Astrocytes as information processors in the brain.

In summary, astrocytes regulate synaptic strength through a mechanism involving ATP release, P2Y1 receptors, Ca influx, and glutamate release. This glutamate then binds to the pre-synaptic cells' NR2B subunit, increasing mESPC frequency and potentiating the post-synaptic cell. Additionally, astrocytes are connected in gap-junction networks, allowing for diffusion of Ca between cells and potential influences on perisynaptic glutamate release. This mechanism has been observed in both the Nature Neuroscience and ASN NEURO papers, with the latter also mentioning the role of physiological astrocytic calcium levels in stimulating glutamate release.
  • #1
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Below are two excellent papers that outline the mechanism by which astrocytes regulate synaptic strength. The first one shows the most important pathway, I think. Here's my summary of the story from the first paper:

1) ATP released locally by local activity (either from the granule neurons or neighboring astrocytes)
2) P2Y1 receptors bind ATP, initiating Ca influx in the perisynaptic compartment of the astrocyte
3) Ca influx triggers glutamate release (fyi, astrocytes have glutamate vesicles primed at the tripartate synapse).
4) glutamate from astrocytes binds to the NR2B subunit on the NMDA receptors on the pre-synaptic cell
5) NR2B binding increases the frequency of mESPCs, potentiating the post-synaptic cell, bringing it closer to threshold.

Note: astrocytes are connected to each other in gap-junction networks. It would be interesting to see what kind of influences they have on each other with respect to perisynaptic glutamate release. The paper shows how Ca diffuses through the astrocyte network via these gap junctions, but it just mentions it in passing, more-or-less.

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Glutamate exocytosis from astrocytes controls synaptic strength
Pascal Jourdain, et al. Nature Neuroscience 10, 331 - 339 (2007)
Published online: 18 February 2007 | doi:10.1038/nn1849

http://www.ncbi.nlm.nih.gov/pubmed/17310248 (pubmed entry)
http://www.nature.com/neuro/journal/v10/n3/full/nn1849.html (paper)
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Plasmalemmal Na+/Ca2+ exchanger modulates Ca 2+ -dependent exocytotic release of glutamate from rat cortical astrocytes.
Reno C Reyes, et al. ASN NEURO 4(1)
:art:e00075.doi:10.1042/AN20110059

http://www.asnneuro.org/an/004/e075/004e075.pdf[/URL] (paper)
 
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  • #2
Since these are cultured cells, it might be good to supplement with this paper:

Physiological astrocytic calcium levels stimulate glutamate release to modulate adjacent neurons.

Vladimir Parpura, et al. PNAS 2000 97 (15) 8629-8634;
doi:10.1073/pnas.97.15.8629

http://www.pnas.org/content/97/15/8629
 

1. What are astrocytes and how do they function in the brain?

Astrocytes are a type of glial cell found in the brain. They are responsible for maintaining the structural and functional integrity of the brain, as well as providing support and nourishment to neurons. They also play a role in regulating neurotransmitter levels and modulating neuronal activity.

2. How do astrocytes process information in the brain?

Astrocytes act as information processors in the brain by responding to and integrating various signals from neurons and other cells. They have specialized processes called "end feet" that make contact with blood vessels and synapses, allowing them to communicate with both the circulatory system and neurons. They can also release and absorb neurotransmitters and other signaling molecules, influencing the activity of nearby neurons.

3. What is the significance of astrocytes as information processors?

Astrocytes play a crucial role in maintaining the overall health and function of the brain. By processing information and communicating with other cells, they help regulate the activity of neurons and support the proper functioning of synapses. They also play a critical role in neuroplasticity, the brain's ability to change and adapt to new experiences.

4. How do astrocytes contribute to brain disorders and diseases?

Research has shown that astrocytes can be involved in the development and progression of various brain disorders and diseases. For example, they have been implicated in the formation of plaques in Alzheimer's disease and the abnormal neural activity in epilepsy. Dysfunction of astrocytes can also lead to neurological disorders such as multiple sclerosis and Huntington's disease.

5. Can astrocytes be targeted for potential treatments of brain disorders?

Due to their important role in brain function and their involvement in various disorders, astrocytes have become a target for potential treatments. Researchers are exploring ways to manipulate astrocyte activity to treat or prevent brain diseases. Some studies have shown promising results in using stem cells to replace damaged or dysfunctional astrocytes in animal models of brain disorders.

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