TWiN 50: Neurological sequelae after COVID-19

Summary

Podcast Summary: TWiN 50 – Neurological Sequelae after COVID-19

Podcast: This Week in Neuroscience (TWiN)
Episode Number: 50
Host: Vincent Racaniello
Date: April 29, 2024
Panelists: Jason Shepherd, Vivian Morrison, Tim Chung
Main Theme: Exploring how exposure of brain tissue to SARS-CoV-2 affects synaptic homeostasis, and implications for COVID-19 neurological symptoms.

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Episode Overview

In this milestone 50th episode, the TWiN team discusses a Nature Microbiology study examining whether exposure of the brain to SARS-CoV-2 virions disrupts synaptic balance, potentially shedding light on COVID-19’s neurological sequelae, such as “brain fog” and psychiatric changes. Using both human-derived organoids and postmortem brain slices, the panel dissects the study’s experimental approaches, findings, and their implications for understanding neuro-COVID.

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Key Discussion Points & Insights

1. Background & Importance of the Study

• COVID-19’s Brain Effects: Both acute and long COVID have been linked to neurological issues, including sensory loss, brain fog, and psychiatric changes, sparking debate over whether the effects are due to direct viral infection or indirect immune/inflammatory mechanisms.

  “It’s really this sort of long Covid symptoms that are concerning, where some people say that they get brain fog for weeks to months. There’s also sort of personality and psychiatric disorders…”
  — Jason Shepherd [05:26]

• Unresolved Questions: Is the virus infecting neurons and causing notable changes, or are brains simply collateral damage from inflammation? Human studies are challenging—often only possible post-mortem.

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2. Study Design and Technical Approaches

• Organoids as a Model: The team explains brain organoids—clusters of human neurons and glia grown in 3D from induced pluripotent stem cells (iPSCs). Useful for modeling, but with limitations: lack of full cell diversity, random “wiring” (circuitry), and absence of microglia unless specifically added.

  “These 3D cultures, these organoids, maybe have a little better circuitry…But…the circuitry is just random.”
  — Jason Shepherd [08:44]

• Questions about Neural Diversity: The team notes that these organoids are mostly excitatory neurons plus astrocytes, typically lacking inhibitory neurons and microglia, possibly affecting the results’ relevance.

  “I think this is just a straightforward organoid protocol. So I don’t think they included those. This is mostly excitatory neurons…”
  — Jason Shepherd [10:17]

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3. Infection Findings: Degree of Susceptibility and Permissivity

• Minimal Replication: The study reveals that while neural cells are “permissive”—i.e., have the machinery to allow infection—the actual amount of productive replication is extremely low. Most viral detection is likely lingering input virus, not newly produced infectious particles.

  “They measure by PCR…but they hardly find any infectivity…They say that the low amount of infection…is mostly in neurons, not in glia.”
  — Vincent Racaniello & Jason Shepherd [12:34–15:41]

• Plaque Assays Commended: Unlike many studies, this work included infectivity (plaque) assays—rare in the field and providing a higher standard of evidence.

[Notable Quote | 14:46]

“The problem is you can add virus and then it doesn’t replicate, but you’re just measuring the input virus... So that tells me it’s not even clear that it’s making any infectivity.”
— Vincent Racaniello

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4. Synaptic Alterations: Key Experimental Results

A. Proteomics on Organoids:

• Main Finding: Upon (minimal) infection, most altered proteins were synaptic, especially components of the presynaptic terminal (notably the protein Bassoon).

  “Most of the proteins that they see that are altered and increased are synaptic proteins…most on that presynaptic side.”
  — Jason Shepherd [16:08]

• Morphological Change: Presynaptic terminals became enlarged and oddly elongated—a phenotype not typically observed, raising mechanistic questions.

  “There’s an enlargement of the synapse, this presynaptic terminal…not only bigger but…longer…really a phenotype I’ve not really ever seen before.”
  — Jason Shepherd [18:27]

B. Human Postmortem Brain Slices:

• Replication of Phenotype: Postmortem slices cultured ex vivo (sometimes 12–24 hours after death) showed similar synaptic protein changes post-exposure, suggesting phenomenon is not unique to immature organoids.

  “It is interesting…they can culture these pieces of brain that they’ve taken…they show similar things…”
  — Jason Shepherd [24:46]

[Notable Quote | 18:55]

“The phenotype is so—like the picture is so different.”
— Tim Chung

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5. Diving into Mechanisms: The Role of Latrophilin/FLRT3

• Upregulated Proteins: Latrophilin, a GPCR implicated in synapse formation, was upregulated both at protein and mRNA levels after infection/exposure.

• Functional Assays: Researchers used an agonist peptide for latrophilin, finding it increased cyclic AMP and could partially revert the synaptic enlargement phenotype—though panelists debate if the peptide’s effect is strictly agonistic.

  “They found that SARS CoV2 significantly increased this statue…induced cyclic AMP levels, even in UV-inactivated samples…”
  — Jason Shepherd [31:10] “Sometimes you can…max out a receptor so that it can’t…the value…is that it can be turned on and turned off…if you have this agonist…can actually prevent that cycling…”
  — Vivian Morrison [29:48]

• Physical Proximity: Using protein proximity labeling, virions—alive or UV-inactivated—were found to colocalize at synapses, particularly with latrophilin and FLRT3, suggesting viral particles may “clog up” these protein interactions.

[Notable Quote | 42:07]

“Even those [UV-inactivated virions] accumulate at these synaptic compartments…They conclude that they think that the virion somehow interacts specifically with latrophylin 3 and…alters the signaling…”
— Jason Shepherd

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6. Functional Consequences & Electrophysiological Data

• Electrode Recordings: Organisms infected/exposed to SARS-CoV-2 showed altered local field potentials (LFPs). But the limitations of population-level (rather than single-cell) recordings in random neural circuits make interpretations difficult.

  “I would like to have seen much better resolution where you’re actually looking at specific synapses like patch clamp electrophysiology…This is just a population response.”
  — Jason Shepherd [33:01]

• Peptide’s Protective Effect: Again, the latrophilin agonist peptide reduced the observed synaptic pathology and electrical aberrations.

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7. Additional Findings: Immune and Glial Modulation

• Microglia Absence as a Caveat: Classic organoids lack microglia. When monocytes (blood-derived immune cells) were added to cultures, the abnormal synaptic increase was dampened—suggesting that in vivo, microglia may prune abnormal synapses after infection.

  “When you add in the infiltrating monocyte, then it can do its job and get rid of the kind of surplus presynaptic terminals.”
  — Tim Chung [50:32]

• Context in Disease: The discussion notes that excessive synapse pruning by microglia is a known component of neurodegenerative disease.

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8. Interpretation & Caveats

• Little Infectious Virus in Neurons: The panel repeatedly highlights the very low level of neuronal infection and particle production.

  “These neuronal cultures are really poorly susceptible and permissive. Very little virus. So it’s not like polio where the virus replicates like gangbusters…It’s far more subtle.”
  — Vincent Racaniello [58:17]

• Debate over Pathogenesis: The virus’ low presence in the brain casts doubt on the idea that direct infection drives neuro-COVID; inflammation or circulating cytokines may be more relevant.

  “Your neuro Covid symptoms…are independent of how much…virus…may or may not be…in your brain. And it’s also not correlated with…peripheral inflammation that you had.”
  — Vivian Morrison [58:55]

• Experimental Limitations:

  • Organoids are more like immature brains, missing blood vessels and microglia.
  • Human postmortem brain slices may not fully recapitulate in vivo context—especially after death, with prior medical treatments (e.g., steroids, which dampen inflammation), and possible loss of cytokines.

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Notable Quotes & Memorable Moments

• On Study Ambiguity:

  “So you could potentially just achieve the same outcome by just…treating the cells with the viral proteins…Take us out of BSL3 and just do it in your lab where you can just throw proteins on there.”
  — Vivian Morrison [14:56]

• On Instrument-Themed Synaptic Proteins:

  “There’s bassoon and there’s piccolo…What about oboe?”
  — Vivian Morrison [17:54]
  “I think it’s just woodwind.”
  — Tim Chung

• On Clinical Relevance:

  “I see this paper as…a small piece in the puzzle…It may not…have eventual clinical utility or…it’s just going to help us learn something…”
  — Vivian Morrison [59:13]

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Timestamps for Important Segments

| Segment | Topic | Timestamp (MM:SS) | |---------|--------------------------|-----------------| | Episode opening, eclipse banter | 00:00–03:29 | | Introduction to main paper & controversy over neuro-COVID | 03:33–06:47 | | Organoid model and technical discussion | 07:08–11:20 | | Discussion of infectivity findings | 12:23–15:41 | | Proteomic and synaptic changes in organoids | 15:59–18:55 | | Human postmortem slice experiments | 21:17–24:46 | | Latrophilin/FLRT3 and mechanistic assays | 27:41–32:22 | | Electrophysiology and activity findings | 32:30–36:31 | | Pathophysiological implications and microglial role | 48:55–52:23| | Inflammation vs. direct infection, limitations | 55:16–57:51 | | Take-home conclusions | 58:17–61:24 |

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Conclusion & Take-Home Messages

• There is little productive infection of human neurons by SARS-CoV-2, contrasting with classic neurotropic viruses (e.g., polio).
• Viral exposure still alters synaptic proteins and morphology, potentially via physical interactions between viral particles (even inactivated) and specific synaptic adhesion molecules like latrophilin/FLRT3.
• Inflammatory (indirect) mechanisms remain likely culprits for neuro-COVID symptoms. Direct viral effects on synapses, while possible, may not be sufficient to explain the clinical picture—especially given the low viral load and observation of symptoms in the absence of clear infection.
• The results highlight important questions for future study, particularly around indirect effects, glial responses, and real-world human pathology.

“It dispels the notion that there’s gangbusters replication in the brain, which is...”
— Vincent Racaniello [58:49]

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Panelist Acknowledgements

• Jason Shepherd (@JasonSynaptic, University of Utah)
• Vivian Morrison (Tulane University)
• Tim Chung (NYU)
• Host: Vincent Racaniello (@profvrr, MicrobeTV)

Show notes and past episodes: microbe.tv/twin
Contact: [e-mail]

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This summary provides a comprehensive look at the key arguments, findings, and debates from TWiN 50, offering a nuanced understanding for listeners and non-listeners alike.

Transcript

[A]

From Microbe TV, this is Twin this Week in Neuroscience, episode number 50, recorded on April 8, 2024. I'm Vincent Racinello, and you're listening to the podcast about the nervous system. Joining me today from Salt Lake City, Jason Shepherd.

[B]

Hey, Vincent. Good to see everyone. Welcome back, Vivian.

[C]

Thank you so much. Good to see you.

[A]

From New Orleans, Vivian Morrison.

[C]

Hey, everybody.

[A]

And from New York, NYU Tim Chung.

[D]

Hello. Hi, everyone. It's great to be here. Very nice and sunny day.

[A]

I hear the sun's going to go out in a bit.

[D]

Not for long. Not for long.

[B]

Yeah. How's the weather in New York?

[D]

It's a little bit cloudy. It's getting. It was, like, really nice and clear this morning, and then it got increasingly more and more cloudy, so I don't know whether we'd get any. So for the listener, today is when the eclipse is going to occur. But hopefully we get something here.

[C]

So many children's eyes will be protected by those clouds. They're like, don't look at the sun.

[A]

Jason, are you going to go outside and look at it?

[B]

Well, here in Salt Lake, it's only like 50%, so. Yeah. What a neat. I did see and photograph the last one in 2017. That was epic. Yeah.

[D]

You sent the picture. It was amazing.

[B]

Yeah. No, it was. I should have done my. I mean, the thing with this one is that because of where ghosts are in America, you had to have bought, like, flights if you wanted to get there early because flights were just insane. So sadly.

[D]

And you're considering driving. Well, I guess that was even more insane.

[C]

How long would it have been for you to get somewhere? Where to drive to get somewhere?

[B]

Like 20 hours.

[A]

Oh.

[C]

Because I was going to say, I think in Baton Rouge, which is an hour away from where I am, there's a. I don't know if it's perfect, but it's pretty close.

[B]

Yeah. Yeah. I think the south to Texas, although it looks like bummer for Texas, it's cloudy for most of the state, so.

[D]

They have to like what they did for the last eclipse and hire a plane and go above the clouds.

[B]

Yes. That's what I should have done with.

[C]

All of your extra cash from your extremely lucid academic job.

[B]

I think a couple of commercial airlines did have special flights that you could be a part of where they would just fly along that route.

[D]

Oh.

[C]

Oh, cool.

[D]

Yeah. A thousand planes just hovering.

[A]

Tim, what's the timing in New York City? Do you know?

[D]

I think it's about three plus, maybe three plus or minus one hour. Don't quote me on this, I didn't look too careful.

[A]

Plus or minus an hour. Wow.

[D]

Because I didn't check. I think it's around three. So once this is done, I'm going to check a bit.

[B]

I think the peak. The peak is at. In about an hour or so.

[D]

It would depend on where you are. Right. Like.

[B]

Yeah, in New York, I think.

[D]

Oh, okay. Really? I'll have to go check.

[B]

In which case an hour and a half. Yeah, I think here.

[D]

Yeah. Anyway.

[A]

What about Salt Lake, Jason? When is it starting? In about less than an hour.

[B]

Yeah, I think it started now, and then it peaks in about an hour.

[A]

Okay. All right, well, we'll do. Today we have a paper that combines viruses and the central nervous system, and I'm not doing it. It's actually Jason, he brought it to.

[C]

The table for you.

[B]

I did, yeah. Well, it caught my attention because it talks about SARS CoV2, which of course is the virus that causes Covid, and the title is Brain Exposure to SARS CoV2 Virions Perturbed Synaptic Homeostasis. Now, I'm interested in synapses. So that caught my attention, and I think there's been some interesting papers that have suggested that SARS CoV2 can infect cells in the brain. But there's some controversy of trying to disentangle cause and effect here, and that's very difficult to do in humans because, of course, you have to rely on mostly autopsy kind of studies. So this study, I think, will bring up some interesting points and observations, but also, I think, quite interesting in terms of the approaches they used. So this is from a French group in Montpelier. The first author is Emma Poitier. I don't know how to pronounce these. The last author is Rafael Gauden, and this was published in Nature Microbiology, and really what they wanted to set out to do. So like I mentioned, there was this controversy of, do SARS CoV2 viruses, virions, actually infect cells in the brain? Is there enough infection, enough replication happening that there could be causative effects? We know that both acute and chronic forms of COVID result in neurological deficits. And the classic one initially was that people would lose their sense of smell and taste. And that was before the vaccines came along. But even vaccinated folks. Now, there are some symptoms that are associated with getting Covid, and it's really this sort of long Covid symptoms that are concerning where some people say that they get brain fog for weeks to months. There's also Sort of personality and psychiatric disorders. There's an increase in the prevalence after getting Covid. So, you know, this is, I think, a big issue to tackle in terms of so many people have had Covid. Is there really effects on the brain that are sort of direct from the virus or are they indirect? Because you just have an inflammatory response and your immune system gets activated. So, you know, I think there's obviously a lot to figure out here, but important topic.

[A]

So I want to point out that early in the pandemic here on twin, we had an episode with. Forgot his name, but he worked on olfactory epithelium and probably Bob Dassa.

[B]

Bob Dada. Yeah.

[A]

Right. He was saying that the sustentacular cells that are infected, not actually the neuronal cells.

[D]

Yeah.

[B]

Okay. So in this paper, they delve into this, and they use a combination of techniques. And the first technique they use is something called an organoid, which I think we've discussed before. But essentially, you can isolate cells from a human, and usually these are blood cells or fibroblasts from skin, and then you give them a cocktail of goodies, usually some transcription factors that can convert those cells into stem cells, those stem cells. Then you can direct them to turn into different cell types, even neurons. We Talked about these IPSCs, these induced pluripotent stem cells. They've revolutionized a fair that you can now pretty easily study human cells and even neurons. Then the next step of using these stem cells is that you can put them in a dish where you can encourage them to form what's called an organoid, where in the case of neurons, they can start to connect to each other. It's a 3D culture, as in you've got layers versus a 2D culture, which is basically putting cells on a dish. The idea is that these 3D cultures, these organoids maybe have a little better circuitry. They connect to each other that you can start to see neuronal activity. But the big caveat here, of course, is that you're just still plating cells together. They don't have all the cell types of the actual brain. And that circuitry is just random. It's not directed. So there's going to be a lot of caveats of what they see.

[D]

Jason.

[B]

But it's human cells.

[D]

Jason, I got a question. Do you know whether in 3D organoids, culture. Well, I don't know whether you call it culture or not. Growing 3D organoids, do they have both excited. I'm guessing they have excitatory neurons. But do they Also have inhibitory neurons. And if not, does it have epileptic seizure, similar type of activities?

[B]

Yeah. So there are types of organoids that do include inhibitory cells, but that's a good question. I don't think I ever picked up on this. The technique they use, whether they.

[D]

I don't think they're labeled for excitatory versus inhibitory for this.

[B]

No, they just don't.

[C]

I bet you that that heterogeneity doesn't exist in the natural prep, you know, because they come. Those types of cells come from different progenitors. Right. They have different transcriptional profiles. So I bet you'd have to have like neighboring cultures.

[B]

Exactly. So I think, and I think this is just a straightforward organoid protocol. So I don't think they included those. This is mostly excitatory neurons that they're looking at. They do show that this organoid also includes astrocytes. Those are the glia cells that are supportive. They don't initially include microglia. And they'll talk about that.

[D]

Because that's from a very different progenitor cell. Yeah.

[B]

So you have to add those separately, exogenously.

[D]

So.

[B]

So they grow these organoids and you know, they grow them for a couple of months. It takes a couple of months for them to get form this sort of blob of tissue.

[C]

Why are you laughing, Vincent?

[A]

You spend a couple of months growing them and then they get contaminated and.

[D]

You have to start. They put in a lot of anti. Anti. Antimicrobial and antibacterial.

[C]

Yeah. Which is not good for cells either.

[A]

But you know, and they're so expensive. I mean, the medium's expensive, right.

[B]

And yeah, this is not a cheap exercise for sure.

[C]

Yeah, it was an investment.

[B]

Then they infect these organoids with SARS COV2 and then did a bunch of experiments from looking at both gene expression changes, protein expression changes. They do see low levels of infection. And so the abstract is interesting where they say, let's see, we find that neural cells are permissive to SARS CoV2 to a low extent. Now I'm like, permissive to me means then they can get infected. But then they add a qualifier below extinctinum. So I'm like, what does that mean?

[C]

It should be either you are or you aren't, kind of. It's like you either let it happen or you don't let it happen.

[B]

At that point when I. They could see some infectivity, but not a ton, I'd have gone, oh, okay, well, we'll move on.

[D]

Vincent is the right Word here susceptible instead of permissive.

[A]

So susceptible means you have a receptor and permissive means the internal environment supports viral replication. So if you want to make infectious particles, you have to be susceptible and permissive. So, I mean, they, you know, they measure by pcr, but they also say they don't. They hardly find any infectivity. They actually do infectivity plaque assays, which is what very few people do in these kinds of experiments. So I'm very impressed by that.

[D]

Yeah. Is it possible for the virus to get in and then make viral protein? Like they show, like they did some staining and they saw some viral protein, but at the same time it's not infectious still, like, doesn't get released. Is that a word for. I'm guessing that's not a word for that.

[A]

I mean, permissivity means you make infectious virus, you go through the whole cycle.

[B]

They just say propagation is pretty low. Permissive environment that can make the virus, but propagation in the organoid itself seems low.

[A]

They say that, you know, they make very little virus. I didn't look at this extended data figure 1e. Did anybody look at that? The question is, is there a time zero? And if there's not, you can't conclude anything. And does the titer go up more than a half a log? Because if it's a half a log, it's just random. It's got to be at least tenfold. So that's, that's. I didn't have access to the extended data. Does anyone have it?

[B]

Yeah, so they, they do have a time zero.

[A]

Good.

[B]

And they look at four days after and ten days after infection. And let's see, there's a log scale, but that goes from like 50 to 100.

[A]

So how much does the virus go up?

[B]

The difference between 50 to 100.

[A]

Yeah, that's, that's twofold difference. Right. So the problem is you can you add virus and then it doesn't replicate, but you're just measuring the input virus, Right?

[D]

Yeah.

[A]

And that can go up slightly experimental error or whatever. So that tells me it's not even clear that it's making any infectivity.

[B]

Right.

[C]

So you could potentially just achieve the same outcome by just injecting, by just treating the cells with the viral proteins. Right.

[A]

The same outcome in what sense?

[C]

Like they're putting the virus in there. But if it's not replicating and nothing is changing in terms of the presence of the viral proteins, then take us out of BSL3 or whatever and just do it in your lab where you can Just throw proteins on there.

[D]

They do talk about it later on where they irradiated the virus and repeated some of the experiments. So they killed the virus and see what would happen.

[C]

What did they find?

[D]

We'll find out when it comes to that.

[C]

Okay, sorry.

[B]

Just to finish this sort of characterization here. So they say, in agreement with observation, there's almost no infectious particles for detecting supernatant that you can collect from the organoids.

[C]

It's pretty telling.

[B]

As we said, the virus propagation isn't low. There was no significant cytotoxicity or apoptosis, so the cells weren't dying. So that's something else to keep in mind. They also saw no growth defects. And they also saw. They say that the low amount of infection that they do see is mostly in neurons, not in glia. The model here then says they can get some low amounts of virus replication and neurons, but it's not super toxic. The cells aren't immediately dying. Then they looked at what I thought was interesting. A lot of these newer papers will jump straight to RNA sequencing where they look at gene expression and transcription. Here they actually went straight to the proteomic profiling, which I like. They now actually looking to see what proteins are altered with infectivity. The conclusion here was that most of the proteins that they see that are altered and increased are synaptic proteins. They concentrate on as reminder. Synapses have two sides. The presynaptic terminal, we have neurotransmitter release and the postsynaptic terminal where most of the receptors are. What they noticed was that most of the synaptic proteins that were increased were on that presynaptic side where you get neurotransmitter release. They then went to look at whether there was any functional or morphological changes in synapses. And they use this protein called bassoon. There's a couple of interesting. So there's bassoon and there's piccolo.

[C]

I was like, what about oboe?

[D]

I think that's an oboe as well.

[B]

Yeah. I would have loved to see the whole orchestra. Wouldn't that be great?

[D]

But I think it's just woodwind. And I'm wondering, like, they do some staining of this oboe protein, like in the organoids, and it does look like long strand, like long sticks. You mean kind of like an oboe, like. So maybe that's why they call it like all these woodwind.

[B]

Yeah. Generally, I would say they don't really look like the instruments that they're supposed to.

[D]

Oh, it's only after SARS. COV 2. Okay.

[B]

Okay, yeah. So normally they're just puncta, they're sort of roundish. So anyway, so that's Tim got to the punchline there. So what they noticed was that there's an enlargement of the synapse, this presynaptic terminal. And for some sort of weird reason, they're not only bigger, but they also longer. So they have this weird shape that's really a phenotype I've not really ever seen before.

[D]

The phenotype is so like the picture is so different.

[A]

So not ever seen in Covid or ever, ever really.

[B]

So I don't know what to make of that.

[C]

What is bassoon? Like, what is it? Where would we expect it to be? Like, what is role. Is it playing in the synapse?

[B]

So it's a very big protein, it's 420 kilodaltons and it's mostly thought to be like a scaffold for a bunch of other proteins. So it sits there at the synapse and a whole bunch of other proteins interact with it, dock with it. And without that machinery there at the presynaptic terminal, you get deficits in neurotransmitter release. And usually the size of the synapse correlates with how much neurotransmitter can get released. So it's indicative that there is something going on there. We'll get back to this. Functional. They'll do some functional experiments, but the next experiment, you know, before you go.

[A]

On, let me just comment. That would have been nice of them to try some other viruses. Right. Maybe viruses that are never known to get in the CNS and others that are known to get in and see if they do similar things.

[B]

Right, right, that's true. They don't. They didn't have any other.

[A]

Yeah, that's the only one viruses in there.

[B]

And so this, the kind of phenotype is not clear if it's specific to SARS CoV2 or would you see this with other viruses?

[D]

And also it would also be nice if they would be able to co label the bassoon, which in the infected guys it's all elongated and weird. If they can co label them with some SARS COV2 protein so that you can see if it's actually the infected cells that are showing this phenotype.

[B]

Well, they do do that next. So they look for variants and they do see, we'll go into that. But they look, they find that there are small punct of SARS cov2 that do correlate with the presynaptic terminals now, I don't know. And they kind of did some frequency distribution there with the size of the bassoon as well.

[D]

Okay, okay.

[B]

That's in figure three. They bring up the point that we talked about that organoids are immature. They're not really modeling a proper adult cortex system. This is something new. What they do here now is they actually had pieces of brain that were excised from living humans for various reasons. I don't think they did this. And of course, you couldn't get permission to just do this for this experiment. Usually there's surgical reasons why they're taking out bits and pieces of brain.

[C]

But.

[B]

What they do then is they take those pieces of cortex and they actually culture them.

[D]

Sorry, Jason, just to quickly button. These aren't surgically removed. These are postmortem brain sizes. They are postmortem, which are surprising to me because.

[C]

But still immediately post mortem.

[D]

Well, between 12 and 24 hours post mortem, like, if you check out the methods at the back.

[A]

What.

[D]

Which is interesting because that's kind of exactly what. So that's one of the advances of this paper, is that they can try to culture postmortem brain sizes. And they describe in the discussion that you have much better supply, sadly, during a pandemic of post mortem brain sizes than surgically taken out.

[B]

I was skeptical of that. So I was like, it can't be.

[D]

It is post mortem, which is weird because in slice electrophysiology, Jason, you know much better than I do. Like, we use postmortem brain slices from mice, and then we don't really normally keep them for more than one day after the experiment, but here they're growing it for, like, maybe a week at least.

[B]

Well, so actually, there are. It was one of the workhorses of hippocampal slices was that you can make these, what they call organotypic slices, and you can culture them for weeks. So. So that is. That is not then. So that is an established technique that electrophysiologists have used for a long time. But of course, there you can control when you take out the brain versus autopsy, where, if you're lucky, you're not going to get, you know, access until like, you know, 30 minutes after the.

[D]

I think this is hours, perhaps. I put me on that.

[B]

But yeah, so kind of surprising that it works. But they. They show that, yeah, they can culture these pieces of brain that they've taken. I was kind of a little annoyed with. And, you know, this is common in papers where they, they don't really go into this technique in detail. Even in the methods you have to read like another two or three papers to completely understand what, what they're doing. And then there's has this like acronym opab, which they don't even explain what that is.

[D]

I think it stands for. I have to look it up. Organotypic post mortem adult human brain slices. Yeah.

[B]

Okay, so they grow these brain slices. Well, not grow them, but they culture them. So they slice those pieces, they're in a tissue culture incubator. So then they do the same kind of experiment that they just did with the organoids. They infect different pieces with SARS COV2 and they show similar things in that this leads to viral RNA expression. And initial, yeah, they're just using pcr, but that there were close two of them. So they, you know, two of the pieces that they had got from different humans, they barely detected anything even with pcr. So again, this is really low levels of expression and yeah, kind of similar to what they're seeing with the organoids. But then they wanted to see if this synaptic phenotype was also evident in these pieces in these gonotypic slices. So they say that they couldn't look at overall protein levels of bassoon, for example, because it's so big, which is, I guess, true. They did look at MRNA and the MRNA levels weren't correlated with the infection. But they do see overall this increase in presynaptic terminals. And so then they're sort of thinking, okay, well this at least seems to replicate what they saw in organoids. So now they want to delve deeper into what's going on with this synaptic phenotype. And so what they do now is they try to figure out, are there any interesting mechanisms here? Now they're going to concentrate on a protein called latrophylin. Latrophylin is actually a post synaptic gpcr, but it's involved in the development and formation of synapses. They see that this is one of the most upregulated proteins in their organoid model. And in these organotypic slice cultures they also see an increase in MRNA for this latrifillin. It has this name actually because it's a target for some venom, and I think it's spider venom that can actually attach itself to this receptor and interferes with neurotransmission. And so they then look at whether this function, whether SARS CoV2 can affect the function of this latrial Fillin.

[C]

And.

[B]

They see that, they look at the downstream signaling of this gpcr, which is looking at cyclic amp. They do see an increase in cyclic AMP when they infect these cells. This is now in a cell culture model, not in the brain slices. Then they have this small peptide that, that had previously been shown to sort of antagonize this latrophilin downstream signaling. And when they give that to the cells that were infected with SARS CoV2, it reduces this overactivation of the receptor.

[D]

Jason? I think the peptide that they use is an agonist, actually. So it activates lactrophylin receptor. I believe on the abstract it says agonist.

[B]

It's an agonist. But it's, It's. But the consequence is that can't continue to turn over.

[C]

So it just gets like.

[D]

But it increases. Oh, sorry, Vivian.

[C]

Oh, no, I was just going to. You know more about this than me, without a doubt. So go on.

[D]

Oh, I don't know anything about. I've never heard of lactrophylin before. But it increases, I think the agonist increase cyclic AMP production, which kind of make me guess that it probably is an agonist, like probably a GS coupled gpcr. But yeah, it's just on the abstract it says it's an agonist.

[C]

Yeah, it did say it was an agonist. But sometimes you can have. What is that? You can basically max out a receptor so that it can't. The value of the receptor or part of its function is that it can be turned on and turned off and turned on and turned off, you know, successively. And so if, maybe if you have this agonist based on like, whether or not it binds and it has a really high affinity or something like that, it can actually like prevent that cycling. Right. Which could lead to a kind of antagonistic effect. Even though in terms of the pharmacokinetics and all of that.

[D]

Yeah, like a partial.

[C]

I think, yeah, reverse agonist or something like that.

[B]

Well, I think it's complicated because this, this kind of GPCR is, Is activated by a receptor. And so they talk about this, the receptor, which is FLRT3.

[C]

I don't know if that's how they say it, but if they're not, they're missing an opportunity.

[B]

And so this peptide interacts with both of those. So it. Yeah, but as, as you said, it enhances cyclic AMP induction. I guess, anyway.

[D]

Yeah, it does something.

[B]

Well, what they found was in these cells, we found that SARS CoV2 significantly increased this statue, which is what the peptide is called induced cyclic AMP levels even in UV inactivated samples. This was then they went back to the organoids and then they showed that they give this peptide to. They apply it to these and that increased cyclic AMP production and it somehow reverted the phenotype of the presynaptic enlargement in the SARS CoV2 infected cells. Then they use that as a way to conclude that the virus induced presynaptic abnormalities are dependent on this latrophilin signaling in some way. But that's where they left it. They don't really go more into how that actually why you would expect to see this enlargement of the synapse if you over activate this or under activate this receptor.

[D]

They have a little bit of speculation in the discussion but yeah, maybe we can get to it when we get to the discussion later.

[B]

Yeah, I think up until now what they've just looked at is the size of the synapse and there's only so much you can figure out from that. Then they wanted to look at neuronal activity and what they actually do here is that they kind of use. Now it's called a sort of. Now it's a common way of doing this that you have basically electrodes that are underneath the culture dish and they can sort of record the population responses of the cells in that dish. So it's sort of a quick and easy way of looking at neural activity. I would say it's not super. The, the resolution of this is not great. I would like to have seen much better resolution where you're actually looking at specific synapses like patch clamp electrophysiology where you can actually figure out exactly what's happening at synapses. This is just a population response. I presume that they did this because it's doable for non expert neuroscientists. I'm not sure there's anyone here. That's all I'll say. I would like to see more resolution there. But what they do see is that when they record that the LFPs, these population responses are altered in CoV2 infected organoids and they sort of go into some detail about what that looks like. But I would say it's not clear what those. There is alterations but I don't know what those alterations are actually showing you with this particular method.

[D]

Yeah, because like if you look at. So the difference is probably because they're literally sticking electrodes into an organoid and no one really know what it's supposed to look like.

[C]

They don't know where it's going or.

[D]

Like what it's supposed to look like.

[C]

What is it supposed to look like?

[D]

But if you stick it in, like if you stick electrodes into the board brain and measure lfp, look a few potentials. Normally people plot like on the x axis the frequency and on the Y axis the power. And think of it like, you know, like almost like an acoustic fingerprint of like someone's voice. Like if someone is really bassy, it will have a lot of power in the low frequency. If someone's very high pitched, it will be a lot of power in the high frequency. And in the brain there's like a very characteristic shape and you can look at different brainwaves. This is what brainwave is about. Like, is it in the alpha range or delta range, theta range, all those stuff. They don't really show that in the organoids. So we don't know what the brainwave in an organoid actually looks like.

[C]

I doubt it looks like anything in particular unless you give the organoid more information about how to wire itself. Oh, but I don't know if people have tried to do that.

[D]

Yeah, but it would be interesting to see because I think how the brain wave looks like might depend on like how the. Exactly how the circuitry is wired. How many like synapses does the brain jump through before it goes back to the same neuron again? That kind of stuff. And it'll be fun to see what.

[B]

Yeah, I mean, I think, you know, that's why I would have liked to see single cell resolution here because then you could look at, you could see sort of get the actual functional properties of the synapse versus this population response, which is always going to be very random in an organoid. That's randomly. The circuits themselves are random.

[D]

But. Jason, have you seen any paper where they patch clamp from an organoid?

[B]

Yeah, I actually have a colleague here who Alex, who's done this a lot in his organoids. So it's definitely doable.

[D]

And they look relatively reasonable. Like it seems similar to normal brain cells.

[B]

Yeah, I mean, you can see. Yeah.

[D]

Okay.

[B]

Reasonable.

[C]

Okay.

[B]

I think you can't tell anything about circuitry, but. But they're functional anyway, so they, they see perturbations. There's differences in the neuronal activity at a gross level in these organoids when you infect them with COVID And then I think interestingly, they do act. Add that peptide, that stashal peptide, and that seems to revert the phenotype. So they correlate the synaptic, the reduction in the Size of the abnormal synapses with this functional output.

[C]

I have a question.

[D]

Yeah.

[C]

So do they do anything to show you where the bassoon is located in the cells? Because I know that in a normal neuron, right, we know where bassoon would be. But just because we see in like this more bassoon and it's in strange shapes, can we really confidently say that there are more synapses? Because even like the changes in activity doesn't necessarily mean that there's more synapses or. And since we're not seeing anything that like fills up the neuron to show us where the spines are, maybe there's a problem with bassoon trafficking or turnover and like, did. How confident are we that there's actually a, like, change in the number of synapses? And it's not that the changes that they see electrophysiologically are caused by just kind of clumping up of stuff in the cells at random places.

[B]

That kind of characterization they did not do. And that goes to Tim's point as well, where they didn't really look at other synaptic markers per se and whether there's differences in total numbers of synapses. The postsynaptic side, they did look at P.S.

[D]

They did have one graph where they looked at post synaptic density. Protein 95, it's a post synaptic protein marker.

[B]

But I think that was just expression levels. I'm not sure. I don't.

[D]

Oh, that's true.

[B]

That's mRNA, But I think they actually looked at staining.

[C]

I guess I'm just curious because, like in the organoid situation and I. The organoid situation, they make the point that they mention that it's more like an embryon and Jason mentioned it earlier, it's more like an embryonic brain rather than a mature brain. In those very early stages of development, the systems in place for plasticity are really robust. I would expect to see big changes in things like synapse number or dendrite branching or all that stuff. But in the mature brain, like in these postmortem, this organotypic slices that they have, it's interesting to see the same changes, the same kind of protein expression changes occurring. But this is in an environment where there are a lot of signals saying, don't be too plastic. We know that in order to drive plasticity, you have to have repeated excitation of particular networks. That's what makes me think maybe we should take a step back because you can achieve the same outcome. The same changes in bassoon localization et cetera, without changing the number of spines just by kind of mucking up the neuron as a whole, like a traffic jam or something inside. I don't know that it really matters for their conclusion. Maybe it does or it doesn't. I don't know. I didn't make it halfway through the. I only made it halfway through the paper. But.

[B]

Well, I'd say this next experiment kind of gets at this a little bit and I kind of want to. I do wonder how they landed on this latch of fillin. I mean other than the fact that this latrophillon won was upregulated. I guess that was the main way they got into it. But so, so they want to know so why would this virus affect this particular signaling at synapses when you're not getting a ton of actual viral replication? So they, they hypothesize that it may be direct that there's actually the virus itself somehow interacts with the. This signaling compartment or synapses or the proteins at synapses. They do this protein proximity labeling assay to see when they add virions. Do the virions actually get into the synapse or close to the synapse? This is a technique where you can say if you do see fluorescence, there's an interaction between those two proteins spatially at least. They even use as Tim said before, they use UV inactivated variants and even those accumulate at these synaptic compartments that then they stain with letrophylin and the Flirt 3. They see a co localization of the variants at synapses and in particular the synapses that are stained with these proteins. They conclude that they think that the virion somehow interacts specifically with latrophyllin 3 and that they get trapped there or there's some physical interaction that then alters the signaling of.

[D]

Of the.

[B]

Those two, the FLIRT three and the lateral.

[D]

It's quite nice. I saw so they actually showed. So yeah, just to re some reiterate Jason's point, the, the lacto fillin and flirt three are kind of like a couple and they talk to each other. They kind of are, I guess flirt. Flirt three is the. They say it's the receptor for lactrophylin but they talk to each other and they act as cell adhesion molecules so that the. Presumably the pre synapse would talk to the post synapse and kind of couple together. And it seems like when they added the SARS CoV2 virions, even virulons, that's been like UV inactivated. When they kind of sprinkle it in, the virus or the virion kind of gets in, they keep getting associated with the Flirt 3. Like wherever the Flirt 3 goes, the Virion would go and it kind of sticks around the flirt 3. And the authors seem to propose this is like when they discuss in the discussion the virus. What the virus is doing is it's getting in the way of Flirt3 and Lactofilin3, the two cell adhesion molecule. And when that happens, the pre and post synapse, they're like, oh, they don't talk. We don't talk to each other anymore. We must make more of each. So that's why you see increase in expression of both Flirt 3 and Lectrophylin 3. And when that happens, it seems like that might correlate with the increased expression of bassoon because it's trying to find or like presynaptic markers, because a presynapse is trying to find its postsynaptic partner. And the SARS CoV2 virus kind of in the synapse is getting in the way. I think that's the assumption that they're making based on the data.

[B]

And then they sort of hypothesize that the spike protein of COV2 is somehow doing this. Although they weren't able to show a direct interaction of the spike protein with any of these protein with the synaptic proteins. But that's what they discussions.

[C]

Can I ask something that might be kind of like out of left field maybe? And it's also, it's a question for Vincent. Do we know anything about COVID or SARS CoV2 infection during pregnancy and how much like the virus can be found in the placenta or anything like that?

[A]

Your knowledge, as far as I know, there's no transplacental crossing.

[C]

Okay.

[A]

I mean, it's more lethal in pregnant people because they're typically immunosuppressed.

[C]

Right, Right. So the reason I bring this up is because I have heard of latrophilin and I think flirt, but definitely latrophylin. And I don't know if any of you guys have seen these papers, but they are two proteins that are necessary for homing of neurons from certain places, from one place to another place in the hippocampus. Latrophilin 3 expression is restricted to certain places and it's necessary for axon homing to those regions. So connectivity. I was thinking an interesting, totally off the wall idea of an experiment based off of what Tim was saying was what if you take A very early developing hippic brain organotypic slice. If you put the virion on there, if you put the spike protein on there, can you disrupt normal circuit formation of the hippocampus because you're. Or can you also drive increased expression of Latrifillin or Flirt3 and do you guys. It's kind of just off the wall but I had heard of latrophylin before and I thought that since it was associated with circuitry in the hippocampus that it would be kind of cool. Could provide a cool way to test. Some of these ideas to me is.

[A]

Inconsistent is to say that these interactions are driving neuro Covid. It doesn't. There's not a lot of virus around so I don't know how that would work. Right. If they see very few, very small numbers of particles and they actually look in some of these post mortem brain tissues and they find clusters of particles. Even people who don't have symptomatic Covid. So I just don't know if the amount of virus particles that we see is consistent with them having some kind of interrupting effect. You know, I don't know how many synapses would have to be perturbed to get some outcome.

[B]

Yeah, no, I mean that's a good point. I think, you know, to be honest though, you don't need a ton of synapses to get to have a functional effect. But I think the jury's out with this mechanism here because they don't really go into more functional experiments. This was the last real real experiment they did and they acknowledge that. And you know, I think it's, I think it's worth following up on this. But you know, even if you get. And I guess you don't really know, I think the problem here is also do the. Does the amount of virus in the brain correlate with the symptoms? If you have, if you. If it is the case that the, the variants themselves get trapped at synapses and they stay there for a while, maybe you don't need a ton of infectious virus to do that. And then over time maybe perhaps some people have more of these variants hanging out than others. But yeah, I think it's an interesting hypothesis and certainly this latrophil and signaling could be worth looking at in a more sort of functional model. And they talk about of course doing some of these experiments in mice and sort of really delving into it.

[D]

Yeah, they mentioned using the peptide that would activate lactofilin and you know, they show that it brings down the bassoon, the presynaptic expression and some of this kind of pathology in the EEG recording. So maybe that's one of the drug. But what's interesting is they actually did another experiment we didn't have time to get into. But maybe I'll quickly bring it up here in the like figure one or maybe figure two. They actually showed that in organotypic slice. Even when you add in, sprinkle in some SARS cov2 and you get drastic increase in bassoon and presynaptic terminals. If you then add, if you also add some monocytes. So these are kind of macrophages from the blood that you can extract from patients. If you add some monocytes in that access infiltrating monocytes, you can actually drastically reduce this increase in presynaptic density.

[B]

So that suggests that, and that's well known, of course, that the microglia, what they can do is they prune synapses. And especially if they're sort of in disease contexts, what's known is that they can eliminate the bad synapses. Um, but even the healthy ones, that's a major problem where you, you sort of want to maybe get rid of some bad synapses, but you don't want to get rid of all the synapses. And so there, there's also evidence for over activation of, of microglia and, and pathology, like Alzheimer's.

[D]

So. But yeah, but I was wondering. So. So the whole thing about the purpose of this is that in the brain organoids they don't have, they lack microglia. So when you add in the infiltrating monocyte, then it can do its job and get rid of the kind of surplus presynaptic terminals. It's interesting that in patients you still see increase in presynaptic terminal. Even though they presumably have monocytes flowing around. The monocytes might be busy.

[C]

Microglia in the brain, you mean in their culture or in the.

[D]

Ah, so the patients in the. When they were alive. When you say patients when they were alive, they would have monocytes in the blood. Unless they are all recruited to combat the disease in the lungs.

[C]

But I, I would be. I mean, typically, unless they had some major blood brain barrier leakage, you would not see. I don't, I mean, I don't think you would see a lot of infiltrating monocytes. You would, you might see kind of like.

[B]

But they were infecting microglia.

[C]

Yeah, that's what I was going to say.

[B]

But I think actually what's really known about Rat and mouse organotypic slices is that when you culture them, there's actually a massive increase in synaptic numbers and there's new connections made that are abnormal. And so that's actually one reason why that technique has fallen out of favor. Because if you're looking at circuit again, they sprout all these abnormal synapses. It is interesting. I actually don't know off the top of my head if there have been any experiments looking at microglia and these organotypic slices and how normal they are. Anyway, that's what I. Vivian is doing.

[D]

That right now under the micro.

[C]

I mean, yes, it's. Yes, right side as we speak. No, that's definitely like there's so many unanswered questions about microglia in the developing brain. And then, you know, Jason was saying, yeah, it's well known that microglia and also astrocytes contribute to synaptic pruning. But like it kind of ends there. Like there's not a lot known about how it happens in the developing brain. I actually wonder if maybe there's not more known about it in diseased conditions.

[B]

Yeah, I would say I think it's.

[C]

Yeah. But yeah, I think it. Yeah.

[B]

One easy hypothesis to come up with here is that when those synapses get trapped with virions, there's probably this eat me signal that gets expressed. So the microglia can selectively, one would think, perhaps remove those abnormal synapses, but they don't show that here.

[C]

I think another variable to take into account is that, you know, there's going to be. We know that the endothelium, we know that blood vessels are directly affected by SARS COV2 and I think if I have. I haven't read much on this in a long time, but they are like, I think a place where the virus can replicate pretty easily or like it gets into the cell through the like angiotensin receptor. Right.

[A]

ACE2M.

[C]

And so one thing, a couple of things. Their organoids don't have blood vessels in them. The organotypic slices do. I would expect there'd be differences between those two assays, but the brain always has blood vessels. I'm like, well, the organoid is cool and can maybe help us get to look at some of those really fine grained interactions between proteins. But at the end of the day, if we're trying to understand neuro Covid, we have to look at everything together, which is going to involve the blood vessels and the relationship between the blood vessels and the microglia. Because they will talk to each other. If you have systemic inflammation that is going to activate indirectly, the message is going to get to the microglia in their system here with the organoids, they're adding kind of like, we'll just say like naive quote unquote monocytes, which may not reflect what the microglia actually look like during infection. And the phagocytic ability and then the cytokine production ability of the microglia will probably changes as the. As the cell becomes activated.

[D]

Right.

[A]

So, you know, there's. There's very little virus in the blood during COVID So even though the virus can reproduce in endothelial cells, it's not clear that it does.

[C]

That's not the place where it happens a lot.

[A]

So these clotting issues that you see, you know, and vascular damage, you see them throughout the body and you know, in the legs is in even where there's very little virus. And so the idea is that they're inflammatory processes, you know, they're not direct results of virus. In fact, in one of the studies here in this paper, they had brains from people with COVID And they end up. They make the comment that it's not likely that virus got there through the blood for various reasons, you know. Yeah, they don't have no viremia and other things.

[C]

So it's just cytokine, the whole cytokine.

[A]

Storm thing, you know, I mean, that could even explain this. Right. The neuro Covid, they seems to discount it, although, because they say we've looked for neuroinflammation and Covid, we don't see it, but other people do. So I mean, that's the easiest explanation because the same can get in. Right.

[C]

It might also depend on where they're looking in the brain. I mean, the brain has got so many different places at so many different times at so many different. In so many different conditions. It's like. Well, you know, and different parts of the brain are vascularized differently and the endothelial cells at those regions have different properties. So different tightness of the blood, brain barrier, different potentially susceptibility to certain cytokines. So I'm like, you know, it. We're just the entire thing.

[B]

I think that's the problem. Right. Is also, of course, in if patients have respiratory or hypoxia. I mean, that we know of course has a lot of downstream effects on the brain. So it's always complicated. You have to really know what's going on. And there's probably multiple ways to get brain and cognitive damage One thing they.

[D]

Don'T talk about is if you actually go through the supplemental data because I wanted to see what's going on for the post mortem organocyclic sizes. A lot of the COVID patients got steroid treatment, corticosterone before they died because they are severe Covid. So maybe that would affect like any inflammation that might happen in the brain. So it's a complicated thing. Yeah, it's a complicated. And then you don't know like what happens to all these cytokines if you take the brain out and put it in a dish for like a week? Sure. So yeah, no, that's a good point.

[B]

I give this group of kudos to trying to really tackle this at different ways and, and looking directly in human tissue. Even with all those caveats.

[D]

I wonder if they could get induced pluripotent stem cells from patients with or without long Covid and see if they would respond differently to SARS CoV2 particles or virulons.

[C]

Yeah, that would be interesting.

[A]

So what I take from this is that these neuronal cultures are really poorly susceptible and permissive. Very little virus. So it's not like polio where the virus replicates like gangbusters and neurons and destroys them and that's why you get paralyzed. It's not like that. It's far more subtle. And I don't think, I don't think the amount of virus that we see, if you can extrapolate it, you can't really. I don't think it would be enough to cause the syndrome, but. Hard to know, right?

[B]

Yeah, yeah.

[D]

Vincent.

[A]

I think it dispels the notion that there's gangbusters replication in the brain. Which is, which is.

[C]

Yeah, I feel like that's a take home, a take home message that we've gotten a few years after, after Covid. Is that like your neuro Covid symptoms or your long Covid symptoms are independent of how much is, how much may or may not, how much of the virus may or may not be or, or have been in your brain. And it's also not correlated with your, the degree of peripheral like inflammation that you had. Like there are people who had, you know, very mild Covid respiratory symptoms but then have cognitive effects and then others that just got slammed by it had to be hospitalized but didn't have, don't have long Covid. I think it's like, I see this paper as being like it's a small piece in the puzzle. Although I always try to think about how are we going to use this down the road. It may not. I don't know if you guys see there's being any eventual clinical utility or if it's just going to help us learn something about how peripheral immunity and.

[B]

Yeah, so, you know, I think that, you know, perhaps this peptide could be used. But my worry is that that peptide is going to have a lot of non specific effects and affect all synapses. And how would you target the bad synapses? I don't know.

[D]

So yeah, I wonder if this virulon affect peripheral nervous system because there are also synapses there. But if what Vincent mentioned is not SARS. COV2 doesn't go into your bloodstream, so it probably doesn't circulate, you know, a lot. So yeah, probably isn't relevant.

[A]

I mean it's not an essential part of the pathogenesis. With any infection you're going to find something in the blood because it's inevitable, whatever. If it's replicating in your upper tract, it's going to get into the blood and just circulate. But it doesn't mean that it's going, it's bringing it anywhere else. You know, for some viruses, the viremia is an essential part of the disease. Right. Measles gets into your blood from your respiratory tract and then goes to your skin and you get the rash. So the viremia is essential for that. But I would think even with flu, you could amplify some RNA out of the blood. Doesn't mean anything. Right?

[C]

Very interesting.

[B]

Yeah, well, I think.

[D]

But like, so this virus particle seem to interact with things in the synapse and another viral linked particle, capsid, which is arc, seems to kind of do a lot of stuff at the synapse. Is that just like a general case of synapse and capsid viral chain?

[B]

This is a common theme. So rabies virus interacts with something at the synapse and we still don't know how to what that protein. Is that rabies? Because as you know, rabies preferentially infects neurons and then jumps from one neuron to another. And that mechanism is still not clear either. So viruses and hsv, I mean many of these neurotropic viruses affect synapses and some require synapses for their transmission.

[D]

I guess it makes sense because there's a lot of exocytosis, endocytosis occurring at the synapse. Yeah, but then you, I mean HIV.

[B]

Though, for example, does not infect neurons per se. So the, the most of the, the reservoir of HIV Variants are in microglia or glia.

[C]

Which Glia?

[B]

I think microglia.

[C]

Microglia. Okay. But then I was like, don't they need CD4?

[B]

Yeah. So that's why microglia. Probably because they have the right receptors.

[D]

Okay.

[C]

Yeah.

[A]

All right. Thank you, Jason. Yeah, that's twin number 50.

[B]

Yeah, 50.

[A]

And you can find the show notes at Microbe TV Twin. You can send us questions or comments to TwinMicrobe TV. And if you enjoy these kinds of programs, we'd love to have your support. You can deduct it from your taxes if you live in the us Your federal taxes. Anyway, taxes are due in not too long from now. Go to Microbe tv. Contribute for various ways. Unfortunately, you can't contribute now and get a deduction for 2023, but you could do it for next year. Anyway, it helps us. Jason shepherd is at the University of Utah. Jason, Synaptic on Twitter. Thank you, Jason.

[B]

Yep.

[A]

I still call it Twitter. You can tell that I still quoted Twitter.

[C]

I didn't even notice.

[A]

I don't like X. I think Twitter was a great name because it was what it was. People chattering, right?

[C]

Yeah.

[A]

Oh, well, Vivian Morrison's at Tulane University. Thank you, Vivian.

[C]

Thanks, guys.

[A]

And Tim Chung is at New York University. Thank you, Tim.

[D]

Thanks, everyone. Thanks, Jason. It was fun.

[A]

I'm Vincent Racinello. You can find me at microbe T tv. Been listening to this week in Neuroscience. Thanks for joining us. We'll be back next month.