source glias cells in the brain

For decades, neuroscientists thought neurons did all the communicating in the brain and nervous system, and glial cells merely nurtured them, even though glia outnumber neurons nine to one.
Improved imaging and listening instruments now show that glia communicate with neurons and with one another about messages traveling among neurons. Glia have the power to alter those signals at the synaptic gaps between neurons and can even influence where synapses are formed.
Given such prowess, glia may be critical to learning and to forming memories, as well as repairing nerve damage. Experiments are getting under way to find out.

GLIA AND NEURONS work together in the brain and spinal cord. A neuron sends a message down a long axon and across a synaptic gap to a dendrite on another neuron. Astrocyte glia bring nutrients to neurons as well as surround and regulate synapses. Oligodendrocyte glia produce myelin that insulates axons. When a neuron’s electrical message (action potential) reaches the axon terminal (inset), the message induces vesicles to move to the membrane and open, releasing neurotransmitters (signaling molecules) that diffuse across a narrow synaptic cleft to the dendrite’s receptors. Similar principles apply in the body’s peripheral nervous system, where Schwann cells perform myelination duties.

ASTROCYTES REGULATE SIGNALING
across synapses in various ways.
An axon transmits a signal to a dendrite
by releasing a neurotransmitter
( green)—here, glutamate. It also
releases the chemical ATP ( gold).
These compounds then trigger an influx
of calcium (purple) into astrocytes,
which prompts the astrocytes to
communicate among themselves by
releasing their own ATP. Astrocytes
may strengthen the signaling by
secreting the same neurotransmitter,
or they may weaken the signal by
absorbing the neurotransmitter or
secreting proteins that bind to it (blue),
thereby preventing it from reaching its
target. Astrocytes can also release
signaling molecules (red) that cause
the axon to increase or decrease the
amount of neurotransmitter it releases
when it fires again. Modifying the
connections among neurons is one way
the brain revises its responses to stimuli
as it accumulates experience—how it
learns. In the peripheral nervous system,
Schwann cells surround synapses.

Schwann glia could be key to treating nerve diseases such as MS.

MOVIE MADE using scanning-laser confocal microscopy (later colorized) shows that glial cells respond to chattering neurons. Sensory neurons (two large bodies, 20 microns in diameter) (a) and Schwann glial cells (smaller bodies) were mixed in a lab culture containing calcium ions (invisible). Dye that would fluoresce if calcium ions bound to it was introduced into the cells. A slight voltage applied to the neurons prompted them to fire action potentials down axons (long lines), and the neurons immediately lit up (b), indicating they had opened channels on their membranes to allow calcium to flow inside. Twelve seconds later (c), as the neurons continued to fire, Schwann cells began to light up, indicating they had begun taking in calcium in response to the signals traveling down axons. Eighteen seconds after that (d), more glia had lit up, because they had sensed the signals. The series shows that glia tap into neuronal messages all along the lines of communication, not just at synapses where neurotransmitters are present.

HOW DO GLIA communicate? Glia called astrocytes (a) and sensory neurons (not shown) were mixed in a lab culture containing calcium ions. After a neuron was stimulated to fire action potentials down long axons (lightning bolts) (b), glia began to light up, indicating they sensed the message by beginning to absorb calcium. After 10 and 12.5 seconds (c and d), huge waves of calcium flux were sweeping across the region, carrying signals among many astrocytes. Green to yellow to red depicts higher calcium concentration.

Thought for a few seconds

Glial Cells in Synapse Formation and Regeneration

1. Historical Assumptions

For decades, neuroscientists believed that only neurons determined which cells they connected to and where those connections (synapses) would form. Glial cells—the non-neuronal cells of the nervous system—were thought to play merely supportive roles.

2. Astrocytes Promote Synaptogenesis

Key finding (Ben A. Barres et al., Stanford University):

Experiment: Rat retinal neurons were cultured without astrocytes.
Observation: Neurons formed very few synapses.
Rescue: Addition of astrocytes—or even just the medium in which astrocytes had grown—led to abundantsynapse formation.
Detection methods:
- Microscopy to visualize and count synapses.
- Microelectrode recordings to measure synaptic electrical activity.
Molecular mediators identified:
1. ApoE/cholesterol complex (a fatty complex)
2. Thrombospondin (a secreted protein)
  Both are released by astrocytes and directly stimulate synapse development.

3. Nonneuronal Influence on Synaptic Dynamics

Key finding (Jeff W. Lichtman’s group, Washington University):

Approach: Time-lapse imaging of mouse muscle synapses over days to weeks.
Observations:
- Both the formation and pruning (elimination) of synapses during development—and after injury—appeared to be guided by “ghost-like” nonneuronal forces at the axon terminal.
- These influences suggested an active role for glial cells in both building and dismantling neural connections.

4. Schwann Cells Guide Axonal Regeneration

Key finding (Le Tian, Wesley Thompson et al., University of Texas at Austin):

Model: Transgenic mouse with fluorescent Schwann glia.
Collaboration: Thompson’s team worked with Lichtman’s group to visualize glial activity at neuromuscular junctions in real time—previously impossible.
After nerve injury:
1. The axon withdraws, but postsynaptic neurotransmitter receptors remain clustered.
2. Regeneration path: Growing axons follow the residual Schwann cells back to their original targets.
3. When misrouting occurs: Neighboring Schwann cells detect a “stranded” synapse and extend fluorescently labeled processes to form a bridge.
4. The regenerating axon uses this Schwann-cell bridge to reconnect with its receptor cluster.

5. Therapeutic Implications

Spinal cord injury: Researchers are exploring transplantation of Schwann cells into damaged spinal regions.
Goal: Harness glial-mediated guidance to promote accurate axonal regrowth and functional recovery.

Conclusion:
These landmark studies collectively demonstrate that glial cells—astrocytes and Schwann cells—play active, instructive roles in both the formation and regeneration of synaptic connections. This paradigm shift opens new avenues for treating nervous system injuries by leveraging the intrinsic guidance cues provided by glia.

Summary

chatbot
The note titled source glias cells in the brain provides a comprehensive overview of the roles and implications of glial cells in the brain. Here are the key findings and implications:

Communication and Signal Modulation: Glial cells, once thought to only support neurons, are now known to communicate with neurons and each other. They can alter neuronal signals at synaptic gaps and influence synapse formation, suggesting a critical role in learning, memory, and nerve repair.
Astrocytes and Synaptogenesis: Astrocytes promote synapse formation. Experiments showed that neurons form few synapses without astrocytes, but abundant synapses when astrocytes or their growth medium are present. Astrocytes release molecules like ApoE/cholesterol complex and thrombospondin to stimulate synapse development.
Nonneuronal Influence on Synaptic Dynamics: Glial cells actively participate in the formation and pruning of synapses, guiding neural connections during development and after injury.
Schwann Cells and Axonal Regeneration: Schwann cells guide axonal regeneration by forming bridges for axons to reconnect with their targets after nerve injury. This highlights their potential in treating nerve diseases like multiple sclerosis (MS).
Therapeutic Implications: The active roles of glial cells in synapse formation and regeneration open new avenues for treating nervous system injuries. Researchers are exploring Schwann cell transplantation to promote axonal regrowth and recovery in spinal cord injuries.

Important Words: Communication, Signal Modulation, Astrocytes, Synaptogenesis, Nonneuronal Influence, Synaptic Dynamics, Schwann Cells, Axonal Regeneration, Therapeutic Implications, Learning, Memory, Nerve Repair.

Sources:

Source

Fields, R.D. (2004). The other half of the brain. Sci. Am. 290, 54–61.

Created: 05-05-25 17:23

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source glias cells in the brain