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glial cells

Dr. Nathan A. Smith receives $600,000 DOD ARO grant to study the role of glial cells in neural excitability and cognition

glial cells

Microglia are the resident immune cells of the central nervous system that have highly dynamic processes that continuously survey the brain’s microenvironment, making contact with both neurons and astrocytes.

In his pursuit to understand the function of neural circuits within the brain, Nathan A. Smith, M.S., Ph.D., principal investigator at Children’s National Hospital, is examining how specialized glial cells, known as astrocytes and microglia, work together to influence neural networks and potentially enhance neuro-cognition.

Dr. Smith has just secured a new $600,000 grant from the Department of Defense Army Research Laboratory to pursue cutting-edge experimental approaches to examine the role of astrocytes in Ca2+-dependent microglia modulation of synaptic activity. This project will enhance our understanding of neuronal excitability and cognition, and define a new role for microglia in these processes.

“Glia cells play an important role in modulating synaptic function via Ca2+-dependent mechanisms,” says Dr. Smith. “It’s time for these cells to receive recognition as active participants, rather than passive contributors, in fundamental neural processes.”

Dr. Smith and his laboratory at Children’s National Research Institute are using novel experimental models to study the dynamics underlying Ca2+-mediated microglia process extension and retraction to further our understanding of how microglia, astrocytes and neurons interact in the healthy brain.

“Completion of the proposed studies has the potential to redefine the role(s) of microglia in higher brain functions and highlight the significant contribution of these cells,” Dr. Smith says. “Most importantly, elucidating the mechanisms that underlie glial cell modulation of neural circuits will not only further our understanding of normal brain function but also open new avenues to developing more accurate computational models of neural circuits.”

Dr. Nathan Smith

Dr. Smith and his laboratory at Children’s National Research Institute are using novel experimental models to study the dynamics underlying Ca2+-mediated microglia process extension and retraction to further our understanding of how microglia, astrocytes and neurons interact in the healthy brain.

Microglia are the resident immune cells of the central nervous system that have highly dynamic processes that continuously survey the brain’s microenvironment, making contact with both neurons and astrocytes. However, because of our inability to directly monitor Ca2+ activity in microglia, very little is known about the intracellular Ca2+ dynamics in resting microglia and their role in surveillance and modulation of synaptic activity.

Dr. Smith’s research team and his use of cutting-edge technology are a perfect match with the Army’s new modernization priorities. Dr. Smith’s research program and the new Army’s initiatives will greatly benefit from each other and ultimately contribute to a better understanding of the human brain.

“This research will help address a major gap in our understanding of the roles that glial cells play in regulating the computations of the nervous system through their interactions with neurons, which could also inspire a new class of artificial neural network architectures,” said Dr. Frederick Gregory, program manager, Army Research Office, an element of the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory.

The grant will begin on July 1, 2020, and will last over three years. Dr. Smith’s research is also supported by other grants, including awards from the NIH and the National Science Foundation.

“As Dr. Smith’s mentor, the ultimate joy for a mentor is to see his mentees follow their dreams and be recognized for their accomplishments,” said Vittorio Gallo, Ph.D., Chief Research Officer at Children’s National Hospital. “I couldn’t be prouder of Nathan, and I am fully confident that this new research grant will help him continue to grow an exceptional research program.”

allopregnanolone molecule

Autism spectrum disorder risk linked to insufficient placental steroid

allopregnanolone molecule

A study led by Children’s National Hospital and presented during Neuroscience 2019 finds that loss of allopregnanolone, a key hormone supplied by the placenta, leads to long-term structural alterations of the cerebellum – a brain region essential for smooth motor coordination, balance and social cognition – and increases the risk of developing autism.

An experimental model study suggests that allopregnanolone, one of many hormones produced by the placenta during pregnancy, is so essential to normal fetal brain development that when provision of that hormone decreases – as occurs with premature birth – offspring are more likely to develop autism-like behaviors, a Children’s National Hospital research team reports at the Neuroscience 2019 annual meeting.

“To our knowledge, no other research team has studied how placental allopregnanolone (ALLO) contributes to brain development and long-term behaviors,” says Claire-Marie Vacher, Ph.D., lead author. “Our study finds that targeted loss of ALLO in the womb leads to long-term structural alterations of the cerebellum – a brain region that is essential for motor coordination, balance and social cognition ­– and increases the risk of developing autism,” Vacher says.

According to the Centers for Disease Control and Prevention, about 1 in 10 infants is born preterm, before 37 weeks gestation; and 1 in 59 children has autism spectrum disorder.

In addition to presenting the abstract, on Monday, Oct. 21, Anna Penn, M.D., Ph.D., the abstract’s senior author, will discuss the research with reporters during a Neuroscience 2019 news conference. This Children’s National abstract is among 14,000 abstracts submitted for the meeting, the world’s largest source of emerging news about brain science and health.

ALLO production by the placenta rises in the second trimester of pregnancy, and levels of the neurosteroid peak as fetuses approach full term.

To investigate what happens when ALLO supplies are disrupted, a research team led by Children’s National created a novel transgenic preclinical model in which they deleted a gene essential in ALLO synthesis. When production of ALLO in the placentas of these experimental models declines, offspring had permanent neurodevelopmental changes in a sex- and region-specific manner.

“From a structural perspective, the most pronounced cerebellar abnormalities appeared in the cerebellum’s white matter,” Vacher adds. “We found increased thickness of the myelin, a lipid-rich insulating layer that protects nerve fibers. From a behavioral perspective, male offspring whose ALLO supply was abruptly reduced exhibited increased repetitive behavior and sociability deficits – two hallmarks in humans of autism spectrum disorder.”

On a positive note, providing a single ALLO injection during pregnancy was enough to avert both the cerebellar abnormalities and the aberrant social behaviors.

The research team is now launching a new area of research focus they call “neuroplacentology” to better understand the role of placenta function on fetal and newborn brain development.

“Our team’s data provide exciting new evidence that underscores the importance of placental hormones on shaping and programming the developing fetal brain,” Vacher notes.

  • Neuroscience 2019 presentation
    Sunday, Oct. 20, 9:30 a.m. (CDT)
    “Preterm ASD risk linked to cerebellar white matter changes”
    Claire-Marie Vacher, lead author; Sonia Sebaoui, co-author; Helene Lacaille, co-author; Jackie Salzbank, co-author; Jiaqi O’Reilly, co-author; Diana Bakalar, co-author; Panagiotis Kratimenos, M.D., neonatologist and co-author; and Anna Penn, M.D., clinical neonatologist and developmental neuroscientist and senior author.
illustration of brain showing cerebellum

Focusing on the “little brain” to rescue cognition

illustration of brain showing cerebellum

Research faculty at Children’s National in Washington, D.C., with colleagues recently published a review article in Nature Reviews Neuroscience that covers the latest research about how abnormal development of the cerebellum leads to a variety of neurodevelopmental disorders.

Cerebellum translates as “little brain” in Latin. This piece of anatomy – that appears almost separate from the rest of the brain, tucked under the two cerebral hemispheres – long has been known to play a pivotal role in voluntary motor functions, such as walking or reaching for objects, as well as involuntary ones, such as maintaining posture.

But more recently, says Aaron Sathyanesan, Ph.D., a postdoctoral research fellow at the Children’s Research Institute, the research arm of Children’s National  in Washington, D.C., researchers have discovered that the cerebellum is also critically important for a variety of non-motor functions, including cognition and emotion.

Sathyanesan, who studies this brain region in the laboratory of Vittorio Gallo, Ph.D., Chief Research Officer at Children’s National and scientific director of the Children’s Research Institute, recently published a review article with colleagues in Nature Reviews Neuroscience covering the latest research about how altered development of the cerebellum contributes to a variety of neurodevelopmental disorders.

These disorders, he explains, are marked by problems in the nervous system that arise while it’s maturing, leading to effects on emotion, learning ability, self-control, or memory, or any combination of these. They include diagnoses as diverse as intellectual disability, autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder and Down syndrome.

“One reason why the cerebellum might be critically involved in each of these disorders,” Sathyanesan says, “is because its developmental trajectory takes so long.”

Unlike other brain structures, which have relatively short windows of development spanning weeks or months, the principal cells of the cerebellum – known as Purkinje cells – start to differentiate from stem cell precursors at the beginning of the seventh gestational week, with new cells continuing to appear until babies are nearly one year old.  In contrast, cells in the neocortex, a part of the brain involved in higher-order brain functions such as cognition, sensory perception and language is mostly finished forming while fetuses are still gestating in the womb.

This long window for maturation allows the cerebellum to make connections with other regions throughout the brain, such as extensive connections with the cerebral cortex, the outer layer of the cerebrum that plays a key role in perception, attention, awareness, thought, memory, language and consciousness. It also allows ample time for things to go wrong.

“Together,” Sathyanesan says, “these two characteristics are at the root of the cerebellum’s involvement in a host of neurodevelopmental disorders.”

For example, the review article notes, researchers have discovered both structural and functional abnormalities in the cerebellums of patients with ASD. Functional magnetic resonance imaging (MRI), an imaging technique that measures activity in different parts of the brain, suggests that significant differences exist between connectivity between the cerebellum and cortex in people with ASD compared with neurotypical individuals. Differences in cerebellar connectivity are also evident in resting-state functional connectivity MRI, an imaging technique that measures brain activity in subjects when they are not performing a specific task. Some of these differences appear to involve patterns of overconnectivity to different brain regions, explains Sathyanesan; other differences suggest that the cerebellums of patients with ASD don’t have enough connections to other brain regions.

These findings could clarify research from Children’s National and elsewhere that has shown that babies born prematurely often sustain cerebellar injuries due to multiple hits, including a lack of oxygen supplied by infants’ immature lungs, he adds. Besides having a sibling with ASD, premature birth is the most prevalent risk factor for an ASD diagnosis.

The review also notes that researchers have discovered structural changes in the cerebellums of patients with Down syndrome, who tend to have smaller cerebellar volumes than neurotypical individuals. Experimental models of this trisomy recapitulate this difference, along with abnormal connectivity to the cerebral cortex and other brain regions.

Although the cerebellum is a pivotal contributor toward these conditions, Sathyanesan says, learning more about this brain region helps make it an important target for treating these neurodevelopmental disorders. For example, he says, researchers are investigating whether problems with the cerebellum and abnormal connectivity could be lessened through a non-invasive form of brain stimulation called transcranial direct current stimulation or an invasive one known as deep brain stimulation. Similarly, a variety of existing pharmaceuticals or new ones in development could modify the cerebellum’s biochemistry and, consequently, its function.

“If we can rescue the cerebellum’s normal activity in these disorders, we may be able to alleviate the problems with cognition that pervade them all,” he says.

In addition to Sathyanesan and Senior Author Gallo, Children’s National study co-authors include Joseph Scafidi, D.O., neonatal neurologist; Joy Zhou and Roy V. Sillitoe, Baylor College of Medicine; and Detlef H. Heck, of University of Tennessee Health Science Center.

Financial support for research described in this post was provided by the National Institute of Neurological Disorders and Stroke under grant numbers 5R01NS099461, R01NS089664, R01NS100874, R01NS105138 and R37NS109478; the Hamill Foundation; the Baylor College of Medicine Intellectual and Developmental Disabilities Research Center under grant number U54HD083092; the University of Tennessee Health Science Center (UTHSC) Neuroscience Institute; the UTHSC Cornet Award; the National Institute of Mental Health under grant number R01MH112143; and the District of Columbia Intellectual and Developmental Disabilities Research Center under grant number U54 HD090257.