Hey all, I know that astrocyte calcium changes are potentiated by neuronal firing (both directly and indirectly), and that the calcium fluxes that correspond with gliotransmitter release from astrocytes are maximized when the calcium fluxes occur in rhythmic patterns, but has anyone tried to link these astrocytic oscillations with cortical oscillations?
Asking specifically in terms of the Hippocampus where most of this work is being done, does there exist a relationship between Theta oscillations and the Calcium dynamics of affected astrocytes? Do they have a temporal relation? Could anyone point me to a good paper on this topic?
You know, it depends. Please, evaluate some papers (in the attachment).
I know of two papers that may be of interest:
http://www.ncbi.nlm.nih.gov/pubmed/22027012
http://www.ncbi.nlm.nih.gov/pubmed/27122314
A comment regarding the concept of "gliotransmission". The evidence for it is not monolithic, and a large part of the field has moved away from the concept. There is also a debate as to what astrocytes calcium signaling actually does, and what the sources of that calcium are.
One issue is that while you can cause an astrocytes to do something (such as trigger a chance in network state or release gliotransmitters) whether that actually occurs under normal physiology is in question. For example this paper (http://www.ncbi.nlm.nih.gov/pubmed/24174673) found that if you uncage calcium in an astrocyte you can trigger glutamate release, that activating a Gq-GPCR that lead to an increase in calcium did not. The same caution should be applied to the recent wave of papers using tools for optogenetic activation of astrocytes. See some reviews here:
http://www.ncbi.nlm.nih.gov/pubmed/26814587
http://www.ncbi.nlm.nih.gov/pubmed/25941472
http://www.ncbi.nlm.nih.gov/pubmed/22811669
http://www.ncbi.nlm.nih.gov/pubmed/25502516
There are some papers in the hippocampus that suggest that astrocytes do scale their calcium activity in response to increase neuronal activity, mostly at Schaffer collateral synapses that might give you some insight (apologies if you've run across them already):
http://www.ncbi.nlm.nih.gov/pubmed/26074766
http://www.ncbi.nlm.nih.gov/pubmed/24484772
Astrocytes calcium does something, but what it is exactly doing is still under debate.
Thank you both for your responses, I truly appreciate it! They revealed a few papers I had not yet had the opportunity to read. I think your last comment that Astrocyte Calcium signaling 'does something' is right on in its non specificity, at this point that's all we can say without some goofiness!
That's said however, it does strike me that even if we put aside gliotransmitters in favor of the well established K+ buffering capacities relegated to astrocytes in the context of the complex and multifaceted CA2+ signals that have been recorded, Astrocytes could be seen as entities with the potential to potentiate synchrony (or at the very least improve signal to noise ratio) on a dyamic time scale. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3515082/
I suppose the follow up question I have then, is how relevant are oscillatory dynamics in neurons on large and small scales for the plasticity seen in astrocytic responses, I've read a bunch of papers linking the two in terms of plasticity, but it still seems unclear to me what the spatiotemporal components are. I think it's a really relevant question to pursue in the context of things like divisive normalization/ correlational noise. It seems if what seem to be neuronal idiosyncracies were in fact not noise but designed for non neuronal reconfigurations the questions could be considered in a new light.
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