Super Glue

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The majority of cells in the nervous system are not neurons. They are glia. There are several subtypes of glia, one of which is astrocytes. Glia means glue. In general, people think of glia in their support role in the nervous system. Holding it together, disposing of waste and other menial tasks.

This little commentary here (pdf) in the current Cell describes a change in thinking that is occuring with regard to glia. They are stepping into a more active role. In this case, they modulate the ability of hypothalamic synapses to undergo plasticity. Compared to lactating rats, virgin rats have closer astrocyte encasement of synapses. The astrocytes release a chemical called D-serine into synapses that binds to a co-agonist site on NMDA receptors. NMDA receptor activation is considered the first checkpoint for increases in synaptic strength. More D-serine = more effective NMDA receptor activation.

In the study described, virgin rats have a lower threshold for LTP induction than do lactating rats. This is nicely illustrated below the fold.


So better glia encapsulation of synapses = more D-serine in synapses = more NMDAR activation = easier to undergo synaptic enhancement. This is in the hypothalamus mind you, not usually a major locus for memory studies. I’d like to see what’s going on during these states in the hippocampus. For those of you interested in intelligence and Ashkenazis and all that business, you might note that the major abnormality of Einstein’s brain was an greater glia to neuron ratio. I don’t know what that means either.

5 Comments

  1. Not in a position to download PDFs right now, but thanks, Coffee Mug, for the basic play-by-play. You always read in textbooks something along the lines of, “It is now thought that glial cells also play a role in information processing,” so it’s nice to see a possible concrete example. 
     
    By the way, would you recommend the new edition of Kandel when it comes out at the end of June?

  2. A coating of glia cells also increases the electrical conductivity of the axons, dendrites, and thus leads to faster neuronal functioning.

  3. I can’t really say about the new Kandel. I don’t know what they’ve modified, and my knowledge isn’t anywhere near as broad as that book goes. I do enjoy having my current edition though. It’s a great reference.

  4. Glia are cool; they’re what most caught my eye when I was reading basic neuroscience to better understand creativity. 
     
    My recent post on g and creativity noted that many creativity researchers think that a central piece of the puzzle is having a “flat” associative hierarchy — rather than, say, a binary-branching only tree of associations b/w ideas, idea-nodes are connected to many diverse idea-nodes. 
     
    In their well known passive role, glia increase speed of transmission and encourage preservation of the signal — so, even if you had a binary-branching only associative web, it would be faster and more faithful to connect two distant ideas. Let’s say Nodes A and D aren’t directly connected: the only path is through Node B and then Node C. The slower and the less faithful the process, the more difficult it is to get from Node A to Node D. 
     
    But if glia also play an active role in strengthening the connection b/w two neurons, then having more glia should allow you to develop strong connections b/w Node A and Nodes B, C, and D, rather than just Node B. So, this creates a direct path between ordinarily distant nodes. 
     
    That’s probably how it ties back to Einstein. Lots more to say, obviously.

  5. This is interesting-not just for giving astrocytes a more active role, but also for giving the NMDA glycine site (to which D-serine binds) importance. As I remember from reading textbooks, the general belief (I don’t know if consensus is the right word) was that this modulator site was almost permanently occupied at physiological glycine concentrations, and thus likely had little, if any, role in determining receptor function. It always seemed unlikely (to me) that such a site was conserved through evolution just to sit there and hold onto some glycine, a suspicion that is validated by this finding.

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