Epigenetics is the process by which environmental factors affect the way a person’s genes are transcribed. These changes, which may include the addition or subtraction of methyl groups from DNA, change the DNA’s structure (how tightly it is wound around the histones that give it shape) but not its sequence. These structural changes, which affect how easily the DNA is transcribed, can then be passed on to future generations. A new study by Ulrike Stadlbauer and colleagues presented at the Society of Biological Psychiatry explored a particular pathway by which an infection in a pregnant mouse can lead to behavioral changes in three following generations of mice.
Pregnant mice were given injections that produced an infection. A first generation of offspring were interbred to create a second generation of offspring, and these were interbred to create a third generation of offspring. The first generation of offspring had epigenetic changes in methylation and hydroxymethylation to promoter regions of two enzymes that regulate synthesis of the neurotransmitter GABA, and these epigenetic changes were associated with reduced mRNA expression of these two genes.
All three generations of offspring had deficits in social interaction, short-term memory, and cued fear conditioning. Interestingly, the second and third offspring generations also exhibited depression-like behavior that had not been present in the original mothers or the first generation of offspring.
Editor’s Note: This is another fascinating demonstration of how environmental occurrences, which can include stressors, exposure to drugs, and now immune challenges, can have effects across generations, likely through epigenetic changes that persist in ova or sperm. Amazingly, it turns out that the environment can change traits in future generations, not by inducing changes to gene sequences, but through epigenetic changes to the structure of DNA or histones that persist across generations.
It is well established that certain early experiences can affect a person’s risk of developing a mental illness. Adversity in childhood, including abuse or the loss of a parent, is a risk factor not only for diagnosis of a mood disorder, but also for a more difficult course of illness. This may occur through epigenetic means. Epigenetics refers to a process by which environmental factors can change the way that DNA is transcribed, for example through the addition of methyl groups to strands of DNA. This tends to inhibit DNA from being transcribed and producing protein growth factors and other neurochemicals that are important for development.
A study by Kieran J. O’Donnell and colleagues presented at the 2015 meeting of the Society of Biological Psychiatry investigated whether epigenetics play a role in the success of a parenting intervention called the Nurse Family Partnership. Participants were 27-year-olds born to women who had received the intervention or a control intervention. Genome-wide DNA methylation was measured in the 188 participants’ blood.
Analysis of the blood revealed that the Nurse Family Partnership intervention was associated with DNA methylation at 1015 sites across 593 genes. Some of these sites were enriched for certain neurodevelopmental processes. Maltreatment in childhood was also associated with methylation at 1552 sites across 878 genes.
Editor’s Note: The take-home message of this landmark study is that maltreatment in childhood exerts lasting effects on the genome via epigenetic mechanisms, but early positive intervention also exerts lasting epigenetic effects, which likely have a normalizing impact.
Studies of primates suggest that the amygdala plays an important role in the development of anxiety disorders. Researcher Ned Kalin suggested at the 2015 meeting of the Society of Biological Psychiatry that the pathology of anxiety begins early in life. When a child with anxiety faces uncertainty, the brain increases activity in the amygdala, the insula, and the prefrontal cortex. Children with an anxious temperament, who are sensitive to new social experiences, are at almost sevenfold risk of developing a social anxiety disorder, and later experiencing depression or substance abuse.
A study by Patrick H. Roseboom and colleagues presented at the meeting was based on the finding that corticotropin-releasing hormone (CRH) plays a role in stress and is found in the central nucleus of the amygdala (as well as in the hypothalamus). The researchers used viral vectors to increase CRH in the central nucleus of the amygdala in young rhesus monkeys, hoping to determine what impact increased CRH has on a young brain. Rhesus monkeys and humans share similar genetic and neural structures that allow for complex social and emotional functioning.
Roseboom and colleagues compared the temperaments of five monkeys who received injections increasing the CRH in their amygdala region to five monkeys who received control injections. As expected, the monkeys with increased CRH showed increases in anxious temperament. Brain scans also revealed increases in metabolism not only in the central nucleus of the amygdala, but also in other parts of the brain that have been linked to anxiety, including the orbitofrontal cortex, the hippocampus, and the brainstem, in the affected monkeys. The degree of increase in amygdala metabolism was directly proportional to the increase in anxious temperament in the monkeys, further linking CRH’s effects in the amygdala to anxiety.
Adolescence can be a time of vulnerability to illness. Anxiety disorders increase during this period, and three-quarters of adults with anxiety disorders trace the illness back to their childhood or adolescence. The most common treatments for anxiety disorder are based on the idea of fear extinction. A certain stimulus, like a social situation or seeing a spider, provokes a fear reaction in the brain. Through gradually increasing exposure to the stimulus and extinction training, the person becomes desensitized to the stimulus. New research on rodents presented by Francis S. Lee at the 2015 meeting of the Society for Biological Psychiatry suggests that the extinction process is diminished during adolescence.
At specific stages of maturation, neural circuits related to particular abilities can become flexible. Brain and behavior become sensitive to and are increasingly shaped by experience. Studies of rodents and humans have shown that adolescence is a time when the neural circuitry for fear extinction is in flux. In mice, this period falls around their 29th day of life. Lee reported that around this time, the mice begin to exhibit resistance to extinction of fear learning.
In adolescent rodents, there is a surge of contextual fear learning and retrieval that is mediated by hyper-connectivity of the ventral hippocampus and the amygdala to the prelimbic part of the prefrontal cortex. In contrast, the pathway from the amygdala to the infralimbic cortex mediates the extinction of this type of learning. Because the prelimbic pathway for fear learning is overactive, the infralimbic pathway for extinction learning is less effective.
Adolescent mice temporarily lose their ability to retrieve memories related to cue-dependent (as opposed to context-dependent) fear learning. Remarkably, when these animals proceed into adulthood, the fear learning associated with cues returns and becomes accessible again.
This could help explain how teenagers can lose fear conditioning to cues (for example, speeding through a red light) they learned in childhood. The fear is forgotten (or becomes inaccessible) in adolescence, but then what had been learned is again “remembered” (retrieved) in adulthood. Read more
Studies of rodents with depression-like behaviors revealed that the combination of low (sub-therapeutic) doses of lithium and infusions of ketamine produced antidepressant-like effects. Researchers believed this might mean that in humans, lithium might have a unique effect potentiating the effects of ketamine.
In a small study by Mark J. Niciu presented at the 2015 meeting of the Society for Biological Psychiatry, patients with bipolar depression taking lithium or valproate mood stabilizers were given ketamine infusions or control infusions. In the 23 patients taking lithium and the 13 taking valproate, ketamine’s antidepressant effects were significantly better than placebo, but there was no difference between lithium and valproate with regard to these antidepressant effects. These preliminary data in a small number of subjects do not support the proposition that lithium augments the effects of ketamine in depression.
Intravenous ketamine can bring about rapid improvement in depressive symptoms among people with treatment-resistant depression. Because of its rapid effects, which can appear after only two hours, ketamine is being investigated as a treatment for people with suicidal thoughts.
At the 2015 meeting of the Society of Biological Psychiatry, Laili Soleimani and colleagues presented a poster about their recent double blind, randomized, controlled pilot study of ketamine inpatients and outpatients who scored highly on a measure of suicidal ideation. The 24 participants were randomized to receive either a single intravenous infusion of ketamine (0.5mg/kg) or a single infusion of midazolam (0.045 mg/kg), which shares ketamine’s anxiety-reducing effects but does not have antidepressant effects. They reported suicidal thoughts at 24 hours post-infusion, 48 hours, 72 hours, and 7 days. At 48 hours, those who received ketamine reported significantly reduced suicidal ideation compared to those who received midazolam, but this effect was no longer significant at the 72-hour mark.
The findings show that ketamine can briefly reduce suicidal ideation, and that the treatment is safe and tolerable for patients. This pilot study paves the way for further study of ketamine to reduce suicidal thinking in people who are at high risk for suicidal behavior.
Intravenous ketamine is known for its fast-acting antidepressant effects, which can appear within two hours of an infusion. Researchers are now investigating its use for the reduction of suicidal thoughts. In a study presented in a poster at the 2015 meeting of the Society of Biological Psychiatry, Jennifer L. Vande Voort and colleagues compared the sleep of patients whose suicidal thoughts decreased after a single ketamine infusion (0.5 mg/kg over 40 minutes) to those whose suicidal thoughts remained.
Study participants whose suicidal thoughts diminished after one infusion of ketamine had better sleep quality the following night, with fewer disruptions in sleep than among those who did not have an anti-suicidal response to ketamine. The participants who responded well to ketamine had sleep quality similar to that of healthy controls.
Vande Voort and colleagues hope that these new findings about ketamine’s effect on sleep may provide clues to the biological mechanism behind ketamine’s effect on suicidal ideation.
Pediatric acute neuropsychiatric syndrome (PANS) is a little-known syndrome in which a child has an acute onset of psychiatric symptoms following a bacterial or viral infection, when the antibodies generated to fight the infection instead attack neurons in the brain. The behavioral alterations can be severe and resistant to the usual psychotropic drug treatments. PANS often requires antibiotics and immune-targeted therapies.
The following is a case report of a real child who had a sudden onset of depression and violence after getting sick with the flu, pneumonia, and a strep infection at the age of 4. (Names have been changed for privacy.)
Anne contacted this editor (Robert M. Post) seeking a consultation on her 6-year-old son, Jake. Two years earlier, he had suddenly become difficult—depressed, angry, and even violent. This coincided with the emergence of obsessive compulsive symptoms and urinary incontinence. He went from being able to read short sentences in pre-kindergarten, to being cognitively dull and not even able to recognize letters of the alphabet. He had been diagnosed with a mood disorder, and Anne was told it was probably bipolar disorder. But he didn’t respond to any of the typical medications, and suffered side effects including hallucinations, nightmares, bowel accidents, and worsening depression.
The best results came with the atypical antipsychotic risperidone. While it didn’t reduce all of Jake’s symptoms, Anne described it as “heaven” compared to earlier treatments. But Jake’s levels of prolactin started to increase, and he lost bladder control, so he had to stop taking risperidone. Jake’s doctor tried 18 different medication regimens with 8 different medications in less than a year without finding one that worked well. Jake had a horrible time in school, and Anne fretted about the lack of an effective, stable medication, saying, “He’s actually worse than I’ve ever seen him.”
Dr. Post recommended that they consider using high doses of quetiapine and valproate for Jake’s aggression and behavioral dyscontrol, along with the antioxidant N-acetylcysteine and vitamin D3. However, given that Jake’s symptoms were severe, involved cognitive and neurological abnormalities, and had begun after a flu-like illness, and was unresponsive to conventional treatment, Dr. Post suggested that Anne get Jake checked out for PANS and start charting Jake’s mood on a daily basis.
Jake began taking higher doses of quetiapine and valproate, and improved to the point that Anne said they restrained him only once a day, rather than four times per day. But his behavioral dyscontrol continued. In one memorable incident, after feeling picked on by other children at a baseball game, he lashed out at Anne, kicking her in the face with his cleats and punching her glasses off her face.
Anne told Dr. Post that the family had visited a neurologist, who said that she had never heard of PANS and suggested that Anne would have to travel across several states to see Dr. Post if she wanted to pursue that diagnosis.
Dr. Post encouraged Anne to keep looking for a doctor who would take the PANS idea seriously. He sent her a comprehensive review article about PANS by Dr. Kiki Chang and colleagues published in the Journal of Child and Adolescent Psychopharmacology in 2014.
This past June, Anne found a doctor who understood PANS and was willing to run the appropriate tests on Jake. The tests revealed that Jake had at one time been infected with the bacteria mycoplasma. Read more
Dysregulation of the brain in early life can have lasting effects, and the effects of stress and depression can also accumulate. At the 2015 meeting of the Society of Biological Psychiatry, researcher Huda Akil explained that behavioral pathology can “take on a life of its own, leading to deteriorating course of illness and treatment resistance.” She illustrated how preclinical work in animals can help clarify the molecular biology of depression and develop new targets for therapeutics.
Early Life Experiences are Key
Akil discuss studies of rodents in which she used new molecular genetic techniques to increase the number of glucocorticoid receptors in the hippocampus early in life (prior to weaning). Glucocorticoid receptors mediate the effects of the stress hormone cortisol in people and corticosterone in rodents. More receptors help shut off cortisol secretion after a stressful event. People with post-traumatic stress disorder (PTSD) have high levels of glucocorticoid receptors while people with depression have low levels, leading to over-secretion of cortisol in depression.
The increased glucocorticoid receptors led to a long-term increase in anxiety behaviors and response to stimulants. When Akil carried out the same manipulation on rats that had already been weaned, it had no long-lasting effects, showing that there is a vulnerability window for some long-lasting effects on behavior.
CLOCK Genes and Circadian Rhythms
Akil also studied CLOCK genes in rodents. These genes, including BMAL-1, Per 1, Per 2, and Per3, play a role in circadian rhythms, and their transcription induces these 24-hour cycles. In rodents who were induced into a depression-like state, the CLOCK genes were dysregulated and did not correspond to normal circadian rhythms. These data show that depressive states can induce changes in CLOCK genes and circadian rhythms. Others have shown the converse, that abnormal CLOCK genes can induce behavioral abnormalities including mania-like behaviors.
Fibroblast Growth Factor
Levels of fibroblast growth factor 2 (FGF2) in the hippocampus are low in people with depression. In rodents, FGF2 inhibits anxiety. Decreases in FGF2 are seen in the hippocampus of animals in a depression-like state following repeated defeat by a larger animal. It appears that FGF2 is an endogenous antidepressant (i.e. one that is produced by the brain). When the rodent brain is manipulated to eliminate FGF2, the animals become anxious.
In addition, animals bred to have high stress, low social responsivity, and resistance to new learning also have low FGF2. Treatment with FGF2 reversed these behavioral abnormalities and also increased the production of new neurons. For the stressed rats, receiving FGF2 on their second day of life increased new neuron production, decreased anxiety, decreased proneness to social defeat stress and increased the bonding hormone oxytocin in the amygdala into adulthood.
FGF2 had no effect on rats bred for low stress and high social responsivity, indicating that it only worked for the rats that needed it. Akil compared FGF2 to “personalized medicine for rats.”
Defeat stress affects the way genes are transcribed, and FGF2 was able to reverse one of these specific transcriptional effects, suggesting it could potentially ameliorate some of the long-lasting effects of stress and depression.
The Human Brain
Akil also studied the brains of people who had died of depression, bipolar disorder, or schizophrenia. In bipolar disorder, the nucleus accumbens, the reward center of the brain, was enlarged.
In contrast, Akil described the brains of those people who had died with depression as being “low on fertilizer.” That is, they showed less cell growth, less production of new neurons, more abnormalities in cell shape, and more cell death. Akil said that by the time someone is severely ill, the pathology is all over the brain. The changes Akil saw in the brains of people who were depressed are also consistent with data indicating that several neuroprotective factors, including BDNF and VEG-F, are low in the frontal cortex and the hippocampus of depressed people (while BDNF is high in the nucleus accumbens).