Episode 19: Forming Gut Circuits

Peter 0:15
Hi, and welcome back to the Gastronauts podcast. My name is Peter, and my name is Reem hasnah. And we’ll be your hosts. Here at Gastronauts we are committed to exploring communication throughout the body with a focus on the crosstalk between gut and brain. We invite speakers in this field to share both their research and their life journeys. So come join me as we explore the steps that go into shaping a scientist on the Gastronauts Podcast.

I want to introduce Dr. Piali Sengupta. She received her PhD from MIT where she studied pheromones signaling and yeast in Brent Cochran’s laboratory. She then did her postdoc at UCSF where she identified genes that encode how olfactory receptors are encoded in C. elegans with Corey barman. She was then recruited to Brandeis University in 1996, and she is currently a professor of biology at Brandeis University, and is recently elected as a fellow in 2019. For her pioneering work on the molecular genetics of chemical communication and thermo sensation in C. elegans. Her lab work has two primary research focuses. One is the cilia squad, which is focused on the mechanisms by which cilia form and function. And the other is this axis of taxes, which is aimed at uncovering how thermal and chemical stimuli are sensed by C. elegans.

Reem 1:53
I’ll introduce Dr. Brian. So Dr. Brian received his PhD from the University of Colorado Health Science Center, where he studied chemoreceptor cells. He is currently an associate professor in the physiology department at Michigan State University. The focus of his lab is to understand how inflammation in the nervous system, neuroinflammation leads to long term changes in the neuronal circuitry. So welcome Dr. Brian.

To make this episode easier for you. We wanted to try something new this time around and give you some context for some of the terms and words introduced later in the episode. First, Hirschprung’s disease is a disease, which is a condition that affects the large intestine the colon and causes problems with passing stool. That condition is present at birth, as a result of missing nerve cells in the muscle of the baby column. Then, glia. Glia can be called as glial cells or neuroglia, which are non neuronal cells in the central nervous system, and the peripheral nervous system that do not produce electrical impulses. They maintain the homeostasis. Finally, cilia. Cilia are fine hair like projections from certain cells, such as those in the respiratory tract that helped to sweep away fluids and particles.

Winston 3:29
Hi, I’m Winston Liu, I’m from Duke University. Really great talks from both speakers today. Thank you guys for coming. My question is for Dr. Sengupta. As I guess I was thinking about your talk, you know, for example, we have chemo sensation, you know, things that we prefer that are innate, like, you know, loving, sweet things, avoiding better things, for example, versus some things we learn over time. And I’m wondering for something like a C. elegans, do you see the same types of things? Are there sort of innate categories and learn categories? And there’s some insights you can draw about how those things are determined in the field against?

Dr. Piali Sengupta 3:59
Yeah, thank you for that question. So yes, the answer is yes. So there are innate chemicals, obviously, like for. So for example, for not us specifically, but for mammals. Some of the innate responses obviously, are to toxic chemicals to things like pheromones. So worms actually also have all of those responses. So worms actually, and I can talk about this for an hour. But worms actually produced like 150 different types of pheromones. And they have the most amazingly complex responses to those pheromones. So those are what we consider innate behaviors. And a lot of the responses that I was talking about, again, just like for toxic chemicals, they’re also innate, there are learned behaviors. So there are chemicals that can be you know, they’re generally indifferent to it. But if you’re associated with food, they can become attractive, for instance, so there is that kind of associative plasticity as well. So yeah, so the short answer is there are both types of responses.

Winston 4:56
Thank you.

Reem 4:56
Talking about innate and learned, I have a question. Do we make memories of these different experiences and different stimuli that alter the future of sensory behavior?

Dr. Piali Sengupta 5:08
So it’s funny you asked that question, because this is not our work at all. But there is actually now recent work from a number of labs, specifically Coleen Murphy’s lab at Princeton. So worms, when I say the bacteria, they actually a lot of the bacteria, as you can imagine, are pathogenic, make them sick. And so once they’ve actually eaten a pathogenic bacteria, and so initially, they don’t know that it’s pathogenic, they like it, they eat it, they get sick. And then when you expose them to the same bacteria, now they run away from it, which makes sense, right. And so, Callie’s lab has actually shown recently, in some some very nice papers, where that avoidance of a pathogenic bacteria can actually be transmitted through generations through its progeny, it actually is mediated so the worm eats it, it’s in the gut, there’s a small RNA from this pathogenic bacteria that it senses, the signal goes from the gut, to the germ line to the neuron, and that information is passed down through five generations. And then those project even though they’ve never seen that pathogenic bacteria will avoid it. So it’s super cool. There might be other behaviors that are also passed down transgenerationally, but hasn’t been looked at.

Reem 6:18
Dr. Brian, what do you think of glial cells? Do they make memory also of the different stimuli? Or they just forget as it comes over and over?

Dr. Brian Gulbransen 6:30
That’s a great question. I, I’m not aware of any work really showing memory in the gut, necessarily. I mean, there’s a lot of work showing neural plasticity in the circuits. And most of that is in the context of inflammation. So if you perturb the system in some way, you know, the properties of the neurons and the glia change over a long time course. And I don’t know if you necessarily call that learning, but with the glial cells, they’re very plastic, I could imagine that if you, you change the circumstances in any way that glial cell is going to adapt to maintain homeostasis, because that’s their main function. So I think that they would probably display some types of, I guess you could call it sort of learning, I guess, in in terms of how the circuit responds and how the circuit adapts and the glial cell adapting to that circuit. But yeah, I don’t know if we all cells would do anything really what we would call learning, necessarily,

Peter 7:20
When you find some things that are being secreted or released by cells, how do you choose which one to focus on? I know that you mentioned that this octopamine story was the one that you focused on there, Piali. But I guess both of you like you focused on ATP, Brian.

Dr. Piali Sengupta 7:37
So I think for us, it’s actually pretty straightforward, because a lot of our work is based on genetics. So we just screened through a lot of mutants. And then if you have a phenotype, we essentially focus on that one. So a lot of these neurons are expressed multiple neurotransmitters that express multiple neuropeptides. But it’s very straightforward for us to just read through them and look to see if there’s a defect in behavior.

Dr. Brian Gulbransen 7:58
Yeah, I mean, for us, we we focused on purines and acetylcholine to begin with anyway, because those are two of the main neurotransmitters and excitatory circuits in the gut, there’s probably every neurotransmitter that’s in the brain and the gut. And so once you get into, you know, the effects of all these, it could probably get complicated. And there, there are probably many, many more that have effects. But these were two of the most likely candidates. And so we started with them, just because nothing else was known.

Maya Kaelberer 8:22
Hello. Yeah, my name is Maya Kaelberer. And I’m interested to know, the worm has such a reduced nervous system, I should say, fewer neurons. And in a lot of these models, there’s a lot of redundancy in the system. So at some point, if you were to silence this neuron saying, Go this way, or go or don’t go this way, will you eventually have a different circuit that will pick up that signal?

Dr. Piali Sengupta 8:47
That’s a really good question. And so there’s sort of two short answers to that, that I’ll give. So one of them is that so if you continuously either optogenetically or chemo genetically silence or activate a given neuron, eventually that neuron will stop responding just because it’s sort of adapts to the whole process. Right. But then as soon as you release that inhibition, it’ll actually continue to respond again. Your second question is actually sort of a very deep question is about this whole the small nervous system? And so one, if you don’t mind, if I sort of rephrase it, are there circuits that are sort of dedicated to specific tasks? And then so if you get rid of that circuit, for example, with something else kick in? And that’s a really interesting question, because this sort of is an issue of degeneracy in circuit function, where you can actually have multiple circuit components giving rise to the same output. This has been described in many different small nervous systems, for instance, and in fact, we actually find that so if you get rid of a specific set of neurons, you can have a defect in behavior, but then depending on how long you’ve gotten, so suppose you’ve got like you have genetically a blade a set of neurons, there are behaviors for which a completely different set of neurons will kick in and managed to generate that same behavior. But if you acutely block that specific neuron, genetically or optogenetically, then the second set of neurons, it doesn’t give it enough time to kick in. So there’s actually plenty of degeneracy in the system, which actually gives the system a lot of flexibility in terms of generating behaviors. And it’s a very interesting question that we’re looking at, as well.

Maya Kaelberer 10:24
Can I just follow that up? So that’s so cool. So if you get rid of the neuron, another neuron mites will come in and take its place, do you find that its structure then mimics the structure of the neuron that, you

Dr. Piali Sengupta 10:36
No, when I say another neuron, I actually mean a circuit. And so essentially, another circuit can compensate for it. But the way it compensates for it can be very different from the way the original circuit was actually doing that specific function. We don’t fully understand it, but it’s something that’s starting to come up in a couple of months of different experiments. And so people are starting to look at it.

Maya Kaelberer 10:57
Thank you.

Peter 10:59
That was really fascinating. Yeah, it just made me think of like, we used to use knockout models a ton, we knockout and we assumed that that’s the only thing that happens, and there’s so much compensation that occurs. And there’s so much learning, I guess, if we want to use that term,

Dr. piali sengupta 11:11
what is known about the lineages of some of these glia if they actually are sort of circuit specific, and they come from, like, some common lineage, or they come from completely different ones?

Dr. Brian Gulbransen 11:20
Yeah, that’s a great question, you know, so most of them come from neural crest, and they migrate into the gut along with the neurons. And then there, there are some of these precursor cells that have a glial potential. And there’s, there’s others that have a neuron potential. And then there’s some that have this remaining neuron glia potential, and the has done great work describing this population and how the gut patterns itself with these populations of precursor cells. But some of the really interesting work coming out now is about these schwann cell precursors. And these actually are later population of cells that comes in along these extrinsic nerves and populates the gut. And in some of the models of hirschsprungs, these cells are actually able to repopulate the gut and actually form new new enteric neurons and glia. And since in enterically in schwann cells are so similar, and they’re driven towards a similar phenotype in the same environment, it would be very difficult to tell if some of these cells in the myenteric ganglia are actually derived from the schwann cell precursors as opposed to the neural crest cells that come in early in development. And so I think you may actually have a mix of cells of different lineages possibly.

Peter 12:28
So we have another question from Brad.

Brad 12:31
Hi there. I have a question for Dr. Gulbransen, about what sort of effects you’ve seen with stimulating glia and the effects that it has on motility. And also some of this discussion on the lineage of these cells and Dr. patchiness, his work? Are there any opportunities there to treat some of these motility disorders that we see in the gut? Whether it’s a short term motility disorder, or something that’s more long term genetically linked like Hirschsprung? Or something like that?

Dr. Brian Gulbransen 12:56
Yeah, that’s a great question. I, you know, we definitely hope so something like chronic constipation, we could see where, you know, activating glial cells and potentially eating the activity of these circuits might be beneficial, because that would be a prokinetic at that point. So we would hope that, you know, something like that would come out of this. Mustafa was also working on a project on chronic intestinal pseudo obstruction. And there we’ve been doing some collaboration with Roberta de Georgia we found there is that glial bio lipid signaling is impaired. And that if you blocked by a lipid signaling in mice, it gives you a phenotype where you develop these intestinal obstructions. And so, you know, potentially, by restoring that kind of signaling mechanism and the glia, you might be able to restore some of the function in some some of these severe motility disorders like Cpo. Also, another part of the research in the lab right now is on visceral pain. And so several of the people in the lab […] working on visceral pain. And she has been studying how glial cells potentially ate the visceral nociceptors in the context of inflammation. I think that’s another really promising area where modulating glial cell activity could benefit. visceral pain in people with IBS

Brad 14:08
Vry interesting. Thank you.

Peter 14:09
I was really interested in this, I guess the cross generational learning that we had talked about, this made me think whether or not there would be any sex differences. And we actually have a question from Amy Shephard calling in from Boston.

Amy 14:23
And I think your sex differences, Brian in the responses to the ascending and descending neurons in response to glia are really fascinating. I wondered if you saw any when you were doing your more specific call, no joke and courage. Was that true for both sexes? Or did you see sex differences there as well?

Dr. Brian Gulbransen 14:41
That’s a great question. Thanks. Thanks, Amy. That sex differences I think we’re really interesting because, you know, we started doing these stimulations. We weren’t really sure if we would pick up any sex differences in the circuits because, you know, we’ve never looked at this before. And, you know, we thought maybe organ level maybe, but maybe not the circuit level. Actually.What we saw most of the time was that the populations of neurons and glia, that responded were similar, at least the magnitude of the sizes of the cohorts of cells that responded as seemed like there was similar. So it seemed like the the circuitry was wired in a similar way in males and females. But what we saw in the females was consistently the neurons and glia responded with larger calcium responses to anything, so that the female neurons and glia were just amped up, they responded, much larger than the neurons and glia. In males, that was consistent in all our experiments, whether we were doing a fiber track stimulation, the field stimulation, or with the drugs, the drugs seemed like they affected the males and females in a similar way, you know, altering the cohorts of neurons and glia that responded, but just the magnitudes of those responses were different in the calcium responses.

Amy 15:51
Any idea? Why do you have any favorite?

Dr. Brian Gulbransen 15:54
That’s? That’s a good question. I mean, there are probably many, many things that could cause this, you know, I don’t know if it has something to do with the endoplasmic reticulum being different in females or something about calcium release being different in the females at this point, your guesses is probably as good as mine, or better.

Reem 16:10
As a follow up, does age have an effect on the cells?

Dr. Brian Gulbransen 16:14
Yeah, so actually, it does. So what one of the things we’ve observed with age is that there’s a drop off in these connection 43 channels expressed by the glia, the glia seem like they’re less able to respond and less able to convey that response to the neurons. And so we think that this probably is involved in the slowing of gut motility with age and you lose this potential rating effect of having the glial cells recruited by neurons. And we see similar things when we knock out connexin-43 channels and younger animals as these old animals with lower connexin-43 expression.

Paula 17:05
Hi, I’m Paula also from Duke University. And so since we were speaking about innate and learned responses, so I was just curious is the like, lifespan of these worms, and now for us to study all these differentiators in made and like learned? And how do we do that? Just curious.

Dr. Piali Sengupta 17:23
So the typical lifespan of of wild type C. elegans is about 30 days or so. And in any kind of associative conditioning experiments that people have done, that’s actually very fast. So it only happens, like, you know, takes a couple of hours at most. So whether a young warm and an older worm, if they have sort of different responses to different stimuli, they do. But it I think, in that case, it’s a little bit hard to sort of differentiate between whether that’s been learned over time, or whether they’re age dependent, independent, age dependent, changes in the responses. So I don’t know if I can, I don’t know if I can actually directly answer your question of whether over the lifespan there is learning that’s happening that’s changing that responses later.

Paula 18:09
I see. Thank you.

Peter 18:11
To Brad’s question on, I guess translational impact made me think a lot of times, some of the work that we do feels a little bit removed from the direct clinical effects that we can see. And I was wondering, really taking like a 30,000 foot view. How did you get into studying glia? Brian, and how did you get into studying C. elegans purely and how did you choose to really start on this field of research?

Dr. Brian Gulbransen 18:33
Sure. So I actually started studying the enteric nervous system. When I was an undergraduate at the University of Wyoming, I had gone there. I was interested in wildlife biology, and didn’t know what kind of research I wanted to get into was wandering around the halls and the Waluigi department ran into this lab that had a poster outside that was on the enteric nervous system. And I said, hey, that’s pretty cool. I should go in there and talk to that guy. And so I went in there it was Paul Wade, who now works at Takeda. He gave me a job in there doing some research and I studied aging in the gut as an undergrad, then as a graduate student, I wanted to see what else was out there. So I studied chemo reception in the nasal cavity. But it was also communication between non neuronal cells and neurons in the periphery. I knew after doing my PhD work that I wanted to get back into doing in tech neuroscience. And I had also had this experience with signaling between non neuronal cells and neurons. And so I had talked to Keith Sharkey, and he was doing some work on enteric glia, and was interested in glia to neuron signaling and, you know, communication between neurons and glia. As I said, that’s a great fit and what they’re for my postdoc loved it, and just kind of stuck with it from from then on.

Dr. Piali Sengupta 19:38
For me, I mean, as you mentioned, I was a as a graduate student, I also worked on pheromone signaling and yeast, and it sort of became really interested in seeing how animals respond so precisely to their environment. And then, you know, use doesn’t have a nervous system. So as a postdoc, I wanted to find an organism where I could really connect specific genes to behavior.And I think this is something like C. elegans flies, I mean, mouse. Now, of course, also, I guess, absolutely, I still find it absolutely amazing that you can mutate a single gene and see this amazingly dramatic effect on behavior. And then especially in worms, you can, you can actually follow it all the way from the effect of the gene on a specific neuron through the circuit all the way to exactly how the behavior is being altered. And that just even after three decades of this never ceases to amaze me. That’s, I think there’s so much to learn. Just it’s I think it’s a really exciting area. So both of you really study a very interesting area.

Reem 20:37
Not only this, I can see that you have really interesting lab websites. So how did you determine what to publish on your website? Why did you choose to have these illustration in your websites? And why did you choose to put these things and these lab websites?

Dr. Piali Sengupta 20:54
Yeah, so my website is actually set up by a graduate student in the lab, Lauren Tresco, who is went around the lab, and I think just chose the most beautiful pictures that she could find. So I think a lot of the appeal of a website, of course, is the visual appeal, the part of my lab that I didn’t talk about the cellular biology part, they generate a lot of very beautiful pictures. And so I don’t think this was a particularly reasoned decision. I mean, I had a little bit of input, but I basically let them design the website on their own.

Dr. Brian Gulbransen 21:25
Yeah, I kind of did the same thing I you know, I’m sure mine is very outdated at this point, I need to update it, because I’m the one that’s maintaining it. And I usually get around to doing that maybe once a year. So I should probably update it. But I did the same thing and shows, you know, some nice images, some some videos and things that would be kind of eye catching. And then just basically bullet point types of information of what we do. And who’s here.

Peter 21:48
Just as a quick follow up, I thought it was really neat. I was taking a look on your website, Brian, I don’t know if a lot of labs really published, I guess, the methodological detail, and you have like methods for each one of the protocols out there. And then I think, Piali, I thought it was really neat that you have like this section on lab values, and core values in your laboratory. And what was the motivation behind putting this information out there? And why did you feel it was important to share?

Dr. Brian Gulbransen 22:13
It’s, you know, in the efforts to be more transparent, and to have data be more reproducible. I mean, we’ve been trying to publish more than methods, get more of that out there. Eventually, we want to be able to have a part of the labs website actually devoted to a lot of the transcriptomics work that we’re doing right now, and have searchable databases on there. So we can have some of these glial databases all together. So it would be a tool for the community, you know, we don’t want to be operating in a vacuum and kind of with this in this black box, we want to let people know what we’re doing. So they can trust the data. And if other people want to repeat the experiments, they can do it exactly how we did it.

Dr. Piali Sengupta 22:48
So that’s actually that’s really great. I think that I should, we should look into doing that as well. I mean, we tend to actually, for some of the journals, if they allow it, we do tend to upload our Excel spreadsheet, which has all the raw data for every single figure that we’ve generated. But to put in the details of the protocols are actually on the website is a really good idea. I mean, in terms of the core values for my lab, I mean, so like many of your labs, my lab is fairly diverse. I have people from all over the world, from very different backgrounds. And I, myself am an immigrant, I came to this country when I was 18. And so I think it’s really important for me to specify upfront, what are the things that I value, and what I hope that my lab will have in terms of respecting everyone’s opinions, respecting their the diversity and having this having sort of shared values of collaboration, of interaction, and also, very importantly, the scientific ethics. And I think I wanted to just put it up there so that it’s just very obvious to anyone who’s interested in joining my lab. And it’s a conversation that I also have with individuals as well as a group.

Reem 23:59
They’re interesting. I see science, communication nowadays is a very important aspect of science. Because when we communicate science in a better way, we can have science spread all around the world. So thank you so much, both of you for joining us.

Dr. piali sengupta 24:16
Thank you so very much. This was super fun. Thanks for inviting me.

Dr. Brian Gulbransen 24:19
Yeah, thank you so much for the opportunity to share some of our work is this is great.

Peter 24:23
Yeah. Thank you so much.

Reem 24:35
Thank you all for listening, and we’ll see you on the next episode. For more of our content, you can follow us on Twitter at the gut brain matters, or visit our website thinkgastronauts.com. The gastronauts podcast would be impossible without our incredible team. Meredith Schmehl, our producer and theme music composer and a special thanks to the founder of Gastronauts Dr. Diego Gohorquez and the Bohorquez laboratory