Shaping the brain: Before, during and after birth

CHRIS HATZIS
Eavesdrop on Experts, a podcast about stories of inspiration and insights. It’s where expert types obsess, confess and profess. I’m Chris Hatzis, let’s eavesdrop on experts changing the world - one lecture, one experiment, one interview at a time.

TRACY BALE
Hi, my name is Tracy Bale, I am a Professor of pharmacology and psychiatry at the University of Maryland and Baltimore, Maryland, USA and I am also the Director of a new centre called the Centre for Epigenetic Research in Child Health and Brain Development.

CHRIS HATZIS
In February of this year, Dr Tracy Bale was a special guest of the The Florey Institute of Neuroscience and Mental Health, University of Melbourne, where she gave a public lecture titled “Stressed parents: Shaping the brain before, during and after birth.”

The lecture focused on the role that stress and trauma play in disease across generations and how our life experiences can be transmitted biologically to the next generation, affecting not only how a child’s brain develops but also how they interact with their environment as they grow into adulthood.

Dr Tracy Bale sat down to chat about her work with Dr Andi Horvath.

ANDI HORVATH
Professor Tracy, what are you really known for? What do your friends refer to you as?

TRACY BALE
Well that might be out of the context of this podcast right now, but scientifically a lot of my colleagues think of me as being someone who has studied intergenerational and transgenerational effects of stress and how it’s passed from parent to offspring, including both mum and dad.

ANDI HORVATH
I know you sometimes start your talks with a joke. So let’s go with a joke. I know it starts with three scientists walk into a bar and they see a mother mouse and a son mouse lapping up gin from a thimble.

TRACY BALE
So the mother mouse, who is clearly an alcoholic and now has a child who is also an alcoholic, turns to these scientists - including a politician, I’m going to add in this joke - and she says to them, hey geniuses, can you tell me why my child is in this very sad state? Of course Gregor Mendel says it must be something to do with…

ANDI HORVATH

Gregor Mendel the great geneticist, says?

TRACY BALE
Yeah. So Gregor Mendel says of course it must be something to do with your genetics. Then Freud says, no, no, no I think it has something to do with your helicopter parenting style. Then of course Donald Trump enters in and said no it’s because your ancestors were a bunch of idiots. At this point five hiply dressed, somewhat ageing men from the '80s walk in and say, in fact no it is because you didn’t feed enough Vegemite to your child while your child was developing...

ANDI HORVATH
Got it, and it does have Vitamin B.

TRACY BALE
[Laughs].

ANDI HORVATH
So what you’re saying is it’s a complex thing between genes, environment and behaviours as well as lifestyle and the interaction between your ancestral makeup.



TRACY BALE

That is exactly right and it’s funny, that over decades we keep coming back to this concept, and each decade it’s sort of reframed in a different way, but really what it is what we like to refer to as G by E, by D. That means your genes, that which you inherit from your mum and your dad, your environment, that which you are exposed to, both positively and negatively, this is not all just negative and it’s not dogmatic in that your genes determine or are deterministic, right? It’s the influence of the environment within an area of which those genes determine your path. Then the D is the developmental windows, and what that means is when these different environmental exposures - again, mum was obese, dad was stressed, you have a specific type of enrichment, your parents read to you more or less.

Those sorts of environmental influences. Your diet, illnesses that you were exposed to. The time periods in which those exposures happen, did they happen prenatally, postnatally? Did they happen during puberty? Our brain continues to respond to its environment. So all of them together determine exactly how we function in our risk and our resilience.

ANDI HORVATH
Now I believe that our total make up, being a combination of all those things you describe, can also transcend a generation. So it’s not just our children but our children’s children.

TRACY BALE
Yeah so this comes from studies that are decades old, coming from an Överkalix region of Sweden. This is a very northern area of Sweden. There was a time period really early on where, because of its isolation, the individuals, the inhabitants of this area of Överkalix were exposed to periods of abundance in terms of harvest and large periods of famine.

The church records, which were classically kept in the basement of these churches, kept incredible details of the inhabitants’ birth weights, illnesses, other diseases, in addition to the crop records. So there were a number of investigators, Bygren and others, who took this data and they examined them really closely and they studies in which they would say, okay in a period of time in which there was famine versus a period of time in which there was abundance and the children who were exposed, perhaps when mum was pregnant or when children were going through developmental periods. Then how did that predict? The first studies really examined how it predicted their longevity.

Okay so a child, let’s say was going through that pre-pubertal growth spurt of which the germ cells, the cells that will give rise to the next generation, are maturing. They said, okay so if we’re exposed to an overabundant crop, meaning we had lots of calories during that window, or if the same child was exposed to a famine during that window, did that abundance or famine lead to signals that affected the germ cells and thereby then affected the next generation? That would be intergenerational.

What was truly remarkable about these studies, which seems pretty straightforward, was not just because they studied women or females, which seems very obvious about exposure, but these were really the first studies that indicated male germ cell vulnerability and that was really impactful because it gave us our first evidence to say that if a male was exposed, especially during unique windows of when their germ cells were forming – because remember the male germ cell continues to turn over continuously, that there might be a window in which exposure to something like a famine, could be stored, that signal itself stored, and continue to impact those boys well into manhood when they were having children.

The first studies demonstrated, actually, that a famine signal was propagated in a way that the next generation lived longer. It enhanced longevity. So it was probably signals which we don’t really fully understand yet, and that’s a lot of the studies that my lab does, what are these signals? What are the biological signals? Where are they stored and how do they give rise then to why the next generation may live longer? It’s probably something metabolic in nature, but how does that happen for the next generation? Those are really the first studies that indicated, wait a minute, it’s not just females and their eggs but men and their germ cells as well, the sperm are somehow storing signals that impact how the next generation develops.

ANDI HORVATH

Tell us more about the uterine environment. We know just from public education that alcohol affects the growing foetus, and we know the uterine environment is actually very important for a growing foetus.

TRACY BALE

It seems surprising that only within the last few decades have we really gained this information and this vantage point so for instance the placenta. Let’s talk about the placenta. The placenta is this incredibly endocrine tissue and what that means is, is that the placenta is not just a freeway of information travelling back and forth between the maternal compartment and the foetal compartment. It is actually a tissue that grows and develops and differentiates into all these different important actually key cell types that transfer information as well as produce its own information that is required by the developing foetus.

Meaning that the developing foetus, and especially the developing foetal brain, relies on this information over the course of development. And if you alter how the placenta develops, you may change its function, thereby, what we define as transplacental signals, which tells the brain, wow this is an environment that is going to have lots of calories available. Or this is an environment that’s not going to have enough calories available. Therefore allowing the foetus, the brain, to be born into what it would define as a best fit environment.

Then we have what is called the mismatch, which is kind of the DOHaD, the Developmental Origins of Health and Disease idea, which was really coined by a scientist named Barker who called it the Barker hypothesis. Barker has subsequently passed away, but Barker had this idea that it was so important that the intrauterine environment, the information that the foetus and the brain think are going to be a best guess for how it’s going to develop once it's born, match. When the mismatch happens, so we think it’s going to be an abundant environment because mum has gestational diabetes and sugar levels are high and it turns out you’re born into an environment that’s not so, that it’s the mismatch that may put us at risk.

ANDI HORVATH
So you’re in an area referred to as epigenetics, which is sort of like the non-genetic influences on gene expression. Tell us about your research.

TRACY BALE
Epigenetics is in fact - think of it as a biochemical mark on the DNA. So it doesn’t change the DNA sequence, we still inherit that from mum and dad. It is the environment’s way of allowing specific genes to be expressed or not expressed, expressed more or during given times or in specific tissues, and that’s really what epigenetics is about.

Now, epigenetics can be cell type specific, it can be tissue specific and it can be developmental time period specific. Some of those marks will last, others will not. Some of them can have a temporary influence that may resolve, others, especially if those epigenetic marks end up in a germ cell of a developing baby - so that gives rise again to that next generation. You can imagine a way in which you can have an inter and even potentially a transgenerational effect on how the offspring may develop, again based on what this idea would be for a best fit environment.

ANDI HORVATH
How did you set about examining the markers that are transmitting the information across the generations.

TRACY BALE
That’s a great question and something that this field has been struggling with for quite some time. How do we really understand? It seems obvious, mum is exposed to an illness which may be viral or a dietary challenge, she may be diabetic, or in case of my lab we study stress, which is really ultimately all of those things. How does it pass its effect not just to the developing foetus, but what if she experienced those perturbations before she was even pregnant?

Or dad, and this is really where those studies from the Överkalix region of Sweden come in, what if dad had been exposed to those stressors or perturbations? How on earth would those - because sperm is turning over, so the signal would have to be stored somewhere along dad’s reproductive tract, but not directly in the sperm. That’s really where the field has been making the greatest advances, trying to understand dad’s somatic storage of information along the reproductive tract, that could pass on those signals to the sperm in such a way that the sperm transiting dad’s reproductive tract, eventually meet up and carry that signal to the egg in a way in which a signal, sort of like telephone game. In which it is the same signal propagated, or a signal to a signal, to a signal, sort of the A to B to C to D, that eventually alter what happens at fertilisation.

ANDI HORVATH
So the combination of egg, sperm and womb, does it affect a female foetus or a male foetus in a different way?



TRACY BALE
So understanding sex differences during development has become an enormous focus in the field of understanding brain development. Some of the reasons for that are just a vast appreciation for research understanding at the cellular level, what does sex mean? So if a cell is XX or XY meaning XX for female cell, XY for a male cell, that the signals all the way down at the level of the chromatin, the DNA itself may be different, so it may be different in how it’s responding to the environment. The best evidence we have is thinking about the placenta.

In animal research, which we use to try to understand mammalian development, we look at both male and female within the same uterus. So we can take a mouse, for example, and we can expose that mum while she’s pregnant to multiple different types of stressors throughout her pregnancy. Then we can ask the question for - because mice have litters, right? So there’s a developing male and a female within the same uterus and we can look at the effect of mum’s stress on how that placenta - how the cells differentiate, the different transplacental cues that they’re giving to the foetus and how that might be different.

What we found is all the way down to the level of an XX placental cell, and an XY - because remember, I’m going to back up here, that the placenta develops out of the embryo, so at fertilisation, if you go back to your developmental biology. Once fertilisation happens egg cell you get a two cell embryo, four cell, blastocyst et cetera before we develop the foetus remember. The outside of that blastocyst is called the trophectoderm, and that gives rise to the trophoblast cells that comprise the placenta that eventually invades mum’s uterus. So because of that, the placenta is largely XX if it’s a female foetus and XY if it’s a male foetus. So we can ask sex specific questions in the same intrauterine environment. Mum has been stressed, how does that placenta respond.

If you actually take a look at the evidence from - if you ask any neonatologist, paediatrician, obstetrician, if you say, well we know from history of studying effects of mum having a dietary challenge, diabetes, stress, immune infection et cetera, the evidence is largely in the favour of the fact that a baby who is male is at much greater risk, somewhere - depending on the diseases we’re talking about - four to 10 times more likely intrauterine, to the same perturbation than a female baby. The evidence also demonstrates that if you look at a NICU, the neonatal intensive care unit, where if something has gone wrong during a pregnancy the baby ends up, there’s way more male babies in the NICU than female babies. If a male baby and a female baby end up in the NICU it is in fact that the female babies will go home sooner.

If you look - if you just compound all that evidence and think about neurodevelopmental disorders. Autism, schizophrenia, ADHD, any of those things that we label as neurodevelopmental because we know that the perturbation, because the changes in the brain happen intrauterine, those are all slanted towards a male bias compared to females. There’s four times more males affected than females, this is also true for schizophrenia, this is true for ADHD. So we know that if something happens intrauterine, a male baby is at much greater risk than a female baby.

ANDI HORVATH

The poor chaps. So what’s the cause of that?

TRACY BALE

Well, let me tell you though, if perturbation happens after birth, females are at much greater risk in terms of the brain. So we pay for it somewhere.

ANDI HORVATH
Okay so it evens out in the end. What do evolutionary biologists make of this sex difference?

TRACY BALE
Well it may be that for - if you think about evolution, so I’m going to give you an example. Think about the current obesity epidemic, at least we have a huge obesity epidemic in the US. Okay, so why is that? If something puts you at risk for all kinds of diseases, everything from cancer to diabetes, et cetera, why, evolutionarily, do we continue to overeat? Well the reason for that is, our brains, which are on an evolutionary scale, have been programmed to desire calories, because the biggest perturbation our brains, as human beings, is concerned about, is actually famine. Our brains are wired - this is why no drug company has been able to manufacture a drug to get us to stop eating. Because there is so much redundancy built into our brains, on an evolutionary scale, to continue to eat calories.

The best evidence I can provide for you, in the US we call it the thanksgiving dinner effect. Thanksgiving in the US is a gluttonous holiday, full of all kinds of calorically dense food, everyone knows that experience, you overeat dinner to the fact where you are just so full you couldn’t possibly eat any more turkey and then somebody brings out the pie. Despite how full you are, you are going to eat pie, because again, the part of your brain that seeks reward in terms of, oh that looks so good, will override the fact that you don’t need those calories, you didn’t need any of those calories, probably. But you want to eat them. That is the evolutionary scale.

The same is true for stress and our environment and the evolutionary scale has not caught up yet with the fact that we can eat too much, that calories are too available. Nor has it really caught up with the consequences of autism or schizophrenia or stress. So eventually the evolution will catch up with it, but right now, the acute effects, autism, schizophrenia, these are not diseases that kill off a species and in fact in a given environment may actually provide some benefit. That is evolution and we have not really caught up or figured that out yet.

Evolution, so why is the benefit? We think - and I’ll give you an example again of the placenta. One of the reasons that females are so protected in the intrauterine environment has to do with - again if you think of a cell and you focus all the way in to the level of how our DNA in the nucleus works, and because females have a lot of genes on the X chromosome - females have two Xs, males have one - that there is a way in which the genes in the females that are not what we call X inactivated. There are some genes that escape and it allows females to express things that buffer them. You can think of this as a car, a gas and a brake. Many of these genes, in terms of responding to the environment, females have more of the brake and so they sort of survey an environment, well we’re not going to respond to this, we’re just going to let this one go by, and they put the brake on.

In the placenta, right next door in a mouse environment, is a male, and it’s got less of that brake so it’s got more of that gas and it says oh my gosh what is this? We should respond. Oh my goodness what is this? We should respond. That continuous responding to mum’s change in environment, be it flu, or a cold, or a diabetic environment, or what is this stress, what is this stress, what is this stress? They react, react, react. The females are braking, braking, braking. Those signals change the placenta in the male, and by the end of gestation now, the developing male brain has seen all of these continuous responses and the female brain has not.

What that may do then is, you’re now born into a world where how you’re going to respond to the environment as a male is very different than the female and then the right genetic background - let’s go back to our G by E by D, on the right genetic background it may put that male at greater risk for later development of schizophrenia or by age two development of autism. Or, think about this, if that placenta is sending cues to that male brain, changing environment, changing environment, what do you think evolutionary that it may place upon that male? Let’s say now you’re in elementary school, going into middle school. Your brain may have now been wired to be vigilant, constantly responsive. What do we call that? We call that ADHD.

So why we’re seeing more and more of this in males and we see less of it in females, may just have to do with that - a vigilance on an evolutionary scale, may have been advantageous if you’re out somewhere and there’s more lions, et cetera, that you need to be vigilant. So the right environment has you watching what’s going on outside the window instead of listening to a teacher in a classroom. Because you may have survived, whereas the other students who are paying attention to the teacher and not watching the environment would not have.

ANDI HORVATH
This is extraordinary research on stress and the foetus. But beyond, this has shed insights into other disorders. Tell us more.

TRACY BALE
So related to ADHD, exactly, why is it do we think - there’s different evidence that suggests perhaps males in a given classroom environment, the teachers are just impatient, so it could also be a diagnosis issue, I don’t want to ignore that, that we have differences. That’s for sure.

But why it may be again at an evolutionary perspective, that it may be again advantageous to behave in a certain way. So perhaps with the right cues during development, it may be that you don’t want to be socially interactive. If that cue during development was that there was lots of infection around, I’ll give you an example, perhaps you don’t want to be social once you’re born, you want to be a little more private or withdrawn to prevent yourself from picking up that the flu in the environment could be infectious. So you can think about ways in which evolutionary scale may suggest advantageous behaviours as opposed to just detrimental.



ANDI HORVATH
So from an evolutionary biology point of view, we need all types in the tribe because it’s survival.

TRACY BALE
That’s exactly right, survival.

ANDI HORVATH
I love this, because one might be thinking pregnant women, watch out, take care, take a seat. But in actual fact they’ve just got to be pregnant normally.

TRACY BALE
Right, I guess it takes a village and that village may represent a wide swath of how we all interact with our environment and at an evolutionary scale that could provide some benefit in terms of risk if a given virus comes through or a given famine comes through, et cetera. How do we utilise our calories? Those are important signals as well. We have a breadth, some people store calories really well, in a given environment, that might look like a disadvantage, but actually evolutionarily storage of calories is advantageous. Those scrawny people out there who didn’t store their calories, the first famine that comes around, they’re gone, they’re not reproducing. So the breadth of how we respond and adapt to our environment, again that developmental window piece of it may provide some benefit as well. But I think the thing we can overthink is that we can’t protect - here the key word is protect - the developing foetus from everything because there may be some advantageous longevity to aspects of having some resilience built into effects of our environment.

I’m going to add to that another euphemism that we have in the US right now, we started with helicopter parenting and we now call it snowplough parenting, where it’s actually seen as a disadvantage. Kids whose parents move every obstacle out of their way, turns out is not a good thing. Because what we have are children going off to college and beyond who haven’t learned how to deal with conflict or stress, having them all removed from them. This is not advantageous because now they’re out in the world and they’re not sure how to cope. This is not just about mental health, although this is critically important for mental health, but even physiologically, how do I deal or adapt to a perturbation of my environment when I should have learned that skill, let’s say when I was eight or 10 and now I’m 22 and I’m not sure, nor is my body or brain able to handle it.

ANDI HORVATH
Professor Tracy, what has surprised you about this journey of research?

TRACY BALE

You know what I’ve found most surprising is that when you start off with a, hey let’s try this just to see what happens. Or the best thing is when a graduate student comes in your office and says, you know what I was thinking, I’d like to try - and you think to yourself, it’s early in your PhD, it’s probably not going to work, but let’s see what happens.

This is the question related to that intergenerational. If we take a male and just - just a mouse, and expose we them to these chronic stressors every day for a period of time, and then we give them weeks off of stress, so they haven’t been stressed for weeks. It’s the equivalent of, your job is super stressful, something bad is happening, a new boss has come in, but you go on a, let’s say four week vacation, you’ve forgotten all about it, and then you come home and you get pregnant. So you’re the male, you come home and your wife gets pregnant. You would think, well it’s been four weeks, I haven’t been stressed. Well it’s incredible that this information gets passed on to their offspring, and changes how those offspring’s brains develop.

Here’s the most surprising part. Three months later - so this is the good thing about mice, we can breed them again and again. We take the same dad, the same mum, breed them multiple litters. We can ask the question, how long does this effect last? Three months, which in the life of a mouse I’m going to tell you - so a year old mouse is the equivalent of late middle age. Three months later that male is breeding still, and passing on the same effect. That to me is, A, a little bit scary, but B gives us a model that says, wow something really is happening here, now we can try to delve really deep into the biology and then see how that translates. In my lab, all of our animal studies have a human component to them as well. So we study, believe it or not, all of these effects as well in humans, and we collect lots of sperm samples to ask those same questions.



ANDI HORVATH
Tracy, where did your passion for science stem from?



TRACY BALE

My passion for science, you know what, it’s one of those things where when I look back I had some really - I grew up in southern Minnesota in a little small town, mostly a farm town. My father was actually a pharmacist, a druggist, so clearly science is in my DNA and I always just loved science, I loved my science classes. I never dreamed, I had no idea that being a scientist was in my future. But to me in thinking, even as a high schooler and into college, what is more fascinating than our brain? Nothing, I challenge you, nothing is more fascinating, nothing is more puzzling of course, than our brain, but nothing is more fascinating.

I just think that the opportunity to develop a career where I can do - I can listen to a podcast, as a good example, and I have this experience all the time where I’m at home on a Sunday and I’m baking and I’m listening to a podcast in the background and I think oh my gosh, that’s a fascinating question and I come into the lab on Monday and we have a lab meeting and I get everybody pumped up and we can ask that question and say, okay how do we model that, how do we ask that question? Is it something we can scientifically study to help answer for human disease and translate that? It’s a super opportunity, I feel very lucky.

ANDI HORVATH
So Tracy, leave us with a shareable idea.





TRACY BALE
I think the aspect - in recent move to Baltimore in the US which has its challenges as a city, has a lot of race disparities and a lot of issues with discrimination. I’ve spent a lot of time engaging in that community and one of the things that crosses between my stress research and thinking about that community is when you’re standing in line and you see an individual behaving in a certain way and you’re impatient with their decision process or you’re impatient that they don’t understand how something should work, to take a moment and reflect upon how they got there and the disadvantage that may have put them in that position and not just their disadvantage or their different perspective but that of probably their parents as well and how that has contributed to your opportunities, their opportunities and again thinking about this breadth of how we all come together with our different perspectives.

This is not just about somebody being ignorant or somebody being disadvantaged. But it can also be what we really gain together by bringing those perspectives of, wow your brain developed in a very different environment than my brain and how I really have come to appreciate everybody’s unique opportunity and unique perspective and what it brings. It has really shaped how we think about a lot of the science that we do in my lab, of how that brain perspective may see the world in a very different way and how it’s responding to its environment and what that really affords us as opportunities together.

ANDI HORVATH

Professor Tracy Bale, thank you.

TRACY BALE
No, thank you, this has been super fun.

CHRIS HATZIS
Thank you to Dr Tracy Bale, Professor of Pharmacology at the University of Maryland School of Medicine and Director of the Center for Epigenetic Research. And thanks to our reporter Dr Andi Horvath.

Eavesdrop on Experts - stories of inspiration and insights - was made possible by the University of Melbourne. This episode was recorded on February 12, 2020. You’ll find a full transcript on the Pursuit website. Audio engineering by me, Chris Hatzis. Co-production - Silvi Vann-Wall and Dr Andi Horvath. Eavesdrop on Experts is licensed under Creative Commons, Copyright 2020, The University of Melbourne. If you enjoyed this episode, review us on Apple Podcasts and check out the rest of the Eavesdrop episodes in our archive. I’m Chris Hatzis, producer and editor. Join us again next time for another Eavesdrop on Experts.