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).
Certain nutritional supplements may help people cope following natural disasters. Following a 7.1 magnitude earthquake in Christchurch, New Zealand, in 2010, researchers there who were working on a clinical trial of a broad spectrum mineral and vitamin formula for ADHD realized that they could compare participants who had been taking the nutritional supplements at the time of the earthquake with those who had either already completed the trial or had not yet begun it. Two weeks after the quake, those who had been taking the multivitamin at the time of the quake were less anxious and stressed than those who hadn’t been taking the formula.
When another large earthquake struck five months later, the researchers implemented a randomized trial comparing two doses of the same broad spectrum supplement with a B Complex vitamin formula that had previously shown efficacy for stress and anxiety. Those participants taking any supplement showed fewer symptoms of post-traumatic stress disorder (PTSD) a month after the second quake compared to controls, and those taking the higher dose of the broad spectrum formula had greater improvements in mood and anxiety than those taking the B Complex supplement.
More recently, in Alberta, Canada, flooding forced many people from their homes. Researchers there who were studying the effects of micronutrients on stress and anxiety realized they had the opportunity to replicate the research from New Zealand in a different type of environmental disaster.
Researcher Bonnie J. Kaplan and colleagues recruited adults who had been affected by the flood, and randomized the participants to receive different types of supplements: vitamin D (1 pill/day); a B complex vitamin containing B6, B12, and several other nutrients (1 pill/day); or a broad spectrum supplement containing 24 vitamins and minerals and several botanical extracts (4 pills/day). No placebo was used—it was considered unethical to deny participants access to a potentially helpful treatment.
In a 2015 article in the journal Psychiatry Research, the Alberta team reported that while all of the nutrient supplements minimized stress after the flood, patients randomized to the B complex vitamin or the broad spectrum formula had less stress and anxiety following the flood than those randomized to vitamin D.
We have previously described a broad spectrum vitamin preparation called EMPowerplus, used by psychiatrist Charles Popper and psychologist Mary A. Fristad to treat children with treatment-resistant bipolar disorder. This may be the same formula used in the Alberta study. We await larger trials of this preparation in children with bipolar disorder.
Enduring stressful life events in childhood can affect children long-term. Children who experience neglect can show increased levels of cortisol, a stress hormone. Family interventions can reduce these levels, and a new study shows that the impact of these interventions can be lasting. The study, by Kristin Bernard and colleagues in the journal JAMA Pediatrics, included 115 children whose families had been referred to Child Protective Services after allegations of neglect. After an incident of neglect in early childhood, the families received either an experimental intervention called ABC (focused on increasing parental nurturance to child distress, increasing synchronous interactions, and decreasing frightening parental behavior) or a control intervention (which provided educational information about child development). When the children reached preschool age about three years later, the researchers collected the children’s cortisol levels at waking and bedtime on three different days.
The children whose families received the ABC intervention had more typical cortisol levels than those whose families had received the control intervention. The ABC children had higher morning cortisol, with a steeper decline throughout the day, compared to a more blunted cortisol rhythm in the control group children. These patterns resembled differences in the two groups observed three months after the initial intervention. The authors concluded that the ABC intervention has long-term effects on children’s physiological stress system, helping them maintain health and adjustment.
Adolescence may be a period of particular vulnerability to the effects of stress. New research by Shannon Gourley indicates a possible mechanism for this vulnerability. When Gourley exposed adolescent mice to low levels of the stress hormone corticosterone (the equivalent to human cortisol), they developed habit-based rather than goal-oriented decision-making, leading to behaviors that resembled human depression, which lasted into adulthood. Adult mice that were exposed to the low levels of corticosterone were not affected by it.
Gourley also used an alternative method of producing these stress responses a second time by silencing the trkB receptor for brain-derived neurotrophic factor (BDNF) in the amygdala and hippocampus of the mice. The depression-like behaviors that resulted, such as lack of motivation, were able to be reversed by treating the mice with 7,8-dihydroxyflavone, a drug that activated the trkB receptor. In the adolescent mice, this treatment had antidepressant effects that lasted into adulthood, even though the treatment stopped earlier.
Mice subjected to chronic defeat stress (being placed in the home cage of a larger, more aggressive mouse) behave in ways that resemble human anxiety and depression. In new research by Miles Herkenham and colleagues at the National Institute of Mental Health, in which they explored the adaptive immune system’s affect on mood, mice exposed to this type of stress showed increases in inflammatory cytokines in the blood (including TNFalpha, IL-1beta, IL-2, IL-3, IL-6, IL-17, and IFNgamma) compared to a control group. Interestingly, when white blood cells (lymphocytes) from stressed animals were transferred to a new set of animals, the recipient mice seemed to benefit from greater resilience to stress in a variety of ways.
Mice that received white blood cells from defeat-stressed animals had lower levels of TNFalpha, IL-1beta, IL-2, IL-3, and IL-17 than a control group that received white blood cells from unstressed mice. The recipient mice also exhibited reduced anxious and depressive behaviors in a litany of behavioral tests compared to both the group that received white blood cells from unstressed mice and a group that received a saline injection instead. Lastly, the recipients of the white blood cells from stressed animals showed more new neurons in the dentate gyrus of the hippocampus. (Hippocampal neurogenesis is decreased by stressors and increased by antidepressants.)
Herkenham and colleagues concluded that psychopathology is not just a downward spiral—the immune system plays an active role in adapting to stress, with lymphocytes being programmed by stress to provide antidepressant functions.
Editor’s Note: These data add a new twist to the studies of Scott Russo, who found that IL-6 secreted by white cells of animals subject to defeat stress was the cause of the depressive-like behaviors they exhibited. If IL-6 was blocked, the behaviors did not occur. Now it would appear from Herkenham’s work that something about the timing, the type of cytokines, or the transfer of the white cells conveyed protective antidepressant-like effects in this case.
Researchers hope to map out the neurocircuitry by which stress leads to compulsive drug taking. A recent study by Klaus Miczek and colleagues examined different rodents’ responses to the stress of being repeatedly placed in the cage of a larger, more aggressive rodent, developing what is known as defeat stress, a set of behaviors that mimic human depression. Mice and rats showed increases in the stress hormone corticosterone that did not diminish over repeated run-ins with a larger animal. Rodents who were exposed to this stress became sensitized to cocaine or amphetamine, showing hyperactivity that increased each time they accessed the drug (the opposite of a tolerance response). Some also “binged” on cocaine, which they were able to self-administrate by pushing a lever to receive infusions. The mice and rats that went through the social defeat showed elevated levels of dopamine in the nucleus accumbens, the brain’s reward center. Levels were related to the severity of their stressful experience.
Later the rodents had a choice between water and a 20% alcohol solution. The researchers determined what type of stress led the rodents to consume the alcohol solution instead of the water. The maximal effect was seen in two types of mice that suffered an attack of less than five minutes that resulted in a moderate number of attack bites (30); this resulted in the mice consuming large amounts (15–30 g/kg/day) of the alcohol solution. Earlier sensitization to cocaine or amphetamine did not predict later alcohol or cocaine self-administration.
When the researchers injected the rodents with antagonists of the receptors for corticotropin-releasing factor, a hormone and neurotransmitter important in stress response, prior to each episode of social defeat, the rodents did not escalate their cocaine or alcohol self-administration, indicating that CRF plays an essential role in the process by which stress makes animals prone to using substances.
In related research by Camilla Karlsson and colleagues, IL-1R1 and TNF-1R, the receptors for two inflammatory cytokines, mediated the effects of social stress on escalated alcohol use in mice.
Stress can trigger former drug users to begin taking drugs again. In clinical trials, the bonding hormone oxytocin has been found to reduce stress-induced cravings for certain drugs, including alcohol and marijuana. A new study in animals suggests that oxytocin may be able to reduce stress-induced cocaine cravings as well.
Brandon Bentzley and colleagues combined an unpredictable shock to the foot with an alkaloid called yohimbe that comes from a particular tree bark to apply stress to animals who had previously developed a cocaine self-administration habit that had since been extinguished. The combination of the foot shocks and yohimbe brought back robust reinstatement of the animals’ cocaine seeking behaviors, but pretreatment with oxytocin (at doses of 1 mg/kg) prevented this reinstatement.
This research suggests that oxytocin has potential to prevent stress-induced cocaine cravings in people.
In a study of the effect on infant health of a mother’s experience of adversity in childhood by researcher Deborah Kim and colleagues, both adversity in childhood (such as physical abuse or the loss of a parent) and stress during pregnancy were associated with low infant birth weight and lower gestational age at birth.
Among 146 women enrolled in the study, 58.2% percent scored a 0 on the Adverse Childhood Experience Questionnaire (ACE), 24% scored a 1, and 17.8% scored a 2. Those who scored higher on the ACE also scored higher on a scale measuring perceived stress. A score of 2 or higher on the ACE was associated with lower gestational age at birth, indicating infants born prematurely. Greater stress during pregnancy was associated with lower gestational age at birth and lower infant birth weight. When potential confounding demographic factors were removed from the analyses, ACE scores of 2 or higher were still associated with lower infant birth weight, while perceived stress was no longer associated with either low birth weight or gestational age.
Childhood adversity is associated with increases in inflammation and multiple adverse medical consequences in adults. The researchers called childhood adversity a “significant predictor of poor delivery outcomes” for women.
Editor’s Note: This research shows that a mother’s health and earlier life stressors could have an adverse effect on her child.
Childhood adversity leaves behind a residue of neuroendocrine and neuroclinical alterations that can persist into adulthood. Many are mediated by epigenetic changes, consisting of small chemical marks that attach to DNA and the histones around which it is wrapped.
In addition to these neurobiological alterations mediated by epigenetic effects, there is new evidence that some epigenetic marks can be passed on to the next generation via a mother’s egg or a father’s sperm. Thus, either directly or indirectly, parents’ adverse life experiences can influence the health of their offspring.
Disruptions to circadian rhythms are common in mood disorders, leading some researchers to believe that normalizing these daily rhythms may improve the illnesses. Several genes, called CLOCK genes, are implicated in circadian rhythms. In animal studies, researcher Marco Riva and colleagues are examining the expression of CLOCK genes in different brain regions as a result of chronic stress that is meant to produce behaviors resembling human depression.
Male rats were exposed to chronic mild stress for two weeks, and divided into those that were susceptible to stress (identified by their loss of interest in sucrose) and those who were not. Then the rats were randomized to receive either a placebo treatment or 3 mg/kg/day of the atypical antipsychotic lurasidone (trade name Latuda), which has been effective in bipolar depression, during five more weeks of the stress procedure.
The researchers observed the expression of clock genes Clock/Bmal1, Per1, Per2, Cry1, and Cry2. In susceptible rats, the chronic mild stress decreased the clock genes Per1, Per2, and Cry2 in the prefrontal cortex. Lurasidone reversed these CLOCK gene abnormalities and the rats’ depression-like behaviors, which may explain some of the drug’s efficacy in bipolar depression.
Editor’s Note: Lurasidone is also a potent inhibitor of 5HT7 serotonin receptors, an effect that has been linked to antidepressant efficacy. Lurasidone also increases brain-derived neurotrophic factor (BDNF), which is important for learning and memory, and prevents stress from decreasing BDNF. Now it seems that lurasidone’s normalization of CLOCK genes may be another mechanism that explains the drug’s antidepressant effects.
Women are more likely than men to experience depression, and this difference begins in adolescence, when girls show more sensitivity to stress. Researchers are studying how animals react to stress in the hopes of learning what mediates these gender differences in mental illness.
At a recent scientific meeting, researcher Jodi Lukkes and colleagues presented a recent study of stress and inflammation in female rats. The rats were exposed to different types of stressors. Some were separated from their mothers for four hours a day during the first 20 days of their lives. Later, some rats were exposed to an acute stressor, witnessing another rat receiving shocks. All the rats were placed in a box in which they could escape a shock by jumping to the other end of the box, in order to measure their motivation. Because drugs that inhibit the inflammatory enzyme COX-2 had reversed the effects of maternal separation in earlier studies, the researchers also treated some rats with these anti-inflammatories.
The researchers found that anti-inflammatory treatment could prevent behavioral consequences of stress in adolescent female rats. Witnessing another rat being shocked brought about deficits in motivation (a depression-like behavior), but in rats that had received treatment with a COX-2 inhibitor, these deficits were reduced. The COX-2 treatment was only helpful to rats that had experienced an acute stressor in their lifetime, either maternal separation in infancy, or witnessing another rat receive the shocks. A history of stress was required for the anti-inflammatories to improve motivation.
Lukkes and colleagues hope that this research begins to clarify the relationship between stress, inflammation, and gender. This may eventually lead to new targets in the treatment of depression.