I need to make sure whether I did correctly in the surgery. I need to implant tetrodes in the mPFC of 4 month old rats. I have a confusion about dura removal. After removing a small piece of dura, I could see the thick white layer shown in the attached file. And when I removed the white layer, I could see clearly the vessels. Here comes the problem. Sometimes, even after removing the white layer, my tetrodes still couldn't get through. I have to remove another transparent thin layer containing vessels. But sometimes, my tetrodes could get through without removing the transparent vessel layer. So I am thinking whether below the white thick layer, there are acturally two transparent layers. For tetrodes implantation, I need to remove the first transparent layer and leave the second transparent vessel layer? But in my operation, sometimes I remove both transparent layers and cause bleeding. I searched the structure of meninges, and I got to know dura consisted of two parts. So I am curious the white thick layer is only one part of dura or what? And what about the arachnoid and pia mater? I couldn't see them under microscope and I don't need to remove them for my tetrodes, right?
Hi Tianyang,
A picture says a thousand words. I didn't really get your question, but actually a really easy way to know that you haven't removed dura, is by seeing how the light shines off the tissue, if its pretty reflective, you probably haven't removed dura. In this pic I would say the dura is still on (though it is a bit out of focus).
Here is what to do, take a very fine needle (30 gauge) and slightly bend the tip of the needle so it resembles a hook of sorts. Then under the scope, poke around outside your area of interest (obviously carefully). You should be able to stick the point through the dura (and maybe a bit of cortex) and then lift the dura so it separates from the brain tissue. That is how you will know what to remove. From there you can use the ripped dura as an entry point to start cutting dura 2. Bleeding; blood vessles are every surgeons' nightmare, so you are not alone. Just try to avoid breaking it when you remove the dura, sometimes you can't avoid it. Have a syringe with saline prepared in a bucket of ice, and gently spray the area with saline until it stops bleeding (I also recommend non-toxic absorbant gelfoam). Good luck!
Hello Cullen,
Thanks for your reply! You are right, from the photo, I haven't removed the dura. I just removed the skull and expose the dura.(Sorry that I made a mistake in describing my question) And usually I remove this white thick layer with hooked needle and sometimes with microscissors. Then the vessel layer is exposed. The strange thing is not all the time my tetrodes could go through the vessel layer and I am sure the surface is clean enough. And do you know the name of the vessel layer? Because I doubt on the vessel layer, there is another thin transparent layer my tetrodes couldn't penetrate. Sometimes I removed this layer and expose the vessel layer, but sometimes this transparent layer wasn't removed and my tetrodes couldn't penetrate. And because the transparent layer is too thin, I couldn't tell whether I had already removed it without trying with tetrode implantation. I don't know whether what I doubt is correct.
And I also don't know after tetrode implantion through the vessel layer, whether my tetrodes could still get good signals. Because I could see under microscope there is a slight pressure for the tetrode tips.
Dear Tianyang,
You are probably talking about piamater, that includes the surface blood vessels. See my brain membranes and blood brain barrier paper from 2010 for definitions. Piamater is below the duramater and it is not easy to remove and you should not try to remove it, as it will cause far more bleeding and broosing, and local necrosis. I used to use a hand operated electro-coagulator (battery operated size of a mini torch) and I used to gentle make a tiny hole with the tip of the coagulator without any bleeding. If there is bleeding, you can also use surgicel.
best wishes,
Refik
Dear Refik,
Thanks for helping me. I read the paper you mentioned to me. I agree the vessel layer should be the piamater. But where is the arachnoid layer? And also I read dura consists of two layers, the second layer also contains vessel. But I have never seen the vessels in the dura. I think my main problem is I don't know which one I damaged is the arachnoid layer and whether I could see it under microscope. And I am sure my electrodes could go through the piamater, but I don't know whether they could also go through the arachnoid layer.
Dear Tianyang,
You cant really see the arachnoid with naked eye, it is just an epitelial layer and you can really separate it from the piamater. Arachnoid will not stop or resist your electrode going through. I think the blood vessels in duramater are just very small capillaries feeding the membrane and again probably not easy to see their network. Once you remove the duramater, as long as you avoid vessels on the surface, your tetrodes should go straight through.
best wishes,
Refik
Dear Refik,
So under microscope, I could separate the arachnoid from the piamater, is that true? How do you do this? I am just curious. I think my electrodes could pass into both layers.
And the arachnoid layer is closer to dura or piamater? Because I read at some point the dura and arachnoid layer fuse together. I am thinking when I remove the dura, whether I also remove part of arachnoid layer.
Also, another naive question is that CSF only exsits between arachnoid layer and pia mater? Everytime when I use needle to break dura, I could see CSF coming out. I don't know whether that means I also break the arachnoid layer.
Thanks!
Dear Tianyang,
I dont think you can see arachnoid with stereo microscope. You can only see this epithelial layer in thin sections of tissue with high magnification. Yes most likely you are removing it with your duramater, especially if you notice CSF is leaking out. CSF is not just arachnoid and pia, it fills all the ventricles of the brain and central canal of the spinal cord. It basically bathes the entire brain.
best wishes,
refik
Tianyang, if possible it is also good to see a surgery in person with someone who is experienced with this. Training someone through text is very difficult. Maybe there is someone in your department or at another institution in Germany with experience doing this. You might want to reach out to someone nearby and ask if you can observe a couple surgeries. It doesn't have to be a mPFC surgery necessarily, just someone using rats with lots of experience. That is usually the best way to feel confident. Just a suggestion.
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