Home > Biology, Deep Brain Stimulation, Neuroscience, Parkinson's, Rats, Science > Investigating Deep Brain Stimulation (Continued)

Investigating Deep Brain Stimulation (Continued)

So the second thing the researches wanted to test was whether the electrical  stimulation was stimulating glial cells to secrete inhibitory chemicals.  To do this they introduced channel rhodopsin (this protein activates cells wheras the halorhodopsin inhibits them) using viruses but put it under a glia-specific promoter so instead of excitatory cells expressing the protein it was the surrounding glial cells. Here are the results:

Protein was expressed in the proper cells. Activation of glial cells caused a reduction in firing rate

With all studies like this the researchers must include histological verification that the proteins they’re trying to express are, indeed, being expressed, and in the right places. Here we see a stain for GFAP (a glial-specific protein) in green and the channel rhdopsin in red. In the overlay it is clear that there is strong colocalization. In short, the protein is where it should be. It’s very important to check but fairly repetitive and uninteresting so I’ll neglect it in the next few figures.

The proteins are activating proteins so you might expect to see an increase in spiking, but… we don’t. We don’t because the cells creating those large spikes are the neurons, and the neurons were not being activated by the light. Instead the light was activating the glia which secreted chemicals that inhibited the surrounding neurons resulting in an overall decrease in firing.

This treatment had no effect on parkinson’s symptoms.

The researchers found that causing the excitatory cells in the STN to fire at normal rhythms (by supplying light pulses to transfected cells at those normal rhythms) also had no therapeutic effect.

At this point the researchers take a moment to prove that the light they’re supplying is really hitting the places they think it is.  They take small samples of brain tissue and simply shine their lasers through it, measuring the intensity at various distances. The light-activated proteins being used require a light intensity of about one mW/ square mm.

Light intensity caused by the optical fiber is high enough throughout the entire infected region.

The top graph shows that the two colors of light being used each are sufficiently intense after passing through up to 1.5 mm of tissue. Below shows what cells have been activated by the light. Neurons produce the protein c-fos when they are activated which can later be stained for. By measuring how far from the epicenter of the light application c-fos appears the researchers can determine what volume of tissue could have its light-sensitive proteins activated. It turned out that about 1 cubic millimeter of tissue received bright enough light. The viral injections that introduce the DNA for these proteins affect about one cubic millimeter, so any infected cell can be successfully activated by this light application technique.

Up next: an optogenetic interference that had therapeutic effect. Stay tuned!

  1. May 23, 2011 at 7:19 AM

    Great to see you’re blogging again! Who’s your target audience? If it’s anyone other than fellow neurobio people you’re going to have the extremely difficult job of explaining your topics while avoiding (or at least defining) jargon.

    I get off easy on jargon: it’s a lot easier to talk about rocks and lasers in non-technical terms than it is to talk about rhodopsin and glial cells and optogenetic interference.

    Good luck!

  2. May 23, 2011 at 10:11 AM

    Yeah, I’ve been meaning to write things, but it’s really hard to feel like doing something that needs to end up good when you’re already busy doing school and everything else. I realized while writing this that if I wanted it to be really accessible I’d have to define just about every other word I used or not be able to really say what I wanted to. I think my audience for this one is people in a similar position to mine, or people with a pretty good biology background to be able to follow talk about introducing a protein by introducing its respective DNA into the cells. In this class the professor emphasized going through the methods of the experiments and really making sure we understood and believed what the researchers were doing and I think that while that’s good that level of specificity doesn’t totally belong here.

  3. May 23, 2011 at 10:42 AM

    ” it’s really hard to feel like doing something that needs to end up good when you’re already busy doing school and everything else.”

    Heh, tell me about it. Writing about papers is definitely a good way to help yourself understand them! I’ve always thought that biology bloggers have the hardest job because as you said, you would have to define every other word to go completely jargon-less. Don’t underestimate the need for higher-level science blogging though. Summarizing papers is a great service to others in the field who might be interested but don’t have time to read them (and to the authors, because you draw attention to their work).

    Bottom line, think about your audience, but any writing is a good thing!

    • May 23, 2011 at 10:59 AM

      Yeah, at this point I’m happy to be writing something and I’m going to try aiming for different audiences with different posts. I think practicing writing can only be a good thing for when I really need to write something.

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