The Excitable Mitochondria | Hacker News Reader

The Excitable Mitochondria

inference-review.com

112 pointsmrkgnao20 comments

When Hewitt started wrapping up his musings near the end I got one of those moments of clarity.

I love the fairy wasps, just an ingenious technique they employ to be so small. I wrote a paper about them and xenophyophores in my 200-level Biology class. Fairy wasps discard many of their cellular machinery to maintain their small size, xenophyophores have massive redundancy of organelles and nuclei to service their absolutely massive size for a single celled organism. I am fascinated by these techniques and I made comparisons to techniques we perform in Computer Science like compiling, parallel processing, and forking.

Now I discover from this article's sources that we mammals possess organelle movement that brings us closer to Multinucleate fungi. The description of the use of mitochondria by white blood cells was also fascinating.

Still only understand like 20% of this article, but I'm damn interested.

I suppose sharing of mitochondria would explain why the number of glial cells corresponds linearly to brain volume rather than scaling with the number of neurons. When you think about it extremely long cells like neurons do have a problem with control and intra-cellular tranfer of organelles would solve a lot of problems. I'm not at all sure about other aspects of that article but it's in the nature of man to be mistaken about some things while they are correct about others.

I've also been surprised to read about genetic differences between brain cells recently that are as large as the genetic differences between immune cells and far larger than the normal sort of somatic mosaicism you get by typical errors copying that you see in other organs.

It's essential to the growth pattern of dendrites that neurons are able to recognize and avoid themselves. There's evidence that alternative splicing (the genetic differences you mentioned) arose in cadherins before even the immune system. Basically alternative splicing provides each neuron with a random key that has a ~1/30,000 chance of collision.

This gets encoded into some sort of external marker I assume?

Yup, cadherins are transmembrane proteins and the variable domains are exposed on the external surface.

Out of curiosity - do you have any suggested reading to learn more about the brain at this depth?

Mitochondria are fascinating, and it seems probably very very old too! Nick Lane (http://www.nick-lane.net/) writes a lot about the subject in;

https://www.amazon.co.uk/Power-Sex-Suicide-Mitochondria-mean...

https://www.amazon.co.uk/Vital-Question-Why-life-way/dp/1781...

The introduction is rather lengthy, if you're looking to skip to the part regarding mitochondria:

"The Brain is What, Exactly?" section starts a bit before halfway scroll.

Wow, if mitochondria need to be modeled in that level of detail for accurate simulations of neurons that could be problematic. Exaflops of computational power were already the estimate just for simulating the neurons/synapses of a human brain[0], and this would increase that computational requirement orders of magnitude I imagine. Still quite fascinating. [0]http://www.riken.jp/en/pr/press/2013/20130802_1/

Relax. No one simulates hardware down to separate electrons, the same thing applies here, I suppose.

We just need to find and agree on enough high-level representation and proceed with it.

P.S. that electronics CAD analogy the author used is really confusing and incorrect.

Its more the difference between a cycle accurate system simulator and a functionally accurate system simulator.

Understanding the additional input from the mitochondria however might help with building more accurate FMRI type systems.

That is a good distinction to make, but if we don't know exactly what the cycle is things get harder to figure out. Neurons hold state and we aren't sure how much yet, let alone a deterministic method of computing it. https://www.scientificamerican.com/article/new-estimate-boos...

I agree the CAD analogy doesn't work well here. I don't think any of us can say for sure whether or not a high level representation will need to account for such details. You are right that it might not, but it sounds like it is a possibility worth considering

I don't know enough about neuroscience to determine if this is a possible genius revelation or quackery or somewhere in between. Any scientists willing to comment?

I skimmed it and figured it was quackery, but I didn't dig in deep enough to find the invalidating errors.

I'm in the same position as you, but I checked one especially interesting claim near the beginning: "We know that organelles, such as mitochondria, are transferred from neuron to neuron. This presents a challenge to any doctrine based on discrete parts." This is supported by a ref to a paper on mitochondria being transferred from neurons to glia for autophagy, i.e. disposal. This makes the original sentence seem misleading to me, or at least lazy about finding a reference to similar transfers that are more functionally central. This makes me less interested in understanding the rest of the article.

I did a quick search and found this: http://physiologyonline.physiology.org/content/28/6/414

  > First, in vitro intercellular organelle transfer has been described in a highly diverse 
  > assortment of cell types, including human and rodent, differentiated and multipotent, 
  > malignant and benign, epithelial and mesenchymal, and neuronal. Thus it is safe to 
  > conclude that the capability of one cell to donate or receive an organelle from another 
  > cell is clearly widespread throughout mammalian cell types in culture.

Stressed cells being rescued from apoptosis by organelle transfer through tunneling nanotubes (TNTs):

http://www.nature.com/cdd/journal/v22/n7/full/cdd2014211a.ht...

  > Further studies demonstrated that microtubule-containing TNTs were formed by stressed cells, 
  > which had lost cytochrome c but did not enter into the execution phase of apoptosis 
  > characterized by caspase-3 activation. Moreover, mitochondria colocalized with microtubules in 
  > TNTs and transited along these structures from healthy to stressed cells.

http://www.the-scientist.com/?articles.view/articleNo/43835/...

Thanks Noseshine for your supporting links. No need for imagination, it's all very well documented. Some of the recent studies of transfer to and from healthy neurons have been weakly critiqued earlier this year, while others, for example showing that mitochondrial transfer through the formation of syncytial networks is ESSENTIAL for the survival of glioblastoma in the brain seem fairly indisputable.

Thanks so much for posting this. I've always been partial to mitochondria but that takes the cake. It's going to take me a while to digest.

Related to mitchlorians which power The Force?

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