Neurobiologists find chronic stress in early life causes anxiety, aggression in adulthood

In recent years, behavioral neuroscientists have debated the meaning and significance of a plethora of independently conducted experiments seeking to establish the impact of chronic, early-life stress upon behavior – both at the time that stress is experienced, and upon the same individuals later in life, during adulthood.

These experiments, typically conducted in rodents, have on the one hand clearly indicated a link between certain kinds of early stress and dysfunction in the neuroendocrine system, particularly in the so-called HPA axis (hypothalamic-pituitary-adrenal), which regulates the endocrine glands and stress hormones including corticotropin and glucocorticoid.

Yet the evidence is by no means unequivocal. Stress studies in rodents have also clearly identified a native capacity, stronger in some individuals than others, and seemingly weak or absent in still others, to bounce back from chronic early-life stress. Some rodents subjected to early-life stress have no apparent behavioral consequences in adulthood – they are disposed neither to anxiety nor depression, the classic pathologies understood to be induced by stress in certain individuals.

This week, a research team led by Associate Professor Grigori Enikolopov of Cold Spring Harbor Laboratory (CSHL) reports online in the journal Plos One the results of experiments designed to assess the impacts of social stress upon adolescent mice, both at the time they are experienced and during adulthood. Involving many different kinds of stress tests and means of measuring their impacts, the research indicates that a “hostile environment in adolescence disturbs psychoemotional state and social behaviors of animals in adult life,” the team says.

The tests began with 1-month-old male mice – the equivalent, in human terms of adolescents – each placed for 2 weeks in a cage shared with an aggressive adult male. The animals were separated by a transparent perforated partition, but the young males were exposed daily to short attacks by the adult males. This kind of chronic activity produces what neurobiologists call social-defeat stress in the young mice. These mice were then studied in a range of behavioral tests.

“The tests assessed levels of anxiety, depression, and capacity to socialize and communicate with an unfamiliar partner,” explains Enikolopov. They showed that in young mice, chronic social defeat induced high levels of anxiety and helplessness, and less social interaction, including diminished ability to communicate with other young animals. Stressed mice also had less new nerve-cell growth (neurogenesis) in a portion of the hippocampus known to be affected in depression: the subgranular zone of the dentate gyrus.

Another group of young mice was also exposed to social stress, but was then placed for several weeks in an unstressful environment. Following this “rest” period, these mice, now old enough to be considered adults, were tested in the same manner as the other cohort. 

In this second, now-adult group, most of the behaviors impacted by social defeat returned to normal, as did neurogenesis, which retuned to a level seen in healthy controls. “This shows that young mice, exposed to adult aggressors, were largely resilient biologically and behaviorally,” says Enikolopov.

However, in these resilient mice, the team measured two latent impacts on behavior. As adults they were abnormally anxious, and were observed to be more aggressive in their social interactions. “The exposure to a hostile environment during their adolescence had profound consequences in terms of emotional state and the ability to interact with peers,” Enikolopov observes.

Study finds stem cell combination therapy improves traumatic brain injury outcomes

Traumatic brain injuries (TBI), sustained by close to 2 million Americans annually, including military personnel, are debilitating and devastating for patients and their families. Regardless of severity, those with TBI can suffer a range of motor, behavioral, intellectual and cognitive disabilities over the short or long term. Sadly, clinical treatments for TBI are few and largely ineffective.

In an effort to find an effective therapy, neuroscientists at the Center of Excellence for Aging and Brain Repair, Department of Neurosurgery in the USF Health Morsani College of Medicine, University of South Florida, have conducted several preclinical studies aimed at finding combination therapies to improve TBI outcomes.

In their study of several different therapies—alone and in combination—applied to laboratory rats modeled with TBI, USF researchers found that a combination of human umbilical cord blood cells (hUBCs) and granulocyte colony stimulating factor (G-CSF), a growth factor, was more therapeutic than either administered alone, or each with saline, or saline alone.

The study appeared in a recent issue of PLoS ONE.

“Chronic TBI is typically associated with major secondary molecular injuries, including chronic neuroinflammation, which not only contribute to the death of neuronal cells in the central nervous system, but also impede any natural repair mechanism,” said study lead author Cesar V. Borlongan, PhD, professor of neurosurgery and director of USF’s Center of Excellence for Aging and Brain Repair. “In our study, we used hUBCs and G-CSF alone and in combination. In previous studies, hUBCs have been shown to suppress inflammation, and G-CSF is currently being investigated as a potential therapeutic agent for patients with stroke or Alzheimer’s disease.”

Their stand-alone effects have a therapeutic potential for TBI, based on results from previous studies. For example, G-CSF has shown an ability to mobilize stem cells from bone marrow and then infiltrate injured tissues, promoting self-repair of neural cells, while hUBCs have been shown to suppress inflammation and promote cell growth.

The involvement of the immune system in the central nervous system to either stimulate repair or enhance molecular damage has been recognized as key to the progression of many neurological disorders, including TBI, as well as in neurodegenerative diseases such as Parkinson’s disease, multiple sclerosis and some autoimmune diseases, the researchers report. Increased expression of MHCII positive cells—cell members that secrete a family of molecules mediating interactions between the immune system’s white blood cells—has been directly linked to neurodegeneration and cognitive decline in TBI.

“Our results showed that the combined therapy of hUBCs and G-CSF significantly reduced the TBI-induced loss of neuronal cells in the hippocampus,” said Borlongan. “Therapy with hUBCs and G-CSF alone or in combination produced beneficial results in animals with experimental TBI. G-CSF alone produced only short-lived benefits, while hUBCs alone afforded more robust and stable improvements. However, their combination offered the best motor improvement in the laboratory animals.”

“This outcome may indicate that the stem cells had more widespread biological action than the drug therapy,” said Paul R. Sanberg, distinguished professor at USF and principal investigator of the Department of Defense funded project. “Regardless, their combination had an apparent synergistic effect and resulted in the most effective amelioration of TBI-induced behavioral deficits.”

The researchers concluded that additional studies of this combination therapy are warranted in order to better understand their modes of action. While this research focused on motor improvements, they suggested that future combination therapy research should also include analysis of cognitive improvement in the laboratory animals modeled with TBI.

Stray prenatal gene network suspected in schizophrenia

Researchers have reverse-engineered the outlines of a disrupted prenatal gene network in schizophrenia, by tracing spontaneous mutations to where and when they likely cause damage in the brain. Some people with the brain disorder may suffer from impaired birth of new neurons, or neurogenesis, in the front of their brain during prenatal development, suggests the study, which was funded by the National Institutes of Health.

“Processes critical for the brain’s development can be revealed by the mutations that disrupt them,” explained Mary-Claire King, Ph.D., University of Washington (UW), Seattle, a grantee of NIH’s National Institute of Mental Health (NIMH). “Mutations can lead to loss of integrity of a whole pathway, not just of a single gene. Our results implicate networked genes underlying a pathway responsible for orchestrating neurogenesis in the prefrontal cortex in schizophrenia.”

King, and collaborators at UW and seven other research centers participating in the NIMH genetics repository, report on their discovery Aug. 1, 2013 in the journal Cell.

“By linking genomic findings to functional measures, this approach gives us additional insight into how early development differs in the brain of someone who will eventually manifest the symptoms of psychosis,” said NIMH Director Thomas R. Insel, M.D.

Earlier studies had linked spontaneous mutations to non-familial schizophrenia and traced them broadly to genes involved in brain development, but little was known about convergent effects on pathways. King and colleagues set out to explore causes of schizophrenia by integrating genomic data with newly available online transcriptome resources that show where in the brain and when in development genes turn on. They compared spontaneous mutations in 105 people with schizophrenia with those in 84 unaffected siblings, in families without previous histories of the illness.

Unlike most other genes, expression levels of many of the 50 mutation-containing genes that form the suspected network were highest early in fetal development, tapered off by childhood, but conspicuously increased again in early adulthood – just when schizophrenia symptoms typically first develop. This adds to evidence supporting the prevailing neurodevelopmental model of schizophrenia. The implicated genes play important roles in migration of cells in the developing brain, communication between brain cells, regulation of gene expression, and related intracellular workings.

Having an older father increased the likelihood of spontaneous mutations for both affected and unaffected siblings. Yet affected siblings were modestly more likely to have mutations predicted to damage protein function. Such damaging mutations were estimated to account for 21 percent of schizophrenia cases in the study sample. The mutations tend to be individually rare; only one gene harboring damaging mutations turned up in more than one of the cases, and several patients had damaging mutations in more than one gene.

The networks formed by genes harboring these damaging mutations were found to vary in connectivity, based on the extent to which their proteins are co-expressed and interact. The network formed by genes harboring damaging mutations in schizophrenia had significantly more nodes, or points of connection, than networks modeled from unaffected siblings. By contrast, the network of genes harboring non-damaging mutations in affected siblings had no more nodes than similar networks in unaffected siblings.

When the researchers compared such network connectivity across different brain tissues and different periods of development, they discovered a notable difference between affected and unaffected siblings: Genes harboring damaging mutations that are expressed together in the fetal prefrontal cortex of people with schizophrenia formed a network with significantly greater connectivity than networks modeled from genes harboring similar mutations in their unaffected siblings at that time in development.

The study results are consistent with several lines of evidence implicating the prefrontal cortex in schizophrenia. The prefrontal cortex organizes information from other brain regions to coordinate executive functions like thinking, planning, attention span, working memory, problem-solving, and self-regulation. The findings suggest that impairments in such functions — often beginning before the onset of symptoms in early adulthood, when the prefrontal cortex fully matures – appear to be early signs of the illness.

The study demonstrates how integrating genomic data and transcriptome analysis can help to pinpoint disease mechanisms and identify potential treatment targets. For example, the mutant genes in the patients studied suggest the possible efficacy of medications targeting glutamate and calcium channel pathways, say the researchers.

"These results are striking, as they show that the genetic architecture of schizophrenia cannot be understood without an appreciation of how genes work in temporal and spatial networks during neurodevelopment," said Thomas Lehner, Ph.D., chief of the NIMH Genomics Research Branch.

Scientists Coax Brain to Regenerate Cells Lost in Huntington’s Disease

Researchers have been able to mobilize the brain’s native stem cells to replenish a type of neuron lost in Huntington’s disease. In the study, which appears today in the journal Cell Stem Cell, the scientists were able to both trigger the production of new neurons in mice with the disease and show that the new cells successfully integrated into the brain’s existing neural networks, dramatically extending the survival of the treated mice.

“This study demonstrates the feasibility of a completely new concept to treat Huntington’s disease, by recruiting the brain’s endogenous neural stem cells to regenerate cells lost to the disease,” said University of Rochester Medical Center (URMC) neurologist Steve Goldman, M.D., Ph.D., co-director of Rochester’s Center for Translational Neuromedicine.

Huntington’s disease is an inherited neurodegenerative disease characterized by the loss of a specific cell type called the medium spiny neuron, a cell that is critical to motor control. The disease, which affects some 30,000 people in the U.S., results in involuntary movements, problems with coordination, and, ultimately, in cognitive decline and depression. There is currently no way to slow or modify this fatal disease.

For Goldman, the idea behind his strategy to treat the disease emerged from his decades-long study of neural plasticity in canaries. Songbirds like canaries have intrigued biologists because of their ability – unique in the animal kingdom – to lay down new neurons in the adult brain. This process, called adult neurogenesis, was first discovered by Goldman and Fernando Nottebohm of the Rockefeller University in the early 1980s, when the two realized that when learning new songs new neurons were added to regions of the bird’s brain responsible for vocal control.

“Our work with canaries essentially provided us with the information we needed to understand how to add new neurons to adult brain tissue,” said Goldman. “Once we mastered how this happened in birds, we set about how to replicate the process in the adult mammalian brain.”

Humans already possess the ability to create new neurons. Goldman’s lab demonstrated in the 1990s that a font of neuronal precursor cells exist in the lining of the ventricles, structures found in the core of the human brain. In early development, these cells are actively producing neurons. However, shortly after birth the neural stem cells stop generating neurons and instead produce glia, a family of support cells that pervade the central nervous system. Some parts of the human brain continue to produce neurons into adulthood, the most prominent example is the hippocampus where memories are formed and stored. But in the striatum, the region of the brain that is devastated by Huntington’s disease, this capability is “switched off” in adulthood.

Goldman and his team spent the past decade attempting to unravel the precise chemical signaling responsible for instructing neural stem cells when to create neurons and when to create glia cells. One of the most critical clues came directly from the earlier research with canaries. In the part of the bird’s brain were new songs are acquired and neurons added, the scientists observed the regulated expression of a protein called brain derived neurotrophic factor, or BDNF.  When the production of this protein is triggered, the local neural stem cells are instructed to produce neurons.

At the same time, the scientists also realized that they had to simultaneously suppress the bias of these stem cells to produce glia. They found that when BDNF was combined with another molecule called noggin – a protein that inhibits the chemical pathway that dictates the creation of glial cells – they could successfully switch the stem cell’s molecular machinery over to the production of neurons.

The next challenge was how to deliver these two proteins – BDNF and noggin – precisely and in a sustained fashion to the area of the brain involved in Huntington’s disease. To do so, they partnered with scientists at the University of Iowa to modify a viral gene therapeutic, called an adeno-associated virus, to deliver the necessary molecular instructions to the neural stem cells.

The virus infected the target cells in the brains of mice with Huntington’s disease and triggered the sustained over-expression of both BDNF and noggin. This, in turn, activated the neighboring neural stem cells which began to produce medium spiny motor neurons. The new neurons were continuously generated and migrated to the striatum, the region of the brain impacted by Huntington’s disease, where they then integrated into the existing neuronal networks. 

The researchers were able to significantly extend the survival of the treated mice, in some cases doubling their life expectancy. The researchers also devised a way to tag the new neurons and observed that the cells extended fibers to distant targets within the brain and establish electrical communication. 

After having established the ability to generate new replacement neurons in mouse models of Huntington’s disease, the researchers also demonstrated that they could replicate this technique in the brains of normal squirrel monkeys, a step that brings the research much closer to tests in humans. 

“The sustained delivery of BDNF and noggin into the adult brain was clearly associated with both increased neurogenesis and delayed disease progression,” said Goldman. “We believe that our data suggest the feasibility of this process as a viable therapeutic strategy for Huntington’s disease.”

Weird: Nuclear Bomb Tests Reveal Adults Grow New Brain Cells

Aboveground nuclear bomb testing in the 1950s and 1960s inadvertently gave modern scientists a way to prove the adult brain regularly creates new neurons, research reveals.

Researchers used to believe that the brain changed little once it finished maturing. That view is now considered out of date, as studies have revealed how changeable — or plastic — the adult brain can be.

Much of this plasticity is related to the brain’s organization; brain cells can alter their connections and communications with other brain cells. What has been less clear is whether, and to what extent, the human brain grows brand-new neurons in adulthood.

"There was a lot in the literature showing there was neurogenesis in rodents and every animal studied," said study researcher Kirsty Spalding, a biologist at the Karolinska Institute in Sweden, "But there was very little evidence of whether this happens in humans."

Tantalizing clues

Scientists had reason to believe it does. In adult mice, the hippocampus, a structure deep in the brain involved in memory and navigation, turns over cells all the time. Some of the biological markers linked to this turnover are seen in the human hippocampus. But the only direct evidence of new brain cells forming in the region came from a 1998 study in which researchers looked at the brains of five people who had been injected with a compounded called BrdU that cells take up into their DNA. (The compound was once used in experimental cancer studies, but is not used anymore for safety reasons.)

The BrdU study revealed that neurons in the hippocampuses of the participants contained the compound in their DNA, indicating these brain cells had formed after the injections. The oldest person in the study was 72, suggesting new neuron creation, known as neurogenesis, continues well into old age.

The 1998 study was the only direct evidence of such neurogenesis in the human hippocampus, however. Spalding and her colleagues wanted to change that. Ten years ago, they began a project to track the age of neurons in the human brain using an unusual tool: spare molecules left over from Cold War-era nuclear bomb tests.

Learning to love the bomb

Between 1945 and 1962, the United States conducted hundreds of aboveground nuclear bomb tests. These tests largely stopped with the Limited Test Ban Treaty of 1963, but their effects remained in the atmosphere. The neutrons sent flying by the bombs reacted with nitrogen in the atmosphere, creating a spike in carbon 14, an isotope (or variation) of carbon.

This carbon 14, in turn, did what carbon in the atmosphere does. It combined with oxygen to form carbon dioxide, and was then taken in by plants, which use carbon dioxide in photosynthesis. Humans ate some of these plants, along with some of the animals that also ate these plants, and the carbon 14 inside ended up in their bodies.

When a cell divides, it uses this carbon 14, integrating it into the DNA of the new cells that are forming. Carbon 14 decays over time at a known rate, so scientists can pinpoint from that decay exactly when the new cells were born.

Over the past decade, Spalding and her colleagues have used the technique in a variety of cells, including fat cells, refining it along the way until it became sensitive enough to measure tiny amounts of carbon 14 in small hippocampus samples. The researchers collected samples, with family permission, from autopsies in Sweden.

They found the tantalizing 1998 evidence was correct: Human hippocampuses do grow new neurons. In fact, about a third of the brain region is subject to cell turnover, with about 700 new neurons being formed each day in each hippocampus (humans have two, a mirror-image set on either side of the brain). Hippocampus neurons die each day, too, keeping the overall number more or less in balance, with some slow loss of cells with aging, Spalding said.

This turnover occurs at a ridge in the hippocampus known as the dentate gyrus, a spot known to contribute to the formation of new memories. Researchers aren’t sure what the function of this constant renewal is, but it could relate to allowing the brain to cope with novel situations, Spalding told LiveScience.

"Neurogenesis gives a particular kind of plasticity to the brain, a cognitive flexibility," she said.

Spalding and her colleagues had used the same techniques in other regions of the brain, including the cortex, the cerebellum and the olfactory bulb, and found no evidence of newborn neurons being integrated into those areas. The researchers now plan to study whether there are any links between neurogenesis and psychiatric conditions such as depression.

The new findings are detailed in the journal Cell.

New neuron formation could increase capacity for new learning, at the expense of old memories

Cause of infantile amnesia revealed

New research presented today shows that formation of new neurons in the hippocampus - a brain region known for its importance in learning and remembering - could cause forgetting of old memories by causing a reorganization of existing brain circuits. Drs. Paul Frankland and Sheena Josselyn, both from the Hospital for Sick Children in Toronto, argue this reorganization could have the positive effect of clearing old memories, reducing interference and thereby increasing capacity for new learning. These results were presented at the 2013 Canadian Neuroscience Meeting, the annual meeting of the Canadian Association for Neuroscience - Association Canadienne des Neurosciences (CAN-ACN).

Researchers have long known of the phenomenon of infantile amnesia: This refers to the absence of long-term memory of events occurring within the first 2-3 years of life, and little long-term memories for events occurring until about 7 years of age. Studies have shown that though young children can remember events in the short term, these memories do not persist. This new study by Frankland and Josselyn shows that this amnesia is associated with high levels of new neuron production - a process called neurogenesis - in the hippocampus, and that more permanent memory formation is associated with a reduction in neurogenesis.

Dr. Frankland and Dr. Josselyn’s approach was to look at retention of memories in young mice in which they suppressed the usual high levels of neurogenesis in the hippocampus (thereby replicating the circuit stability normally observed in adult mice), but also in older mice in which they stimulated increased neurogenesis (thereby replicating the conditions normally seen in younger mice). Dr. Frankland was able to show a causal relationship between a reduction in neurogenesis and increased remembering, and the converse, decreased remembering when neurogenesis increased.

Dr. Frankland concludes: ” Why infantile amnesia exists has long been a mystery. We think our new studies begin to explain why we have no memories from our earliest years.”

Fish oil may stall effects of junk food on brain

Data from more than 180 research papers suggests fish oils could minimise the effects that junk food can have on the brain, a review by researchers at the University of Liverpool has shown.

The team at the University’s Institute of Ageing and Chronic Disease reviewed research from around the world to see whether there was sufficient data available to suggest that omega-3s had a role to play in aiding weight loss.

Stimulating the brain

Research over the past 10 years has indicated that high-fat diets could disrupt neurogenesis, a process that generates new nerve cells, but diets rich in omega-3s could prevent these negative effects by stimulating the area of the brain that control feeding, learning and memory.

Data from 185 research papers revealed, however, that fish oils do not have a direct impact on this process in these areas of the brain, but are likely to play a significant role in stalling refined sugars and saturated fats’ ability to inhibit the brain’s control on the body’s intake of food.

Dr Lucy Pickavance, from the University’s Institute of Ageing and Chronic Disease, explains: “Body weight is influenced by many factors, and some of the most important of these are the nutrients we consume.  Excessive intake of certain macronutrients, the refined sugars and saturated fats found in junk food, can lead to weight gain, disrupt metabolism and even affect mental processing.

“These changes can be seen in the brain’s structure, including its ability to generate new nerve cells, potentially linking obesity to neurodegenerative diseases. Research, however, has suggested that omega-3 fish oils can reverse or even prevent these effects.  We wanted to investigate the literature on this topic to determine whether there is evidence to suggest that omega-3s might aid weight loss by stimulating particular brain processes.”

Research papers showed that on high-fat diets hormones that are secreted from body tissues into the circulation after eating, and which normally protect neurons and stimulate their growth, are prevented from passing into the brain by increased circulation of inflammatory molecules and a type of fat called triglycerides.

Molecules that stimulate nerve growth are also reduced, but it appears, in studies with animal models, that omega-3s restore normal function by interfering with the production of these inflammatory molecules, suppressing triglycerides, and returning these nerve growth factors to normal.

Positive step

Dr Pickavance added: “Fish oils don’t appear to have a direct impact on weight loss, but they may take the brakes off the detrimental effects of some of the processes triggered in the brain by high-fat diets.  They seem to mimic the effects of calorie restrictive diets and including more oily fish or fish oil supplements in our diets could certainly be a positive step forward for those wanting to improve their general health.”

The research is published in the British Journal of Nutrition. Dr Pickavance will also be discussing the effects of high-fat diets on meal patterns and the impacts of high-saturated fats on muscle composition at the 20^th European Congress on Obesity at the Liverpool Arena and Convention Centre later this month.