A limited study of parental transmission of anxiety/stress-reactive traits

BehavioralTraitsThis 2016 New York rodent study found:

“Parental behavioural traits can be transmitted by non-genetic mechanisms to the offspring.

We show that four anxiety/stress-reactive traits are transmitted via independent iterative-somatic and gametic epigenetic mechanisms across multiple generations.

As the individual traits/pathways each have their own generation-dependent penetrance and gender specificity, the resulting cumulative phenotype is pleiotropic. In the context of genetic diseases, it is typically assumed that this phenomenon arises from individual differences in vulnerability to the various effects of the causative gene. However, the work presented here reveals that pleiotropy can be produced by the variable distribution and segregated transmission of behavioural traits.”

A primary focus was how anxiety was transmitted from parents to offspring:

“The iterative propagation of the male-specific anxiety-like behaviour is most compatible with a model in which proinflammatory state is propagated from H [serotonin1A receptor heterozygote F0] to F1 [first generation] females and in which the proinflammatory state is acquired by F1 males from their H mothers, and then by F2 [second generation] males from their F1 mothers.

We propose that increased levels of gestational MIP-1β [macrophage inflammatory protein 1β] in H and F1 mothers, together with additional proinflammatory cytokines and bioactive proteins, are required to produce immune system activation in their newborn offspring, which in turn promotes the development of the anxiety-like phenotype in males.

In particular, increase in the number of monocytes and their transmigration to the brain parenchyma in F1 and F2 males could be central to the development of anxiety.”

Due to my quick take on the study title – “Behavioural traits propagate across generations..” – I had expectations of this study that weren’t born out. My criticisms below relate to my expectations of what the researchers could have done versus what they did.

The researchers studied parental transmission of behavioral traits and epigenetic changes. Their study design removed prenatal and postnatal parental behavioral transmission of behavioral traits and epigenetic changes as each generation’s embryos were implanted into foster wild-type (WT) mothers.

The study design substituted the foster mothers’ prenatal and postnatal parental environments for the biological parents’ parental environments. So we didn’t find out, for example:

  • What effects the anxious F1 males’ behaviors may have had on their offsprings’ behaviors and epigenetic changes
  • Whether the anxious, hypoactive, overly stress-reactive, hypothermic F2 males’ behaviors affected their offsprings’ behaviors and epigenetic changes
  • To what extents the overly stress-reactive F1 mothers’ prenatal environments and postnatal behaviors induced behaviors and/or epigenetic changes in their children, and whether the F2 children’s parental behaviors subsequently induced behaviors and/or epigenetic changes in the F3 generation.

How did the study meet the overall goal of rodent studies: to help humans?

  1. Only a minority of humans experienced an early-life environment that included primary caregivers other than our biological parents.
  2. Very few of us experienced a prenatal environment other than our biological mothers.
  3. Maybe the researchers filled in some gaps in previous rodent studies, such as determining what is or isn’t a “true transgenerational mechanism.”

As an example of a rodent study that more closely approximated human conditions, the behavior of a mother whose DNA was epigenetically changed by stress induced the same epigenetic changes to her child’s DNA when her child was stressed per One way that mothers cause fear and emotional trauma in their infants:

“Our results provide clues to understanding transmission of specific fears across generations and its dependence upon maternal induction of pups’ stress response paired with the cue to induce amygdala-dependent learning plasticity.”

How did parental behavioral transmission of behavioral traits and epigenetic changes become a subject not worth investigating? These traits and effects can be seen everyday in real-life human interactions and physiology. But when investigating human correlates with behavioral epigenetic changes of rodents in the laboratory, parental behavioral transmission of behavioral traits is often treated the way this study treated it: as a confounder.

I doubt that people who have reached some degree of honesty about their early lives and concomitant empathy for others would agree with this prioritization.

http://www.nature.com/ncomms/2016/160513/ncomms11492/full/ncomms11492.html “Behavioural traits propagate across generations via segregated iterative-somatic and gametic epigenetic mechanisms”

A one-sided review of stress

The subject of this 2016 Italian/New York review was the stress response:

“The stress response, involving the activation of the hypothalamic-pituitary-adrenocortical axis and the consequent release of corticosteroid hormones, is indeed aimed at promoting metabolic, functional, and behavioral adaptations. However, behavioral stress is also associated with fast and long-lasting neurochemical, structural, and behavioral changes, leading to long-term remodeling of glutamate transmission, and increased susceptibility to neuropsychiatric disorders. Of note, early-life events, both in utero and during the early postnatal life, trigger reprogramming of the stress response, which is often associated with loss of stress resilience and ensuing neurobehavioral (mal)adaptations.”

A key point in the review was the intentional dismissal of the role of GABA in favor of the role of glutamate:

“The changes in neuronal excitability and synaptic plasticity induced by stress are the result of an imbalance of excitatory (glutamatergic) and inhibitory (GABAergic) transmission, leading to long-lasting (mal)adaptive functional modifications. Although both glutamate and GABA transmission are critically associated with stress-induced alteration of neuronal excitability, the present review will focus on the modulation of glutamate release and transmission induced by stress and glucocorticoids.”

No particular reason was given for this bias. I inferred from the review’s final sentence that the review’s sponsors and funding prompted this decision:

“In-depth studies of changes in glutamate transmission and dendrite remodeling induced by stress in early and late life will help to elucidate the biological underpinnings of the (mal)adaptive strategies the brain adopts to cope with environmental challenges in one’s life.”

The bias led to ignoring evidence for areas the reviewers posed as needing further research. An example of relevant research the reviewers failed to consider was the 2015 Northwestern University study I curated in A study that provided evidence for basic principles of Primal Therapy that found:

“In response to traumatic stress, some individuals, instead of activating the glutamate system to store memories, activate the extra-synaptic GABA system and form inaccessible traumatic memories.”

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4812483/ “Stress Response and Perinatal Reprogramming: Unraveling (Mal)adaptive Strategies”

The current paradigm of child abuse limits pre-childhood causal research

As an adult, what would be your primary concern if you suspected that your early life had something to do with current problems? Would you be interested in effective treatments of causes of your symptoms?

Such information wasn’t available in this 2016 Miami review of the effects of child abuse. The review laid out the current paradigm mentioned in Grokking an Adverse Childhood Experiences (ACE) score, one that limits research into pre-childhood causes for later-life symptoms.

The review’s goal was to describe:

“How numerous clinical and basic studies have contributed to establish the now widely accepted idea that adverse early life experiences can elicit profound effects on the development and function of the nervous system.”

The hidden assumption of almost all of the cited references was that these distant causes can no longer be addressed. Aren’t such assumptions testable here in 2016?

As an example, the Discussion section posed the top nine “most pressing unanswered questions related to the neurobiological effects of early life trauma.” In line with the current paradigm, the reviewer assigned “Are the biological consequences of ELS [early life stress] reversible?” into the sixth position.

If the current paradigm encouraged research into treatment of causes, there would probably already be plenty of evidence to demonstrate that directly reducing the source of the damage would also reverse the damaging effects. There would have been enough studies done so that the generalized question of reversibility wouldn’t be asked.

Aren’t people interested in human treatments of originating causes so that their various symptoms don’t keep bubbling up? Why wouldn’t research paradigms be aligned accordingly?

The review also demonstrated how the current paradigm of child abuse misrepresents items like telomere length and oxytocin. Researchers on the bandwagon tend to forget about the principle Einstein expressed as:

“No amount of experimentation can ever prove me right; a single experiment can prove me wrong.”

That single experiment for telomere length arrived in 2016 with Using an epigenetic clock to distinguish cellular aging from senescence. The seven references the review cited for telomere length that had “is associated with” or “is linked to” child abuse findings should now be viewed in a different light.

The same light shone on oxytocin with Testing the null hypothesis of oxytocin’s effects in humans and Oxytocin research null findings come out of the file drawer. See their references, and decide for yourself whether or not:

“Claimed research findings may often be simply accurate measures of the prevailing bias.”

http://www.cell.com/neuron/fulltext/S0896-6273%2816%2900020-9 “Paradise Lost: The Neurobiological and Clinical Consequences of Child Abuse and Neglect”

Beneficial epigenetic effects of mild stress with social support during puberty

This 2016 Pennsylvania rodent study found:

“Stress in the context of social support experienced over the pubertal window can promote epigenetic reprogramming in the brain to increase the resilience to age-related cognitive decline in females.

These findings are actually consistent with previous studies showing that some amount of adversity, or adversity under more favorable circumstances such as social support or a protective gene polymorphism, provides a measure of ‘grit’ in coping with later life challenges.

Our findings provide a unique perspective on this relationship, as they highlight the important link between experience during the pubertal window and cognitive health during aging.”

The researchers made efforts to further investigate causes of unexpected results, such as:

“Peripubertal stress alone did not significantly alter Barnes maze performance in aging compared to aged Controls. Mice that had experienced stress with concurrent social support (CVS + SI) actually performed better than Control aged mice, specifically in learning the reversal task faster.

Peripubertal stress had no effect on corticosterone levels in response to an acute restraint stress or in sensorimotor gating and baseline startle reactivity.”

The investigations led to epigenetic findings:

“Consistent with our behavioral findings, stress in the context of social interaction resulted in long-term reprogramming of gene expression in the PFC [prefrontal cortex]. While there were no differentially expressed genes between Control and CVS females, there were 88 genes that were significantly different between Control and CVS + SI groups. Of the genes that were downregulated, a large portion (23 genes; 35%) were microRNAs.

We found that the PFC transcriptome of CVS + SI aged females was significantly enriched for predicted targets of the 23 microRNAs that were downregulated in the PFC in these mice. This suggests that microRNAs represent a mode of regulation capable of enacting far-reaching programmatic effects, and are a critical epigenetic gene expression regulatory mechanism.”

Applicability to humans was suggested by associations such as:

“A single microRNA can target more than a hundred different mRNA targets, and more than 45,000 conserved microRNA binding sites have been annotated in the 3′ UTR of 60% of human genes.”

A few limitations were noted:

“Given that mice at this age (1 year) are commonly compared to ‘late middle aged’ humans, later aging time points may yield differences in this group. Alternatively, it is possible that there was an effect of peripubertal stress that was not long-lasting due to the mild nature of our chronic stress model.

To include early neglect as a part of the stressor experience, CVS females were weaned one week earlier (PN21) than Control and CVS + SI mice. The addition of the stress of this earlier weaning likely poses a significant contribution to the programming of the PFC.”

One of the study coauthors was also a coauthor of:

http://press.endocrine.org/doi/pdf/10.1210/en.2015-1876 “Peripubertal stress with social support promotes resilience in the face of aging”

What’s the underlying question for every brain study to answer?

Is it:

  • How do our brains internally represent the external world?

Is it:

  • How did we learn what we know?
  • How do we forget or disregard what we’ve learned?
  • What keeps us from acquiring and learning newer or better information?

How about:

  • What affects how we pay attention to our environments?
  • How do our various biochemical states affect our perceptions, learning, experiences, and behavior?
  • How do these factors in turn affect our biology?

Or maybe:

  • Why do we do what we do?
  • How is our behavior affected by our experiences?
  • How did we become attracted and motivated toward what we like?
  • How do we develop expectations?
  • Why do we avoid certain situations?

Not to lose sight of:

  • How do the contexts affect all of the above?
  • What happens over time to affect all of the above?

This 2015 UCLA paper reviewed the above questions from the perspective of Pavlovian conditioning:

“The common definition of Pavlovian conditioning, that via repeated pairings of a neutral stimulus with a stimulus that elicits a reflex the neutral stimulus acquires the ability to elicit that the reflex, is neither accurate nor reflective of the richness of Pavlovian conditioning. Rather, Pavlovian conditioning is the way we learn about dependent relationships between stimuli.

Pavlovian conditioning is one of the few areas in biology in which there is direct experimental evidence of biological fitness.”

The most important question unanswered by the review is:

  • How can its information be used to help humans?

How does Pavlov conditioning answer:

  • What can a human do about the thoughts, feelings, behavior, epigenetic effects – the person – that they’ve been shaped into?

One relevant hypothesis of Dr. Arthur Janov’s Primal Therapy is that a person will continue to be their conditioned self until they address the sources of their pain. A corollary is that addressing symptoms will seldom address causes.

How could it be otherwise? A problem isn’t cured by ameliorating its effects.

As an example, the review pointed out in a section about fear extinction that it doesn’t involve unlearning. Fear extinction instead inhibits the symptoms of fear response. The fear memory is still intact, awaiting some other context to be reactivated and expressed.

How can that information be used to help humans?

  • Is inhibiting the symptoms and leaving the fear memory in place costless with humans?
  • Or does this practice have both potential and realized adverse effects?
  • Where’s the human research on methods that may directly address a painful emotional memory?

http://cshperspectives.cshlp.org/content/8/1/a021717.full “The Origins and Organization of Vertebrate Pavlovian Conditioning”

Use it or lose it: the interplay of new brain cells, age, and activity

This 2015 German review was of aging and activity in the context of adult neurogenesis:

“Adult neurogenesis might be of profound functional significance because it occurs at a strategic bottleneck location in the hippocampus.

Age-dependent changes essentially reflect a unidirectional development in that everything builds on what has occurred before. In this sense, aging can also be seen as continued or lifelong development. This idea has limitations but is instructive with regard to adult neurogenesis, because adult neurogenesis is neuronal development under the conditions of the adult brain.

The age-related alterations of adult neurogenesis themselves have quantitative and qualitative components. So far, most research has focused on the quantitative aspects. But there can be little doubt that qualitative changes do not simply follow quantitative changes (e.g., in cell or synapse numbers), but emerge on a systems level and above when an organism ages. With respect to adult neurogenesis, only one multilevel experiment including morphology and behavior has been conducted, and, even in that study, only three time points were investigated.

In old age, adult neurogenesis occurs at only a small fraction of the level in early adulthood. The decline does not seem to be ‘regulated’ but rather the by-product of many age-related changes of other sorts.

From a behavioral level down to a synaptic level, activity increases adult neurogenesis. This regulation does not seem to occur in an all-or-nothing fashion but rather influences different stages of neuronal development differently. Both cell proliferation and survival are influenced by or even depend on activity.

The effects of exercise and environmental enrichment are additive, which indicates that increasing the potential for neurogenesis is sufficient to increase the actual use of the recruitable cells in the case of cognitive stimulation. Physical activity would not by itself provide specific hippocampus-relevant stimuli that induce net neurogenesis but be associated with a greater chance to encounter specific relevant stimuli.

Adult hippocampal neurogenesis might contribute to a structural or neural reserve that if appropriately trained early in life might provide a compensatory buffer of brain plasticity in the face of increasing neurodegeneration or nonpathological age-related functional losses. There is still only limited information on the activity-dependent parameters that help to prevent the age-dependent decrease in adult neurogenesis and maintain cellular plasticity.

The big question is what the functional contribution of so few new neurons over so long periods can be. Any comprehensive concept has to bring together the acute functional contributions of newly generated, highly plastic neurons and the more-or-less lasting changes they introduce to the network.”

I’ve quoted quite a lot, but there are more details that await your reading. A few items from the study referenced in the first paragraph above:

“The hippocampus represents a bottleneck in processing..adult hippocampal neurogenesis occurs at exactly the narrowest spot.

We have derived the theory that the function of adult hippocampal neurogenesis is to enable the brain to accommodate continued bouts of novelty..a mechanism for preparing the hippocampus for processing greater levels of complexity.”

The role of the hippocampus in emotion was ignored as it so often is. It seems to me that the way to address many of the gaps mentioned by the author may be to Advance science by including emotion in research.

For example, from the author’s The mystery of humans’ evolved capability for adults to grow new brain cells:

“Adult neurogenesis is already effective early in life, actually very well before true adulthood, and is at very high levels when sexual maturity has been reached. Behavioral advantages associated with adult neurogenesis must be relevant during the reproductive period.”

When human studies are designed to research how “behavioral advantages associated with adult neurogenesis must be relevant” what purpose does it serve to exclude emotional content?

http://cshperspectives.cshlp.org/content/7/11/a018929.full “Activity Dependency and Aging in the Regulation of Adult Neurogenesis”

Chronic pain causes epigenetic changes in the brain and immune system

This 2015 Canadian rodent study by McGill researchers found:

“The critical involvement of DNA methylation in chronic pain. We show that in the PFC [prefrontal cortex], a brain region strongly implicated in chronic pain, a stunning number of promoters [control gene expression] are differentially methylated 9 months after injury. These changes are distant both in time and space from the original injury.

The changes in DNA methylation are highly organized in functional pathways that have been implicated in pain such as dysregulation of dopaminergic, glutamatergic, opioid and serotoninergic systems and important signaling and inflammatory pathways.

Genome-wide DNA methylation modifications of T cells [circulating white blood cells that control immune response] are also associated with nerve injury.

Most of the promoters (72%) identified as differentially methylated in T cells after nerve injury were also affected in the brain. While the methylation profiles in some of these modules were affected in the same direction in the brain and the T cells, others went in opposite direction. This is consistent with the idea that the brain and the immune system play different roles in chronic pain.

These data suggest that persistent pain is associated with broad and highly organized organism-wide changes in DNA methylation, including two critical biological systems: the central nervous and immune systems. This work also provides a possible mechanistic explanation for commonly observed comorbidities observed in chronic pain (i.e anxiety, depression). Finally, the sheer magnitude of the impact of chronic pain, particularly in the prefrontal cortex, illustrates the profound impact that living with chronic pain exerts on an individual.”

The news coverage focused on how the study’s findings may lead to non-invasive DNA methylation measurements of chronic pain as well as treatments of the effects. I’d argue that the researchers’ concluding statement of the Discussion section deserved the most focus:

“Beyond the example of chronic pain, the robust and highly organized DNA methylation changes seen here in response to nerve injury provides some of the strongest evidence to date that experience effects DNA methylation landscapes at large distances in time and space.”

The study provided “some of the strongest evidence to date” that experiences caused widespread, long-lasting epigenetic changes. Given experiences’ etiologic functions, research with working hypotheses that experiences may potentially reverse epigenetic changes should be green-lighted.

“DNA methylation landscapes at large distances in time and space” warrant systematic examination of how experiential epigenetic changes during early life may be reversed by experiential therapies later in life. In 2016, there’s sufficient evidence for modifying research goals to primarily address causes, not just effects.

http://www.nature.com/articles/srep19615 “Overlapping signatures of chronic pain in the DNA methylation landscape of prefrontal cortex and peripheral T cells”