Sometimes, the world gets Sci down a little. Perhaps it's being a whole YEAR old. That's very old indeed in bloggy years. Ok, it's not as old as the ancients who started back in '04. They're REALLY old. So maybe Sci is just entering blog middle age.
Be that as it may, Sci need to raise her spirits. And she's going to do it in the only way Sci CAN: with chocolate, and with one hell of an amazing paper.
First, here's your chocolate:
Chocolove's Crystallized Ginger in Dark Chocolate Bar. This is Sci's favorite chocolate. Easy to get, rich, dark, and makes you feel kind of healthy while you're eating it. After all, both dark chocolate and ginger are supposed to be good for you! But really, the dark chocolate on this is lovely and rich, and the crystallized ginger adds both the sweetness and the spice. Lovely. Sci has also been known to enjoy the dark chocolate with raspberries in it.
And now, here's your paper! I warn you, this one is technical. Explanations ahead. Possibly also drawings. Which may be very bad. We all know how much I suck at art...
We shall begin with the background. And the background is a dopamine synapse.
(Originally via NIDA, but now via me!)
Up top we have the presynaptic neuron, the bottom is the post-synaptic neuron. The blue things are receptors, and the fuschia thing is the dopamine transporter. In her normal life, Sci is more likely to focus on things like the receptors and transporters, but today I want you looking at something different. I want you looking at the clear, transparent bubble. That bubble is called a vesicle.
The vesicles are the...freight trains of the synapse. They are little bits of membrane which hold dopamine, serotonin, or other neurotransmitters. When they are stimulated by an action potential coming down the neuron, they move to the membrane and fuse with it, releasing their contents at the synapse. Like this:
You can see, as you look from left to right, the vesicle coming in and fusing with the membrane, and all the little neurotransmitters spilling out. How do the neurotransmitters get IN the vesicle in the first place, you might ask? In the membrane of each vesicle there are transporters (like dopamine transporters, only not) called "vesicular monoamine transporters" (VMAT). They come in two flavors, and transport specific kinds of neurotransmitter into the vesicle, depending on type.
So how do we know all this? To be honest, no one's ever seen it in action, VMAT taking up something, putting it in a vesicle, and fusing with the membrane to spit it back out. We know this from tons and tons of studies, looking at the kinetics of dopamine in the synapse, the rates of uptake back out, what happens when you specifically inhibit VMAT. But no one ever SAW it happen.
I'm sure some of you are aware of the coolness that is GFP. GFP is green flourescent protein, originally isolated in jellyfish. The people who discovered and isolated it actually just won the Nobel Prize in Chemistry for their discovery. GFP, which now comes in a multitude of flavors and colors, is a relatively small protein tag that makes things GLOW. Following the discovery of GFP, other, smaller proteins were discovered that, while not glowing in general, will glow when put under certain types of light. Some of these chemicals are so small that they can be attached to something like...a neurotransmitter.
And that's what the authors did. They attached a flourescent tag to a modified dopamine molecule. The VMAT protein, when it comes down to it, isn't very picky. As long as the neurotransmitter has the same basic shape in certain key places, the VMAT still takes it up. So this new compound, FFN511 (flourescent false neurotransmitter 511), acts as a fake neurotransmitter, a fake dopamine, tricking the VMAT into taking it up into vesicles so it can be released just like a real neurotransmitter.
In chemical terms, it looks like this:
The one on the far right is FFN511. You can see how it still has some shape in common with dopamine and serotonin (in particular that amine tag on the end and the ring structure), but has just enough of a difference to make it glow. And so, when they put it in to a mouse brain, they watched to see what it did.
YOU SEE THAT?! YOU SEE IT?! THAT, kids, is a VESICLE. A super tiny vesicle. In your super tiny neuron. Clear as day.
Really, doesn't this blow your mind? Sorry, that's one of the things that blows my mind. I'm better now.
FFN511 is taken up just like dopamine and serotonin, and in face with very similar affinity (at the same rate and same potency). And with a little of this in a mouse brain, the scientists were able to label every single dopamine terminal. Every single one! Not the cell bodies, the terminals!
If that first picture didn't blow your mind, I hope the terminals did. If my mind blows any more in this post, I'll be a wreck.
There it is. That's a shot of the mouse striatum and cortex. Only the dopamine terminals are labeled. It's so...lovely...
So anyway, the scientists invented glowing fake dopamine. I imagine they are getting a patent on this thing so fast it hurts. But most importantly, they've already USED It. They've used it to look at something called synaptic plasticity. I may not have talked about it much before, but it's the idea that synapses CHANGE in response to stimuli. Synapses can grow and shrink, become more or less sensitive, depending on what has happened to them, and it's thought that synaptic plasticity underlies a whole lot of how your brain learns things, from memories to the fact that cocaine feels DIVINE.
So anyway, this glowing FFN allows you to look at release as it is stimulated, watching the glow move out of the vesicles and disperse into the synapse. And they've already found some cool stuff. For instance, we know that an individual action potential, moving down a neuron, can be either really strong, or fairly weak, just strong enough to cause vesicular release. But it turns out that the strength of the signal doesn't matter. The same amount of vesicles will be released. The frequency is what matters, a series of rapid pulses will provoke more release than a single one.
And they found evidence of synaptic plasticity in the labeling of the synapses. Some synapses had vesicles with a high likelihood of release, while others had a low likelihood. Synapses with a high likelihood of vesicular release were more active than those with lower release. Use it or lose it. Not only that, the "strength" of a synapse (high or low likelihood of release) was dependent on dopamine receptors, giving more evidence to support the nice little loop that we neurotransmitter people like:
Stimulus hits receptor. Receptor responds and something happens. Something happens both in the short term, and in the long term. In the short term, the neuron might fire. In the long term, the neuron will change the receptors available, so when the next stimulus comes around, there will be either more or less receptors around waiting for it, and more or less response. Behold! Brain changes in motion.
Chocolate and a darn good paper. Sci feels better already!
Gubernator, N., Zhang, H., Staal, R., Mosharov, E., Pereira, D., Yue, M., Balsanek, V., Vadola, P., Mukherjee, B., Edwards, R., Sulzer, D., & Sames, D. (2009). Fluorescent False Neurotransmitters Visualize Dopamine Release from Individual Presynaptic Terminals Science DOI: 10.1126/science.1172278