On MIA Radio this week, MIA’s Zenobia Morrill interviewed Dr. Vance Trudeau, a professor at the University of Ottawa in Canada. Dr. Trudeau describes a recent study he conducted, alongside a team of researchers, led by Dr. Marilyn Vera-Chang, that has implications for understanding of the long-term impact of antidepressant drug exposure (see MIA report).

The study, titled “Transgenerational hypocortisolism and behavioral disruption are induced by the antidepressant fluoxetine in male zebrafish Danio rerio,linked antidepressant exposure to decreased coping behaviors in zebrafish that lasted several generations.

Dr. Trudeau is the research chair in neuroendocrinology at the University of Ottawa, where he studies how the brain regulates hormonal activity in fish and frogs. Such analyses offer important insights into the effects of environmental exposures on human health because these hormonal systems are shared across species.

What follows is a transcript of the interview, edited for clarity.


ZM:  Welcome, Doctor Trudeau, thanks for joining us.

VT:  It’s nice to be here.

ZM: We really appreciate having you here to tell us more about this interesting study. Could you start by giving us a brief overview of the study, what you did and what you found?

VT:  We’ve been interested in how pollutants get into the environment, especially pollutants that we generate through our use of pharmaceuticals. So when you take any pill, aspirin or Prozac or what have you, it goes into the sewage treatment plant, it degrades a little bit, but not all, and then, it’s released to the environment, to lakes or streams or rivers. So we started looking at fluoxetine, the active ingredient of the drug Prozac, quite a few years ago.

Our angle was much more on the impacts on the environment. But then, of course, you realize that these are bioactive substances that we’re taking quite a lot, depending on the statistics, it can be quite high in the human population. So we started from there and then we had questions about, uh, you know, how long would an effect last? And that’s where we started getting into this first generation, second generation, third generational studies. So that’s kind of where we came from to begin this study.

Right. And so you ended up looking specifically at fluoxetine and zebrafish for this study?

VT:  Yes. fluoxetine has gone generic, so it’s in quite a few different antidepressant medications now, and it’s considered an environmental pollutant along with quite a few other of these types of chemicals. And we chose the zebrafish because it’s a very powerful biomedical and environmental model.

The study system was, of course, the stress hormone system, which is identical in fish, frogs, cats, dogs, and humans. The hormone cortisol is the same in fish as it is in humans, and the brain control and the pituitary control of that hormone production in the adrenal gland are very similar between all of these different animal groups. And you can do transgenerational studies in a small fish in a few years. It would take a few lifetimes if you wanted to do it in humans. So, we can get an answer, at least hints, of what might be happening across generations relatively quickly.

ZM: And so what did you observe and how did you go about exposing the zebrafish to fluoxetine?

VT: We started with an early exposure: three hours after fertilization. And that lasted for six days. In the zebrafish embryo, this is very early. This is when you’re getting the formation of organs, and formation of the brain and the actual brain circuits that would be affected by something like fluoxetine, and also, within a day or so as well, the stress hormone system is also being formed. We targeted this first six days of life because those two systems are forming.

Fluoxetine affects a brain system called the serotonin system, and it affects the uptake and the amount of serotonin that might be in the brain. So that’s why we started very early. And then we let them grow into adults, so six months later, in freshwater, so they were only exposed for six days. And then we found that their stress hormone levels, in sort of normal daily life, and under different stresses, were much reduced.

This was a first big surprise. So, we looked at that and tried to figure out what was going on. At six months, they’re adults so we can breed them. We said, “What about the next generation?”

Their reproduction was normal, but the next generation had the same effects: reduced cortisol in daily life and under stressful conditions. And then we did it again in the third generation, and we saw virtually the same thing. So this was obviously quite surprising to us that it would last three generations. That’s a long time, in human terms. That means your great grandparents are affecting your stress, ability to deal with stress now. You don’t even know your great grandparents, probably.

ZM: Yeah, I think that’s part of what readers are wondering is how much can we take a six-day fluoxetine exposure in zebrafish and understand how that might affect humans?

VT: There’s a couple of things. We also observed that these animals had altered behavior. We use a test that’s kind of a test of exploratory behavior; it’s called the “novel tank” test. You put an animal in a tank, and they swim around, and they swim a lot, looking for hiding places. In animals that were treated six months before with fluoxetine, they don’t explore very much.

We have some videos available too that could be very interesting for people to look at. But this is exploratory behavior. What was remarkable is that lasted for two generations. So also a very long time. And we could link the two observations.

One of the more basic discoveries was that the hormone cortisol actually controls this behavior. Cortisol is allowing the animal to explore its environment. And if you lower it by Prozac or by other treatments, they explore less.

The equivalent is in a child, you know, if they go into a room and there are new people, and they look around, and they say “hello,” that’s normal behavior. If you don’t explore the room, it’s called kind of like an internalization of behaviors. And that’s an odd thing. And that’s what Prozac does to kids too. If the mom is taking Prozac, her children have more internalized behaviors. That is kind of a similar thing.

So we have the behavior change lasting for two generations and the stress hormone changes for three generations. How does that translate into potential effects in other animals, including our own species, including humans? Well, cortisol is cortisol. It’s the same hormone, and the same brain hormones control the same hormones in the pituitary and the identical steroid hormones in the adrenal gland. It’s clearly related to other species and the way we think this inheritance is happening, how it gets transferred from one generation to the next, even when the fluoxetine is no longer around for generations, is that it is an epigenetic mechanism. Not a DNA mutation, but something that alters the structure of the DNA. So not the sequence change, something on top of the DNA or DNA methylation or some other mechanisms.

Epigenetics is all the rage at the moment, of course, in the scientific literature. And we haven’t proven that. That’s some of our next studies, but it’s clearly the next thing we should do. And this mechanism, of epigenetic inheritance, is conserved. The mechanism is the same in every single vertebrate.

There’s no reason to think that humans would be different. I mean we study mice and worms and fish and human cells in a dish to get ideas, and it’s shown that these epigenetic mechanisms are really the same. This raises the question of whether it might happen in other species for sure, including humans. So that’s the next big question for medical researchers. Is it happening in humans?

ZM: I know that you mentioned having cited some studies in the actual article that you published about human studies and what happens when that fluoxetine can pass the placental barrier.

VT: This is very interesting work. It was a couple of different labs around the world, looking at what happens when you have a prepartum– during pregnancy–treatment of antidepressants to help moms in trouble, and also postpartum as well. But prepartum, what professor Tim Oberlander at the University of British Columbia has found is that there are effects on the children.

He’s done a few studies in early life, uh, three months, a few years, I forget exactly, but he sees low cortisol levels, and in these people, whose moms took antidepressants, he also sees an increase in internalization behaviors. The lack of exploration of novel environments, for example. So he sees what we were able to see over several generations, and I believe his studies are ongoing. Those patients are, I don’t know how old they are, but it’s a very longterm study to try to see what’s happening to those now young adults.

ZM: Sure. And that’s the advantage, right, of looking at Zebrafish?

VT: Well, any fast-growing, fast-breeding animal would be a great model. Mice, zebrafish, other models have been used for these types of studies. We chose fish because we can ask two questions. What if you control the embryonic environment with human-relevant doses, or if you give them a much lower concentration of fluoxetine than would be found in the environment, would it affect the fish? And we found it did. Low environmental levels that might be in a sewage pipe, in a contaminated river, affected the cortisol levels for several generations. It wasn’t so effective at changing the behavior over generations, but it definitely affected the cortisol.

A fish living in the wild, they need cortisol for many things. They need it for aggression; they need it for growth; they need it for exploratory behavior. Cortisol is super important for survival in changing environments. I mean it is the adaptive hormone. Stress is an adaptive response.  The work of Hans Selye in the 40s and 50s shows that what stress hormones are important for is helping us cope. Coping behaviors and the coping response, in terms of hormones, is altered over generations. There is less of an ability to cope with the daily challenges–kind of the opposite to what you’d expect for an antidepressant.

ZM: That’s what I was about to say. It sounds like the suppression of the ability to cope or the ability to have exploratory behaviors would almost read as a depressed sort of state for someone.

VT: It’s the opposite of what you might expect. There, we have to explore that a little bit, but we’re treating very early in life, the first six days of life, and that’s setting up those hormone systems that I was talking about before, and it looks like it’s changing their path of function and development for several generations.

ZM: I think these findings are are major and have a lot of implications that we ought to be considering. I know that, l to quote one of our Mad in America commenters, Sylvain Rousselot,  why is it that such an important study is not on the front page of scientific journals?

VT: I read that too. And it wouldn’t be on the front page of other scientific journals; it was published in one, the Proceedings of the National Academy of Sciences. They made press releases that many, many, journals, took up, popular articles, radio shows, et cetera, et cetera. And also your own show as well. So I’ve been very happy with the press coverage. Many people are asking detailed and important questions. SoI believe that people are becoming aware. And, you know, there’s the big media splash in the first weeks, but you know, people have to think and read about these types of studies and really get into it before you start worrying about it. Some of the questions you’re asking are really important.

We have to face these facts now that pharmaceuticals can have long impacts, not only Prozac. There are other chemicals that have been shown to have transgenerational effects.

One is a fungicide; this is the most famous study. And another one is, is bisphenol a (BPA), the estrogenic chemical that’s found in plastics. And this can alter offspring behavior and reproductive outcomes.

So we should be asking ourselves as a society, are we ready to face up to this challenge, which is that some of the things we do last generations. Is that a good thing or a bad thing?  We have to ask that question. I think it’s going to depend on which treatment and which chemical. In the case of this example, an inability to cope across generations is not a good thing, no matter what you do, what you say, it’s clearly not a good thing for the fish.

ZM: Y I think there are people who hear this and read these findings and wonder what they should be considering, and should they be worried on their antidepressants, or should prescribers be thinking about prescribing these differently?

VT: This is a really loaded question that many people have. I’m not a medical doctor, and I’ve been asked this question a few times, and for me, it is very clear. If you have concerns, you must discuss it with your physician or psychiatrist or psychologist, to whoever you’re talking with, and do not change treatment until you get professional, expert advice. I think it’s important to ask questions of your physician, about what is going on. Ask them to read this article, and other articles, because I should imagine many people are not yet aware. So, certainly, do not change what you’re doing. You really must seek professional advice on that, and I can’t emphasize that any more. It’s really important to discuss it with people who are helping you.

ZM: It seems that there is that important piece of integration: discussing this with your physician, but also making sure physicians get the information in a study like this, that maybe they’re not necessarily looking.

VT:  I mean we have to ask ourselves now, does it have implications for our own species? And that’s what I think the next wave of research, for example, Oberlander’s work, will help to answer.

ZM: Do you know about cortisol and humans? We were talking a bit about a child who maybe wouldn’t demonstrate exploratory behaviors or ways to cope, but what might that look like in people?

VT: Well, suppressed cortisol, in the human condition, is called hypocortisolism. So most people think of the bad aspects of stress as too much stress and too much cortisol. So that’s hypercortisolism, and there are all kinds of studies on that. It can affect memory, it can immunosuppress you, when you get more susceptible to colds and viral infections and what have you, and that’s been studied quite a lot.

But in the last decade, it’s becoming apparent that low cortisol is also not very good. There’s kind of an appropriate level of cortisol to have for you to be able to adapt. Too low cortisol means you won’t be able to adapt to the daily challenges as efficiently as if you had regular cortisol levels.

The kinds of human conditions that have been associated with low cortisol are PTSD. These unfortunate people have trouble dealing with challenges in life, in PTSD situations. Some disruptive behaviors in children, both boys and girls, are often associated with having low cortisol levels.

So there are certain behavioral problems like that that are associated with low cortisol. There seems to be a good amount of cortisol, if I can say it like that, and too little or too much seems to get us in trouble. This is relatively new, but hypocortisolism is also going to be something to look for in the future as researchers dig through the data and try to understand what low cortisol means as well. There are a few important examples.

ZM: In doing your research and looking at examining pollutants in the environment, did you expect that you would get these studies or that you would be here having this discussion about antidepressant medication?

VT: That’s a good question. I mean, our earlier studies, where we’re treating adult fish on the short term and looking at reproductive outcomes, you can alter reproductive hormones on the short term in various treatment regimes. So, we set out thinking that we were going to give an early life exposure and affect reproduction, but we didn’t. There’s no change in reproduction over three generations. The big surprise was an effect on stress.

In the past 20 years, I have not worked very much on stress hormones. In fact, I avoided it because there are so many other good researchers working on stress hormones. But here we are, this is a major effect, and we are trying to figure out what’s going on.

The tissue that produces cortisol is the adrenal gland in mammals, and in fish, it’s a got a slightly different structure, but the cells are virtually the same, they’re just embedded in the kidney instead of on top of the kidney, like our own adrenal gland is, and those cells are altered. We did something called RNA sequencing to look at all the different genes that would be up and down regulated in the animals treated three generations before. And we found that the enzyme pathways, important for cortisol synthesis, were altered in these animals three generations later.

That tells us that the adrenal gland is functioning differently in these animals. We also think that the brain will be functioning a little bit differently. So, in the next wave of studies, we’re trying to examine where cortisol is acting in the brain, and where fluoxetine is acting in the brain, and finding where they transect. Which cells in the brain are actually affected in these animals? The next study is really trying to understand a little bit more on the brain side of things.

ZM: That is what you are going to pursue?

VT: We’re doing it right now. Yes.

ZM:  I guess you couldn’t avoid studying stress then?

VT: Nope, I have to go for it.

ZM: I think for most people, at first glance, if you don’t and aren’t familiar with cortisol and what that means, it can be hard to understand why that feels important. But as you talk about the effects of fluoxetine exposure, it feels like cortisol and low cortisol, or too high cortisol levels, potentially, can be implicated in presentations where people receive diagnoses, like you were saying, PTSD or disruptive behavior. So, I see how you’ve ended up there when you didn’t expect to, and I see how it’s something that we ought to be, as you said, rethinking in terms of what that means for our species.

VT: Well, cortisol is such an interesting hormone because it has many, many functions. It’s considered a metabolic hormone because it helps you generate energy and metabolize things. It’s the coping hormone. It’s a super important for many, many processes, memory, behavior, all kinds of things. It’s a multifunctional hormone. That’s why I became very, very interested because it has implications for many processes in the body, not just coping behaviors.

We have to dig a little deeper in there. Cortisol can affect many, many tissues in the body as well, both in a good way, for metabolism and daily life, and in a bad way, in super stress situations. For example, suppressed immune system, you know? How many times have you studied like crazy and you’re stressed and you take the exams and you feel great, but three days later you get a cold? This is immunosuppression because of stress. So there are lots of angles to this?

ZM: So it’s really far-reaching that cortisol would be implicated and that we see this across two, three generations. And correct me if I’m wrong, but that was without a diminished effect, right?

VT: Yes. It was especially evident in the males, and we also saw it in the females, but we focused most of the study on the males because it was a little bit more obvious. And we’re now pursuing this sex differences as well. We’re just writing the next paper in the series to look at early exposure and then following males and females a little more closely. So there is a difference in the response.

The other thing is we just published a paper a week or so ago that’s showing that at least part of this reduced cortisol is inherited from the mother. The mom seems to be putting things in the egg before fertilization to set up her children to be having lower cortisol levels. This is something that’s very fascinating, and we have to dig a little deeper. It’s kind of just getting going, and we don’t completely understand our own observations yet. But it’s something to look for in the future, how the parents are actually telling the offspring what’s going to happen.

So the drug treatment is being passed on to the next generation through, in this case, the mother. In other situations, it can be through the father. So the parents are actually passing on this epigenetic information and kind of instructing the embryo what to expect in a way. It’s so fascinating. I mean, it has many, many implications for many types of studies. And there’s a lot of great labs working on it.

ZM: Absolutely. And I’m so fortunate to have you here explaining, talking us through what this means. Are there any other significant aspects of these findings that you’d want to bring up?

VT: I think we’ve covered most of it. There are still lots of questions of course. And, and we’ve covered a bit of that and some of the future studies we will do. Hopefully, other researchers also get some ideas, and we can expand and get to the answer.

ZM: What are some of the other questions that maybe we haven’t gotten to, but that are on your mind?

VT: Well, what are, what are the implications for other bodily functions? So we just looked at the exploratory behavior as a coping response, but what are some of the other cortisol-depend things?

The immune system. For a fish, cortisol helps the animal deal with the aquatic environment. It regulates functions in the gill. In our own species, it helps the formation of the surfactant in the lungs at birth. So it’s important for respiration as well.

There are many other things that one could look at in terms of what would low cortisol do to the animal. I suspect that some functions will be just fine because you can adapt to lower hormone levels over time. And we saw that with the behavior, they eventually adjusted their exploratory behavior even though cortisol was low, but there may be some functions that are permanently changed so we could get into that as well.

ZM: Right. I was curious, how did that eventual adaptation look?

VT: Well, if we look at the exploratory behavior in the third generation, it kind of looks normal, but they still had low cortisol levels. It’s almost like an adaptation to a lower level. That’s all we could conclude.

We don’t really have a good idea of how it would happen. But you know, your body, it’s called homeostasis, your body tries to adjust to changes, right? Short term and long term. And eventually, some other parts of the hormonal system may help to deal with that low cortisol. We really don’t know how, but they did return sort of to normal in their behavior at the third generation. But in the second generation, they were still having very, very low exploratory behavior. That’s like your grandparents affecting your behavior. It’s still a very long time in human terms.

ZM: Yes it is. And I think that point, of what we do know is that cortisol is implicated in a lot of different mechanisms and functions, paired with, and there are a lot of things we still have yet to understand about that, brings up—does bring up a lot of questions about, so what does that mean for interrupting that process or changing the structure of genes through fluoxetine?

VT: I mean that’s where we’re going to go in the next couple of years, for sure.

ZM: Any other questions coming up for you?
VT: That’s about it. That’s going to keep me really busy, and hopefully, I can get some help from some other labs.

ZM: Who is funding this research and are you able to get collaboration from other people?

VT: Who is funding? That’s a good question. It was myself and professor Tom Moon, co-supervisors of Dr. Chang, and we used our research funding, but we did not have a specific grant for this study. It would be hard to convince an agency to fund for three years when you don’t know what’s going to happen. I think maybe now we would have better luck getting funding because we’ve published the paper, but this is NSERC in Canada that’s provided the money.

ZM: In a way, some of these findings are presenting a warning for antidepressant medication, or a cautionary sort of thing to consider. Have you gotten any reactions that weren’t positive to this study?

VT: Not really. There was a couple of people commenting on “It’s always bad, antidepressants are always bad,” saying, you know, that it adjusts, and all that. But this was one or two people.

Most people are being very analytical–they are less public members, other scientists–and asking deep questions about what it means rather than being hyped up about it. I mean, people are being extremely careful. I was contacted by a patient from another country. They were asking about things, and I could not give them advice, of course, but the news is getting out there. I recommended to that person that they discuss in detail with their own physician. Most people are being very, very thoughtful and insightful, actually.

That’s heartening to hear because I think there are a lot of steps that need to be taken next based on what you’ve found. Thank you for your work and thank you for being here with us.

VT: Well, thanks for a great interview. Very interesting questions to get me thinking about other things to do.

Photo credit: Isabelle Mailloux Pulkinghorn, University of Ottawa


MIA Reports are supported, in part, by a grant from the Open Society Foundations


  1. I disagree with the underlying premise that supports this study; it is a generally accepted foundation for much of Behavioral Neuroscience but should not qualify as real science. Studying animal behavior to glean an understanding of human behavior and human genetic influences is based on two generations of abstractions. First scientists must decide how to model human behavior to study it; modeling human behavior is a difficult abstraction since scientists do not understand human behavior. Thereafter, behavioral scientists often attempt to apply the modeled human behavior to an animal population for research; this is so fraught with wild assumptions that the description of “wild abstraction” is an extreme understatement. Studying human psychology and genetic influences from an animal population is two levels of abstraction from directly studying human psychology and genetic influences; it should not qualify as real science.

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    • Thanks Steve for this. I think the term Behavioural Neuroscience is in itself a misnomer and starts with the a priori assumption that behavior is rooted in the brain. There have been enough non psychological studies now showing the influence our bacterial makeup (microbiome) has on our thoughts, feelings and behaviors to make it clear to everyone but those with a vested interest in the status quo that the brain is not the sole (or perhaps even the primary) “home” of cognition and affect.

      About 12 years ago, there was a little girl named Jessie (something) who had a severe seizure disorder and she became internet famous for undergoing a hemisperectomy at JHU (performed by Ben Carson). One of the things I learned from following her and her families ordeal was the concept of neuroplastiticty. If behavior and cognition are domains of certain parts of the brain and you take one or more of those parts out, how does the person go on functioning at all? It should be a medical mystery. And yet it isn’t because just because an area lights up on a brain scan and we say as a result that that’s where certain cognitive or behavioural functions reside, that doesn’t make it true.

      There probably is a lot to be learned from animal behavior in terms of evolutionary psychology because we are actually animals – mammals – with similar evolutionary drivers of behavior and emotion, namely survival. The same as what you said could be said in reverse – that applying human concepts, for example, the mirror test, to animals and saying they don’t have personal awareness and cognition because we don’t see them “recognize themselves” in the mirror, leads to a lot of abuses against animals being justified because we don’t see them as being individuals with lives of their own that matter to them.

      I agree that none of this should qualify as science, but then “science” as an unassailable entity really needs to be knocked down a peg anyway. Just my thoughts…

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      • I do not understand how “the influence our bacterial makeup (microbiome) has on our thoughts, feelings and behaviors” implies that “the brain is not the sole (or perhaps even the primary) ‘home’ of cognition and affect.” Brain “health” (from nutrition, bacteria balance, rest, etc.) affects thoughts and behaviors.

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        • It’s old school thought to believe that “brain health” is what effects thoughts and behaviors actually. Nutrition is tertiary to brain health via gut health. The bidirectional biochemical connection via the vagus nerve is why the gut is called the second brain. Without a healthy gut you cannot have “brain health” because it’s bacterial digestion of food stuff in the gut that produces the chemical state that positively effects the brain. Without a healthy bacterial load in the gut, you cannot be happy. Ever. And no amount of self help, professional therapy, or adjusting brain chemicals will change that. The nearly instant changes in affect seen among chronically depressed patients receiving fecal transplant pills from healthy happy donors when being treat for c diff infections made it pretty clear.

          There have been studies showing that immigrants who move to America quickly adapt their gut bacterial load to mimic those of Americans despite keeping a traditional diet. And immigrants have far higher rates of depression and “psychosis” than native born peoples – their gut changes coupled with discrimination are a double whammy. Other studies are showing that gut bacteria species are going extinct at similar rates to the extinction of other plants and animals, and it’s reasonable to believe that environmental toxins (the amount of roundup in our diets) is contributing to this decline in bacterial diversity in our gut.

          Again, butterflies in your stomach? That’s not your brain. That’s your gut. Those are signals from gut bacteria directly effecting feeling and behaviors. It’s a fascinating subject of study. 🙂

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        • https://www.sciencemag.org/news/2019/02/evidence-mounts-gut-bacteria-can-influence-mood-prevent-depression

          I have a theory that the inflammatory state caused by trauma (as shown with the ACE studies) may be directly toxic to bacterial health and diversity, and is probably responsible for the “leaky gut” concept in a sort of inflammation – leaky gut – brain toxicity – inflammation feedback loop.

          Of course, I’m not a scientist, so what do I know?

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  2. “ZM: And so what did you observe and how did you go about exposing the zebrafish to fluoxetine?”

    You’ll say “they’re just fish” and I’ll say why do we need to torture fish to know right from wrong, to know that doing good is always the right choice, that treating everything in our environments (humans, animals, plants, water, air, etc) as sacred to survival is the right thing to do. Why do people have to protest war or abuse or authoritarian control? Why are good people who break down when exposed to harm vilified instead of being treated as the canary in the coal mine? Why is dominion better than cooperation?

    You’ll say they’re just fish and I’ll say this is why planet Earth is dying.

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