Things I like to Blog About: Neurotransmission

I suppose I thought for a while that if I was talking about dopamine and serotonin and GABA and things enough, people would just kind of “get” neurotransmission. And most people do. But it’s still a good thing to cover, partially because it’s kind of mind boggling to think about (well, Sci finds it mind-boggling), and partially because it helps you understand why changes in receptors, changes in transporters, or changes in release will have different effects. This comes in very handy when talking about various psychiatric and addictive drugs of which I am very fond. And so, your general post today: Neurotransmission.

And also, I get to DRAW!!! w00t.
neurotransmission1.png
The synapse. Do not be fooled by its commonplace appearance. Like so many things, it is not what is on the outside, but what is on the inside that counts. 🙂


So what are we looking at here? That blue bulbous portion that looks like a nose is the presynaptic neuron. The smiley below it in pink is the postsynaptic neuron. And neurotransmission is what gets a signal from one side to the other.
neurotransmission2.png
Now the presynaptic neuron has a signal. This stimulus is transmitted as an action potential eletrically down the neuron until it gets to the bulge in the picture, the synaptic buton.
neurotransmission3.png
But the electrical signal cannot just bounce on to the next neuron. There’s too much space in between the two neurons in the synaptic cleft. Instead, the stimulus of the action potential causes a rush of calcium ions into the synaptic buton, rapidly changing the potential inside.
neurotransmission4.png
This change in potential is going to affect little vesicles, little blobs of membrane inside the presynaptic neuron. These vesicles contain neurotransmitters, chemicals synthesized in the presynaptic cell, and stored in the vesicles until stimulated.
neurotransmission5.png
When the vesicles are stimulated by this influx of calcium caused by the approaching action potential, the vesicles begin to migrate to the cell membrane. Then, they can either merge with the membrane and release all their neurotransmitter into the synapse, or they can perform a “kiss and run” opening briefly at the membrane and only releasing a little of the neurotransmitter. It’s thought right now that the kiss and run is more common than dumping all the neurotransmitter in there.
neurotransmission6.png
So now the neurotransitting chemicals are in the synapse. They float across the tiny space in a random way, and in the process, bump into receptors on the other side.
neurotransmission7.png
Keep in mind, though. The neurotransmitters are not taken up by the receptors. Instead, they bind, and the receptor, which runs through the membrane in the postsynaptic cell, changes conformation on the inside of the cell, causing activation of pathways.
The receptors here are important. This is because there tend to be many different types of receptor for one type of neurotransmitter. For example, serotonin has 17 known receptors, and there might be more. The type of receptor on the postsynaptic neuron determines how the cell will react to the signal. This is a lot more refined than depending on neurotransmitter release. You can only change the AMOUNT of neurotransmitter released, not whether or not that neurotransmitter will be excitatory or inhibitory. That is left to the receptors. So depending on what the neurotransmitter hits, the result could be excitation or inhibition of the postsynaptic neuron’s action potential, or something even more complicated, like activation of specific gene pathways to produce specific proteins.
Not only that, receptor sensitivity to stimulation can change, either by changing the number of receptors at the postsynaptic membrane, or changing the sensitivity of the receptors that are there. There are lots of way to control how much and what kind of signals are getting across, and previous stimulations received will influence how the postsynaptic cell is capable of reacting later. These changes can be short-term or long-term, and can be responsible for starting processes like memory formation, learning, and addiction, as well as tons of other things.
So what happens then? You don’t want to leave the neurotransmitter sitting around in the synapse. Because it’s floating around at random, sitting in the synapse means it will continue to bump into receptors and pass signals on to the post-synaptic neuron. So the signal must be terminated. Depending on the neurotransmitter you’re dealing with (dopamine, serotonin, GABA, glutamate, acetylcholine, the list goes on), there are carious things that can happen. An enzyme can break down the neurotransmitter chemical into its component parts, or the presynaptic neuron can have transporters, which suck the neurotransmitter up back into the synaptic buton, either to be shoved back into vesicles, or to be degraded.
neurotransmission8.png
And the synapse clears out, vesicles fill up, calcium goes back out of the presynaptic neuron, and it’s all ready to begin again.
That’s a really, really basic picture of what’s going on at a synapse. But what, you may ask, is so mind-boggling about that? What boggles Sci’s mind is the tiny scale on which this is happening (the order of microns, a micron is 0.000001m), and the SPEED. This happens FAST. Every movement of your fingers requires THOUSANDS of these signals. Every new fact you learn requires thousands more. Heck, every word your are looking at, just the ACT of LOOKING and visual signals coming into your brain. Millions of signals, all over the brain, per second. And out of each tiny signal, tiny things change, and those tiny changes determine what patterns are encoded and what are not. Those patterns can determine something like what things you see are remembered or not. And so, those millions of tiny signals will determine how you do on your calculus test, whether you swerve your car away in time to miss the stop sign, and whether you eat that piece of cake.
If that’s not mind-boggling, what IS?!

61 Responses

  1. That is, indeed, mind-boggling.

  2. Can I steal that post?
    Complex stuff; excellently, put simply.

  3. Hi Sci, some minor points:
    So what are we looking at here? That blue bulbous portion that looks like a nose is the presynaptic neuron. The smiley below it in pink is the postsynaptic neuron. And neurotransmission is what gets a signal from one side to the other.
    The drawing may confuse people (“why is one neuron shaped like a doorknob, the other like a crescent?”). Really, what you drew was a bouton facing the postsynaptic membrane of maybe a dendritic spine. So it’s parts of the two neurons, not the whole neurons.
    But the electrical signal cannot just bounce on to the next neuron. There’s too much space in between the two neurons in the synaptic cleft.
    It’s probably not the size across the cleft but fact that the membrane resists the flow of charge.
    Instead, the stimulus of the action potential causes a rush of calcium ions into the synaptic buton, rapidly changing the potential inside…This change in potential is going to affect little vesicles, little blobs of membrane inside the presynaptic neuron.
    As far as I know, it is not the change in potential that affects the vesicles (besides, the action potential alone is a huge change in potential, so there’d be no need for calcium-carried potential) but the presence of increased calcium levels itself. This is because the calcium ions bind to proteins that guide the vesicles to the membrane, etc.
    The neurotransmitters are not taken up by the receptors. Instead, they bind, and the receptor, which runs through the membrane in the postsynaptic cell, changes conformation on the inside of the cell, causing activation of pathways.
    Well, sometimes it causes activation of pathways. Sometimes it just opens an ion channel.

  4. I’m going to skip over your excellent explanation to say that the illustrations are wonderful, especially the Pac-Man enzymes at the end.

  5. cm: excellent points. I left most of them out in an effort to get this across as simply as possible, but they’re really good for those who want more detail, but yeah, I left out the ion channel. Oops. I also left out things like VMAT and how vesicles bind to the membrane, which of course only makes the bind boggle MORE when you learn about all the complexity.
    Mr Ian: cite your source, and steal away. 🙂

  6. Neurons are totally awesome, and excitability rocks the house too. Especially the action potential part. Synaptic tranmission is all well and good, but let’s remember it starts with an action potential. Not that I’m biased or anything. 🙂

  7. just to comment on CM’s post. The calcium doesn’t guide the vesicles to the membrane, rather it causes conformational changes in a particular synaptic vesicle protein (the calcium sensor which is thought to be synaptotagmin) which allows for vesicle fusion and release of contents. But this I know is far too detailed for the general audience. 🙂

  8. great post..
    reading this reminded me of a professor in grad school that was very very particular about what you call a neurotransmitter.
    Her opinion, was that if it didn’t gate a channel directly, then it wasn’t a neurotransmitter.

  9. Nat: I’ve got an awe-inspiring post on the action potential, if I do say so myself. 🙂
    neuropostdoc: yeah, bit too detailed. But awesome. I could spend ages on all the little conformational changes…
    Pinus: when you say “gate a channel directly”, do you mean open an ion channel? That seems like a bit of a limiting definition. Most neurotransmitters DO have activity at an ion channel or two, but often most of the receptors hit are G-protein coupled (consider, for example, serotonin, where the only ion channel receptor is the 5-HT3). And what about dopamine, where the all receptors are G-protein coupled, but that activation could OPEN ion channels? Did she have another term for chemicals released across the synapse to hit receptors on the other side, if those receptors are not ion channels? And was she basing her distinction on findings in the lit on chemical distinction? This is the first time I’ve heard this idea, please let me know!

  10. yes, I mean ion channel.
    so basically…GABA, Glycine, Glutamate, Acetylcholine and 5HT (at 5HT3).
    everything else would be a neuromodulator.
    I have used the term neurotransmitter loosely in manuscripts before and had reviewers tell me that I should replace neurotransmitter with neuromodulator.
    her distinction was based on the fact that only chemicals that directly gate ion channels…everything else modifies excitability or responsiveness…thus they were modulators.

  11. pinus: *headdesk* now that you explain it, I HAVE heard that before. I guess it’s more specific, but it seems to me that it’s almost a question of semantics. Those that directly gate ion channels would just be directly modulating the excitability (by causing excitation), rather than indirect modulation through making the area less or more responsive. Is there concern that people are formulating ideas improperly because of lack of clarity? I could see that happen with grad students who haven’t had the receptor ideas drilled into their heads yet.

  12. Nice post!
    Depending on the neurotransmitter you’re dealing with … there are carious things that can happen… the presynaptic neuron can have transporters
    Hey, let’s not forget our glial friends! They mop up both GABA and glutamate (the MAJOR CNS neurotransmitters — heresy I know) from the synapse.
    Where does all this ‘excitation-secretion coupling’ leave neurotransmitters like adenosine, neuropeptides, endocannabinoids, etc.?

  13. The neurotransmitter/neuromodulator distinction seems like bunk to me.
    My definition is that a neurotransmitter is something released from a neurons that transmits information to a separate cell. I might further limit the information to electrical excitability, rather than other intracellular signalling events.
    Now some of those transmitters will have rapid effects on excitability (via ionotropic receptors) and some will have slower effects (via metabotropic receptors).
    I can kinda get the idea of neurotransmitter as that thing mediating a fast effect, whereas a neuromodulator mediates a slower effect. What about in the middle though, where metabotropic responses can be rapid? Is it still a modulator is the response is complete within 1 second? In 250 ms?
    It’s not clear to me what purpose the distinction serves.

  14. Oh yeah, I liked your action potential post too (IIRC my first comment on Neurotopia was there).

  15. I am not saying I buy in to it, just wanted to point out that there are people who think this way, and they review papers and grants. 🙂

  16. What is mind boggling is that a pre synaptic neuron looks like a penis, and a post synaptic neuron looks like a vagina.
    Or maybe they look like that because it the best template for that kind of job.

  17. Nat: kisses up against the presynaptic neuron, and the whole thing is surrounded by glia, which can ALSO take stuff up and break stuff down. At least, it might look like that…
    pinus: a fair point.
    Tex: Excellent point about the glia, especially with GABA and glutamate. I tend to speak from the neurotransmitters I know the most about, and forget stuff like that.
    And speaking of stuff I don’t know a lot about: adenosine, neuropeptides, and cannabinoids would be among them. I shall have to do some more reading, I think.

  18. This is very nice. Reminiscent of a lecture I had once regarding ion exchanges in blood. This, as everyone else has pointed out, is very, very well done.

  19. Nice post, Sci. cm’s clarifications are very on point, as is the very important distinction between ligand-gated ion channel neurotransmitter receptors–such as those for glutamate, GABA, glycine, acetylcholine, and ATP–and the metabotropic receptors, which are all seven-transmembrane-domain G protein-coupled receptors (as are just about all neuropeptide receptors).

  20. neuropostdoc said:
    just to comment on CM’s post. The calcium doesn’t guide the vesicles to the membrane, rather it causes conformational changes in a particular synaptic vesicle protein (the calcium sensor which is thought to be synaptotagmin) which allows for vesicle fusion and release of contents. But this I know is far too detailed for the general audience. 🙂
    But I didn’t write that “calcium guides the vesicles in the membrane.” That would be wrong twice: calcium can guide nothing, and what would it mean for vesicles to be guided *in* the membrane?
    What I wrote was, “calcium ions bind to proteins that guide the vesicles to the membrane, etc.” Perhaps “guide” and “etc.” was too sloppy of a shorthand form of “controls the elaborate process of docking, priming, fusion pore opening, clathrin (un)coating, etc.”, but I didn’t want to go into it that much. But sure, I gave credit to the synaptic proteins as doing the “vesicle management” work.

  21. Great post, Scicurious. I wish I could create posts like that.
    Couple comments:
    I’ve never heard of neuromodulators; IIRC there are G protein-coupled receptors for GABA, glycine, and glutamate, (so says Wiki re GABA and glutamate, IIRC the G protein-coupled GABA receptor also responds to glycine although I couldn’t find ref’s in a quick search). This sort of breaks down the distinction between neurotransmitters and neuromodulators.
    The NMDA receptor responds to glutamate but can be “modulated” by voltage, Hallucinogens, Zn2+, pH, Glycine, and Polyamines. This means that “neuromodulators” can affect at least one ion channel (and likely more) as well as 2nd messenger receptors.
    I would break things down into neurotransmitters, which are acting across the synaptic cleft, neurohormones, which are released from parts of the axonal arbor (especially the presynaptic areas) in response to action potentials and affect receptors within a short (~1mm) diffusion distance, and hormones, which circulate in the bloodstream. Many chemicals can act as two or all three (e.g. noradrenaline). Since all types can act as modulators, and modulation can take place at almost neurotransmitter speed (when it affects an ion channel such as the NMDA receptor), I would leave them out of the classification and define them entirely functionally.
    The issue with glia is very important. When it comes to purely chemical communications, glia such as astrocytes have no disadvantage compared to interneurons, and there’s no reason to assume they don’t participate in the slower calculations.
    I’ve seen mention of adenosine and ATP receptors, and participation in the communication process by astrocytes, such as , “Regulation of cell-to-cell communication mediated by astrocytic ATP in the CNS” (DOI:10.1007/s11302-005-6321-y, open access, I won’t give more than one link because my post will get stalled in the moderation queue, so I’m just giving the DOI here). I’ve been meaning to write a post on the whole subject, but it’s going to be a while, and anyway yours make much better introductions for people not already somewhat familiar with the subject.
    BTW, I’ve run across ref’s saying that the same neuron can release both GABA and glycine, and many types of neuron are thought to release both a “fast” neurotransmitter and a slower peptide “modulator”, presumably with varying ratios depending on recent activation history (and perhaps many other things).

  22. Tex said:
    Where does all this ‘excitation-secretion coupling’ leave neurotransmitters like adenosine, neuropeptides, endocannabinoids, etc.?
    It leaves them in the rather large bin of “stuff in neuroscience that doesn’t quite fit the standard conception of how neurons do things”. Well, endocannabinoids for sure. Neuropeptides can, AFAIK, be released in the traditional way, due to influx of calcium, just with somewhat different requirements for the levels and dynamics of that calcium (they are also released from a different kind of vesicle called a large dense core vesicle).
    Endocannabinoids are actually not THAT different, in a sense. They are also thought to be released due to excitation and rising calcium, just in the postsynaptic cell. And they are not thought to be secreted, but more like oozing out through the membrane. And of course, they are going in the “wrong” direction! They are a fun class of neurotransmitters for sure.
    I can’t recall the state of knowledge on how adenosine is released or just builds up as ATP is cleaved or both–do you happen to know?

  23. Here’s a good link:
    Astrocyte Control of Synaptic Transmission and Neurovascular Coupling

    From a structural perspective, the predominant glial cell of the central nervous system, the astrocyte, is positioned to regulate synaptic transmission and neurovascular coupling: the processes of one astrocyte contact tens of thousands of synapses, while other processes of the same cell form endfeet on capillaries and arterioles. The application of subcellular imaging of Ca2+ signaling to astrocytes now provides functional data to support this structural notion. Astrocytes express receptors for many neurotransmitters, and their activation leads to oscillations in internal Ca2+. These oscillations induce the accumulation of arachidonic acid and the release of the chemical transmitters glutamate, D-serine, and ATP. Ca2+ oscillations in astrocytic endfeet can control cerebral microcirculation through the arachidonic acid metabolites prostaglandin E2 and epoxyeicosatrienoic acids that induce arteriole dilation, and 20-HETE that induces arteriole constriction. In addition to actions on the vasculature, the release of chemical transmitters from astrocytes regulates neuronal function. Astrocyte-derived glutamate, which preferentially acts on extrasynaptic receptors, can promote neuronal synchrony, enhance neuronal excitability, and modulate synaptic transmission. Astrocyte-derived D-serine, by acting on the glycine-binding site of the N-methyl-D-aspartate receptor, can modulate synaptic plasticity. Astrocyte-derived ATP, which is hydrolyzed to adenosine in the extracellular space, has inhibitory actions and mediates synaptic cross-talk underlying heterosynaptic depression. Now that we appreciate this range of actions of astrocytic signaling, some of the immediate challenges are to determine how the astrocyte regulates neuronal integration and how both excitatory (glutamate) and inhibitory signals (adenosine) provided by the same glial cell act in concert to regulate neuronal function.

    Please let me know if you don’t like me posting this sort of thing, I’m hoping you’ll think they add value.

  24. AK: knock yourself out! I’m learnin’ stuff! I would say, though, that the neurotransmitter vs neuromodulator would indeed be a distinction based on the result from their binding at a receptor (ion channel vs metabotropic). This makes sense to me and I can see where people would make the distinction. I could also see making the point that a neurotransmitter acts across the synaptic cleft, regardless of what it ends up binding to. But I think the majority is going to end up making the decision for us.

  25. AK: knock yourself out! I’m learnin’ stuff! I would say, though, that the neurotransmitter vs neuromodulator would indeed be a distinction based on the result from their binding at a receptor (ion channel vs metabotropic). This makes sense to me and I can see where people would make the distinction. I could also see making the point that a neurotransmitter acts across the synaptic cleft, regardless of what it ends up binding to. But I think the majority is going to end up making the decision for us.

  26. hah! endocannabinoids are BACKASSWARDS, no less!

  27. OK, here’s the next: Astrocytes, from brain glue to communication elements: the revolution continues.
    I’d agree that “neurotransmitter vs neuromodulator would indeed be a distinction” the problem being that many (perhaps all) “classic” neurotransmitters also act on metabotropic receptors. Thus the distinction is functional rather than dependent on molecular identity. Another problem is that there are many chemicals that “modulate” the action of ionotropic receptors.
    Anyway, I usually post these sort of links to a draft post on my blog, where they sit until I can get around to finishing it, often weeks. This way other people will get the advantage of my search without having to wait until I finish my post (if they even read my blog). And I’ll be able to come back an get them when I’m ready to finish the post (if ever). So I’ll keep posting them here (one by one) until my posts start going to the moderation queue.

  28. This paper is so full of exciting implications that I’m not going to try to list them: NMDA Receptors Mediate Neuron-to-Glia Signaling in Mouse Cortical Astrocytes:

    Chemical transmission between neurons and glial cells is an important element of integration in the CNS. Here, we describe currents activated by NMDA in cortical astrocytes, identified in transgenic mice that express enhanced green fluorescent protein under control of the human glial fibrillary acidic protein promoter. Astrocytes were studied by whole-cell voltage clamp either in slices or after gentle nonenzymatic mechanical dissociation. Acutely isolated astrocytes showed a three-component response to glutamate. The initial rapid component was blocked by 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX), which is an antagonist of AMPA receptors (IC50, 2 µM), and the NMDA receptor antagonist D-AP-5 blocked the later sustained component (IC50, 0.6 µM). The third component of glutamate application response was sensitive to D,L-threo–benzyloxyaspartate, a glutamate transporter blocker. Fast application of NMDA evoked concentration-dependent inward currents (EC50, 0.3 µM); these showed use-dependent block by (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate (MK-801). These NMDA-evoked currents were linearly dependent on membrane potential and were not affected by extracellular magnesium at concentrations up to 10 mM. Electrical stimulation of axons in layer IV–VI induced a complex inward current in astrocytes situated in the cortical layer II, part of which was sensitive to MK-801 at holding potential –80 mV and was not affected by the AMPA glutamate receptor antagonist NBQX. The fast miniature spontaneous currents were observed in cortical astrocytes in slices as well. These currents exhibited both AMPA and NMDA receptor-mediated components. We conclude that cortical astrocytes express functional NMDA receptors that are devoid of Mg2+ block, and these receptors are involved in neuronal–glial signal transmission.

  29. This one doesn’t say anything about ATP or glia, but it says some important things about synaptic specificity: Synapse-Specific Expression of Functional Presynaptic NMDA Receptors in Rat Somatosensory Cortex (It’s also (barely) recent enough for Research Blogging.):

    Presynaptic NMDA receptors (NMDARs) modulate release and plasticity at many glutamatergic synapses, but the specificity of their expression across synapse classes has not been examined. We found that non-postsynaptic, likely presynaptic NR2B-containing NMDARs enhanced AMPA receptor-mediated synaptic transmission at layer 4 (L4) to L2/3 (L4–L2/3) synapses in juvenile rat barrel cortex. This modulation was apparent at room temperature when presynaptic NMDARs were activated by elevation of extracellular glutamate or application of exogenous NMDAR agonists. At near physiological temperatures, modulation of transmission by presynaptic NMDARs occurred naturally, without the need for external activation. Blockade of presynaptic NMDARs depressed unitary and extracellularly evoked EPSCs at L4–L2/3 synapses, accompanied by increases in paired-pulse ratio and coefficient of variation, indicative of a decrease in presynaptic release probability. NMDAR agonists increased the frequency of miniature EPSCs in L2/3 neurons, without altering their amplitude or kinetics. Focal application of NMDAR antagonist revealed that the NMDARs that modulate L4–L2/3 transmission are located in L2/3, not L4, consistent with localization on terminals or axons of L4–L2/3 synapses, rather than on the somatodendritic compartment of presynaptic L4 neurons. In contrast, presynaptic NMDARs did not modulate L4–L4 synapses, which originate from the same presynaptic neurons as L4–L2/3 synapses, or cross-columnar L2/3–L2/3 horizontal projections, which synapse onto the same postsynaptic target neurons. Thus, presynaptic NMDARs selectively modulate L4–L2/3 synapses, relative to other synapses made by the same neurons. Existence of these receptors may support specialized processing or plasticity by L4–L2/3 synapses.

  30. I can only get the summary, so far: GUPEA: The astroglial syncytium:

    Small aqueous pores, the so-called gap junction channels, couple astrocytes into an extensive syncytium-like organisation. Astroglial gap junctions are mainly composed of connexin-43 proteins. They provide a pathway for intercellular diffusion of ions and small ((1000 Da) molecules, such as second messengers and metabolites. The organisation into multicellular functional units is probably a prerequisite for the participation of astroglial cells in the control of extracellular homeostasis. Waves of increased intracellular Ca2+ concentration can propagate between astrocytes. This is of particular interest, as cytosolic Ca2+ is a second messenger that affects ion channels, carriers, and enzymes and thereby mediates short-, intermediate-, and long-term effects on astroglial function. The aim of this thesis was to study the modulation of gap junction communication and intra- and intercellular Ca2+ signalling induced by various neuroactive substances. Differences in connexin-43 expression, gap junction communication, and Ca2+ signalling in various brain regions were investigated. Enriched astroglial and mixed astroglial-neuronal primary cultures were used as model systems.Stimulation of astrocytic 5-HT2A receptors increased intracellular free Ca2+ concentrations through the release of stored Ca2+ and influx across the plasma membrane. Not only the release of stored Ca2+ but also the influx was dependent on intact Ca2+ stores. The results indicate the opening of depletion-operated Ca2+ channels. The study of intercellular Ca2+ signalling involved developing methods for quantification of Ca2+ wave variables. The amplitude of the Ca2+ increase in cells and the velocity between cells participating in the Ca2+ waves initially showed fast decreases and then stabilised with lower rates of decrease. The areas of Ca2+ wave propagation were increased by glutamate and decreased by 5-HT, noradrenaline, and endothelins in hippocampal astrocytes. In some cases, these modulations varied among astrocytes derived from different brain regions. A relationship was observed between changes in gap junction permeability and changes in the extent of intercellular Ca2+ signalling. Endothelins completely blocked gap junctions and abolished intercellular Ca2+ waves. The levels of Connexin-43 mRNA and protein and the permeability of gap junctions varied among astrocytes derived from different brain regions, but they varied together, such that if levels of mRNA were high in one region, protein expression and gap junction permeability were also high in that region. The extent of Ca2+ signalling was partially related to these three variables.Several lines of data indicate that astrocytes are involved in the regulation of the interstitial fluid and thereby of neuronal physiology. Gap junction coupling of astrocytes into functional networks has been suggested to play a role in spatial buffering of K+, in nutrient supply to neurons, and in dissipation of cell volume changes. Intercellular astroglial Ca2+ waves might have a synchronising role in the regulation of astroglial syncytial functions. The results presented in this thesis indicate that endogenous compounds dynamically modulate astroglial gap junction communications. Increased knowledge about the control of gap junction-mediated astroglial cell-to-cell signalling provides new dimensions in the understanding of neuro-glial interactions in physiological and pathophysiological

  31. P2X1 and P2X5 Subunits Form the Functional P2X Receptor (open access):

    ATP plays an important role in signal transduction between neuronal and glial circuits and within glial networks. Here we describe currents activated by ATP in astrocytes acutely isolated from cortical brain slices by non-enzymatic mechanical dissociation. Brain slices were prepared from transgenic mice that express enhanced green fluorescent protein under the control of the human glial fibrillary acidic protein promoter. Astrocytes were studied by whole-cell voltage clamp. Exogenous ATP evoked inward currents in 75 of 81 astrocytes. In the majority (65%) of cells, ATP-induced responses comprising a fast and delayed component; in the remaining subpopulation of astrocytes, ATP triggered a smoother response with rapid peak and slowly decaying plateau phase. The fast component of the response was sensitive to low concentrations of ATP (with EC50 of 40 nM). All ATP-induced currents were blocked by pyridoxal-phosphate-6-azophenyl-2′,4′-disulfonate (PPADS); they were insensitive to ivermectin. Quantitative real-time PCR demonstrated strong expression of P2X1 and P2X5 receptor subunits and some expression of P2X2 subunit mRNAs. The main properties of the ATP-induced response in cortical astrocytes (high sensitivity to ATP, biphasic kinetics, and sensitivity to PPADS) were very similar to those reported for P2X1/5 heteromeric receptors studied previously in heterologous expression systems.

  32. P2X1 and P2X5 Subunits Form the Functional P2X Receptor (open access):

    ATP plays an important role in signal transduction between neuronal and glial circuits and within glial networks. Here we describe currents activated by ATP in astrocytes acutely isolated from cortical brain slices by non-enzymatic mechanical dissociation. Brain slices were prepared from transgenic mice that express enhanced green fluorescent protein under the control of the human glial fibrillary acidic protein promoter. Astrocytes were studied by whole-cell voltage clamp. Exogenous ATP evoked inward currents in 75 of 81 astrocytes. In the majority (65%) of cells, ATP-induced responses comprising a fast and delayed component; in the remaining subpopulation of astrocytes, ATP triggered a smoother response with rapid peak and slowly decaying plateau phase. The fast component of the response was sensitive to low concentrations of ATP (with EC50 of 40 nM). All ATP-induced currents were blocked by pyridoxal-phosphate-6-azophenyl-2′,4′-disulfonate (PPADS); they were insensitive to ivermectin. Quantitative real-time PCR demonstrated strong expression of P2X1 and P2X5 receptor subunits and some expression of P2X2 subunit mRNAs. The main properties of the ATP-induced response in cortical astrocytes (high sensitivity to ATP, biphasic kinetics, and sensitivity to PPADS) were very similar to those reported for P2X1/5 heteromeric receptors studied previously in heterologous expression systems.

  33. ATP not only helps control calculations, but axon growth: Inhibition of the ATP-gated P2X7 receptor promotes axonal growth and branching in cultured hippocampal neurons (open access):

    During the establishment of neural circuits, the axons of neurons grow towards their target regions in response to both positive and negative stimuli. Because recent reports show that Ca2+ transients in growth cones negatively regulate axonal growth, we studied how ionotropic ATP receptors (P2X) might participate in this process. Our results show that exposing cultured hippocampal neurons to ATP induces Ca2+ transients in the distal domain of the axon and the concomitant inhibition of axonal growth. This effect is mediated by the P2X7 receptor, which is present in the growth cone of the axon. Pharmacological inhibition of P2X7 or its silencing by shRNA interference induces longer and more-branched axons, coupled with morphological changes to the growth cone. Our data suggest that these morphological changes are induced by a signalling cascade in which CaMKII and FAK activity activates PI3-kinase and modifies the activity of its downstream targets. Thus, in the absence or inactivation of P2X7 receptor, axons grow more rapidly and form more branches in cultured hippocampal neurons, indicative that ATP exerts a negative influence on axonal growth. These data suggest that P2X7 antagonists have therapeutic potential to promote axonal regeneration.

  34. Glutamate-induced Exocytosis of Glutamate from Astrocytes (open acess):

    Recent studies indicate that astrocytes can play a much more active role in neuronal circuits than previously believed, by releasing neurotransmitters such as glutamate and ATP. Here we report that local application of glutamate or glutamine synthetase inhibitors induces astrocytic release of glutamate, which activates a slowly decaying transient inward current (SIC) in CA1 pyramidal neurons and a transient inward current in astrocytes in hippocampal slices. The occurrence of SICs was accompanied by an appearance of large vesicles around the puffing pipette. The frequency of SICs was positively correlated with [glutamate]o. EM imaging of anti-glial fibrillary acid protein-labeled astrocytes showed glutamate-induced large astrocytic vesicles. Imaging of FM 1-43 fluorescence using two-photon laser scanning microscopy detected glutamate-induced formation and fusion of large vesicles identified as FM 1-43-negative structures. Fusion of large vesicles, monitored by collapse of vesicles with a high intensity FM 1-43 stain in the vesicular membrane, coincided with SICs. Glutamate induced two types of large vesicles with high and low intravesicular [Ca2+]. The high [Ca2+] vesicle plays a major role in astrocytic release of glutamate. Vesicular fusion was blocked by infusing the Ca2+ chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid, or the SNARE blocker, tetanus toxin, suggesting Ca2+- and SNARE-dependent fusion. Infusion of the vesicular glutamate transport inhibitor, Rose Bengal, reduced astrocytic glutamate release, suggesting the involvement of vesicular glutamate transports in vesicular transport of glutamate. Our results demonstrate that local [glutamate]o increases induce formation and exocytotic fusion of glutamate-containing large astrocytic vesicles. These large vesicles could play important roles in the feedback control of neuronal circuits and epileptic seizures.

  35. Glutamate-induced Exocytosis of Glutamate from Astrocytes (open acess):

    Recent studies indicate that astrocytes can play a much more active role in neuronal circuits than previously believed, by releasing neurotransmitters such as glutamate and ATP. Here we report that local application of glutamate or glutamine synthetase inhibitors induces astrocytic release of glutamate, which activates a slowly decaying transient inward current (SIC) in CA1 pyramidal neurons and a transient inward current in astrocytes in hippocampal slices. The occurrence of SICs was accompanied by an appearance of large vesicles around the puffing pipette. The frequency of SICs was positively correlated with [glutamate]o. EM imaging of anti-glial fibrillary acid protein-labeled astrocytes showed glutamate-induced large astrocytic vesicles. Imaging of FM 1-43 fluorescence using two-photon laser scanning microscopy detected glutamate-induced formation and fusion of large vesicles identified as FM 1-43-negative structures. Fusion of large vesicles, monitored by collapse of vesicles with a high intensity FM 1-43 stain in the vesicular membrane, coincided with SICs. Glutamate induced two types of large vesicles with high and low intravesicular [Ca2+]. The high [Ca2+] vesicle plays a major role in astrocytic release of glutamate. Vesicular fusion was blocked by infusing the Ca2+ chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid, or the SNARE blocker, tetanus toxin, suggesting Ca2+- and SNARE-dependent fusion. Infusion of the vesicular glutamate transport inhibitor, Rose Bengal, reduced astrocytic glutamate release, suggesting the involvement of vesicular glutamate transports in vesicular transport of glutamate. Our results demonstrate that local [glutamate]o increases induce formation and exocytotic fusion of glutamate-containing large astrocytic vesicles. These large vesicles could play important roles in the feedback control of neuronal circuits and epileptic seizures.

  36. Posts like this are why I read here. Well that, and Friday Wierd Sex,..um, Science.
    Seriously, thank you.

  37. Fast Subplasma Membrane Ca2+ Transients Control Exo-Endocytosis of Synaptic-Like Microvesicles in Astrocytes (open access):

    Astrocytes are the most abundant glial cell type in the brain. Although not apposite for long-range rapid electrical communication, astrocytes share with neurons the capacity of chemical signaling via Ca2+-dependent transmitter exocytosis. Despite this recent finding, little is known about the specific properties of regulated secretion and vesicle recycling in astrocytes. Important differences may exist with the neuronal exocytosis, starting from the fact that stimulus-secretion coupling in astrocytes is voltage independent, mediated by G-protein-coupled receptors and the release of Ca2+ from internal stores. Elucidating the spatiotemporal properties of astrocytic exo-endocytosis is, therefore, of primary importance for understanding the mode of communication of these cells and their role in brain signaling. We here take advantage of fluorescent tools recently developed for studying recycling of glutamatergic vesicles at synapses ([refs]); we combine epifluorescence and total internal reflection fluorescence imaging to investigate with unprecedented temporal and spatial resolution, the stimulus-secretion coupling underlying exo-endocytosis of glutamatergic synaptic-like microvesicles (SLMVs) in astrocytes. Our main findings indicate that (1) exo-endocytosis in astrocytes proceeds with a time course on the millisecond time scale (τexocytosis = 0.24 ± 0.017 s; τendocytosis = 0.26 ± 0.03 s) and (2) exocytosis is controlled by local Ca2+ microdomains. We identified submicrometer cytosolic compartments delimited by endoplasmic reticulum tubuli reaching beneath the plasma membrane and containing SLMVs at which fast (time-to-peak, 50 ms) Ca2+ events occurred in precise spatial-temporal correlation with exocytic fusion events. Overall, the above characteristics of transmitter exocytosis from astrocytes support a role of this process in fast synaptic modulation. [emphasis mine]

  38. Substantia nigra osmoregulation: taurine and ATP involvement (open access):

    An extracellular nonsynaptic taurine pool of glial origin was recently reported in the substantia nigra (SN). There is previous evidence showing taurine as an inhibitory neurotransmitter in the SN, but the physiological role of this nonsynaptic pool of taurine has not been explored. By using microdialysis methods, we studied the action of local osmolarity on the nonsynaptic taurine pool in the SN of the rat. Hypoosmolar pulses (285-80 mosM) administered in the SN by the microdialysis probe increased extrasynaptic taurine in a dose-dependent way, a response that was counteracted by compensating osmolarity with choline. The opposite effect (taurine decrease) was observed when osmolarity was increased. Under basal conditions, the blockade of either the AMPA-kainate glutamate receptors with 6-cyano-7-nitroquinoxaline-2,3-dionine disodium or the purinergic receptors with pyridoxalphosphate-6-azophenyl-2′,4′-disulfonic acid modified the taurine concentration, suggesting that both receptors modulate the extrasynaptic pool of taurine. In addition, these drugs decreased the taurine response to hypoosmolar pulses, suggesting roles for glutamatergic and purinergic receptors in the taurine response to osmolarity. The participation of purinergic receptors was also supported by the fact that ATP (which, under basal conditions, increased the extrasynaptic taurine in a dose-dependent way) administered in doses saturating purinergic receptors also decreased the taurine response to hypoosmolarity. Taken together, present data suggest osmoregulation as a role of the nonsynaptic taurine pool of the SN, a function that also involves glutamate and ATP and that could influence the nigral cell vulnerability in Parkinson’s disease.

  39. Tonic activation of NMDA receptors by ambient glutamate of non-synaptic origin in the rat hippocampus (open access):

    In several neuronal types of the CNS, glutamate and GABA receptors mediate a persistent current which reflects the presence of a low concentration of transmitters in the extracellular space. Here, we further characterize the tonic current mediated by ambient glutamate in rat hippocampal slices. A tonic current of small amplitude (53.99 ± 6.48 pA at +40 mV) with the voltage dependency and the pharmacology of NMDA receptors (NMDARs) was detected in virtually all pyramidal cells of the CA1 and subiculum areas. Manipulations aiming at increasing d-serine or glycine extracellular concentrations failed to modify this current indicating that the glycine binding sites of the NMDARs mediating the tonic current were saturated. In contrast, non-transportable inhibitors of glutamate transporters increased the amplitude of this tonic current, indicating that the extracellular concentration of glutamate primarily regulates its magnitude. Neither AMPA/kainate receptors nor metabotropic glutamate receptors contributed significantly to this tonic excitation of pyramidal neurons. In the presence of glutamate transporter inhibitors, however, a significant proportion of the tonic conductance was mediated by AMPA receptors. The tonic current was unaffected when inhibiting vesicular release of transmitters from neurons but was increased upon inhibition of the enzyme converting glutamate in glutamine in glial cells. These observations indicate that ambient glutamate is mainly of glial origin. Finally, experiments with the use-dependent antagonist MK801 indicated that NMDARs mediating the tonic conductance are probably extra-synaptic NMDARs. [emphasis mine]

    The presence of extra-synaptic NMDARs implies the presence of extra-synaptic currents subject to modulation by anything capable of modifying the general extracellular environment. Since NMDA receptors are subject to modulation by a wide variety of neurohormones, as well as internally generated modulators, this implies that the dendritic tubes are non-passive cables of extreme (potential) intelligence. (A subject I’ve discussed on my blog.)
    Evidently, this intelligence gets input from astrocytes as well as other neurons.

  40. Regulation of Synaptic Transmission by Ambient Extracellular (open access via PMC):

    Many neuroscientists assume that ambient extracellular glutamate concentrations in the nervous system are biologically negligible under nonpathological conditions. This assumption is false. Hundreds of studies over several decades suggest that ambient extracellular glutamate levels in the intact mammalian brain are ~0.5 to ~5 μM. This has important implications. Glutamate receptors are desensitized by glutamate concentrations significantly lower than needed for receptor activation; 0.5 to 5 μM of glutamate is high enough to cause constitutive desensitization of most glutamate receptors. Therefore, most glutamate receptors in vivo may be constitutively desensitized, and ambient extracellular glutamate and receptor desensitization may be potent but generally unrecognized regulators of synaptic transmission. Unfortunately, the mechanisms regulating ambient extracellular glutamate and glutamate receptor desensitization remain poorly understood and understudied.

  41. Regulation of Synaptic Transmission by Ambient Extracellular (open access via PMC):

    Many neuroscientists assume that ambient extracellular glutamate concentrations in the nervous system are biologically negligible under nonpathological conditions. This assumption is false. Hundreds of studies over several decades suggest that ambient extracellular glutamate levels in the intact mammalian brain are ~0.5 to ~5 μM. This has important implications. Glutamate receptors are desensitized by glutamate concentrations significantly lower than needed for receptor activation; 0.5 to 5 μM of glutamate is high enough to cause constitutive desensitization of most glutamate receptors. Therefore, most glutamate receptors in vivo may be constitutively desensitized, and ambient extracellular glutamate and receptor desensitization may be potent but generally unrecognized regulators of synaptic transmission. Unfortunately, the mechanisms regulating ambient extracellular glutamate and glutamate receptor desensitization remain poorly understood and understudied.

  42. Glutamate Transporters Regulate Extrasynaptic NMDA Receptor Modulation of Kv2.1 Potassium Channels (open access):

    Delayed-rectifier Kv2.1 potassium channels regulate somatodendritic excitability during periods of repetitive, high-frequency activity. Recent evidence suggests that Kv2.1 channel modulation is linked to glutamatergic neurotransmission. Because NMDA-type glutamate receptors are critical regulators of synaptic plasticity, we investigated NMDA receptor modulation of Kv2.1 channels in rodent hippocampus and cortex. Bath application of NMDA potently unclustered and dephosphorylated Kv2.1 and produced a hyperpolarizing shift in voltage-dependent activation of voltage-sensitive potassium currents (IK). In contrast, driving synaptic activity in Mg2+-free media to hyperactivate synaptic NMDA receptors had no effect on Kv2.1 channels, and moderate pentylenetetrazole-induced seizure activity in adult mice did not dephosphorylate hippocampal Kv2.1 channels. Selective activation of extrasynaptic NMDA receptors unclustered and dephosphorylated Kv2.1 channels and produced a hyperpolarizing shift in neuronal IK. In addition, inhibition of glutamate uptake rapidly activated NMDA receptors and dephosphorylated Kv2.1 channels. These observations demonstrate that regulation of intrinsic neuronal activity by Kv2.1 is coupled to extrasynaptic but not synaptic NMDA receptors. These data support a novel mechanism for glutamate transporters in regulation of neuronal excitability and plasticity through extrasynaptic NMDA receptor modulation of Kv2.1 channels. [bolds mine]

    More grist for the mill of intelligence in the dendritic membrane.

  43. Potassium Channel Phosphorylation in Excitable Cells: Providing Dynamic Functional Variability to a Diverse Family of Ion Channels (open access):

    Phosphorylation of potassium channels affects their function and plays a major role in regulating cell physiology. Here, we review previous studies of potassium channel phosphorylation, focusing first on studies employing site-directed mutagenesis of recombinant channels expressed in heterologous cells. We then discuss recent mass spectrometric-based approaches to identify and quantify phosphorylation at specific sites on native and recombinant potassium channels, and newly developed mass spectrometric-based techniques that may prove beneficial to future studies of potassium channel phosphorylation, its regulation, and its mechanism of channel modulation.

  44. Potassium Channel Phosphorylation in Excitable Cells: Providing Dynamic Functional Variability to a Diverse Family of Ion Channels (open access):

    Phosphorylation of potassium channels affects their function and plays a major role in regulating cell physiology. Here, we review previous studies of potassium channel phosphorylation, focusing first on studies employing site-directed mutagenesis of recombinant channels expressed in heterologous cells. We then discuss recent mass spectrometric-based approaches to identify and quantify phosphorylation at specific sites on native and recombinant potassium channels, and newly developed mass spectrometric-based techniques that may prove beneficial to future studies of potassium channel phosphorylation, its regulation, and its mechanism of channel modulation.

  45. Dendritic Excitability and Synaptic Plasticity (open access):

    [Abstract:] Most synaptic inputs are made onto the dendritic tree. Recent work has shown that dendrites play an active role in transforming synaptic input into neuronal output and in defining the relationships between active synapses. In this review, we discuss how these dendritic properties influence the rules governing the induction of synaptic plasticity. We argue that the location of synapses in the dendritic tree, and the type of dendritic excitability associated with each synapse, play decisive roles in determining the plastic properties of that synapse. Furthermore, since the electrical properties of the dendritic tree are not static, but can be altered by neuromodulators and by synaptic activity itself, we discuss how learning rules may be dynamically shaped by tuning dendritic function. We conclude by describing how this reciprocal relationship between plasticity of dendritic excitability and synaptic plasticity has changed our view of information processing and memory storage in neuronal networks.
    [From introduction:] In recent years, it has been discovered that not only synapses are plastic, but also the dendritic tree itself. Although dendritic morphologies are typically relatively static on the time scales discussed here, their electrical properties can change in an activity-dependent manner with a time course of milliseconds up to hours and perhaps even days, which means there exist dendritic as well as synaptic learning rules. In addition, neuromodulators hold additional sway over dendritic excitability. We discuss in this review how synaptic learning rules may be dynamically shaped by the continuously ongoing tuning of dendritic function.
    […]
    Finally, we show that the activity-dependent regulation of dendritic excitability means synaptic plasticity must indirectly control dendritic computations, just like dendritic integration controls synaptic plasticity. We are thus faced with an intricate set of interdependencies: synapses transmit information via dendrites to the soma to trigger output via axonal action potentials, while dendrites help determine synaptic plasticity, and synaptic activity in turn regulates dendritic excitability. We therefore argue that there must exist an activity-dependent reciprocal loop between synaptic plasticity and dendritic excitability.

  46. Spine Neck Plasticity Controls Postsynaptic Calcium Signals through Electrical Compartmentalization (open access):

    [abstract:] Dendritic spines have been proposed to function as electrical compartments for the active processing of local synaptic signals. However, estimates of the resistance between the spine head and the parent dendrite suggest that compartmentalization is not tight enough to electrically decouple the synapse. Here we show in acute hippocampal slices that spine compartmentalization is initially very weak, but increases dramatically upon postsynaptic depolarization. Using NMDA receptors as voltage sensors, we provide evidence that spine necks not only regulate diffusional coupling between spines and dendrites, but also control local depolarization of the spine head. In spines with high-resistance necks, presynaptic activity alone was sufficient to trigger calcium influx through NMDA receptors and R-type calcium channels. We conclude that calcium influx into spines, a key trigger for synaptic plasticity, is dynamically regulated by spine neck plasticity through a process of electrical compartmentalization.
    […]
    [From the Discussion:] The interaction of multiple inputs we have only started to explore (supplemental Fig. 3, available at http://www.jneurosci.org as supplemental material), and it remains a challenge to design experiments to address the complex nonlinear effects resulting from the synchronous activation of multiple synapses ([refs]).
    In terms of ion channel types, our spine model is intentionally minimalist. Reality is likely to be both more complex and more diverse, with other types of voltage-gated channels contributing to the EPSP in many spines.

  47. Timing and Location of Synaptic Inputs Determine Modes of Subthreshold Integration in Striatal Medium Spiny Neurons (open access, I think: I got in):

    Medium spiny neurons (MSNs) are the principal cells of the striatum and perform a central role in sensorimotor processing. MSNs must integrate many excitatory inputs located across their dendrites to fire action potentials and enable striatal function. However, the dependence of synaptic responses on the temporal and spatial distribution of these inputs remains unknown. Here, we use whole-cell recordings, two-photon microscopy, and two-photon glutamate uncaging to examine subthreshold synaptic integration in MSNs from acute rat brain slices. We find that synaptic responses can summate sublinearly, linearly, or supralinearly depending on the spatiotemporal pattern of activity. Repetitive activity at single inputs leads to sublinear summation, reflecting long-lived AMPA receptor desensitization. In contrast, asynchronous activity at multiple inputs generates linear summation, with synapses on neighboring spines functioning independently. Finally, synchronous activity at multiple inputs triggers supralinear summation at depolarized potentials, reflecting activation of NMDA receptors and L-type calcium channels. Thus, the properties of subthreshold integration in MSNs are determined by the distribution of synaptic inputs and the differential activation of multiple postsynaptic conductances.

  48. Differential Excitability and Modulation of Striatal Medium Spiny Neuron Dendrites (open access):

    The loss of striatal dopamine (DA) in Parkinson’s disease (PD) models triggers a cell-type-specific reduction in the density of dendritic spines in D2 receptor-expressing striatopallidal medium spiny neurons (D2 MSNs). How the intrinsic properties of MSN dendrites, where the vast majority of DA receptors are found, contribute to this adaptation is not clear. To address this question, two-photon laser scanning microscopy (2PLSM) was performed in patch-clamped mouse MSNs identified in striatal slices by expression of green fluorescent protein (eGFP) controlled by DA receptor promoters. These studies revealed that single backpropagating action potentials (bAPs) produced more reliable elevations in cytosolic Ca2+ concentration at distal dendritic locations in D2 MSNs than at similar locations in D1 receptor-expressing striatonigral MSNs (D1 MSNs). In both cell types, the dendritic Ca2+ entry elicited by bAPs was enhanced by pharmacological blockade of Kv4, but not Kv1 K+ channels. Local application of DA depressed dendritic bAP-evoked Ca2+ transients, whereas application of ACh increased these Ca2+ transients in D2 MSNs, but not in D1 MSNs. After DA depletion, bAP-evoked Ca2+ transients were enhanced in distal dendrites and spines in D2 MSNs. Together, these results suggest that normally D2 MSN dendrites are more excitable than those of D1 MSNs and that DA depletion exaggerates this asymmetry, potentially contributing to adaptations in PD models.

    (You can tell I’m running out of steam: too lazy to do the subscripts and superscripts.)

  49. G-Protein-Coupled Receptor Modulation of Striatal CaV1.3 L-Type Ca2+ Channels Is Dependent on a Shank-Binding Domain (open access, I think, I got in):

    Voltage-gated L-type Ca2+ channels are key determinants of synaptic integration and plasticity, dendritic electrogenesis, and activity-dependent gene expression in neurons. Fulfilling these functions requires appropriate channel gating, perisynaptic targeting, and linkage to intracellular signaling cascades controlled by G-protein-coupled receptors (GPCRs). Surprisingly, little is known about how these requirements are met in neurons. The studies described here shed new light on how this is accomplished. We show that D2 dopaminergic and M1 muscarinic receptors selectively modulate a biophysically distinctive subtype of L-type Ca2+ channels (CaV1.3) in striatal medium spiny neurons. The splice variant of these channels expressed in medium spiny neurons contains cytoplasmic Src homology 3 and PDZ (postsynaptic density-95 (PSD-95)/Discs large/zona occludens-1) domains that bind the synaptic scaffolding protein Shank. Medium spiny neurons coexpressed CaV1.3-interacting Shank isoforms that colocalized with PSD-95 and CaV1.3a channels in puncta resembling spines on which glutamatergic corticostriatal synapses are formed. The modulation of CaV1.3 channels by D2 and M1 receptors was disrupted by intracellular dialysis of a peptide designed to compete for the CaV1.3 PDZ domain but not with one targeting a related PDZ domain. The modulation also was disrupted by application of peptides targeting the Shank interaction with Homer. Upstate transitions in medium spiny neurons driven by activation of glutamatergic receptors were suppressed by genetic deletion of CaV1.3 channels or by activation of D2 dopaminergic receptors. Together, these results suggest that Shank promotes the assembly of a signaling complex at corticostriatal synapses that enables key GPCRs to regulate L-type Ca2+ channels and the integration of glutamatergic synaptic events.Voltage-gated L-type Ca2+ channels are key determinants of synaptic integration and plasticity, dendritic electrogenesis, and activity-dependent gene expression in neurons. Fulfilling these functions requires appropriate channel gating, perisynaptic targeting, and linkage to intracellular signaling cascades controlled by G-protein-coupled receptors (GPCRs). Surprisingly, little is known about how these requirements are met in neurons. The studies described here shed new light on how this is accomplished. We show that D2 dopaminergic and M1 muscarinic receptors selectively modulate a biophysically distinctive subtype of L-type Ca2+ channels (CaV1.3) in striatal medium spiny neurons. The splice variant of these channels expressed in medium spiny neurons contains cytoplasmic Src homology 3 and PDZ (postsynaptic density-95 (PSD-95)/Discs large/zona occludens-1) domains that bind the synaptic scaffolding protein Shank. Medium spiny neurons coexpressed CaV1.3-interacting Shank isoforms that colocalized with PSD-95 and CaV1.3a channels in puncta resembling spines on which glutamatergic corticostriatal synapses are formed. The modulation of CaV1.3 channels by D2 and M1 receptors was disrupted by intracellular dialysis of a peptide designed to compete for the CaV1.3 PDZ domain but not with one targeting a related PDZ domain. The modulation also was disrupted by application of peptides targeting the Shank interaction with Homer. Upstate transitions in medium spiny neurons driven by activation of glutamatergic receptors were suppressed by genetic deletion of CaV1.3 channels or by activation of D2 dopaminergic receptors. Together, these results suggest that Shank promotes the assembly of a signaling complex at corticostriatal synapses that enables key GPCRs to regulate L-type Ca2+ channels and the integration of glutamatergic synaptic events.

  50. G-Protein-Coupled Receptor Modulation of Striatal CaV1.3 L-Type Ca2+ Channels Is Dependent on a Shank-Binding Domain (open access, I think, I got in):

    Voltage-gated L-type Ca2+ channels are key determinants of synaptic integration and plasticity, dendritic electrogenesis, and activity-dependent gene expression in neurons. Fulfilling these functions requires appropriate channel gating, perisynaptic targeting, and linkage to intracellular signaling cascades controlled by G-protein-coupled receptors (GPCRs). Surprisingly, little is known about how these requirements are met in neurons. The studies described here shed new light on how this is accomplished. We show that D2 dopaminergic and M1 muscarinic receptors selectively modulate a biophysically distinctive subtype of L-type Ca2+ channels (CaV1.3) in striatal medium spiny neurons. The splice variant of these channels expressed in medium spiny neurons contains cytoplasmic Src homology 3 and PDZ (postsynaptic density-95 (PSD-95)/Discs large/zona occludens-1) domains that bind the synaptic scaffolding protein Shank. Medium spiny neurons coexpressed CaV1.3-interacting Shank isoforms that colocalized with PSD-95 and CaV1.3a channels in puncta resembling spines on which glutamatergic corticostriatal synapses are formed. The modulation of CaV1.3 channels by D2 and M1 receptors was disrupted by intracellular dialysis of a peptide designed to compete for the CaV1.3 PDZ domain but not with one targeting a related PDZ domain. The modulation also was disrupted by application of peptides targeting the Shank interaction with Homer. Upstate transitions in medium spiny neurons driven by activation of glutamatergic receptors were suppressed by genetic deletion of CaV1.3 channels or by activation of D2 dopaminergic receptors. Together, these results suggest that Shank promotes the assembly of a signaling complex at corticostriatal synapses that enables key GPCRs to regulate L-type Ca2+ channels and the integration of glutamatergic synaptic events.Voltage-gated L-type Ca2+ channels are key determinants of synaptic integration and plasticity, dendritic electrogenesis, and activity-dependent gene expression in neurons. Fulfilling these functions requires appropriate channel gating, perisynaptic targeting, and linkage to intracellular signaling cascades controlled by G-protein-coupled receptors (GPCRs). Surprisingly, little is known about how these requirements are met in neurons. The studies described here shed new light on how this is accomplished. We show that D2 dopaminergic and M1 muscarinic receptors selectively modulate a biophysically distinctive subtype of L-type Ca2+ channels (CaV1.3) in striatal medium spiny neurons. The splice variant of these channels expressed in medium spiny neurons contains cytoplasmic Src homology 3 and PDZ (postsynaptic density-95 (PSD-95)/Discs large/zona occludens-1) domains that bind the synaptic scaffolding protein Shank. Medium spiny neurons coexpressed CaV1.3-interacting Shank isoforms that colocalized with PSD-95 and CaV1.3a channels in puncta resembling spines on which glutamatergic corticostriatal synapses are formed. The modulation of CaV1.3 channels by D2 and M1 receptors was disrupted by intracellular dialysis of a peptide designed to compete for the CaV1.3 PDZ domain but not with one targeting a related PDZ domain. The modulation also was disrupted by application of peptides targeting the Shank interaction with Homer. Upstate transitions in medium spiny neurons driven by activation of glutamatergic receptors were suppressed by genetic deletion of CaV1.3 channels or by activation of D2 dopaminergic receptors. Together, these results suggest that Shank promotes the assembly of a signaling complex at corticostriatal synapses that enables key GPCRs to regulate L-type Ca2+ channels and the integration of glutamatergic synaptic events.

  51. Modulation of Voltage- and Ca2+-dependent Gating of CaV1.3 L-type Calcium Channels by Alternative Splicing of a C-terminal Regulatory Domain (Open access):

    Low voltage activation of CaV1.3 L-type Ca2+ channels controls excitability in sensory cells and central neurons as well as sinoatrial node pacemaking. CaV1.3-mediated pacemaking determines neuronal vulnerability of dopaminergic striatal neurons affected in Parkinson disease. We have previously found that in CaV1.4 L-type Ca2+ channels, activation, voltage, and calcium-dependent inactivation are controlled by an intrinsic distal C-terminal modulator. Because alternative splicing in the CaV1.3 1 subunit C terminus gives rise to a long (CaV1.342) and a short form (CaV1.342A), we investigated if a C-terminal modulatory mechanism also controls CaV1.3 gating. The biophysical properties of both splice variants were compared after heterologous expression together with β3 and 21 subunits in HEK-293 cells. Activation of calcium current through CaV1.342A channels was more pronounced at negative voltages, and inactivation was faster because of enhanced calcium-dependent inactivation. By investigating several CaV1.3 channel truncations, we restricted the modulator activity to the last 116 amino acids of the C terminus. The resulting CaV1.3C116 channels showed gating properties similar to CaV1.342A that were reverted by co-expression of the corresponding C-terminal peptide C116. Fluorescence resonance energy transfer experiments confirmed an intramolecular protein interaction in the C terminus of CaV1.3 channels that also modulates calmodulin binding. These experiments revealed a novel mechanism of channel modulation enabling cells to tightly control CaV1.3 channel activity by alternative splicing. The absence of the C-terminal modulator in short splice forms facilitates CaV1.3 channel activation at lower voltages expected to favor CaV1.3 activity at threshold voltages as required for modulation of neuronal firing behavior and sinoatrial node pacemaking.

    This is particularly important given that neurons ship RNA into the dendrites for translation, and may be able to distinguish which RNA goes where.
    That’s it for me tonight. Thanks for letting me use your blog as a notepad, Sci.

  52. Modulation of Voltage- and Ca2+-dependent Gating of CaV1.3 L-type Calcium Channels by Alternative Splicing of a C-terminal Regulatory Domain (Open access):

    Low voltage activation of CaV1.3 L-type Ca2+ channels controls excitability in sensory cells and central neurons as well as sinoatrial node pacemaking. CaV1.3-mediated pacemaking determines neuronal vulnerability of dopaminergic striatal neurons affected in Parkinson disease. We have previously found that in CaV1.4 L-type Ca2+ channels, activation, voltage, and calcium-dependent inactivation are controlled by an intrinsic distal C-terminal modulator. Because alternative splicing in the CaV1.3 1 subunit C terminus gives rise to a long (CaV1.342) and a short form (CaV1.342A), we investigated if a C-terminal modulatory mechanism also controls CaV1.3 gating. The biophysical properties of both splice variants were compared after heterologous expression together with β3 and 21 subunits in HEK-293 cells. Activation of calcium current through CaV1.342A channels was more pronounced at negative voltages, and inactivation was faster because of enhanced calcium-dependent inactivation. By investigating several CaV1.3 channel truncations, we restricted the modulator activity to the last 116 amino acids of the C terminus. The resulting CaV1.3C116 channels showed gating properties similar to CaV1.342A that were reverted by co-expression of the corresponding C-terminal peptide C116. Fluorescence resonance energy transfer experiments confirmed an intramolecular protein interaction in the C terminus of CaV1.3 channels that also modulates calmodulin binding. These experiments revealed a novel mechanism of channel modulation enabling cells to tightly control CaV1.3 channel activity by alternative splicing. The absence of the C-terminal modulator in short splice forms facilitates CaV1.3 channel activation at lower voltages expected to favor CaV1.3 activity at threshold voltages as required for modulation of neuronal firing behavior and sinoatrial node pacemaking.

    This is particularly important given that neurons ship RNA into the dendrites for translation, and may be able to distinguish which RNA goes where.
    That’s it for me tonight. Thanks for letting me use your blog as a notepad, Sci.

  53. Wow there’s a lot of comments!
    Yay for drawing! My mind is thoroughly boggled! I actually just now read this cool article that is a bit to do with neurotransmission that boggled my mind before, so it’s now extra boggled. (If I just failed at html coding, google Your Brain Is a Mess, but It Knows How to Make Fixes by Carl Zimmer)

  54. The modulation also was disrupted by application of peptides targeting the Shank interaction with Homer.

  55. The whole transmitter/modulator/etc stuff IS just semantics. Molecules don’t “have the property” of being any of these things, the words are just shorthand for either their most frequently or first described effects. Biologists are terrible about operationally defining a molecule’s function and then thinking that’s what the molecule somehow “is”–a morphogen, a hormone, a neurotransmitter. This creates a false sense of novelty when we find, for example, a “morphogen” acting as an “axon guidance cue.” It’s fine when it’s jsut used to organize information, but very often it limits the way people think.
    Don’t get me started on the presumed agency of DNA and “the gene for X.”
    Anyway, lots of peer reviewers’ funerals to go before we purge ourselves of the semantics of early molbio.

  56. The whole transmitter/modulator/etc stuff IS just semantics. Molecules don’t “have the property” of being any of these things, the words are just shorthand for either their most frequently or first described effects. Biologists are terrible about operationally defining a molecule’s function and then thinking that’s what the molecule somehow “is”–a morphogen, a hormone, a neurotransmitter. This creates a false sense of novelty when we find, for example, a “morphogen” acting as an “axon guidance cue.” It’s fine when it’s jsut used to organize information, but very often it limits the way people think.
    Don’t get me started on the presumed agency of DNA and “the gene for X.”
    Anyway, lots of peer reviewers’ funerals to go before we purge ourselves of the semantics of early molbio.

  57. A very informative and excellent article. Neurons form networks through which nerve impulses travel. Each neuron receives as many as 15,000 connections from other neurons. Neurons do not touch each other; they have contact points called synapses.

  58. […] of the mesolimbic dopamine system, a system using the neurotransmitter dopamine (more basic posts about neurotransmission here, and about dopamine specifically here), and which is involved in rewarding and reinforcing […]

  59. […] then looked to see whether the smell of lady mouse pee increased the neurotransmitter dopamine in the nucleus accumbens, an area of the brain that is associated with reward-seeking.  […]

  60. […] then looked to see whether the smell of lady mouse pee increased the neurotransmitter dopamine in the nucleus accumbens, an area of the brain that is associated with reward-seeking. […]

  61. […] then looked to see whether the smell of lady mouse pee increased the neurotransmitter dopamine in the nucleus accumbens, an area of the brain that is associated with reward-seeking. […]

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