Omega-3 fatty acids are found in some green vegetables, vegetable oils, and fatty fish. There is some evidence that omega-3 fatty acid supplements can reduce depression, but researchers are trying to clarify which omega-3s are most helpful, and for whom. A new study in Molecular Psychiatry suggests that depressed people with higher inflammation may respond best to EPA omega-3 fatty acids compared to DHA omega-3 fatty acids or placebo. Researchers led by M.H. Rapaport divided people with major depressive disorder into “high” and “low” inflammation groups based on their levels of the inflammatory markers IL-1ra, IL-6, high-sensitivity C-reactive protein, leptin, and adiponectin. Participants were randomized to receive eight weeks of treatment with EPA omega-3 supplements (1060mg/day), DHA omega-3 supplements (900mg/day), or placebo.
While overall treatment differences among the three groups as a whole were negligible, the high inflammation group improved more on EPA than on placebo or DHA, and more on placebo than on DHA. The authors suggest that EPA supplementation may help relieve symptoms of depression in people whose depression is associated with high inflammation levels, a link common among obese people with depression.
Editor’s Note: These data add to a study by Rudolph Uher et al. in which people with high levels of C-reactive protein responded better to the tricyclic antidepressant nortriptylene, while those with low levels of the inflammatory marker responded better to the selective serotonin reuptake inhibitor antidepressant escitalopram.
Studies have found that when a depressed mother’s symptoms remit, her children are less likely to show psychiatric symptoms. A new study by Myrna M. Weissman and colleagues in the American Journal of Psychiatry randomized 76 mothers to treatment with escitalopram, bupropion, or a combination of the two, and assessed the impact of the mothers’ treatment on their 135 children (aged 7–17).
There were no significant differences in the mothers’ symptoms or remission, but children’s depressive symptoms and functioning improved more if their mothers received (only) escitalopram. Only in that group was a mother’s improvement associated with her children’s improvement.
Mothers in the escitalopram group reported greater improvement in their ability to listen and talk to their children compared to the mothers in other groups, and the children of the mothers in the escitalopram group reported that their mothers were more caring.
Children of mothers with low negative affect improved significantly, while children of mothers with high negative affect only improved if their mothers were in the escitalopram group.
The authors suggest that for a mother’s improvement to help her children’s symptoms, her anxious distress and irritability must be reduced, and these may be better targeted with escitalopram than bupropion.
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.
Telomeres are repeated DNA sequences that sit at the end of chromosomes and protect them during cell replication. Telomeres get shorter with aging and with stressors or psychiatric illnesses. Researcher Alexandre Mathe and colleagues recently found that in a line of rats bred to be more susceptible to stress and depression-like behavior, hippocampal telomeres were shorter than in normal rats or rats bred to be less susceptible. The susceptible rats also had lower levels of enzymes that maintain telomere length. Both telomerase activity and Tert (telomerase reverse transcriptase) expression were reduced in the susceptible rat compared to the other rats. However, lithium reversed the low levels of telomerase activity and Tert expression.
Editor’s Note: Lithium increases hippocampal volume in people, and also increases human telomerase. Researcher Lina Martinsson reported in 2013 that lithium increases telomere length in white cells. Now lithium has increased hippocampal telomerase in a rat model of depression. Short telomeres are associated with aging and increased vulnerability to a wide range of medical and psychiatric disorders. Since people with bipolar disorder are prone to memory problems, medical problems, and short telomeres, they might want to talk to their physician about including lithium in their treatment regimen, if they are not already taking it.
Both bipolar disorder and unipolar depression often begin in childhood or adolescence, but it can be difficult to distinguish the two using symptoms only. People with bipolar illness may go a decade without receiving a correct diagnosis. Researcher Jorge Almeida and colleagues recently performed a meta-analysis of previous studies to determine what neural activity is typical of children with bipolar disorder versus children with unipolar depression while processing images of facial emotion. They found that youth with bipolar disorder were more likely to show limbic hyperactivity and cortical hypoactivity during emotional face processing than youth with unipolar depression. Almeida and colleagues hope that this type of data may eventually be used to diagnose these disorders or to measure whether treatment has been successful.
Life experiences such as adversity in childhood have been linked to epigenetic changes to DNA. These changes do not affect the sequence of DNA, but can change how tightly DNA is wound, and thus how easily it is transcribed. One epigenetic change that can occur following adversity in childhood is methylation of the gene for the glucocorticoid receptor (NR3C1). A recent study by Kathryn Ridout and colleagues examined links between early adversity, methylation of this gene, and behavioral problems in childhood. Adversity was linked to methylation of the gene at exons 1D and 1F in the promoter of NR3C1. Methylation of the gene was associated with internalizing behaviors (e.g. depression, anxiety) but not externalizing behaviors (e.g. attention deficit hyperactivity disorder (ADHD) or oppositional defiant disorder) in children of preschool age. The NR3C1 methylation was a significant mediator of the internalizing behaviors in children who had experienced adversity.
Editor’s Note: Similar associations of methylation of the glucocorticoid receptor with childhood adversity have been reported in other clinical and animal studies and provide a mechanism for the long-lasting adverse effects of stressors in childhood.
Stressors in early life can contribute to the risk of developing mood disorders. Given that many treatments for mood disorders work by blocking the serotonin 5-HT transporter, Nicole Baganz and colleagues designed a study to see whether an early life stressor, in this case maternal separation, would affect immune processes that in turn affect serotonin signaling.
In this study as in many before it, mice that were removed from their mothers exhibited behaviors that resembled human anxiety and depression. They were also found to have elevated messenger RNA for several inflammatory cytokines (including IL-1beta and IL-6) in their brain and blood. Mice that had a gene for the interleukin-1 receptor (IL-1R) removed exhibited neither the depressive behavioral effects nor the changes in cytokine levels following maternal separation, showing that the IL-1R gene plays a necessary role in the signaling process that leads to this type of depression. Levels of the stress hormone corticosterone in the blood did not differ in the mice with and without the IL-1R gene.
The researchers concluded that early life stressors can cause lifelong changes in inflammatory cytokine levels in mice.
Rodents that are subjected to social defeat (being overpowered by a bigger, more aggressive animal) develop a syndrome that resembles human depression—they avoid social interaction, lose interest in sucrose, and do less exploring of new places or other animals. A recent finding showed that even witnessing the social defeat of a peer was enough to bring about the depressive behaviors. The same researchers, led by Samina Salim, recently found that young rats (aged 21–27 days) that witnessed their mother go through the trauma of social defeat showed depression-like behavior themselves as adults (at age 60 days).
The rats saw their mothers defeated by the larger rat every day for seven days. As adults, those who witnessed this abuse exhibited depression-like behavior compared to rats of the same age and gender that had not witnessed abuse. The depressive rats gave up more quickly on a test of forced swimming. Male rats showed great depression-like behavior than female rats.
It has been estimated by the American Psychological Association that 15.5 million children in the US witness physical or emotional abuse of a parent (usually their mother). Children who witness domestic violence often show symptoms of post-traumatic stress disorder (PTSD). This rodent research may lead to a better understanding of the consequences of witnessing trauma in childhood, and potential treatments that could help.
Editor’s Note: These data show that rats have something like empathy, and that the psychological aspects of stress (including verbal abuse in humans and witnessing another’s abuse in rodents) may have profound and lasting consequences on behavior.
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.
Telomeres sit at the end of DNA strands and shorten with each cell replication. Shorter telomeres are associated with aging and an increase in multiple medical and psychiatric disorders. New research draws connections between the production of mitochondrial DNA, telomere length, the experience of childhood adversity, and mental illness.
Researcher Audrey Tyrka and colleagues divided 290 healthy adults into four categories based on whether or not they had experienced adversity in childhood and whether they had been diagnosed with a mental illness in their lifetime, including depression, anxiety, and substance abuse. The researchers also analyzed the participants’ telomere lengths and the copy number of their mitochondrial DNA. Both stressful events in childhood (such as maltreatment or the loss of a parent) and a history of mental illnesses (depression and anxiety) were associated with shorter telomeres and higher mitochondrial DNA copy numbers, a measure of cellular aging. Substance abuse was associated with higher mitochondrial DNA copy numbers.
Editor’s Note: This research replicates earlier findings that adversity is associated with shortening telomeres. The finding that mitochondrial DNA could play a role in the long-term effects of early life adversity and mental illnesses is new.