Psychedelics & Cerebral Cortex: Neuroplasticity, Psilocybin, Ketamine | Alex Kwan | 226

Short Summary: Dr. Alex Kwan unpacks the latest neuroscience research on how psychedelics like ketamine & psilocybin reshape the brain.

About the guest: Alex Kwan, PhD, is an associate professor of biomedical engineering at Cornell University. His lab employs advanced imaging to study how psychedelics and other drugs affect the mammalian brain.

Note: Podcast episodes are fully available to paid subscribers on the M&M Substack and everyone on YouTube. Partial versions are available elsewhere. Transcript and other information on Substack.

Episode Summary: Dr. Alex Kwan discusses how psychedelics like ketamine and psilocybin induce rapid neuroplastic changes in the brain, particularly in the prefrontal cortex, contrasting their effects with traditional antidepressants like SSRIs, and exploring their potential for treating depression and chronic pain through structural and functional brain alterations.

Key Takeaways:

• Ketamine & psilocybin rapidly increase dendritic spine density in the prefrontal cortex, enhancing neural connections within days, unlike SSRIs, which take weeks.
• These drugs show sustained neuroplastic changes in mice, lasting weeks to months after a single dose, suggesting long-term brain rewiring.
• Serotonin 2A receptor is critical for psilocybin’s neuroplastic effects, as precise genetic knockouts in adult mice eliminate spine growth.
• Unlike ketamine, psilocybin activates the insula, a brain region linked to chronic pain processing, hinting at new therapeutic potential.
• Both drugs induce similar gene expression patterns in areas like the prefrontal cortex and amygdala, but differ in specific regions like the insula.

Related episode:

• M&M #30: Psilocybin, Ketamine, Neuroplasticity & Imaging the Brain | Alex Kwan

*Not medical advice.

Chapters

• 0:00 Intro
• 4:32 Cerebral Cortex Structure
• 9:00 Excitatory vs. Inhibitory Neurons
• 14:20 Depression & Neuroplasticity
• 19:19 SSRI Effects & Limitations
• 24:34 Ketamine & Psilocybin Rapid Effects
• 30:00 Dendritic Spine Plasticity
• 36:01 Serotonin 2A Receptor Debate
• 41:32 Ketamine vs. Psilocybin Mechanisms
• 46:08 Measuring Psychedelic Effects in Mice
• 52:13 Head Twitch Response Limitations
• 57:10 Serotonin 2A Receptor Knockout Results
• 1:03:19 c-Fos Mapping Insights
• 1:09:28 Future Research Directions

Transcript

Alex Kwan 1:35 

Yeah, so I'm an associate professor in the biomedical engineering department here at Cornell University. This is in upstate New York, in Ithaca. So my lab, we're very interested in drugs that may be useful for treating mental illnesses, and we have a specific focus in ketamine and psilocybin, and we study what they do in the brain, primarily using animal models like mice. And

Nick Jikomes 1:16 

to find all of my content.

Foreign. Thank you for joining me again.

Unknown Speaker 1:29 

Yeah, it's great to be here. Can you remind

Nick Jikomes 1:31 

everyone a little bit about who you are and what your lab studies?

can you give us just sort of a basic sense of the types of things that you look at in mice. What are some of the techniques and what are some of the parts of the brain that you often look at

Alex Kwan 2:08 

for sure? Yeah, I mean, we study mice, mostly because we can do things in animals in terms of having high resolution recording that is not possible in human. So the things that we look at are, we do a lot of imaging to look at individual neurons, so how the neurons make connections with each other, and then, just generally, the mythology. We're also very interested in new activity, so neuron fire action potential, so we like to also record the electrical activity. Often we do these in the context of before drug after drug, and then long after drug to compare what happens when you apply a pharmacological manipulation.

Nick Jikomes 2:53 

So you can look at and record neurons in mice at a resolution that you cannot do in humans. So for example, you can scan a human brain using something like fMRI that gives you sort of a low resolution picture of the brain. You can't actually see individual neurons with the imaging techniques and the recording techniques you guys use in mice, you can get down to the level of individual neurons in specific parts of the brain and literally see and record exactly what they're doing. That's

Alex Kwan 3:19 

a great way to put it, when you think about functional MRI, which I think is very common to use in human and for good reasons, because you can have live in human, doing it during behavior. But when you look at an image like that, each of the voxels, the little thought that you see that provide you a signal will contain 10s of millions of neurons in that one voxel. So the signal is sort of average over many, many neurons that you see in fMRI here, right? We have just high resolution where we can look at individual cells within the animal brain.

Nick Jikomes 3:54 

And so obviously, there's many parts of the brain, and they all have different features. One major part of the brain is the cerebral cortex. It's enlarged in primates and humans, and as I'm sure we're going to get into, this is also an area of focus when people are looking at things like psychedelics and thinking about things like depression and antidepressants, because there are a lot of interesting changes that seem to come back to the cerebral cortex. You look at other brain areas as well. But let's start with the cortex. Can you give people a sense of the basic structure of the cerebral cortex in terms of the cytoarchitecture, the layers and the basic types of neurons that we tend to find there?

Alex Kwan 4:32 

So the cortex is, is, as you as you mentioned, is expanded in mammals, the some animals have it like the mouse habit. That's the reason, one reason why we study mice and then monkeys have it. Humans have it the different regions of the neocortex, so in the back of your brain, it's called, what's called the occipital lobe, where the visual information comes in, towards the middle, where you have the sulcus. You have kind of somatosensory area, where the sensory information. Comes in in a motor cortex. The area that we're most interested in is in the front of the brain, frontal cortex. Another more specific name for the area that we look at is called the anterior singular cortex, or shortest ACC. And this area is quite involved in executive function, so things like resolving conflict or things like decision making. It's also known to be involved in emotional regulation, so we study what the drug do to this area, also, because this area has been heavily implicated in depression. So when people do neuroimaging in human they find that area, such as ACC here, the frontal cortex, tend to have a Hypoactivity where you have reduced activity level in this area, suggesting that they, yeah, their their activity is disrupted in depression. So if you dig down deeper, yeah, you actually, you asking the cytoarchitecture? I'll answer that too. If you dig down deeper within that one region, the cortex is also quite, have quite impressive organization. Also have different layers. So it has six different layers with different cell types in it. So I think there's also argue why, you know, neuroimaging always great, has limited resolution because there are different types of cell within the cortex. There are also different layers that is hard to resolve with fMRI, suggesting that a lot of heterogeneity. I think a good way to think about it is think about a wiring diagram, like a electrical circuit or microchip that you have, you have a lot of little transistor, and they're connected by wires. And it's really quite important to figure out what that wiring is if you want to know what that chip does, and you really need that resolution to go at look at the individual pieces of wiring and transistors. And

Nick Jikomes 6:46 

so I don't think we need to get into all of the gory details at the cellular level, but the cerebral cortex, it does have this sort of stereotype layered structure. If you if you actually look at the cytoarchitecture, the the way the cells look, there are distinct layers that you can often see with the naked eye. And I think the important thing for people to understand here is you get, you know, usually, five or six layers in a chunk of cortex, and the different layers have different connectivity patterns. So each layer tends to get certain inputs and or outputs from certain other areas of the brain. And so the different layers are thought to sort of do or process information in somewhat different ways. Is that a fair description? That is

Alex Kwan 7:26 

an excellent description. I think in general, you have layers like the layer four that receives a lot of input from other areas. Then layer two three is thought to be processing more internally. Then you have a deeper layer five that's thought to generate a lot of the output. And then there are other places, like the layer six that talks a lot with the thalamus. So each of the layer have its own more specialized function. Again, I think try to go back to the analogy of this wiring diagram of a circuit where some parts are circuit that receive input, some that process it, and then some that goes out. So there's a division of labor. And I think understanding, and going back to, you know, why we study it, what drugs do to these different layers, and the different cell type residing in the different layer could tell us quite a lot about what's going on. And

Nick Jikomes 8:12 

so, as you mentioned, when we look at human studies, where we do things like fMRI, you know, each one of those voxels, each pixel in the image, you get is millions and millions of neurons averaged together, and so you can't distinguish the individual neurons. You can't look at specific layers of cortex. But with the calcium imaging techniques that you use, you actually can. You can point your microscope at one layer and do some tricks that lets you look at one type of neuron within that one layer, and then do things like give animals drugs versus a control substance, and then see, like, what is the drug doing to those neurons in that layer?

Alex Kwan 8:48 

Exactly? Yeah. And I think, you know, I think that is the level of detail that could eventually tell us a bit about what these drugs do to the computation that's happening in the cortex. And so

Nick Jikomes 9:00 

one of the things we're going to talk about is how psychedelics and some other drugs affect the dynamics of neural activity and the structure, or the neuro plastic changes that you can see in certain neurons in the cortex and elsewhere in the brain. I think two concepts that are related here that are important for people to maybe understand, is the concept of excitatory inhibitory balance. So let's, let's start there. Oftentimes, we sort of talk about two different general classes of neurons in the brain and in the cortex, excitatory neurons and inhibitory neurons. The name sort of implies what they do. But can you talk a little bit, a little bit about excitatory versus inhibitory neurons? What are their functional differences, and roughly speaking, how how much of each one is in a chunk of cortex.

Alex Kwan 9:45 

The cortex has a lot of neurons, about 80% of them are excitatory and 20% of them are inhibitory. As you imply, you know the name tells you about what they do. The excitatory neuron tend to excite other cells. So they when they fire, outer cell would fire more because they provide excitatory inputs, whereas the inhibitor neuron tend to shut down other cell. So when they fire, they tend to silence other cell, and this is through them releasing different kinds of neurotransmitters, and it's really important to maintain these both excitation and also an inhibition, because you don't want either of them dominate in the brain. So the balance of excitation, inhibition is critical. You can think about how excitation, if you have overrun excitation, then neurons tend to excite each other more and more, and you have this runaway positive loop that would then lead to situations like seizures and epilepsy. On the other hand, if you have too much inhibition, then your brain is not firing properly, and there will be a just a reduction in new activity, and it's just also not running optimally. So I think there has been just decades of studies suggesting that the interaction between these two forces, excitation, inhibition have to be finely tuned and finally maintained at a stable level in the brain in order for us to function properly.

Nick Jikomes 11:07 

And so as development proceeds, you know, the brain develops, and part of what crucially develops is this excitatory inhibitory balance different amounts of excitatory or inhibitory neurons change in different ways that tune the balance, the EI balance, of different parts of the cortex, and that's important for how these areas change and how they sort of stabilize and become mature in terms of what they're doing and how they're processing information. One of the things that people often look at here when they think about how neurons change and mature is the morphological changes that can be induced through activity and experience. One of the things that you guys look at is dendritic spine plasticity. Can you just break down briefly for people, what are dendrites? What are spines? And what do those start to tell us about plasticity?

Alex Kwan 11:55 

Excitatory neurons have dendrites, and the dendrites is the extension of the cell where it receives a lot of inputs, and then specifically so again, if you look at it, what a neuron look at, the cell body is a very compact, kind of egg shaped structure, but the dendrite is elaborate, more like a tree, allows a neuron receive input from very wide extent of area, and then the neuron tend to receive 10s of 1000s of inputs, and it would integrate its input, and then and the cell body decide whether to fire or not. Along the dendrites are little protrusions called dendritic spines. So these are little knobs where the dendrites receive excitatory inputs, so from other neuron, that excitatory neuron, they tend to synapse onto another cell at this location, called the dendritic spines. And just like what you said, my lab really specializes in using optical engineering methods to look at these dendritic spines of individual neurons in a mouse brain.

Nick Jikomes 13:01 

Yeah, and so, as we said earlier, you know, roughly speaking, you can think of the different layers of the cortex as some of them being primarily input layers that are receiving information from, say, another area of the brain. They might send that information to another layer, which is more of a processing layer that will, that will transform that information in in different ways. And then other layers are primarily, or largely output layers. So you know, signals come into one layer of cortex, roughly speaking, they're sent to another one. They're changed and filtered, and then the brain changes them in that area of cortex, and they're sent to another layer to then be outputted, to, say, another part of the brain. And so the dendrites of neurons in these different layers might go up to other layers where they can receive the input, and the spines basically represent synapses where one input is going on to that dendrite.

Alex Kwan 13:50 

That's correct, yeah. I mean, it's not a one to one exact correlation, but vast majority of the dendrite spines are the location of this excitatory synapses where one neuron excite another, particularly when one neuron it's exciting another excitatory cell. So this is sort of the structural correlate of a synapse, although if you really want to prove that it is synapse, you have to do something else, maybe make electrical measurements. But in general, the structure begets the function.

Nick Jikomes 14:20 

And so when we start thinking about spine plasticity, changes of activity, we're going to get to what psychedelics do as compared to, say, SSRIs or other drugs. But let's start with something like depression or stress. When you're looking and imaging and recording from the parts of the brain that you guys often look at, places in the prefrontal cortex, how do conditions like depression or depression like behavior in rodents or stressful situations? What do we know about how that changes leads to neuro plastic changes in certain parts of the cortex?

Alex Kwan 14:54 

There has been several decades of study in this area, I would say, name many of. Pioneers in this area, for example, Bruce McEwen and Ron Duman, who has done many, many elegant studies showing that if you give chronic stress to an animal, this means that you subject them to different type of behavior paradigm that would cause stress anxiety to the animal, and you will also do these over time, the animal would start to express symptoms that mimic aspects of depression, because stress is also a key predictor of depression in people. And then these stress animal, if you when they look at the frontal cortex, they would tend to see a reduction in the number of dendritic spines. What this suggests is the loss of excitatory synaptic connections, or synapses. Ron Duman also has some very elegant work showing that not only in animal, this can occur, but in human you can also find correlates of this. Most notably, he find that if you look at proteins that typically express in these excitatory synapses, they are also decreased in human postmortem tissue when you compare people with depression versus other healthy individuals

Nick Jikomes 16:10 

in this pattern. So this loss of synapses, or things that suggest the loss of synapses and a loss of certain connections, do we tend to find that in very specific parts of the brain, or layers of cortex, more than other areas,

Alex Kwan 16:25 

that's a great question. In human I don't think that's been looked at quite well, mostly because postpartum tissue and processing processing is technically difficult, but also getting the sample itself is also challenging. And then in terms of where it is, I think there are very strong converging evidence showing that it happens in the prefrontal cortex, where we study it most definitely also happens in hippocampus. There has been suggestion that, you know, maybe not everywhere, lose the synapse in other places there could be compensatory changes. A couple of studies have found that, for example, in amygdala, maybe you actually have an aberrant too much synapses there. So I don't think you know, everywhere you're losing the synapses. Maybe one better characterized is just a circuit connectivity has been altered. But in the prefrontal cortex that we looked at, you tend to have a loss of

Nick Jikomes 17:18 

synapses. So so there's different changes in a bunch of different parts of the brain. It's not like everything is happening in one direction in one place, but the prefrontal cortex in general is often heavily implicated as a place where quite a bit of change seems to happen in response to things like chronic stress. And when you look at the cellular level in animals in general, in the prefrontal cortex, there seems to be a loss of spines, a loss of excitatory input onto at least certain cells.

Alex Kwan 17:45 

That's correct, yeah. So, I mean, this has been shown in different ways. You can, you know, take tissue and look at them and fix tissue. In my lab, we specialize in live animal imaging. You can also look at synaptic protein in some of the more other recent study, people have also do sequencing of transcript. These are also can be done from human tissue, where they also can do large scale sequencing to find synaptic changes. So I think all in all, really, there's a very good amount of converging evidence showing synaptic deficit associated with depression

Nick Jikomes 18:20 

and so, okay, so when we see these structural and functional changes in animals that correlate with stress and depression, like behavioral changes, how do things like typical antidepressant drugs affect affect these changes? Do they reverse them partially or completely? Do they lead to other changes? What do we know about the effects of, say, SSRIs?

Alex Kwan 18:44 

Yeah, so it's commonly known thought that the SSRI and drugs that can be useful with treating depression can lead to some restoration of some of these synapses. Now it's funny us ask SSRI, because I think SSRI is actually one that is not as well known. Arguably, there actually been more done on ketamine and psilocybin by recent work, but the idea, and there has been several studies showing that the SSRI does increase synapses, so it may be not as strong as one would like, in terms of the evidence

Nick Jikomes 19:19 

and what about, sort of the dynamics here? One of the things SSRIs, I think, are pretty famous for, is that, you know, in a subset of people, they often work, to some extent, to relieve symptoms of depression, but very often, I think almost in all cases, when that happens, there's a lag. So it takes some amount of time. Is there any sense that the SSRIs are sort of working? What are the timescales of action here? Does it? Does it take some time for us to see changes in the brain after you start giving an SSRI to an animal?

Alex Kwan 19:51 

That might be the reason why it's been harder, in fact, to see changes in the morphology of neurons in these dendritic spines after SSRI. I think what you you. To point out, could be a key reason why it's less often seen. Because in human, you're right, like SSRI would take four to six weeks, typically, to start to become effective in a subset of people, and in animal, you would think that you also need chronic administration. It's not that one or two doses would lead to very dramatic changes. So it's makes it very difficult to find these effects, because you do chronically administer it, yeah,

Nick Jikomes 20:28 

it just makes it infeasible to do some of the measurements, because it takes more time. You'd have to do more looking and more searching over a longer period. And all of the the tricks that you use to record these things can be time sensitive and complicated. Yeah.

Alex Kwan 20:42 

And also, I think the other thing to be aware of is in animal models, I think unlike in the human conditions, when you stress the animal, the animal would tend to exhibit the depressive symptom, but once you stop the stress, the animal will then tend to recover. So you also have some time course issue where you stress the animal, then maybe you give it SSRI, if the animal gets better, is it because you gave it SSRI, or is it because the stress is now gone? Maybe, yeah, all of these, I think, makes it perhaps harder to disentangle the differences. The other thing that we can get into a bit later is, I think there's also a case to be said that maybe not all depression treatments are equal as well, and they don't necessarily need to rely on the same mechanism. I do think that there may be more similarity between certain types of treatment that are a bit more rapid acting, for example, ketamine, maybe some psychedelics, or even transcranial manic stimulation versus other things is a bit slower, like SSRI.

Nick Jikomes 21:43 

Yeah, yeah. And, I mean, think one of the things that people are excited about with respect to the antidepressant effects of things like psilocybin and ketamine is that they seem to be more rapid acting than SSRIs. And so obviously, if someone's depressed, especially if they're severely depressed, you'd like to reverse that. Not only do you want to reverse it, but you'd like to do that as quickly as possible. So talk, give us some of the basics here. What have we observed in animals, maybe even in humans, in terms of the antidepressant effects of things like ketamine and psilocybin, in terms of how fast those effects have their onset compared to traditional treatments,

Alex Kwan 22:20 

ketamine has been well studied. I mean, the related drugs, ketamine, nasal spray, is now approved. So they're a pair of phase three clinical trial where they can see effect as early as, you know, a couple of as early as, basically 24 hours or so. I mean, there's the first difference that you can see, and then some of the larger trial look at on the order of days they can observe that differences. So I think that time scale is quite well established for Psy been the clinical trial differs a little bit in the in their current design. They're also a little bit smaller in phase two clinical trial. So they're on the order of about 50 people per arm, or maybe at most, 100 people. I think some study report differences as early as day two. That would be, for example, I think with Compass study was like that. But the yuzona study, I think, did not see a difference at that point. So maybe somewhere between two to eight days, I think, is when people tend to see differences in these phase two trials. Okay,

Nick Jikomes 23:26 

so I guess the bottom line here is, drugs like ketamine and psilocybin, you start to see antidepressant effects in human clinical trials within a couple of days, roughly speaking, maybe one day, maybe a few days, depending on the drug and the details. But that's, you know, that's quite a stark comparison to SSRIs, which, in which case you're talking about weeks or even months before you really start to see significant change.

Alex Kwan 23:48 

Exactly. Yeah, and that's, I think it's also fun to compare, I think useful to compare with other type of treatment. And even, I think, if you think about the repetitive transcranial magnetic stimulation, there are actually some really good advance there in terms of accelerated protocols, that you can also see effects within days. Another thing that I think you can see fairly rapid effect would be ECT, is another thing, whereas other thing, SSRI, deep brain simulation, is another one that could take a while. So, yeah, I think the time scale of why these treatment work at different timing and the need to wait, and that delay for some of the treatment versus other is something that is just really not understood and quite a mystery. So

Nick Jikomes 24:34 

you've done a variety of experiments, and other people have in the last few years looking at, you know, what are things like ketamine and psilocybin actually doing in the brain. We'll probably eventually get to mechanistic stuff, but let's just start at the level of plasticity. When you do your imaging experiments and you administer these drugs to animals, what do you see change in the brain? Morphologically speaking,

Alex Kwan 24:58 

yeah, so we did a. Study, first study along these lines, in 2016 with ketamine, and then follow up with another one in 2021 with psilocybin. In both cases, what we observe is that the number of dendritic spines increases in the frontal cortex of the mouse, and this increases quite fast. So we would administer the animal a single dose of either of these drugs, ketamine or psilocybin. We go back to the same place and look 24 hours later, you can see start to see the formation of new dendritic spines in the dendrite that we looked at previously. And in both cases, the increase tend to sustain. So in ketamine, case we look at about for about two weeks in sales having case we've looked at in the initial study was one month. Now we've done two months, and these increases are quite sustained in terms of the changes in the number of dendritic spines.

Nick Jikomes 25:57 

When you say sustained, do you mean you administer the drug one time, and then weeks or even a month or two later, you still the same spines that sprouted in response to the drug administration are still there after that amount of time.

Alex Kwan 26:10 

So the density, so the number density, just a raw number, has increased, and that increase in the number is a stain, whether it is the same exact spine that stays there? We've also asked that question, and there are some turnover where, you know, even without the drug, our brain itself is adaptable, and we do have rewiring going on, for example, when we gain new experiences, when we learn something. So there's constant turnover even, you know, as we live our life. So it's not too surprising that even though you you give the dose of drug, it, have this drug ebook increase over time. There's still some turnover later on following it. But what you show though, is that the overall number, the overall increase, that number, stay high after a single dose of psilocybin.

Nick Jikomes 27:01 

So you can give the you can give either of these drugs one time, and you see quite a rapid increase in the overall density of spines in the prefrontal cortex. And that seems the overall density seems to remain elevated for weeks after the drug administration.

Alex Kwan 27:18 

That's correct. Yeah. I think that was also the most striking result, I think, from this early study in 2021 just how long lasting it was, I think it surprised us, and it also, I think, made other people excited about the finding, mostly because if you give the animal a single dose of drug, initially you see a lot of activity changes and other behavioral changes, but very quickly the drug get out of the system, and then to have these long, lasting changes that one can observe, I think these spine density increases is one of the few that I think has been observed now by a number of groups, but it's one of the few things that you can somewhat reliably find in The brain, and it really suggests that, you know, these things might be relevant for some of the beneficial behavioral effects that's seen in humans, and

Nick Jikomes 28:07 

these morphological changes that you can see in neurons in these parts of the brain after an administration of ketamine or psilocybin, do they correlate well with behavioral changes that indicate an antidepressant or anti stress effect.

Alex Kwan 28:23 

So I think that is a unknown, and that's an important question. What we can say is that it correlate with the function of neuron, because when we see the morphological changes, we can also go and put an electro and ask, does the neuron also receive more input? And we did do that experiment, and we can show you that if we record the activity of these neurons, they do receive more excitatory inputs the day after. So there's functional relevance to these morphological changes, whether there's behavioral relevance for these spine growth and the synapse increase, that's a much harder question to answer. I think to do it definitively, one would have to have a way where you can give the drug to the animal and then somehow stop the spine growth, but let all the other things go on in terms of the drugs effect, and then ask whether the behavioral changes will still occur. So that would be a very difficult experiment. I mean, we can talk more about what we have done. We are getting close to it, and we've done something related, but we haven't quite done that final experiment that can really nail it down. Okay,

Nick Jikomes 29:33 

okay, and talk a little bit more about so when you're doing these experiments and you're observing these structural changes in dendritic spine plasticity, which basically, you know what we think they are, is you're increasing the number of inputs to some of these neurons, where specifically, in the brain of the mice are you looking and within that region, what layer are you looking at, a particular layer of cortex, and what neurons are these specifically in terms of their connectivity? Yeah.

Alex Kwan 30:00 

So we have been looking at the excitatory cell. Another name for these cells is called parameter cell. But they're excitatory neurons in the brain. Due to the imaging method that we use, we tend to look quite superficially near the top of the brain. So this would be a correspond to layer one. And as we discussed previously, the cortex is six layers. So this is just, you know, top layer of the cortex, and this layer is special in that that's where the neuron receives a lot of long range input from other cortical areas. So for example, in the frontal cortex, these neurons also receive input from the visual cortex, from the parietal cortex, and these long range input from other cortical region that's far away would come into this layer one. So these dendritic spine likely represent connections that are long range I

Nick Jikomes 30:50 

see. So these neurons would be they're well positioned in terms of their connectivity to integrate signals from multiple areas of the brain.

Alex Kwan 30:58 

Yes, I mean, the neuron is always in the position to do that, but now it seems that that connectivity is modified. And I would say, yeah, it based on the location. Because we're imaging layer one, it suggests it's the long range connectivity that are more preferentially altered. So you're

Nick Jikomes 31:15 

looking at the inputs in layer one that these cells are receiving. Where are their cell bodies located, and where do their outputs go? Do we know that?

Alex Kwan 31:26 

So, yeah, in the recent study, this is what we asked in terms of, you know, when we talk about, okay, we have these neuron that have increased number of spine, but what exactly are these neurons? In the early study, we just say, okay, they're excitatory neurons, but it turns out that there are also many different types of excitatory neuron. There are ones that go back to other cortical areas, and then there are also one that exit the cortex and then go deep into the brain stem and subcortical areas like the thalamus and superior COVID. So in this later study, we start to ask, okay, you can see some structural remodeling. Which particular type of excitatory cell is remodeled? So what we found is that it turns out that both of the cell types were remodeled. So the remodeled could be quite prevalent. So multiple cell types actually exhibit these remodeling and see their spine growth, both in terms of the cortical, cortical connected neurons as well as the cortical, subcortical connected neurons

Nick Jikomes 32:27 

I see. So you see this remodeling, this dendritic spine plasticity in at least two cell types, two excitatory cell types, and they tend to have their cell bodies in layer five. So these are cells that are sort of deep in the cortex, in terms of where the cell body lives, but they're sending their dendrites up to the top of the cerebral cortex, that's where they receive these inputs from a bunch of different parts of the brain. And one of these pyramidal cell groups is sending outputs to other areas of the cortex, and another cell group is sending outputs to deeper structures within the brain, the brain stem and other places that you mentioned, and they're both, they're both exhibiting changes.

Alex Kwan 33:06 

Yeah, that's Yeah. I think you really clarified a view here. These are deep Lane cell and they send different outputs. Both of them exhibit structurally modeling, suggesting that their input pattern have changed. And

Nick Jikomes 33:19 

so what else do we know about these neurons in terms of their molecular features? So for example, the serotonin two A receptors are famous for being the so called psychedelic receptors. We, we I think we know that these are necessary for the psychedelic effects of psychedelics, meaning their subjective effects. Are these cells that you're seeing these neuro plastic changes in are they expressing these receptors or any other Do they have any other key characteristics in terms of their expression pattern?

Alex Kwan 33:50 

They certainly express serotonin receptors. They both. Both of these cell types have the serotonin two A receptors, and then they also have other types of serotonin receptors. For example, serotonin one, a receptor, which is also target of psychedelics. I think it's good to think about even though the two, a receptor is most likely responsible for the trip in human there are total four or 14 different types of serotonin receptors, and these excitatory cells can accept a complement of the serotonin receptors and the psychedelic have the position to bind to many of these Pepto receptors.

Nick Jikomes 34:27 

And so what do we know? Have you, have you been able to dig into sort of what's necessary for these neuro plastic changes to occur? So obviously you can you administer the drug, you observe these neuro plastic changes in these particular neurons in this part of the brain, can you block the five HG to a receptor? Can you, you know, block the output of these neurons and do those types of functional experiments to see, you know, some more detail here.

Alex Kwan 34:53 

Yeah, exactly. I think that is, was one of the key question that going into one of our recent studies, there has been, I think, a lot. Debate in the field on whether the serotonin two way receptors are needed for some of these plastic changes. Just going back a little bit in terms of what other studies have shown. Some of the earlier studies by for example, David Olson and UC Davis, he has shown that if you block the two way receptors in culture neurons, then these cell cultures no longer can exhibit structurally modeling, so the dendrites and the dendritic spines cannot grow in a culture. So this was, I think, very well cited result, although it's not clear where they translate to an actual brain, because these are cell cultures, then there was a very provocative paper by Scott Thompson, who's now in Colorado, who showed that in a live mouse, if you give a blocker the two a receptor called catansarin, the plasticity can still occur, and some of the behavioral changes can still occur. A key piece of context

Nick Jikomes 36:01 

here might be that one of the big questions, I think, is, can you, people are very interested in whether or not you can engineer psychedelic related compounds where you sort of subtract out the subjective effects but retain the neuroplastic and therapeutic effects. In other words, can you create a psychedelic drug derivative without a trip, that doesn't require, you know, a four or five hour trip in a human being, but still gives you some of these rapid acting psychological effects, like antidepressant effects. And so this is tied to the question I think we're talking about, because if the five to a receptor for serotonin is needed for the trip, you have to ask the question, okay, well, is it needed for these neuro plastic changes that we think underlie the therapeutic effects and or can you separate those two things? So is the five to a receptor dispensable? Yeah,

Alex Kwan 36:50 

I think that is the Well, is it one way to put that question? I think that question can be actually attacked at different layers. But I think one of the key point of attack would be the serotonin two way receptor, as you just described, because there's such a strong evidence that the two way receptor is needed in the human for the trip. So But going back to what Scott has found, Scott Thompson has found, he showed that if you give the blocker, if you give the blocker to human, it blocks a trip. But now he gives the blocker to a mouse, it doesn't, you know, block the depression, depressive, anti depressive, like behavior in an animal. So it suggests that his result suggests that maybe you can keep the therapeutic effect, but even though you're actually blocking the two way receptor, so maybe the two a receptor is not needed. Then finally, I think there is another study using now genetic knockout animals, where they suggested to a receptor might be needed again. But I mean, all these have issues, mostly because if you use a knockout animal, you tend to perturb the development because you lack the receptor as animals grow up. In terms of blocker is a drug, another drug that you add to the system, and they're never too clean. Yes, yes. So, yeah. So three things

Nick Jikomes 38:07 

that come to mind here, so, yeah. So you said David Olson has experiments where you block to a in cell cultures, and you find that you don't get these neuro, plastic, morphological changes. The key thing there is, it's in culture. It's not in a live animal, so it's a completely different context that makes it very difficult to interpret in terms of whether it will have the same effect. In vivo, you mentioned this other scientist that's done experiments in vivo, where you give catansarin a five to a receptor blocker, and you find that you still get you don't you

Alex Kwan 38:39 

get, you get the plasticity, and you get the behavioral change. But so we know in humans,

Nick Jikomes 38:44 

it doesn't give you the trip, so that suggests that you can get the neuro plastic changes without the trip. But I guess the question there for me would be, how specific is tanzer and as a five to a blocker? That's

Alex Kwan 38:55 

right, and it turns out that catanswer and also have some other strange effect that doesn't get into the animal's brain very well, particularly animal mouse brain. So maybe the blockage there was not complete. Maybe it blocks it partially. And then finally, the more recent study from Javier Gonzalez may so was the lead group there, showed that if you have a whole body knockout of the serotonin two a receptor, you lose the structural remodeling, but the whole body knockout have issues in that, you the animal basically grew up without the two a receptor, and that lead to other developmental issues. Yeah,

Nick Jikomes 39:31 

yeah. So I think what you're saying there is, you know, we can use genetic tricks to knock out a receptor, like the five to a receptor in the whole animal and every cell it's in or in specific cells, but when you do that, you are taking away a key protein in the animal for its entire life, and so its development is different, and there's going to be other compensatory changes in the brain that you can't really account for from lacking that key protein for your entire life.

Alex Kwan 39:58 

Yeah, so I think. Think, ultimately, I think there's just a lot of debate, and I think there has been a lot of people also still looking for maybe something else that mediate some of these changes. What I mean is that maybe some other receptors, I think I've seen people suggest maybe five sheet one, a receptor that may be maybe important. You know, these drugs also have high affinity the sigma receptors, for example. So I think some people are still looking at other receptor subtypes, yeah.

Nick Jikomes 40:32 

And I think a key thing this might bring us to is so all of the drugs that we might talk about here, from psilocybin to ketamine to anything else that might come up. It's possible that they have different mechanisms of action in terms of the receptors that the drug binds to and sort of kicks off the process with, but it's also possible that they converge downstream in different areas. In other words, you know, two drugs might bind to different receptors, but this might ultimately lead to similar changes downstream of the receptor activation. And so with that in mind, you know, ketamine is a very different drug in some ways than psilocybin. It's they both have strong psychoactive effects, but they have different subjective effects in humans, and their mechanisms of action are different. So what do we so they both have this rapid acting antidepressant effect. They both lead to dendritic spine plasticity in similar parts of the brain, I believe, and yet they have different mechanisms of action. Can you comment on that a little bit? What do we know about the differences there between, say, ketamine and psilocybin?

Alex Kwan 41:32 

Yeah, I think you pretty much told Reto already what we know. And then I think in some way what we don't know, what we know is that they target very different receptors. So the psychedelic target the serotonin receptor in the serotonin system, ketamine is a weak NMDA receptor antagonist. NMDA receptor is a glutamate based signaling system. It also target other things. When I say weak, it just means that it's not that selective compared to other drugs, actually, and you target a whole host of other receptors. So I think both of these compounds actually exhibit what's known as polypharmacology, where they're not that selective on one receptors.

Nick Jikomes 42:19 

Yeah. So each drug, and

Alex Kwan 42:20 

then in terms of that's sort of the starting point I think right for both drugs. Yeah. So, you know, there are places where I think psychedelics and ketamine are quite different. One place is, as you mentioned, the mechanism of action, receptory target. The psychedelic is a excellent serotonin receptor, although, again, not two, a specific sort of one, a, 2c, many other types of serotonin receptors. And then for ketamine, is on the NMDA receptor, which is a glutamatergic signaling, so excitatory signaling, although ketamine, ketamine is known as a weak NMDA receptor antagonist. So it also target many other types of receptors, most notably to the opioid receptors. So both of these drugs has polypharmacology, but clearly the mechanism is different and the receptor set that they target is different. I think we already converge. Is also sort of what you mentioned in terms of the both of them have the propensity to lead to structural plasticity in the brain. So they lead to growth of dendritic spines, and then both of them also have these types of relatively long, lasting antidepressant effect, I think, more forcibly shown for ketamine in human but now there's also increasing evidence for psychedelic I think what you ask is, I think the million dollar question, where do things converge? One thing that I think is a little unsatisfying right now is, once you go past a receptor, in terms of what happens in the cell, those signaling the other protein that will signal the once you activate the receptor, a lot of those are not very clearly laid out. Maybe the next step is also known for psychedelics. That would be, you know, proteins like G protein and beta arrestin, and there's a lot of tox, and maybe those are important. But once you go another couple steps, it starts to become very hazy in terms of, what are the molecular signaling that's involved with the drug action.

Nick Jikomes 44:13 

So in terms of, sort of the initial steps here, we know that the drugs bind to receptors. Psilocybin binds to serotonin receptors of multiple kinds, and other receptors ketamine can bind to the NMDA receptor and probably other receptors as well. So they're different in terms of the pattern of receptors that they bind to. We know, on the other end, the sort of output here is that you have the structural remodeling, this growth of dendritic spines, that seems to be important. So we know that, you know, at the two ends, there's at least, you know, despite the differences in the receptors they activate, the output is somewhat similar. You see the growth of these new dendritic spines in these parts of the brain. What's happening in between is more mysterious, but at some level, to get that structural plasticity to physically build those new synapses, somehow those initial receptor signals need to translate to. Mills inside the cell that ultimately affect the transcription of genes, the creation of proteins that then shuttle out to the synapses to actually build them. So somehow, there's probably some convergence, but it's a question mark. Exactly what's happening after Recep after the receptor activation, but before the remodeling?

Alex Kwan 45:18 

Yeah, I think that is a good way to put it. I think in terms of, you know where that molecular signal converge, I think another place that my lab is very much interested in is also on what cell types do they converge. We talked about their different excitatory cell type. They're also different inhibitory cell type. There are also different brain regions that these plastic co occur. So I think there's also a level of conversions where we're talking about more in terms of the cell types in the brain region where these drugs act on, that also actually makes them different from other things that can cause plasticity. So I think again, if you go into a enriched environment, if you undergoing learning, your brain can also change. If you take other drugs, your brain could also change. So what makes it different that when you're taking ketamine or psychedelic I think, is precisely what cell type and what brain region they act on that make them useful.

Nick Jikomes 46:08 

Can you talk a little bit about so obviously, we know in human beings that things like psilocybin and other psychedelics, things like ketamine, have strong psychoactive or psychedelic effects, because the people have a trip, and you can just ask them, you can't do that in a mouse. How do we ascertain the whether or not the mice are having kind of subjective effects that might be akin to what a human is having? And how do we how do we then go from there to sort of determining whether or not the subjective effects are dispensable or not for the therapeutic effects?

Alex Kwan 46:40 

Yeah, so here, I think I have a part differing opinion than many of the other basic scientists. I think one of the some of the assays that other people use, for example, are what's known as a head switch response, where the mouse would twitch your head. There's another assay known as a drug discrimination, where you would ask the animal depressive lever to tell you what drug they might have gotten, but in my mind, those assays are not doesn't quite have the face value of a trip, because I think in human is a very perceptual, very emotional experience, and like you said, it's also somewhat subjective experience. But I think there are probably maybe other ways that one can maybe ask or measure in an animal whether that has occurred, but I don't think they have been done yet in research. So I would encourage people to start thinking along those lines. One is maybe we should think about starting to record and look at the visual brain areas in the animal. So there's also area in the cortex that receive visual signals. The visual cortex, one can image that part of the brain and see what changes occur after giving animal psychedelic compared to, for example, what you might when you give animal a non house agentic, serotonin, two, a agonist, one of these new drugs, are supposed to not cause a trip. You can compare what happens to the visual brain areas. Another thing that one could do is maybe ask animal to do more visual tasks, so not some of these discrimination tasks, but actually visual processing tasks. You can ask animal to tell you whether it saw a particular grading, whether it sees a visual stimulus of a particular contrast, and then ask whether some of these drug might actually change their visual behavior. So I think these type of behavioral and physiological measurements might be more useful in terms of telling us whether the animal actually have a psychedelic experience or not.

Nick Jikomes 48:39 

I see. So where the field seems to be at right now is so when you look at again, you can ask a human whether or not they tripped, and that's pretty direct, but you can't ask an animal. Obviously, the mouse can't tell you whether it's tripping, so you have to sort of guess based on behavioral changes that the animal exhibits. The state of the art right now is really that head Twitch task where basically, you give the animal a drug like psilocybin, which is already known to cause a trip in humans, and a drug like that, which causes a trip in humans tends to cause these animals to have this very fast, rapid head Twitch response that you can record, but that's a pretty coarse grained measure. At the end of the day, you don't really know whether or not the animal is tripping just because it's doing that kind of weird behavior. What you're saying is we should start doing more experiments where we're looking at the visual cortex, we're looking for signals that imply perceptual changes, and then we're actually asking the animals to do visual discrimination tasks, where, if they are having, say, visual hallucinations, you would expect their ability to do those tasks to be disrupted, and that might perhaps be a better way to read out these things behaviorally in an animal like a mouse. Yeah,

Alex Kwan 49:47 

exactly. And I think what you said in terms of the Hetrick response being somewhat of a weird assay is one way to put it. I mean, it is a very specific assay. So, you know, in human, if we consume aside. That they're like, We don't touch the head like the mouse do. In fact, only a couple of species, the mouse and the rabbit, only a few of these animal species, does it. So I think it's a very species specific response. And again, like, just because you move their head, it's nothing that's perceptual about it. In fact, it's a very in that motor response to the drug. So I don't see why, at least in the face value has to translate to human whereas understanding the actual changes in the visual brain area could give us a lot more insight in terms of what the drugs do to perceptual processing.

Nick Jikomes 50:35 

Yeah, and it's actually, you know, in some sense, some of these initial experiments would be easy to you know, relatively speaking, you know, as far as imaging goes, the visual cortex is a very imageable part of the brain. And you could just, you could do pretty basic experiments where you're passively administering the drug and just watching what happens under very sort of basic conditions that that people know how to image under,

Alex Kwan 50:56 

yeah. And I would say the visual cortex is a well studied area in neuroscience, we know a lot in terms of how the brain and the neurons there represent different kinds of visual information, and in terms of different objects, different contrasts, different oriented stimulus. I think there's quite a lot of good neurobiological questions that can be asked. In fact. I mean, the people are, you know, getting into there. I mean, my lab, we have a couple people working along those lines. One of the more interesting project that come online was, there's also a initiative at the Allen Institute, called Allen Institute called the Open scope, where they they would perform an experiment to anybody who want to propose it, anybody can propose an experiment, and then they would do this experiment for you. And then the condition is that you can analyze the data first, but then the data will become public a year later. So in fact, the very last open scope competition, there was a proposal to suggest that maybe we should record the visual cortex when you give animals the drug. So very soon, we'll actually have a very solid, publicly available data set of how a mouse electric activity would change under the influence of psilocybin. Interesting,

Nick Jikomes 52:13 

so you mentioned this head Twitch response assay that's often used to infer the possibility of hallucinogenic effect in an animal like a mouse, it's very species specific. You see it in mice, you see it in rabbits, but you don't see it in all animals. In mice, the most commonly used model organism here, how good? How tight is the correlation between a known psychedelic causing the head Twitch response in that species? In other words, are there known psychedelics that have subjective effects in humans that don't cause the head Twitch response, or things that aren't strongly psychoactive in humans that do cause the head Twitch response in mice,

Alex Kwan 52:54 

in this sense? Well, first of all, let me say the relationship is quite tight. So there was a very nice study comparing 25 or so different compounds that's been measured in terms of hatch response. And then we also know the potency in human in terms of eliciting hallucination. And then if you plot it just you know the human on one axis, rodent on the other axis looks pretty tight. So I think that's one reason why people use it. That being said, there are a couple of false positives. So there are they do exist, compounds where, for example, I think tryptophan is one, where it's a precursor to serotonin. You give it to rodent, then it could cause hetric response. But it's not, you know, for example, a psychedelic in human. So there are cases like that. Whether that's owing to some different metabolism and metabolite coming online in the rodent is unclear. I mean, there's also these things are a little hard to tell in terms of false positive, because to some extent, maybe in human too, if you give enough dose at some point, maybe, maybe it also become psychedelic. Yeah. So I think it's a little hard to tell, but there are cases, a few exceptions, where could be false positive or false negatives.

Nick Jikomes 54:15 

So you mentioned before, there's some debate out there. There's some mixed data in different systems, in culture, in vivo, give a drug, give a different drug. There's mixed data out there in terms of whether or not the five to a receptor is dispensable for the neuroplasticity. What's so? So there's arguments that some people make that, you know, we really think it's likely that you can dissociate the subjective effects from the therapeutic effects and or the neuro plastic effects. Other people argue in the other direction. It's certainly not settled yet. One of the arguments that people use in favor of the subjective effects being important here is that when you do the human studies, you tend to find a pretty good correlation between the therapeutic effect that people have and the intensity of the experience that they report. In other words, people that report. A stronger trip, basically, tend to have stronger or longer lasting therapeutic benefits. So this question is not resolved, but do you have a sense of how plausible you think it is that we can dissociate the subjective effects from the therapeutic effects, and whether or not you have a strong opinion there, what are the experiments going to look like that actually resolve that for us definitively,

Alex Kwan 55:22 

yeah, I have a couple of things to say about that. I mean, one is the Yeah, there are human data like you said, that suggests the intensity of that subjective effect correlate with the therapeutic outcome. To me, that is a correlation, and there could be some other factor. For example, the intensity of subjective effect would necessarily be large if the dose is also larger. I mean, if the just the drug response in a person is larger, which then could correlate with the therapeutic outcome. So I think, you know, these two things correlate, but I think ultimately they also correlate with the dose of the drug. And then, so I think it's a little hard to tease that apart. And then the other thing I will say, though, is that, uh, even though there has been controversy in the past, right in terms of whether the two way receptor is needed or not, yeah, I was actually trying to get to it. But, uh, given the past result, we have some recent result where we thought we've done this slightly more precise approach to test this ask the same question, where we also now genetically deleted the two way receptor, but we were able to be a bit more precise and only deleted in adult animals, so not affecting development, but also deleting Only in specific brain area and also in specific cell type. And when we do these very precise deletions, so not really affecting the rest of the brain or the body, we find that the two a receptor is needed for some of the behavioral benefit as well as the structural plasticity remodeling. Yeah, so I think, yeah. This more recent evidence kind of pushed me back towards saying that, yes, maybe the two way receptor ultimately is also the key driver for some of the positive effects of the drug I

Nick Jikomes 57:10 

see So sort of the links the logic here, just for people are following, yeah, you give psychedelics human beings like psilocybin, obviously they cause a trip. We know that happens if you give those drugs to humans, but you block the two way receptor. It tends to block the trip. When you give these drugs to animals, they have like the head Twitch, and they do the things that see that correlate with the hallucinogenic levels that you see in humans, and you see these neuro plastic changes. So psilocybin leads to this dendritic spine growth. It gives a head Twitch response, which we think might mean it's hallucinogenic in the mouse as well. And what you're saying is there's been experiments in the past that are somewhat difficult to interpret. You can knock out or block the two way receptor, but there's problems with those experiments. When you knock it out from birth in the whole animal, there's going to be a lot of developmental compensatory changes to make it difficult to really interpret those experiments. When you use a drug like tantrum to block the two a receptor in an adult it does block the two a receptor, but it probably blocks other things, or it might not get in the brain all the way. And you know, it's just not a perfect experiment. You guys did an experiment where you knock out the two a receptor only in adult animals, so you're not messing with development and only in a certain cell type in certain parts of the brain. And what you're saying is, when you give psilocybin in those specific knockout animals for the five to eight, five ht, to a receptor, it does block the neuroplastic spine growth that psilocybin would otherwise induce.

Alex Kwan 58:37 

Yes, exactly. And I think because the genetic deletion strategy that we took was just a lot more precise and also limited to adult animal. It got rid of some of the caveats on some of the early study. And I think that the the effect that we saw, you know, comparing the animals that have still have the intact receptor versus the animal that just have no, absolutely zero amount of two way receptor. It's just such a night and day when they have no two way receptor. There is basically zero structural neuroplasticity. So comparing that differences really highlight the necessity for the two way receptor in terms of meeting some of these long term changes.

Nick Jikomes 59:14 

Okay, so the effect was strong. You basically the plasticity that you saw with the two way receptor intact, almost completely went away without the two a receptor, it could have been very different, right? People could have argued, well, maybe the two a receptor is part of the plasticity, and the one receptor is part of it. And you need, you know, X number of receptors. And, you know, maybe if you knocked out the two receptor, you would see like a 10% or a 20% reduction and change. But you're saying it pretty much all went

Alex Kwan 59:37 

away. It pretty much all went away, yeah. And I think the genetic strategy have disadvantage, where, when we knock out the receptor, the receptor is no longer in a genome, and so the knock the Knockout is very complete, so meaning the receptor is practically gone, yeah,

Nick Jikomes 59:56 

yeah, yeah, you've also done. Experiments where you use different techniques to sort of just look at the broader picture of changes in the brain. So I'm thinking here of the work that you've done, doing CFOs mapping. So I want to give people a sense for what that even means, and then talk about some of the results you've seen for the different drugs you've looked at. Can you explain C FOS for people and the concept of transcription, transcription induced from activity changes in the brain.

Alex Kwan 1:00:27 

Yeah, so C FOS is the is known as an immediately gene. So it's a gene that gets activated in a cell when a cell tends to increase its new activity or receive the external stimulus. So what that means, maybe in a different way, is that sometimes there are things that change. The environment has changed, and the cell or the organism need to respond in some way, need to adapt in some way. Then you need to start changing the protein expression in the cell. For example, if you want to grow a new synapse, you need to start putting in new proteins in there to support the function, then you will start to activate the gene expression program. And CFOs is one of the gene that comes online when that happens. So what we did, there was a couple of studies that we had done now, is to look at, you know, where does this C FOS gene get expressed after a single dose of drug when the animal have received it, and where does the response occur?

Nick Jikomes 1:01:26 

Okay, so basically, when something happens, when the animal is given a drug or it's put into a novel environment, something that we would just call a stimulating experience, let's say you tend to see a gene program turn on in neurons, which is related to neuro plastic remodeling. So as you said, you know, if you want to build a new synapse, you need to turn on certain genes that will lead to the creation or the synthesis of proteins that will physically be the new synapse they need to get shuttled out there. All this physical remodeling needs to happen. And so when you detect the expression of this gene, it's sort of an indication that these neuroplastic events is going to happen. And so what you can do is you can say, give a mouse a drug like psilocybin or put it in a novel environment, whatever it may be. You can then look for what, where, you know, where, what parts of the brain, what neurons are expressing this gene, and that's an indicator that there's some kind of neuroplasticity likely happening in those regions. So you've done that experiment with drugs like psilocybin,

Alex Kwan 1:02:26 

yes, yes, yes. So we've given animal one dose of psilocybin, and then two hours later we would harvest the brain tissue, and then we would basically stain and look at where the C FOS response occur. And the advantage for this measurement is that you can do it in high resolution, but you can also do it high resolution across the whole brain. So it's a little bit different than the previous discussion on trying to measure the dendritic spines. Here we can look at the C FOS changes in the whole mouse brain. So in one of the prior study, we gave animal different drugs. We gave them ketamine and psilocybin, and more recently, we even gave them eight different drugs. And then so different animal, different drugs. And then asked, just asked, you know, how does this induce this different kind of gene expression pattern in different areas in the mouse brain? Yeah,

Nick Jikomes 1:03:19 

so basically, you can give an animal a drug like psilocybin or other drugs, you can wait sometime a couple hours, whatever it may be, and then you can, in some sense, literally freeze the brain in time, and then look in the brain. You can slice up the brain and look everywhere in the brain and see and count and literally look at every single neuron that shows this transcriptional signal that indicates that the drug induced some kind of transcriptional change.

Alex Kwan 1:03:43 

Yeah, and I think the study have been quite interesting in terms of what it reveal. One thing that it reveal is that there are probably, again, more things that are alike between drugs like ketamine and psilocybin than what we think in terms of where the C FOS response it increases. So it increases in the variety of cortical areas, like the prefrontal cortex that we talked about, but also in the visual cortex area, also in other emotional processing area like the amygdala. So there's some commonality, a lot of commonality, and where the C FOS signal get increased after an animal has received a drug like ketamine or psilocybin. In the study, we've also highlighted a couple areas that seems to be psilocybin specific, which we find to be quite interesting. I think it's worthy of some follow up study. One area that seems to be quite psilocybin specific is the insula, so the insular cortex has been implicated in things like pain processing, emotional processing. That's one area that quite specific to psilocybin and not for ketamine. Another area that is a small psilocybin selective, but maybe a more expected, is the dorsal Raphe, which is the nuclei which. The serotonin neuron reside. So normally, you know, the brain itself also can release serotonin, and those serotonergic neurons live in the dorsal Raphe. That area also, specifically is alter has a reduced C FOS response after psilocybin, but it was not changed by ketamine. So there's a few areas like this, which is, you know, have some drug specific differences, which I think are quite intriguing by by and large, many areas show quite similar changes. In terms of ketamine or psilocybin, I

Nick Jikomes 1:05:31 

see so many areas of the brain show these changes that you can detect at specific time points after Drug Administration. Ketamine and psilocybin overall have similar patterns of gene expression change, and you see them in some areas of the brain. So they both have changes in the amygdala, they both have changes in the visual cortex, the frontal cortex, the parts of the brain that you were imaging earlier that we talked about. But then there's also some differences between them, which I think you would expect, right despite any similarities in the behavioral or therapeutic outcome, they do induce different effects, and they have different mechanisms. So parts of the brain, like the insula, are psilocybin specific. You're seeing these transcriptional changes there after psilocybin, but not after ketamine.

Alex Kwan 1:06:09 

Yeah, I think that it's something that to us was quite distinct. I think the effect on insula, I think it might, you know, I think that it might speak to some uses for I think psilocybin in terms of for treatment, like for chronic pain, for example. And there's been, now some studies starting. I know there's one clinical trial now going on, or maybe they're just recruiting out in the Bay Area, I think by people like Josh wooley and Boris Hetz, we're starting to look at whether or suicidal might be useful for chronic pain. So I think, yeah. I think activating and changes to area like the insula could make it useful in that regard, or even other places like the anterior cingulate cortex, which has also been implicated in pain processing.

Nick Jikomes 1:06:54 

Can you unpack for a little bit, a little bit for people, why would the INS Why would you see changes in the insult, and then suspect that something like chronic pain might be important, given that that brain area is changing, what is the insulin sort of doing based on what we know today?

Alex Kwan 1:07:11 

Yeah, so I think so this is not my own specialty, but my understanding is that, you know pain, there's a very physical, visceral kind of pain, which is generally thought to be quite peripheral, where if you touch something and it's painful or it really hurts you, it's a lot of it goes in the sort of at the spinal cord level, it's quite low level. But there are also pain. There are more neuropathic, or there are more chronic, where that pain is quite persistent, and those pain, if you do neuroimaging in people, the area that tend to lit up is actually quite high up, so in the area that we just talked about, for example, in the insula or in the anterior cingulate cortex, and there has been some early work from kind of More neurosurgery that if you actually have some lesion or remove some air, at least pain, and this is now into people that actually have intractable pain. Sometimes people can get relief, for example, with a single autonomy, where they would say that they can still feel the sensation, but they don't care as much about it. So I think, you know, activating these area, I think, is of interest. And why psilocybin have specifically have some of these strong activity in them is quite interesting. And I think, yeah, we'll see what happens in some of the ongoing clinical trial, whether the drug might be of use,

Nick Jikomes 1:08:39 

yeah. So psilocybin sort of lights up the insula in a way that ketamine doesn't. And the insula is basically, it's a part of the brain that is connected to our internal viscera, like our internal organs and stuff. And so you might naturally think, well, given what the insula is connected to and what we know about its processing, you know, if you've got internal chronic pain, that could be a good candidate region to look at,

Alex Kwan 1:09:03 

yeah, what CFOs signal suggests is there also some type of plasticity going on. There's some type of connectivity change there. I think exactly what it is will require some more experiments, because we talked about some of the connectivity change could be differences in the input, what input comes in, also what outputs go out. So it is possible, you know, some of that adaptation could be beneficial, but, yeah, I think we'll see.

Nick Jikomes 1:09:28 

So what? What's coming next for you guys? What are you working on the lab today, to extend the work that you've already done in this

Alex Kwan 1:09:38 

area, we have a couple things that we're interested in. I think one is that one that I already mentioned a little bit in terms of, I think some of the visual changes, I think, you know, the drug itself is obviously at the therapeutic part of it, and I think that's tremendously important, but the acute behavioral effects, you know, is actually was drawn. A lot of neuroscientists into this area back in the 60s and 70s, what does it actually do to perception, and what does it do to an activity in the visual area? So right now, the lab, we have a couple of students who are very interested in these questions. You know, in the frontal cortex, we found that it induces a certain kind of neuro firing pattern in the excitatory neuron, inhibitory neuron, do these same type of excitatory inhibitory cell also change of firing in the same way in the visual cortex. And then, if they do, what does that mean in terms of the processing of the visual stimulus? So that's one area that we're quite keen to pursue, and

Nick Jikomes 1:10:43 

what do you think are, what do you think are some of the biggest unresolved questions in this field of how psychedelic drugs affect the brain that we're probably going to get good answers to in the next two or three years? Say,

Alex Kwan 1:10:58 

one of the things that we want to do, and I think we're close to it, is that we mentioned that the cortex has different cell types, a different excitatory, inhibitory cell type. So my lab and probably other people as well, have now started cataloging the different cell type and how they respond to the drug. And there's also sequencing study now that can tell you which cell type express what kind of serotonin receptor. So we're starting to really have a, if you will, like a parts list and where, where is the serotonin receptor, and how do these cell respond in terms of firing. So I think very soon, we should be able to develop some predictive model in terms of neuro circuits. Given the circuitry that we know that exists in the cortex, how should it respond to any given psychedelic that would target the serotonin receptor? And by that, I mean if you look at psilocybin or psilocin, it activates certain types of receptor in a certain way, and we can maybe predict what happens to the firing neuron if you give some other other drug, for example, five Meo, DMT, that activate the one, a receptor a little bit more than a two, a I think you should have, in five years, be able to predict okay with this change. What does it mean, then, to the cortical firing dynamics and how that differs.

Nick Jikomes 1:12:17 

Interesting. Is there anything you want to reiterate for people about what we've discussed, or any final thoughts you want to leave them with about this field?

Alex Kwan 1:12:27 

Yeah, I think the one thing I will say is, you know, I think the a lot of the research that we do is actually supported by the federal government, so that's one thing. I want to give a shout out to most of the psilocybin research that we study are just supported by the National Institute of Mental Health. I think they find it quite important and that these drugs can be used to useful to treating depression and other also other mental illnesses. Some of our student is supported by a fellowship supported by the NIDA, which is the National Institute with drug abuse. I think the vast majority of our support come from there. So without them, we can't do these studies. So I just want to acknowledge some of the support from the federal grants.

Nick Jikomes 1:13:13 

All right, well, dr, Alex Kwan, thank you for your time. Also, I don't know, do you want to direct people to your website? You've got, you know, all your papers on your website. You've got some cool videos, if people want to check out the what the imaging looks like, and things like that.

Alex Kwan 1:13:27 

Yeah. So we have a lab website. You're welcome to see. We always post all our paper there. So if you find that this journal article you want to read, but they're behind a paywall, you can go to our website, and it should be on there. The Lab website is Alex Kwan, lab.org, and then some of the talks that I do, I also post on a YouTube channel. And if you search my name, you should also find it there if you want to hear any more about our work.

Nick Jikomes 1:13:55 

All right. Dr, Alex Kwan, thank you very much for sharing.

Unknown Speaker 1:13:59 

Okay, great

Nick Jikomes 1:14:10 

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