed in a space where they heard a tone but did not experience a footshock. The scientists observed that stressed rats exhibited freezing during the extinction sessions at a much higher rate than unstressed rats, leading them to believe that rats exposed to acute stress were resistant to fear extinction.

Further quantification of apical and basilar dendritic branching in the pyramidal neurons of the IL, measured with three-dimensional Sholl analysis, confirmed differences between the stressed and unstressed rats’ brains that correlated with fear behavior.

“The main findings of the current study were that acute stress, concurrent with producing resistance to extinction, produced changes in morphology of pyramidal neurons in IL,” the authors say in their paper. “These findings provide evidence that alterations in IL pyramidal neuron morphology occur quickly and differentially in response to acute stress and fear conditioning/extinction.”

Moench KM, Maroun M, Kavushansky A, Wellman C. Alterations in neuronal morphology in infralimbic cortex predict resistance to fear extinction following acute stress. Neurobiology of Stress. 3: 23-33. doi:10.1016/j.ynstr.2015.12.002

Hippocampal Neurons Change After Melatonin Injection

Posted on March 4, 2015 by Celeste Sunderland

Representative dendrites of dentate gyrus neurons of Siberian hamsters injected with melatonin (stained with Cresyl violet). Ikeno et al found hamsters injected with melatonin displayed decreased spine density on neurons in the dentate gyrus. Image courtesy of Tomoko Ikeno, Ph.D.

Night falls and a powerful hormone called melatonin kicks in. The gears of the circadian clock are turning as you get ready for bed and soon drift off to dreamland. But all is not quiet in the brain. In response to the circadian rhythm, neurons are transforming.

A new study published in the journal Hippocampus found that melatonin prompts dendrites to grow longer in one part of the brain, while in another part the hormone causes dendritic spine loss.

In their study, scientists at Ohio State University injected Siberian hamsters with a dose of melatonin in the afternoon, several hours before a natural increase in the hormone would normally occur. Four hours after the injection, they used Neurolucida to examine sections of their brains, reconstructing neurons in two areas of the hippocampus – the CA1 and dentate gyrus. They then used the software to calculate the number of branch points and length of dendrites in their reconstructions. What they saw was longer, more complex dendrites in the CA1 region of the hippocampus of hamsters that received melatonin versus those that received a placebo. Then they analyzed spine density, finding that hamsters that received melatonin had decreased spine density in the dentate gyrus than the control group.

“By using Neurolucida, we found that melatonin treatment induced rapid remodeling of hippocampal neurons and induced a nighttime state of the hippocampal neuronal morphology,” said Dr. Tomoko Ikeno, who worked with Dr. Randy Nelson on the study.

The “nighttime state” she refers to is characterized by the presence of certain hormones produced during the dark hours of night. In their analysis, the researchers saw elevated levels of Period1 and Bmal1 after melatonin injection. These hormones are expressed by genes associated with the circadian clock, and their presence offers evidence that “melatonin functions as a nighttime signal to coordinate the diurnal rhythm” and that this rhythm compels hippocampal neurons to change structurally, according to the paper.

Ikeno, T. and Nelson, R. J. (2014), Acute melatonin treatment alters dendritic morphology and circadian clock gene expression in the hippocampus of Siberian Hamsters. Hippocampus. doi: 10.1002/hipo.22358

Dendritic Spine Loss Reported in Schizophrenia and Bipolar Disorder

Posted on January 23, 2015 by Celeste Sunderland

Golgi-stained human brain tissue from the dorsolateral prefrontal cortex.

Schizophrenia and bipolar disorder are very different mental illnesses, but researchers are discovering evidence that the two disorders have some common pathologies. According to a recent study, a shared characteristic appears to be dendritic spine loss.

The researchers used Neurolucida to study pyramidal cells in human brain tissue from individuals with schizophrenia (n=14), individuals with bipolar disorder (n=9) and unaffected control participants (n=19). The pyramidal cells were located in the dorsolateral prefrontal cortex – a region that plays a key role in working memory. Bipolar patients showed significantly reduced spine density (10.5 percent) compared to control. Schizophrenic patients also showed lower spine density (6.5 percent), but this number just missed significance when compared to control patients. Individuals with both illnesses showed a lower number of spines per dendrite, as well as reduced dendritic length compared to controls.

To obtain these results, researchers analyzed 15 Golgi-stained pyramidal cells in each tissue sample. They used Neurolucida to reconstruct the longest dendrite on the pyramidal cells and to mark spines. After the researchers finished reconstructing the cells, Neurolucida provided them with important data about the dendrites and spines.

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Anorexia Accelerates the Development of the Rat Hippocampus

Posted on October 14, 2014 by Celeste Sunderland

This image stack was used in the study to analyze spine density. Image courtesy of Tara Chowdhury, Ph.D. first author of the study.

To find out how anorexia nervosa changes the brain, scientists at New York University are studying a rat model of the disease called activity-based anorexia (ABA). Previously, they discovered that ABA rats develop unusually robust dendritic branching of neurons in part of the hippocampus. Their new study takes those findings a step further, illuminating more differences between the brains of healthy versus ABA rats, and offering evidence that ABA rats may be developing too early, closing a critical period of development too soon.

But before making any conclusions about ABA brains, the researchers made some interesting discoveries about normal brain development. Using Neurolucida to analyze CA1 pyramidal cells in the stratum radiatum layer of the ventral hippocampus, they found that after puberty, around postnatal day 51, dendrites go through a growth spurt, more than doubling the number of branches seen seven days earlier. This growth spurt is followed by a decrease, or a pruning, which the researchers say is part of the normal maturation process.

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Scientists Use Neurolucida to Create 3D Reconstructions of Placental Villous Trees

Posted on September 26, 2014 by Celeste Sunderland

(a,b) Comparison of the microscopic aspects of a thin (4–6 μm) histological section of a human placenta after staining with hematoxylin/eosin.

When neuroscientists started studying neurons in 3D, it revolutionized brain science. Now, for the first time, scientists are using this same technology to study the human placenta, and they’ve made some fascinating new discoveries about its structure.

Using Neurolucida to create 3D reconstructions of villous trees – three-dimensional structures in the placenta that facilitate gas and nutrient exchange between the fetus and mother – researchers in Munich, Germany uncovered a wealth of information about their architecture.

For the first time, they analyzed the complexity of villous tree branches and branching, determined the number and location of nodes (branching points), and measured branch angles, discovering a surprising correlation between the branching angle of terminal branchesand the fetoplacental weight ratio (BW/PW) – a calculation commonly used to measure fetal health in prenatal medicine.

“The results show that 3D analysis with Neurolucida reaches beyond the horizons of 2D histology, the current gold standard in placenta morphology/pathology,” said Dr. Hans-Georg Frank, an author of the study. Continue reading “Scientists Use Neurolucida to Create 3D Reconstructions of Placental Villous Trees” »

New Neurons Erase Memories

Posted on July 3, 2014 by Celeste Sunderland

Neurogenesis occurs in the dentate gyrus, pictured here, from birth through adulthood.

A baby laughs at an elephant at the zoo. A toddler runs across a beach. Small children make memories all the time, but how many will they recall as the years pass? Maybe none at all. The phenomenon is called “infantile amnesia,” and scientists may have pinpointed a reason for why it occurs – neurogenesis.

Researchers at the Hospital for Sick Children in Toronto say that when new brain cells integrate into existing circuitry, they remodel the structure of networks already in place, wiping out the information previously stored there. This process is prevalent in infancy and early childhood because this is the time when new brain cells are being generated faster and more frequently than at any other time in a human being’s life. Humans and other mammals spawn new neurons throughout their lifespans, although the rate of neurogenesis decreases significantly with age.

In their paper, published in Science, the researchers explain how recent studies have focused on how new brain cells can lead to new memories, but the Toronto team speculated that neurogenesis could also wipe away memories. To test their hypothesis, they conducted a series of studies on populations of newborn and adult mice. Neuron development in mice occurs in much the same way as in humans, with rapid cell genesis in infancy that tapers off with age.

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Brain Cleans Itself During Sleep; Scientists Image Cerebral Fluid Flow With Neurolucida

Posted on April 9, 2014 by MBF Bioscience

With some exceptions, humans and animals prefer to live in an environment free of filth. We clean our bodies and our homes so we can live healthy and productive lives. It turns out, the brain does too.

Researchers at the University of Rochester discovered that the brain cleans itself during sleep—explaining one of the major reasons we partake in a nightly ritual that has mystified scientists for centuries.

“Sleep has a critical function in ensuring metabolic homeostasis,” Dr. Maiken Nedergaard et al say in their paper published in Science. “The restorative function of sleep may be a consequence of the enhanced removal of potentially neurotoxic waste products that accumulate in the awake central nervous system.”

Instead of a lymphatic system, the brain has what the researchers call a “glymphatic system.” Waste products that build up during waking hours flush out through the membranes of glial cells in the brain’s interstitial space as cerebral spinal fluid (CSF) flows in. In the process, proteins like b-amyloid, which are associated with Alzheimer’s disease, are washed away. The exchange of fluids occurs along the brain’s vasculature; CSF flows in around arteries, while interstitial fluid (ISF) exits in the space around veins.

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3D Reconstructions of Neurons Reveal More Branching in Sedentary Rats

Posted on March 14, 2014 by Celeste Sunderland

Left: A neuron from the brain of a rat that exercised for two hours each day.
Right: A neuron from the brain of a sedentary rat. Scientists saw greater branching in inactive versus active rats. (Image courtesy of Dr. Patrick Mueller)

Scientists discovered that inactivity makes brain cells grow, but not in a good way. In a study published in the Journal of Comparative Neurology, researchers found more neuronal branching in sedentary rats compared to active rats. The growth occurred in a region of the brain that controls blood pressure, leading the scientists to hypothesize that these changes may be part of the reason inactivity is linked to an increased risk of heart disease.

Using Neurolucida to reconstruct neurons in 3D, the scientists at Dr. Patrick Mueller’s lab at Wayne State University School of Medicine, in Detroit, saw structural differences between the brains of active and inactive rats.

Focusing on the rostral ventrolateral medulla (RVLM) – an area that controls several critical biological processes that rats as well as humans do unconsciously, like swallowing, breathing, and regulating blood pressure, the scientists saw longer dendrites, more dendritic branching, and more intersections with other neurons in sedentary rats.

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