Brain Science Podcast discussion

2013 > BSP 101: Synapse Evolution with Seth Grant

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message 1: by Virginia (new)

Virginia MD (gingercampbell) | 321 comments Mod
BSP 101 is an interview with Seth Grant. We first talked back BSP 51, but in this episode we catch up with Grant's latest research. His work focuses on the evolution of the synapse. He has discovered that while many of the proteins present in the synapse (such as dopamine) have been present since appearance of single celled life forms, the synapses of vertebrates are much more complex than those of invertebrates.

Not only does this challenge the longstanding assumptions that all synapses are more or less the same, it raises the strong possibility that the complex synapse preceded the evolution of complex (big) brains. In BSP 101 we discuss research that demonstrates how changing a single protein can change cognitive function in measurable ways.

Show notes and episode transcript

Listen to BSP 101

message 2: by A (new)

A | 6 comments As usual, this was a fabulous episode. It was interesting, entertaining, and inspiring.

I have been thinking a lot recently about whether or not I should change my degree type to a BA from a BSc, but this episode reminded me why I want to keep science in my studies. There's a whole context to that story that you're missing out on, but I gather no one wants to hear that much about it. Ha! Anyway, I love fundamental science and I love to hear about people doing that kind of research.

Oh, I do have one question: it was pointed out that to say vertebrate synapses are "more complex" is to say that they are made up of a larger variety of proteins. What, specifically, is meant by saying that vertebrate behaviour is more complex?

message 3: by John (new)

John Brown | 52 comments I agree about the episode and the excitement of finding all these new proteins. As regards non-vertebrates, I think in terms of molluscs on the one hand, which are so slow and badly directed that we can ignore them (but what about squid?), and insects and other arthropods on the other.
I remember seeing a colony of leaf-cutter ants where one ant returning to the nest dropped his leaf, but carried on, and then presented the "leaf" to several nest-workers who all decided it was not for them. I got bored after 15 minutes, but she carried on waiting, I guess till the lights went down.

Vertebrates also routinely recognize hundreds of others of their own species, and the scrub jay remembers hundreds of hiding places for his food. Clearly my ant lacked the equipment to do any of these complicated things, since he did not even realize that he had dropped the leaf.

At one point the speaker said that it was possible that every synapse might have a protein unique to itself. The mind boggles a bit at that, with some 10**15 or more synapses in the brain.

I deeply regret that I have no feeling at all for biochemistry and whilst I find the 3 inch thick books in the library very tempting, I think life is too short to allow me to read them. My doctor has recommended that I leave the subject alone.

It was not too long ago that specialists thought that large parts of our DNA were "junk", but they are now changing their minds.
I wonder if the converse is true of the proteins in the synapse, and that these are just junk from chance mutations, waiting for other proteins to mutate and combine with them to form new structure. I think about all the different cells in the eye, particularly the retina, and it seems unlikely that new proteins could have formed one-by-one in a sequential manner. Frequent mutation looking for combination, seems more likely.

message 4: by Virginia (new)

Virginia MD (gingercampbell) | 321 comments Mod
I think John did a great job of addressing A's questions. I liked the analogy Dr. Grant made when he compared the proteins in the invertebrate and vertebrate synapse to having a bigger set of LEGOS. The extra proteins are the building blocks that have allowed the synapse to become more complex.

I suppose that one could have endless debates about what constitutes "more complex behavior" but I like the examples John cited, as well as his observation that scientists are discovering that what was once considered "junk DNA" is actually very important.

Another thing that Grant's work brings home is the fact that understanding the human brain is what Olaf Sporns has called a multi-scalar problem because the complex proteins of the synapse are just one level of what has been called "the most complex system known to man." In up coming months we will be exploring other levels of the problem.

message 5: by John (new)

John Brown | 52 comments Thanks, Ginger.
I just remembered reading somewhere about the evolution of the flagellum, which appears to resemble an electric motor. Of course wheels on bearings have always been said to be impossible to evolve. I am not sure why, but I expect it is because you can no longer build a blood supply to the rotor inside the "bearing".

But the flagellum is part of a uni-cellular organism, so nutrients can simply diffuse across the junction around the rotor. You could not use that method with an animal that required high energy output.
There seems to be some similarity here with the synapse. Since it is low-power, diffusion is sufficient to carry neurotransmitters across the synapse. But even then, recovery time after saturation is quite long, and neurone replication appears to have evolved as a solution to that.

I have been reading a few fairly recent papers on the retina. Apparently there are special-purpose glial cells that act as fibre-optic transmitters of light through the neural layer onto each cone. That rather negates the claim that cephalopods have a better eye than vertebrates. It probably also explains why people with retinal damage suffer no loss of vision, until the condition is well advanced.

I do look forward to upcoming podcasts on the "multi-scalar problem". I started off just being interested in neural circuits and their analogs in computer programs, but your early episode on the synapse gave me a more biochemical viewpoint.

It would be great to hear a speaker on recent discoveries in the eye, which writers do treat as part of the brain. Microsaccades interest me a lot, in view of my background in Control Engineering.

message 6: by Dalton (new)

Dalton Seymour | 20 comments When it comes to synaptic complexity, I have difficulty with the notion that they are more complex. When you get right down to it, all the brain needs to function is inhibitory and excitory synapses (NPN/PNP - like transistors), they all do the same thing. And, when it comes to all the different types of neurons, they all do the same thing too. Variations on the themes imply adaptations to special purpose and it is my suspicion that those variations are Mother Nature's way of ensuring architectural integrity - who gets to mate with who and how many suitors can be accommodated by a target neuron. It's a way of sorting and isolating the constituents of a structure, a means of implementing predispositions and specializations during development.

message 7: by A (new)

A | 6 comments Dalton wrote: "When it comes to synaptic complexity, I have difficulty with the notion that they are more complex. When you get right down to it, all the brain needs to function is inhibitory and excitory synapse..."

I think if there really is a greater amount of proteins, then it's probably appropriate to use the word complex; if you think about the math, there are just more (non-linearly) possible pathways for reactions to take or more opportunities for the same reactions to take place. That said, if the origin of all bodily behaviours is in the on-versus-off of neurons, then seeminly subtle changes may well have dramatic effects (even if everything is essentially doing the same thing).

Your perspective reminds me of chemistry and physics (a.k.a. the roots of biology). Fundamentally, reactions that occur are going to follow a path of least resistance in any given situation. So, your description of a more elegant organization makes sense to me from that perspective. Elegance is the name of the game because it is (net) energy-conserving. There are different levels of description, though; you could use that description or a biological one which describes the behaviours of the organism that are the inevitable result of those changes in the chemical/molecular environment. I guess what I'm trying to point out is that, for example, both descriptions could be right at the same time and would both do just as well with explaining the "reason" why the change persisted. The architectural integrity matters if the organism is to survive and resproduce and the organism's behaviour matters if the organism is to survive and reproduce.

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