Transgenerational pathological traits induced by prenatal immune activation

The third paper of Transgenerational epigenetic inheritance week was a 2016 Swiss rodent study of immune system epigenetic effects:

“Our study demonstrates for, we believe, the first time that prenatal immune activation can negatively affect brain and behavioral functions in multiple generations. These findings thus highlight a novel pathological aspect of this early-life adversity in shaping disease risk across generations.”

The epigenetic effects noted in the initial round of experiments included:

  • F1 child and F2 grandchild impaired sociability;
  • F1 and F2 abnormal fear expression;
  • F1 but not F2 sensorimotor gating deficiencies; and
  • F2 but not F1 behavioral despair associated with depressive-like behavior.

These transgenerational effects emerged in both male and female offspring. The prenatal immune activation timing corresponded to the middle of the first trimester of human pregnancy.

The effects were found to be mediated by the paternal but not maternal lineage. The researchers didn’t develop a maternal lineage F3 great-grandchild generation.

The next round of experiments done with the paternal lineage F3 great-grandchildren noted these epigenetic effects:

  • The F3 great-grandchildren had impaired sociability, abnormal fear expression and behavioral despair; and
  • The F3 great-grandchildren had normal sensorimotor gating.

Since the first round of tests didn’t show sex-dependent effects, the F3 great-grandchildren were male-only to minimize the number of animals.

Samples of only the amygdalar complex were taken to develop findings of transcriptomic effects of prenatal immune activation.

Items in the Discussion section included:

  1. The F2 grandchild and F3 great-grandchild generations’ phenotype of impaired sociability, abnormal fear expression and behavioral despair demonstrated that prenatal immune activation likely altered epigenetic marks in the germ line of the F1 children which resisted erasure and epigenetic reestablishment during germ cell development.
  2. Abnormal F1 child sensorimotor gating followed by normal F2 grandchild and F3 great-grandchild sensorimotor gating demonstrated that prenatal immune activation may also modify somatic but not germ cells.
  3. Non-significant F1 child behavioral despair followed by F2 grandchild and F3 great-grandchild behavioral despair demonstrated that prenatal immune activation may modify F1 germ cells sufficiently to develop a transgenerational phenotype, but unlike item 1 above, somatic cells were insufficiently modified, and the phenotype skipped the F1 children.
  4. Studies were cited that prenatal immune activation later in the gestational process may produce different effects.

The initial round of experiments wasn’t definitive for the maternal lineage. As argued in Transgenerational effects of early environmental insults on aging and disease and A review of epigenetic transgenerational inheritance of reproductive disease, testing of maternal lineage F3 great-grandchildren was needed to control for the variable of direct F2 grandchild germ-line exposure.

Also, effects that didn’t reach statistical significance in the maternal lineage F1 children and F2 grandchildren may have been different in the F3 great-grandchildren. The researchers indirectly acknowledged this lack by noting that these and other effects of immune challenges in a maternal lineage weren’t excluded by the study.

https://www.nature.com/mp/journal/v22/n1/pdf/mp201641a.pdf “Transgenerational transmission and modification of pathological traits induced by prenatal immune activation” (not freely available)


The study’s lead researcher authored a freely-available 2017 review that placed this study in context and provided further details from other studies:

http://www.nature.com/tp/journal/v7/n5/full/tp201778a.html “Epigenetic and transgenerational mechanisms in infection-mediated neurodevelopmental disorders”

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Experience-induced transgenerational programming of neuronal structure and functions

The second paper of Transgenerational epigenetic inheritance week was a 2017 German/Israeli review focused on:

“The inter- and transgenerational effects of stress experience prior to and during gestation..the concept of stress-induced (re-)programming in more detail by highlighting epigenetic mechanisms and particularly those affecting the development of monoaminergic transmitter systems, which constitute the brain’s reward system..we offer some perspectives on the development of protective and therapeutic interventions in cognitive and emotional disturbances resulting from preconception and prenatal stress.”

The reviewers noted that human studies have difficulties predicting adult responses to stress that are based on gene expression and early life experience. Clinical studies that experimentally manipulate the type, level and timing of the stressful exposure aren’t possible. Clinical studies are also predicated on the symptoms being recognized as disorders and/or diseases.

The researchers noted difficulties in human interventions and treatments. Before and during pregnancy, and perinatal periods are where stress effects are largest, but current human research hasn’t gathered sufficient findings to develop practical guidelines for early intervention programs.


I’m not persuaded by arguments that cite the difficulties of performing human research on transgenerational epigenetic inheritance. There are overwhelming numbers of people who have obvious stress symptoms: these didn’t develop in a vacuum.

Researchers:

  • Design human studies to test what’s known from transgenerational epigenetic inheritance animal studies that will include documenting the subjects’ detailed histories with sufficient biometric samples and data obtained from their lineage.
  • Induce the subjects to at least temporarily avoid what’s harmful for them and/or the offspring, in favor of what’s beneficial.
  • Document the subjects’ actions with history and samples.

I acknowledge that economic incentives may not be enough to get people to participate. I’m familiar with a juvenile sickle-cell study that didn’t get enough subjects despite offering free transportation and hundreds of dollars per visit. The main problem seemed to be that the additional income would be reported and threaten the caregiver’s welfare benefits.

Stop whining that your jobs are difficult, researchers. Society doesn’t owe you a job. Earn it – get yourself and the people in your organization motivated to advance science.

http://www.sciencedirect.com/science/article/pii/S014976341630731X “Experience-induced transgenerational (re-)programming of neuronal structure and functions: Impact of stress prior and during pregnancy” (not freely available)

Does living near a forest keep your amygdala healthier?

A thought-provoking post from A Paper a Day Keeps the Scientist Okay entitled “Living Near a Forest Keeps Your Amygdala Healthier” referenced a 2017 German human study which found:

“..a relationship between place of residence and brain health: those city dwellers living close to a forest were more likely to show indications of a physiologically healthy amygdala structure and were therefore presumably better able to cope with stress.”

The researchers accomplished the imperative of meeting the study’s stated objective:

“We set out to identify and characterize the geographical elements of a city that are associated with these brain structures following a suggestion by Kennedy and Adolph that studies should begin to derive recommendations for urban planning and architecture.

The results of our study may suggest that forests in and around the cities are a valuable resource that should be promoted. However future longitudinal studies are needed to investigate the causal directionality of the effect in order to disentangle whether more forest in ones habitat facilitates brain structural integrity or potentially those people with better brain structural integrity choose to live closer to forests. Moreover we need to investigate whether living close to the forest is associated with an absence of risk factors such as noise, air pollution or stress and thereby has beneficial effects or whether the forest itself constitutes a salutary factor that promotes well-being.”


A major limitation of the study’s methodology that wasn’t noted by the researchers was the intentional non-use of an available data source. Referring to Do we need to study the brain to understand the mind? posted earlier this week:

“..self-report is still the gold standard for assessing emotional experience and the contents of thought..isn’t it easier just to ask?”

The researchers put the forest before the trees, and designed a study that didn’t ask the subjects important questions such as why they lived where they lived. The researchers inferred sketchy fMRI-geography associations because they didn’t solicit relevant primary information via individual self-reports.


I imagined myself as one of the study’s subjects. I don’t live in Berlin, and I’m not part of the selected cohort, but I otherwise generally meet the study’s subject parameters.

Something in my past causes me to actively select housing that isn’t in a noisy environment. If I were asked why I lived where I lived, my answer would have included:

  • A deciding factor in why I sold my second house was the traffic noise in wintertime;
  • A deciding factor in why I bought my fourth house was its location in the center of the housing development, away from street noise; and
  • A deciding factor in why I live where I now live is the house’s orientation away from both direct and reflective traffic noise sources.

Processing my hypothetical fMRI data with my self-reported historical housing choices may or may not have found:

“..geographical features in the proximal participants’ habitat are associated with brain integrity..”

Using the better-quality information of self-reports, though, it’s unlikely that an association this study would have found to be significant – the chance fact that I live within one kilometer of a forest – would have been deemed significant.

https://www.nature.com/articles/s41598-017-12046-7 “In search of features that constitute an “enriched environment” in humans: Associations between geographical properties and brain structure”

Do we need to study the brain to understand the mind?

A coauthor of the studies referenced in:

offered an opinion piece in A Paper a Day Keeps the Scientist Okay entitled “Do We Need To Study The Brain To Understand The Mind?”:

“The emerging consensus appears to be that implementation is important. Interestingly, the inverse question is also being asked by neurobiologists—do we need consider the mind to understand the brain?—and answered largely and increasingly in the affirmative.

Is pain different from negative emotions such as sadness and anger, or are they variants on a common theme?..pain appears to be distinct from negative emotion, but commonalities suggest ways in which they may share underlying processes such as heightened attention.

One of the biggest pitfalls is the temptation to observe brain activity and make inferences about the psychological state—for example, to infer episodic memory retrieval from hippocampal activity, fear from amygdala activity, or visual processing from activity in the ‘visual cortex.’ These inferences ignore the scope of processes which may activate each of these areas and involve a fallacy in reasoning: “if memory then hippocampus” is not the same thing as “if hippocampus then memory.”

The fact that few brain areas, including the ‘visual cortex,’ are dedicated to one process means that self-report is still the gold standard for assessing emotional experience and the contents of thought. This is a serious challenge for those who would like, for example, to assess your brand preferences or your political affiliation from a brain scan. (And isn’t it easier just to ask?)”

Epigenetic effects of early life stress exposure

This 2017 Netherlands review subject was the lasting epigenetic effects of early-life stress:

“Exposure to stress during critical periods in development can have severe long-term consequences..One of the key stress response systems mediating these long-term effects of stress is the hypothalamic-pituitary-adrenal (HPA) axis..early life stress (ELS) exposure has been reported to have numerous consequences on HPA-axis function in adulthood.

ELS is able to “imprint” or “program” an organism’s neuroendocrine, neural and behavioral responses to stress..research focuses along two complementary lines.

Firstly, ELS during critical stages in brain maturation may disrupt specific developmental processes (by altered neurotransmitter exposure, gene transcription, or neuronal differentiation), leading to aberrant neural circuit function throughout life..

Secondly, ELS may induce modifications of the epigenome which lastingly affect brain function..These epigenetic modifications are inducible, stable, and yet reversible, constituting an important emerging mechanism by which transient environmental stimuli can induce persistent changes in gene expression and ultimately behavior.”

In early life, the lower brain and limbic system brain structures are more developed and dominant, whereas the cerebrum and other brain structures are less developed (use the above graphic as a rough guide). Stress and pain generally have a greater impact on the fetus, then the infant, and then the adult.


The reviewers cited 50+ studies from years 2000-2015 in the “Early Life Stress Effects in a “Matching” Stressful Adult Environment” section to argue for the match/mismatch theory:

“Encountering ELS prepares an organism for similar (“matching”) adversities during adulthood, while a mismatching environment results in an increased susceptibility to psychopathology, indicating that ELS can exert either beneficial or disadvantageous effects depending on the environmental context.

Initial evidence for HPA-axis hypo-reactivity is observed for early social deprivation, potentially reflecting the abnormal HPA-axis function as observed in post-traumatic stress disorder.

Interestingly, experiencing additional (chronic) stress in adulthood seems to normalize these alterations in HPA-axis function, supporting the match/mismatch theory.”

Evidence for this theory was contrasted with the allostatic load theory presented in, for example, How one person’s paradigms regarding stress and epigenetics impedes relevant research.


The review mainly cited evidence from rodent studies that mismatched reactions in adulthood may be consequences of early-life events. These events:

“..imprint or program an organism’s neuroendocrine, neural and behavioral responses..leading to aberrant neural circuit function throughout life..which lastingly affect brain function..”

Taking this research to a personal level:

  • Have you had feelings that you were unsafe, although your environment was objectively safe?
  • Have you felt uneasy when people are nice to you?
  • Have you felt anxious when someone pays attention to you, even after you’ve acted to gain their attention?

I assert that mismatched human feelings are one form of mismatched reactions. As such, they may be interpreted as consequences of early-life experiences, and indicators of personal truths.

If researchers can let go of their biases and Advance science by including emotion in research, they may find that human subjects’ feelings produce better evidence for what actually happened during the subjects’ early lives than do standard scientific methods of:

Incorporating this evidence may bring researchers closer to backwardly predicting the major insults to an individual that knocked their development processes out of normally robust pathways and/or induced “persistent changes in gene expression and ultimately behavior.”

https://www.frontiersin.org/articles/10.3389/fncel.2017.00087/full “Modulation of the Hypothalamic-Pituitary-Adrenal Axis by Early Life Stress Exposure”


I discovered this review as a result of it being cited in http://www.sciencedirect.com/science/article/pii/S1084952117302884 “Long-term effects of early environment on the brain: Lesson from rodent models” (not freely available)

Epigenetic effects of THC differ between female adolescents and adults

This 2017 Italian rodent study found:

“THC [delta9-tetrahydrocannabinol, the psychoactive compound of cannabis] exposure affects histone modifications in the brain of female rats in a region- and age-specific manner. Specifically, THC acts on different targets depending on the considered brain area and, remarkably, the adolescent brain is generally more sensitive to THC than the adult brain.

Adolescent exposure to THC, or to synthetic cannabinoids, induced sex-dependent brain and behavioral alterations at adulthood. In female rats, the phenotype was more complex, as both depressive-like and psychotic-like signs were present..the development of the depressive/psychotic-like phenotype is restricted to adolescent THC exposure..not only the behavioral phenotype developed after adolescent, and not adult, exposure, but also changes in both histone modifications and gene expression were more widespread and intense after adolescent treatment, further confirming a specific adolescent susceptibility.

The primary effect in the adolescent brain was represented by changes leading to transcriptional repression, whereas the one observed after adult treatment led to transcriptional activation. Moreover, only in the adolescent brain, the primary effect was followed by a homeostatic response to counterbalance the THC-induced repressive effect, except in the amygdala.”

The authors’ interpretation of the brain area results was:

“..the amygdala is more responsive in adult than adolescent animals..Since it has been established that the amygdala is activated during exposure to aversive stimuli, functioning as a “behavioral brake”, the different response between adult and adolescent animals could represent the biological bases of the adolescent propensity for risk-taking and novelty-seeking behaviors..also in adolescent humans, neuroimaging studies have shown a weaker involvement of the amygdala, and a greater contribution of the NAc [nucleus accumbens], in response to negative and positive stimuli compared to adults.”

http://www.mdpi.com/1422-0067/18/10/2094 “Chronic Δ9-THC Exposure Differently Affects Histone Modifications in the Adolescent and Adult Rat Brain”

A study of perinatal malnutrition where the paradigm excluded epigenetic inheritance

This 2017 New York/Swedish rodent study subject was the epigenetic effects on the F1 children of maternal low protein diet during pregnancy and lactation:

“Male, but not female, offspring of LPD [low protein diet] mothers consistently displayed anxiety- and depression-like behaviors under acute stress.

Our proposed pathway connecting early malnutrition, sex-independent regulatory changes in Egr1 [an Early growth response gene], and sex-specific epigenetic reprogramming of its effector gene, Npy1r [neuropeptide Y receptor Y1 gene], represents the first molecular evidence of how early life risk factors may generate sex-specific epigenetic effects relevant for mental disorders.”


The study was purposely incomplete regarding transgenerational epigenetic effects that may be transmitted from the F1 children to their F2 grandchildren and F3 great-grandchildren. Similar to How one person’s paradigms regarding stress and epigenetics impedes relevant research, the paradigm continued by one of this study’s coauthors restricted inquiry into epigenetic inheritance.

How can the other coauthors respond when a controller of funding publishes the paper referenced in What is epigenetic inheritance? and otherwise makes his narrow views regarding epigenetic inheritance well-known? If the controller’s restricted views won’t allow the funding scope to extend testing to study F2 grandchildren and F3 great-grandchildren, the experiments end, and our understanding of epigenetic inheritance isn’t advanced.

This purposely incomplete study showed that the coauthor only gave lip service to advancing science when he made statements like:

“Further work is needed to understand whether and to what extent true epigenetic inheritance of stress vulnerability adds to the well-established and powerful influence of genetics and environmental exposures.”

The papers of Transgenerational epigenetic inheritance week show the spectrum of opportunities to advance science that were intentionally missed.

https://www.nature.com/articles/s41598-017-10803-2 “Perinatal Malnutrition Leads to Sexually Dimorphic Behavioral Responses with Associated Epigenetic Changes in the Mouse Brain”