17.25: Glial Cells - Biology

17.25: Glial Cells - Biology

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While glia are often thought of as the supporting cast of the nervous system, the number of glial cells in the brain actually outnumbers the number of neurons by a factor of ten. When glia do not function properly, the result can be disastrous—most brain tumors are caused by mutations in glia.

Types of Glia

There are several different types of glia with different functions, two of which are shown in Figure 1.

Astrocytes, shown in Figure 2a make contact with both capillaries and neurons in the CNS. They provide nutrients and other substances to neurons, regulate the concentrations of ions and chemicals in the extracellular fluid, and provide structural support for synapses. Astrocytes also form the blood-brain barrier—a structure that blocks entrance of toxic substances into the brain. Astrocytes, in particular, have been shown through calcium imaging experiments to become active in response to nerve activity, transmit calcium waves between astrocytes, and modulate the activity of surrounding synapses.

Satellite glia provide nutrients and structural support for neurons in the PNS. Microglia scavenge and degrade dead cells and protect the brain from invading microorganisms. Oligodendrocytes, shown in Figure 2b form myelin sheaths around axons in the CNS. One axon can be myelinated by several oligodendrocytes, and one oligodendrocyte can provide myelin for multiple neurons. This is distinctive from the PNS where a single Schwann cell provides myelin for only one axon as the entire Schwann cell surrounds the axon. Radial glia serve as scaffolds for developing neurons as they migrate to their end destinations. Ependymal cells line fluid-filled ventricles of the brain and the central canal of the spinal cord. They are involved in the production of cerebrospinal fluid, which serves as a cushion for the brain, moves the fluid between the spinal cord and the brain, and is a component of the choroid plexus.

Glial Cell Biology

The fruit fly Drosophila melanogaster is emerging as a major invertebrate model for studies of glial cell development and function. Interest in the fly as a model for glial cell biology stems from the combination of its relatively sophisticated nervous system and its access experimentally through robust genetics. Both larval and adult Drosophila have complex compartmentalized brains which house neurons with electrophysiological and functional properties quite similar to mammalian neuronal cell types ( Freeman and Doherty, 2006 ). Fly neural circuits encode a diverse behavioral repertoire, many of the neurons driving these behaviors have been defined in exquisite detail and can be easily studied morphologically or electrophysiologically, and a number of neural circuits are known to exhibit plasticity at either the electrophysiological or behavioral level ( Zhang et al., 2010 ). Importantly, the fly nervous system (like many other ‘higher’ invertebrates) houses glial subtypes with striking morphological and molecular similarities to a number of subtypes of mammalian glia, and it therefore seems likely that studies of fly glial studies will be instructive in understanding mammalian glial biology ( Edwards and Meinertzhagen, 2010 Freeman and Doherty, 2006 ). Finally, there is a vast array of molecular genetic tools available in Drosophila with which to manipulate individual or populations of glial cells and single genes in vivo, so one can incisively address glial gene function in the intact organism, and (as with C. elegans) it is highly feasible to perform powerful forward genetic screens to address either broad or very specific questions in glial cell biology.

Glial cell types and their functions

Glial cells are usually classified into two large groups, macroglial cells or macroglia , which have an ectodermal (neural) origin, and microglia , which have mesodermal origin. Both types are present in both the central and peripheral nervous systems.

Macroglia of the CNS

In the central nervous system (CNS) several types of glial cells can be found, among the most important we find:

Astrocyte function

They also regulate the conditions of the external chemical microenvironment of neurons, removing excess potassium, recycling neurotransmitters and regulating blood vasoconstriction and vasodilation. They also appear to have an inhibitory role in neuronal circuits through the detection of changes in the extracellular calcium concentration.

The recycling of neurotransmitters, removing them from the synaptic space, has an important role in the regulation of synaptic function and in preventing the reaching of toxic concentrations of some neurotransmitters, for example glutamate.


Oligodendrocytes are cells with projections that cover the axons of neurons in the central nervous system and form the myelin sheath . The myelin sheath electrically insulates the axons and allows for more efficient nerve transmission.

Radial glial cells

During embryonic development, radial cells act as progenitors of neurons and at the same time guide the migration of new neurons. In adults they remain as specialized glial cells in some areas, such as the retina and cerebellum . In the cerebellum, Bergmann’s glia regulates synaptic plasticity in the retina, Müller cells are the only macroglia and perform functions similar to astrocytes and oligodendrocytes of the CNS.


  • Pituitcytes : specialized glial cells similar to astrocytes that appear in the neurohypophysis or posterior pituitary. Its main function is the storage and release of pituitary hormones . The pituicytes surround the terminal axons and regulate the release of these hormones.
  • Tanicytes : are a type of specialized ependymocytes that appear in the third cerebral ventricle and in the lower part of the fourth ventricle. They appear to be involved in the release of GnRH (gonadotropin-releasing hormone) by neurons in the hypothalamus.

Macroglia of the SNP

Fewer glial cells appear in the peripheral nervous system and are usually differentiated cells from the macroglia of the central nervous system. Some of the most important are the following:

  • Neurolemocytes : Also called Schwann cells . They have a similar function to oligodendrocytes of the CNS and form the myelin sheath in the axons of the PNS. They have phagocytic activity eliminating cellular debris and also appear to guide the growth of neuronal axons.
  • Satellite cells : they are small cells that surround the neuronal bodies in sensory, sympathetic and parasympathetic ganglia . They have an important role in the regulation of the microenvironment in these ganglia and are very sensitive to lesions and inflammatory processes They seem to be involved in various pathological processes that occur with chronic pain.
  • Enteric glial cells : These are glial cells found in the enteric nervous system , the subdivision of the autonomic nervous system that is responsible for directly controlling the digestive system.


Microglial cells are not really considered glial cells, since they do not have the same embryological origin as the rest of the cells of the nervous system . Microglial cells are specialized macrophages that form in the bone marrow and migrate to the nervous system. They are present only in the central nervous system .

Microglial cells have phagocytic activity and are the cells that regulate the immune system response in the central nervous system by acting as antigen-presenting cells . Microglial cell deficiency is seen in several diseases that affect the central nervous system, such as Alzheimer’s, Parkinson’s, and amyotrophic lateral sclerosis.

Glial cells help mitigate neurological damage in Huntington's disease

Confocal microscopy image showing the striatum in a mouse model of Huntington’s Disease. The astrocytes are visualized in green and cell nuclei in blue. Credit: J. Botas/eLife

The brain is not a passive recipient of injury or disease. Research has shown that when neurons die and disrupt the natural flow of information they maintain with other neurons, the brain compensates by redirecting communications through other neuronal networks. This adjustment or rewiring continues until the damage goes beyond compensation.

This process of adjustment, a result of the brain's plasticity, or its ability to change or reorganize neural networks, occurs in neurodegenerative conditions such as Alzheimer's, Parkinson's and Huntington's disease (HD). As the conditions progress, many genes change the way they are normally expressed, turning some genes up and others down. The challenge for researchers like Dr. Juan Botas, who studies HD, has been to determine which of the gene expression changes are involved in causing the disease and which ones help mitigate the damage, as this may be critical for designing effective therapeutic interventions.

In his lab at Baylor College of Medicine, Botas and his colleagues look to understand what causes the loss of communication or synapses between neurons in HD. Up until now, research has focused on neurons because the normal huntingtin gene, whose mutation causes the condition, contributes to maintaining healthy neuronal communication. In the current work, the researchers looked into synapses loss in HD from a different perspective.

Focusing on glia to understand Huntington's disease

The mutated huntingtin gene is not only present in neurons, but in all the cells in the body, opening the possibility that other cell types also could be involved in the condition.

"In this study we focused on glia cells, which are a type of brain cell that is just as important as neurons to neuronal communication," said Botas, professor of molecular and human genetics and of molecular and cellular biology at Baylor and a member of the Jan and Dan Duncan Neurological Research Institute at Texas Children's Hospital.

"We thought that glia might be playing a role in either contributing or compensating for the damage observed in Huntington's disease."

Initially thought to be little more than housekeeping cells, glia turned out to have more direct roles in promoting normal neuronal and synaptic function.

In a previous work, Botas and his colleagues studied a fruit fly model of HD that expresses the human mutant huntingtin (mHTT) gene in neurons, to understand which of the many gene expression changes that occur in HD are causing disease and which ones are compensatory.

"One class of compensatory changes affected genes involved in synaptic function. Could glia be involved?" Botas said. "To answer this question, we created fruit flies that express mHTT only in glia, only in neurons, or in both cell types."

Comparing changes in gene expression

The researchers began their investigation by comparing the changes in gene expression present in the brains of healthy humans with those in human HD subjects and in HD mouse and fruit fly models. They identified many genes whose expression changed in the same direction across all three species but were particularly intrigued when they discovered that having HD reduces the expression of glial cell genes that contribute to maintaining neuronal connections.

"To investigate whether the reduction of expression of these genes in glia either helped with disease progression or with mitigation, we manipulated each gene either in neurons, glial cells or both cell types in the HD fruit fly model. Then we determined the effect of the gene expression change on the function of the flies' nervous system," Botas said.

They evaluated the flies' nervous system health with a high-throughput automated system that assessed locomotor behavior quantitatively. The system filmed the flies as they naturally climbed up a tube. Healthy flies readily climb, but when their ability to move is compromised, the flies have a hard time climbing. The researchers looked at how the flies move because one of the characteristics of HD is progressive disruption of normal body movements.

Turning down the genes worked

The results revealed that in HD, turning down glial genes involved in synaptic assembly and maintenance is protective.

Fruit flies with the mutant huntingtin gene in their glial cells in which the researchers had deliberately turned down synaptic genes climbed up the tube better than flies in which the synaptic genes were not dialed down.

"Our study reveals that glia affected by HD respond by tuning down synapse genes, which has a protective effect," Botas said. "Some gene expression changes in HD promote disease progression, but other changes in gene expression are protective. Our findings suggest that antagonizing all disease-associated alterations, for example, using drugs to modify gene expression profiles, may oppose the brain's efforts to protect itself from this devastating disease. We propose that researchers studying neurological disorders could deepen their analyses by including glia in their investigations."


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New glial cells discovered in the brain: Implications for brain repair

Neurons, nerve cells in the brain, are central players in brain function. However, a key role for glia, long considered support cells, is emerging. A research group at the University of Basel has now discovered two new types of glial cells in the brain, by unleashing adult stem cells from their quiescent state. These new types of glia may play an important role in brain plasticity and repair.

The brain is malleable well into adulthood. Brain plasticity is not only due to the formation of new nerve connections. Stem cells present in the adult brain also generate new nerve cells. For more than a hundred years, scientists have concentrated on investigating different types of nerve cells.

In the brain, however, another class of cells, called glia, are also essential for brain function. However, the importance of glial cells has been underestimated for decades. How many types of glia there are, how they develop and what roles they play are all still largely unexplored.

Stem cells - unleashed from quiescence

The research group of Prof. Fiona Doetsch at the Biozentrum of the University of Basel is investigating stem cells in the ventricular-subventricular zone in the adult mouse brain. In this region, many of the stem cells are in a quiescent state, sensing signals in the environment that stimulate them to awaken and transform into new nerve cells.

In their study in the journal Science, Doetsch's team identified a molecular signal that awakened the stem cells from their quiescent state, allowing them to uncover multiple domains that give rise to glial cells in this stem cell reservoir.

Stem cells - birthplace of glial cells

"We found an activation switch for quiescent stem cells," Doetsch explains. "It is a receptor that maintains the stem cells in their resting state. We were able to turn off this switch and thus activate the stem cells," Doetsch says. In addition, the researchers were able to visualize the development of the stem cells into different glial cells in specific areas of the stem cell niche.

"Some of the stem cells did not develop into neurons, but into two different novel types of glial cells," Doetsch reports. This brain region studied is therefore a birthplace for different types of glial cells as well as its role as a breeding ground for neurons.

"What was very unexpected was that one glial cell type was found attached to the surface of the wall of the brain ventricle, rather than in the brain tissue." These cells are continuously bathed by cerebrospinal fluid and interact with axons from other brain areas, and therefore are poised to sense and integrate multiple long-range signals.

Glial cells - active in health and disease

The research team also found that both glial cell types were activated in a model of demyelination. These new glial cell types may therefore be a source of cells for repair in neurodegenerative diseases, such as multiple sclerosis or after injury.

As a next step, Doetsch would like to specifically trace these new glial cell types and to investigate their roles in normal brain function and how they respond in different physiological contexts. This will provide important clues to understanding brain plasticity and how the renewal and repair of neural tissue occurs.

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At one time, scientists believed that people were born with all the neurons they would ever have. Research performed during the last few decades indicates that neurogenesis, the birth of new neurons, continues into adulthood. Neurogenesis was first discovered in songbirds that produce new neurons while learning songs. For mammals, new neurons also play an important role in learning: about 1000 new neurons develop in the hippocampus (a brain structure involved in learning and memory) each day. While most of the new neurons will die, researchers found that an increase in the number of surviving new neurons in the hippocampus correlated with how well rats learned a new task. Interestingly, both exercise and some antidepressant medications also promote neurogenesis in the hippocampus. Stress has the opposite effect. While neurogenesis is quite limited compared to regeneration in other tissues, research in this area may lead to new treatments for disorders such as Alzheimer’s, stroke, and epilepsy.

How do scientists identify new neurons? A researcher can inject a compound called bromodeoxyuridine (BrdU) into the brain of an animal. While all cells will be exposed to BrdU, BrdU will only be incorporated into the DNA of newly generated cells that are in S phase. A technique called immunohistochemistry can be used to attach a fluorescent label to the incorporated BrdU, and a researcher can use fluorescent microscopy to visualize the presence of BrdU, and thus new neurons, in brain tissue. Figure 16.6 is a micrograph which shows fluorescently labeled neurons in the hippocampus of a rat.

Figure 16.6. This micrograph shows fluorescently labeled new neurons in a rat hippocampus. Cells that are actively dividing have bromodoxyuridine (BrdU) incorporated into their DNA and are labeled in red. Cells that express glial fibrillary acidic protein (GFAP) are labeled in green. Astrocytes, but not neurons, express GFAP. Thus, cells that are labeled both red and green are actively dividing astrocytes, whereas cells labeled red only are actively dividing neurons. (credit: modification of work by Dr. Maryam Faiz, et. al., University of Barcelona scale-bar data from Matt Russell)

CG11426 gene product negatively regulates glial population size in the drosophila eye imaginal disc

Sang-Hak Jeon, Ph.D., Department of Science Education/Biology Education, Seoul National University, Seoul, Korea.

Department of Biology Education, Seoul National University, Seoul, Republic of Korea

Department of Biology Education, Seoul National University, Seoul, Republic of Korea

Department of Biochemistry & Cellular and Molecular Biology, and Neuronet Research Center, University of Tennessee, Knoxville, 37996 USA

Department of Biochemistry & Cellular and Molecular Biology, and Neuronet Research Center, University of Tennessee, Knoxville, 37996 USA

Department of Biology Education, Seoul National University, Seoul, Republic of Korea

Korea Basic Science Institute, Seoul Center, 02841 Korea

Department of Biology Education, Seoul National University, Seoul, Republic of Korea

Sang-Hak Jeon, Ph.D., Department of Science Education/Biology Education, Seoul National University, Seoul, Korea.

This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as


Glial cells play essential roles in the nervous system. Although glial populations are tightly regulated, the mechanisms regulating the population size remain poorly understood. Since Drosophila glial cells are similar to the human counterparts in their functions and shapes, rendering them an excellent model system to understand the human glia biology. Lipid phosphate phosphatases (LPP) are important for regulating bioactive lipids. In Drosophila, there are three known LPP-encoding genes wunen, wunen-2 and lazaro. The wunens are important for the germ cell migration and survival, and septate junction formation during tracheal development. Lazaro is involved in phototransduction. In the present study, we characterized a novel Drosophila LPP-encoding gene, CG11426. Suppression of CG11426 increased glial cell number in the eye imaginal disc during larval development, while ectopic CG11426 expression decreased it. Both types of mutation also caused defects in axon projection to the optic lobe in larval eye–brain complexes. Moreover, CG11426 promoted apoptosis via inhibiting ERK signaling in the eye imaginal disc. Taken together, these findings demonstrated that CG11426 gene product negatively regulates ERK signaling to promote apoptosis for proper maintenance of glial population in the developing eye disc.

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Accepted, unedited articles published online and citable. The final edited and typeset version of record will appear in the future.


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Glial cells

Glial cells support neurons and maintain their environment. Glial cells of the (a) central nervous system include oligodendrocytes, astrocytes, ependymal cells, and microglial cells. Oligodendrocytes form the myelin sheath around axons.

Glial cells
Glial cells (named from the Greek for "glue") are non-neuronal cells that provide support and nutrition, maintain homeostasis, form myelin, and participate in signal transmission in the nervous system.

glial cells Nonconducting cells that serve as support cells in the nervous system and help to protect neurons.
glomerulus A tangle of capillaries that makes up part of the nephron the site of ?ltration.

Supportive cells that are closely associated with neurons.
global environmental citizenship A shift in our attention from pollution in a specific place to a concern about the life-support systems of the whole planet.

Non-neuronal cells found in the brain and other parts of the nervous system. Their roles include supporting neurons and forming the myelin sheath. Glucose .

Nonexcitable supportive cells in the nervous system also called neuroglial cells. Include astrocytes and oligodendrocytes in the vertebrate central nervous system and Schwann cells in the peripheral nervous system.
glucagon .

(astrocytes, microgliacytes, ependymal cells and oligodendrocytes) are the cells that support, feed and insulate (electrically) the neurons.

constitute the most abundant class of cells in the brain and can generally be subdivided into astrocytes, oligodendrocytes and microglia based on morphology and function.

- supporting cells of the nervous system, including oligodendrocytes and astrocytes in the vertebrate central nervous system and Schwann cells in the peripheralnervous system .

, also called astrocytes, are star-shaped cells found in the brain and spinal cord. They provide nutrients to neurons, maintain ion balance, and remove unneeded excess neurotransmitters from the synaptic cleft.
Ependymal cells are also found in the CNS. There are two types of ependymal cells.

are responsible for immunohomeostatic response to CNS, and have different functions (Kettenmann et al., 2011). The most essential function of Microglia is phagocytosis, known for engulfment of various cells via actin-myosin contractile system (Stuart and Ezekowitz, 2005).

(embryonic neural stem cells) that give rise to excitatory neurons in the fetal brain through the process of neurogenesis.[10][11][12]
Hematopoietic stem cells (adult stem cells) from the bone marrow that give rise to red blood cells, white blood cells, and platelets .

, the V max =53 μM/hr and the K m =4.2 μM for V HNMTg.
We took the K m =24 μM of the monoamine transporter from [23] and we include a linear backleak term from the vesicular compartment to the cytosol as indicated in [24] for dopamine.

The nervous system uses two different kinds of cells one is called

and those are the ones that help support and maintain the other cells and those other cells are the neurons the ones that are considered they' .

There are stem cells in neural tissue that give rise to neurons and astro

and things like that. And muscle has stem cells. And there are many different kinds of stem cells that have been identified in adults.

In addition, there are perhaps nine times as many

, whose exact roles are unclear, but which help to support and maintain neurons. Most neurons are present shortly after birth, and as the brain continues to grow, the number and complexity of neuronal connections increases.

In vertebrates generally, the axons of many neurons are sheathed in myelin, which is formed by either of two types of

: Schwann cells ensheathing peripheral neurons and oligodendrocytes insulating those of the central nervous system.

The small gaps in the myelin sheath between successive

along the axon of a neuron also, the site of high concentration of voltage-gated ion channels.
A graph that allows a third variable to be measured when the values of two related variables are known.

nervous tissue Tissue composed of neurons and

. Nervous tissue is one the four classes to which tissue has traditionally been assigned, the other three being muscle, epithelial tissue, and connective tissue.
Online Biology Dictionary (NEUR-) .

lining the ventricles of the brain and the central canal of the spinal cord. (Google Dictionary) 3. Thin epithelial membrane lining the ventricles of the brain and the spinal cord canal.

A regulatory system of the body that consists of neurons and neuroglial cells. The nervous system is divided into two parts, the central nervous system (CNS) and the peripheral nervous system (PNS).

The results showed that autism shares quite a bit in common with schizophrenia and bipolar disorder, but it also diverges in several key places. Activity in genes specifically related to micro

were unique to autistic brains, .

FIG. 667- Section of central canal of medulla spinalis, showing ependymal and neuroglial cells. (v. Lenhossek.) (See enlarged image) .

the brain are made up of about 100 billion neurons, as well as trillions of support cells called glia. Neurons may be the more important cells in the brain that relay messages about what you&aposre thinking, feeling, or doing. But they couldn&apost do it without a little help from their friends, the

include peripherin, neurofilaments, and glial fibrillary acidic protein (GFAP).

Watch the video: Part 4 - Glial Cells (August 2022).