The evolutionary significance of depression in Pathogen Host Defense (PATHOS-D)

The role of inflammation in depression: from evolutionary imperative to modern treatment target

Crosstalk between inflammatory pathways and neurocircuits in the brain can lead to behavioural responses, such as avoidance and alarm, that are likely to have provided early humans with an evolutionary advantage in their interactions with pathogens and predators. However, in modern times, such interactions between inflammation and the brain appear to drive the development of depression and may contribute to non-responsiveness to current antidepressant therapies. Recent data have elucidated the mechanisms by which the innate and adaptive immune systems interact with neurotransmitters and neurocircuits to influence the risk for depression. Here, we detail our current understanding of these pathways and discuss the therapeutic potential of targeting the immune system to treat depression.

Brain serotonergic activation in growth-stunted farmed salmon: adaption versus pathology

Signalling systems activated under stress are highly conserved, suggesting adaptive effects of their function. Pathologies arising from continued activation of such systems may represent a mismatch between evolutionary programming and current environments. Here, we use Atlantic salmon (Salmo salar) in aquaculture as a model to explore this stance of evolutionary-based medicine, for which empirical evidence has been lacking. Growth-stunted (GS) farmed fish were characterized by elevated brain serotonergic activation, increased cortisol production and behavioural inhibition. We make the novel observation that the serotonergic system in GS fish is unresponsive to additional stressors, yet a cortisol response is maintained. The inability of the serotonergic system to respond to additional stress, while a cortisol response is present, probably leads to both imbalance in energy metabolism and attenuated neural plasticity. Hence, we propose that serotonin-mediated behavioural inhibition may have evolved in vertebrates to minimize stress exposure in vulnerable individuals.

Body Mass Index and Depressive Symptoms: Testing for Adverse and Protective Associations in Two Twin Cohort Studies

Studies have suggested both adverse and protective associations of obesity with depressive symptoms. We examined the contribution of environmental and heritable factors in this association. Participants were same-sex twin pairs from two population-based twin cohort studies, the Older Finnish Twin Cohort (n = 8,215; mean age = 44.1) and the US Midlife Development in the United States (MIDUS; n = 1,105; mean age = 45.1). Body mass index (BMI) was calculated from self-reported height and weight. Depressive symptoms were assessed using Beck's Depression Inventory (BDI; Finnish Twin Cohort), and by negative and positive affect scales (MIDUS). In the Finnish Twin Cohort, higher BMI was associated with higher depressive symptoms in monozygotic (MZ) twins (B = 2.01, 95% CI = 1.0, 3.0) and dizygotic (DZ) twins (B = 1.17, 0.5, 1.9) with BMI >22. This association was observed in within-pair analysis in DZ twins (B = 1.47, CI = 0.4, 2.6) but not in within-pair analysis of MZ twins (B = 0.03, CI = -1.9, 2.0). Consistent with the latter result, a bivariate genetic model indicated that the association between higher BMI and higher depressive symptoms was largely mediated by genetic factors. The results of twin-pair analysis and bivariate genetic model were replicated in the MIDUS sample. These findings suggest an association between obesity and higher depressive symptoms, which is largely explained by shared heritable biological mechanisms.

Weakened Cholinergic Blockade of Inflammation Associates with Diabetes-Related Depression

Emerging evidence demonstrates association of depression with both immune malfunctioning and worsened course of diverse aging-related diseases, but there is no explanation for the pathway(s) controlling this dual association. Here, we report that in post-reproductive and evolutionarily -blind" years, depression may weaken pathogen-host defense, compatible with the antagonistic pleiotropy hypothesis. In 15,532 healthy volunteers, depression scores associated with both inflammatory parameters and with increased circulation cholinesterase activities, implicating debilitated cholinergic blockade of inflammation as an underlying mechanism; furthermore, depression, inflammation and cholinesterase activities all increased with aging. In the entire cohort, combined increases in inflammation and the diabetic biomarker hemoglobin A1c associated with elevated depression. Moreover, metabolic syndrome patients with higher risk of diabetes showed increased cholinesterase levels and pulse values, and diabetic patients presented simultaneous increases in depression, inflammation and circulation cholinesterase activities, suggesting that cholinergic impairment precedes depression. Our findings indicate that dysfunctioning cholinergic regulation weakens the otherwise protective link between depression and pathogen-host defense, with global implications for aging-related diseases.

Postnatal depression and reproductive success in modern, low-fertility contexts

BACKGROUND AND OBJECTIVES

Postnatal depression (PND) presents a puzzling phenomenon to evolutionary anthropologists as it is highly prevalent and yet detrimental to child development and maternal health. Adaptive explanations have been proposed, but have not been tested with data that directly link PND to female fertility.

METHODOLOGY

A survey was designed to gather complete reproductive histories and retrospective measures of PND to measure the effects of PND on fitness. Respondents were born between 1930 and 1967, with the majority based in the UK during their childrearing years. The hypothesis that PND is detrimental to fitness is assessed using Mann-Whitney U tests on completed fertility. Binary logistic regression modelling is used to test the hypothesis that PND reduces the likelihood of parity progression.

RESULTS

Women experiencing PND at their first or second birth have lower completed fertility, with PND at the first birth leading to lowered fertility. Logistic regression analyses show that this is the result of reductions in the likelihood of parity progression to a third birth when PND is experienced at the first birth or when repeat bouts occur.

CONCLUSIONS AND IMPLICATIONS

Our results call into question adaptationist arguments, contribute to the growing understanding of the importance of emotional wellbeing to fertility decision making, and given the economic consequences of markedly below replacement fertility, highlight a potential new source of financial incentive to invest in screening and preventative measures to ensure good maternal mental health.

Systems Genomics Support for Immune and Inflammation Hypothesis of Depression

BACKGROUND

Immune system plays an important role in brain development and function. With the discovery of increased circulating inflammatory cytokine levels in depression over two decades ago, evidence implicating immune system alterations in the disease has increasingly accumulated.

OBJECTIVE

To assess the underlying etiology and pathophysiology, a brief overview of the hypothesis free genomic, transcriptomic and proteomic studies in depression is presented here in order to specifically examine if the immune and inflammation hypothesis of depression is supported.

RESULTS

It is observed that genes identified in genome-wide association studies, and genes showing differential expression in transcriptomic studies in human depression do separately overrepresent processes related to both development as well as functioning of the immune system, and inflammatory response. These processes are also enriched in differentially expressed genes reported in animal models of antidepressant treatment. It is further noted that some of the genes identified in genome sequencing and proteomic analyses in human depression, and transcriptomic studies in chronic social defeat stress, an established animal model of depression, relate to immune and inflammatory pathways.

CONCLUSION

In conclusion, integrative genomics evidence supports the immune and inflammation hypothesis of depression.

Activated immune-inflammatory pathways are associated with long-standing depressive symptoms: Evidence from gene-set enrichment analyses in the Young Finns Study

We used genome wide expression (GWE) data of circulating blood cells and pathway analysis to investigate the inflammatory and other molecular pathways that may be associated with long-standing depressive symptoms. Participants were 607 women and 316 men (mean age 42 years) from the Young Finns Study who participated in three consecutive study phases in 2001, 2007 and 2012. Using Gene-set enrichment analyses (GSEA) we focused our analyses to pathways (available in MSigDB database) that are likely to affect immunological and inflammatory processes. GSEA were performed for blood cell GWE data in 2012. Depressive symptoms were assessed using a modified 21-item Beck Depression Inventory in each of the three study phases. Participants who scored in the top quartile of depressive symptoms in each of the three measurement points (n = 191) differed from other participants (n = 732) in several gene-set pathways related to inflammatory processes or immune-inflammatory signaling including interleukin (IL-1) pathway, and pathways related to various immuno-inflammatory processes, such as toll-like, the NEF protein, the nuclear factor kB, the kinase AKT and the mature B cell antigen receptor pathway (false discovery rates, FDRs<0.12). The results provide novel genome wide molecular evidence that support the association between chronic depressive symptoms and altered immune-inflammatory regulation.

Depression and the risk of autoimmune disease: a nationally representative, prospective longitudinal study

BACKGROUND

Autoimmune diseases are associated with substantial morbidity and mortality, yet the etiology remains unclear. Depression has been implicated as a risk factor for various immune-related disorders but little is known about the risk of autoimmune disease. This study examined the association between depression and the risk of autoimmune disease, and investigated the temporal and dose-response nature of these relationships.

METHOD

A prospective population-based study including approximately 1.1 million people was conducted using linked Danish registries. Depression and autoimmune diseases were diagnosed by physicians and documented in medical records. In total, 145 217 individuals with depression were identified between 1995 and 2012. Survival analyses were used to estimate the relative risk of autoimmune disease among those with, compared to without, depression. Analyses were adjusted for gender, age, and co-morbid mental disorders.

RESULTS

Depression was associated with a significantly increased risk of autoimmune disease [incidence rate ratio (IRR) 1.25, 95% CI 1.19-1.31], compared to those without a history of depression. Results suggest a general increased risk of autoimmune diseases following the onset of depression during first year (IRR 1.29, 95% CI 1.05-1.58), which remained elevated for the ensuing 11 years and beyond (IRR 1.53, 95% CI 1.34-1.76). Findings did not support a dose-response relationship.

CONCLUSIONS

Depression appears to be associated with an increased risk of a range of autoimmune diseases. Depression may play a role in the etiology of certain autoimmune conditions. If replicated, findings could highlight additional clinical implications in the treatment and management of depression. Future studies are needed to investigate the possible social, genetic, and neurobiological underpinnings of these relationships.

Chronic hepatitis C, depression and gender: a state of art

Purpose

– The purpose of this paper is to provide a comprehensive overview of the current knowledge regarding chronic hepatitis C (CHC) infection, antiviral therapy, depression, and gender.

Design/methodology/approach

– CHC and its treatment options were reviewed examining their relationship with depression and gender.

Findings

– CHC is a high prevalent chronic infection worldwide, being similar in men and women. However, the infection shows many gender differences in terms of innate response, genetic variability (i.e. IL-28B), route of transmission (i.e. intravenous drug use), disease progression (i.e. fibrosis), lifetime period (i.e. pregnancy), and risk factors (i.e. HIV). Both the hepatitis C infection and antiviral treatment (especially when using the pro-inflammatory cytokine interferon α), are highly associated with depression, where female gender constitutes a risk factor. It seems that the new direct-acting antiviral combinations produce fewer neuropsychiatric side effects. In fact, the presence of depression at baseline is no longer a limitation for the initiation of antiviral treatment. Antidepressant drugs have been recommended as current depression and prophylactic treatment in risk subgroups. However, caution should be exercised due to the risk of drug-drug interactions with some antiviral drugs. Women should be counselled prenatal, during and after pregnancy, taking into account the clinical situation, and the available evidence of the risks and benefits of antiviral and antidepressant treatments. Multidisciplinary approach shows cost-efficacy results.

Originality/value

– The paper clarifies the complex management of CHC therapy and the importance of individualizing treatment. The results also underline the need for an integrated multidisciplinary approach.

Depression as sickness behavior? A test of the host defense hypothesis in a high pathogen population

Sadness is an emotion universally recognized across cultures, suggesting it plays an important functional role in regulating human behavior. Numerous adaptive explanations of persistent sadness interfering with daily functioning (hereafter "depression") have been proposed, but most do not explain frequent bidirectional associations between depression and greater immune activation. Here we test several predictions of the host defense hypothesis, which posits that depression is part of a broader coordinated evolved response to infection or tissue injury (i.e. "sickness behavior") that promotes energy conservation and reallocation to facilitate immune activation. In a high pathogen population of lean and relatively egalitarian Bolivian forager-horticulturalists, we test whether depression and its symptoms are associated with greater baseline concentration of immune biomarkers reliably associated with depression in Western populations (i.e. tumor necrosis factor alpha [TNF-α], interleukin-1 beta [IL-1β], interleukin-6 [IL-6], and C-reactive protein [CRP]). We also test whether greater pro-inflammatory cytokine responses to ex vivo antigen stimulation are associated with depression and its symptoms, which is expected if depression facilitates immune activation. These predictions are largely supported in a sample of older adult Tsimane (mean±SD age=53.2±11.0, range=34-85, n=649) after adjusting for potential confounders. Emotional, cognitive and somatic symptoms of depression are each associated with greater immune activation, both at baseline and in response to ex vivo stimulation. The association between depression and greater immune activation is therefore not unique to Western populations. While our findings are not predicted by other adaptive hypotheses of depression, they are not incompatible with those hypotheses and future research is necessary to isolate and test competing predictions.

Glia in the cytokine-mediated onset of depression: fine tuning the immune response

Major depressive disorder (MDD) is a mood disorder of multifactorial origin affecting millions of people worldwide. The alarming estimated rates of prevalence and relapse make it a global public health concern. Moreover, the current setback of available antidepressants in the clinical setting is discouraging. Therefore, efforts to eradicate depression should be directed towards understanding the pathomechanisms involved in the hope of finding cost-effective treatment alternatives. The pathophysiology of MDD comprises the breakdown of different pathways, including the hypothalamus-pituitary-adrenal (HPA) axis, the glutamatergic system, and monoaminergic neurotransmission, affecting cognition and emotional behavior. Inflammatory cytokines have been postulated to be the possible link and culprit in the disruption of these systems. In addition, evidence from different studies suggests that impairment of glial functions appears to be a major contributor as well. Thus, the intricate role between glia, namely microglia and astrocytes, and the central nervous system's (CNSs) immune response is briefly discussed, highlighting the kynurenine pathway as a pivotal player. Moreover, evaluations of different treatment strategies targeting the inflammatory response are considered. The immuno-modulatory properties of vitamin D receptor (VDR) suggest that vitamin D is an attractive and plausible candidate in spite of controversial findings. Further research investigating the role of VDR in mood disorders is warranted.

Interleukin-6 as a predictor of symptom resolution in psychological distress: a cohort study

BACKGROUND

Elevated levels of interleukin-6 (IL-6) have been associated with the development of common mental disorders, such as depression, but its role in symptom resolution is unclear.

METHOD

We examined the association between IL-6 and symptom resolution in a non-clinical sample of participants with psychological distress.

RESULTS

Relative to high IL-6 levels, low levels at baseline were associated with symptom resolution at follow-up [age- and sex-adjusted risk ratio (RR) = 1.15, 95% confidence interval (CI) 1.06-1.25]. Further adjustment for covariates had little effect on the association. Symptomatic participants with repeated low IL-6 were more likely to be symptom-free at follow-up compared with those with repeated high IL-6 (RR = 1.21, 95% CI 1.03-1.41). Among the symptomatic participants with elevated IL-6 at baseline, IL-6 decreased along with symptom resolution.

CONCLUSIONS

IL-6 is potentially related to the mechanisms underlying recovery from symptoms of mental ill health. Further studies are needed to examine these mechanisms and to confirm the findings in relation to clinical depression.

Physical Activity Protects the Human Brain against Metabolic Stress Induced by a Postprandial and Chronic Inflammation

In recent years, it has become clear that chronic systemic low-grade inflammation is at the root of many, if not all, typically Western diseases associated with the metabolic syndrome. While much focus has been given to sedentary lifestyle as a cause of chronic inflammation, it is less often appreciated that chronic inflammation may also promote a sedentary lifestyle, which in turn causes chronic inflammation. Given that even minor increases in chronic inflammation reduce brain volume in otherwise healthy individuals, the bidirectional relationship between inflammation and sedentary behaviour may explain why humans have lost brain volume in the last 30,000 years and also intelligence in the last 30 years. We review evidence that lack of physical activity induces chronic low-grade inflammation and, consequently, an energy conflict between the selfish immune system and the selfish brain. Although the notion that increased physical activity would improve health in the modern world is widespread, here we provide a novel perspective on this truism by providing evidence that recovery of normal human behaviour, such as spontaneous physical activity, would calm proinflammatory activity, thereby allocating more energy to the brain and other organs, and by doing so would improve human health.

Effects of chronic interpersonal stress exposure on depressive symptoms are moderated by genetic variation at IL6 and IL1β in youth

AIMS

Close to one third of patients with major depression show increases in pro-inflammatory cytokines, which are in turn associated with risk for inflammatory disease. Genetic variants that enhance immune reactivity may thus enhance inflammatory and depressive reactions to stress. The aim of the present study was to investigate a trio of functional SNPs in the promoter regions of IL6 (-174G>C, rs1800795), IL1β (-511C>T, rs16944), and TNF (-308G>A, rs1800629) as moderators of the relationship between chronic stress exposure and elevations in depressive symptoms.

METHODS

Participants were 444 Australian youth (mean age=20.12) whose exposure to chronic stress in the past 6months was assessed using the semi-structured UCLA Life Stress Interview, and who completed the Beck Depression Inventory II at ages 15 and 20. Between ages 22 and 25, all participants in the selected sample provided blood samples for genotyping.

RESULTS

In line with a hypothesized moderation effect, -174G allele carriers at IL6 had fewer depressive symptoms following interpersonal stress, relative to C/C homozygotes with equal interpersonal stress exposure. However, IL6 genotype did not moderate the effects of non-interpersonal stress exposure (i.e., financial, work and health-related difficulties) on depression. Also in line with hypotheses, the -511C allele in IL1β, previously associated with higher IL-1β expression, was associated with more severe depression following chronic interpersonal stress exposure, relative to T/T homozygotes. Again, the moderating effect was specific to interpersonal stressors and did not generalize to non-interpersonal stress. TNF was not a moderator of the effects of either interpersonal or non-interpersonal stress on later depression outcomes.

CONCLUSION

Findings were consistent with the hypothesis that pro-inflammatory genetic variation increases the risk of stress-induced depression. The present results provide evidence of a genetic mechanism contributing to individual differences in depressive symptomatology following interpersonal stress exposure.

Association of brain immune genes with social behavior of inbred mouse strains

Background

Social deficit is one of the core symptoms of neuropsychiatric diseases, in which immune genes play an important role. Although a few immune genes have been shown to regulate social and emotional behaviors, how immune gene network(s) may jointly regulate sociability has not been investigated so far.

Methods

To decipher the potential immune-mediated mechanisms underlying social behavior, we first studied the brain microarray data of eight inbred mouse strains with known variations in social behavior and retrieved the differentially expressed immune genes. We then made a protein-protein interaction analysis of them to find the major networks and explored the potential association of these genes with the behavior and brain morphology in the mouse phenome database. To validate the expression and function of the candidate immune genes, we selected the C57BL/6 J and DBA/2 J strains among the eight inbred strains, compared their social behaviors in resident-intruder and 3-chambered social tests and the mRNA levels of these genes, and analyzed the correlations of these genes with the social behaviors.

Results

A group of immune genes were differentially expressed in the brains of these mouse strains. The representative C57BL/6 J and DBA/2 J strains displayed significant differences in social behaviors, DBA/2 J mice being less active in social dominance and social interaction than C57BL/6 J mice. The mRNA levels of H2-d1 in the prefrontal cortex, hippocampus, and hypothalamus and C1qb in the hippocampus of the DBA/2 J strain were significantly down-regulated as compared to those in the C57BL/6 J strain. In contrast, Polr3b in the hippocampus and Tnfsf13b in the prefrontal cortex of the DBA/2 J strain were up-regulated. Furthermore, C1qb, Cx3cl1, H2-d1, H2-k1, Polr3b, and Tnfsf13b were predicted to be associated with various behavioral and brain morphological features across the eight inbred strains. Importantly, the C1qb mRNA level was confirmed to be significantly correlated with the sociability in DBA/2 J but not in C57BL/6 J mice.

Conclusions

Our study provided evidence on the association of immune gene network(s) with the brain development and behavior in animals and revealed neurobiological functions of novel brain immune genes that may contribute to social deficiency in animal models of neuropsychiatric disorders.

The role of inflammatory markers in explaining the association between depression and cardiovascular hospitalisations

This study investigated whether inflammation may explain the relationship between depression and incident cardiovascular hospitalisations. Participants (55-85 years) completed baseline depression and physical assessment. Those without self-reported cardiovascular events were followed prospectively for hospital admissions for angina, myocardial infarction and cerebral infarction (median 937 days). Across 5140 person-years of risk (N = 1692), there were 47 incident cardiovascular hospitalisations (2.8 %). Controlling for age and gender, interleukin (IL)-6, C-reactive protein (CRP), body mass index (BMI) and waist-to-hip ratio were associated with future cardiovascular events. Mediation analysis showed that CRP accounted for 8.1 % and IL-6 10.9 % of the effect of depression on cardiovascular events, and including the indirect effect in the model substantially reduced the direct relationship between depression and cardiovascular hospitalisations. BMI and waist-to-hip ratio accounted for indirect effects of 7.7 and 10.4 %, respectively. Inflammatory markers partly explain the association between depression and cardiovascular events, although other shared factors also likely contribute.

Unhealthy lifestyle may increase later depression via inflammation in older women but not men

Depression and inflammatory markers have a reliable cross-sectional association although less is known about the prospective relationship. The current study investigated whether pro-inflammatory markers are prospectively associated with depression, and whether indicators of unhealthy lifestyle, physical health and psychosocial functioning may drive this association. Participants were drawn from the Hunter Community Study, a community-dwelling cohort of individuals aged 55-85 years (N = 1410). Participants completed baseline physiological assessment, health-related questionnaires, and blood sampling for the analysis of inflammatory markers, C-reactive protein (CRP) and interleukin (IL)-6. Participants completed the same depressive symptom questionnaire again after 3.5-5.5 years. Depression outcomes at follow-up were analysed dichotomously using established scale cut-off scores and continuously as a "residual score", representing the variation in follow-up depressive symptoms not explained by baseline symptoms and age. Analyses were conducted on males and females separately. At baseline, indicators of unhealthy lifestyle, physical health and psychosocial functioning were associated with depressive symptoms and inflammatory markers. For males, there were no relationships between inflammatory markers and follow-up depression outcomes. In females, IL-6 was significantly associated with depression outcomes in univariate, but not multivariate analyses. However, IL-6 significantly mediated the association between the predictors of waist-to-hip ratio, smoking and psychological coping at baseline, and follow-up depression outcomes. The results support the inflammatory hypothesis of depression, although females may be more vulnerable to effects. The findings raise the possibility that unhealthy lifestyle and psychosocial stress may drive inflammation and subsequent depressive symptoms.

Greater amygdala activity and dorsomedial prefrontal-amygdala coupling are associated with enhanced inflammatory responses to stress

Psychological stress is implicated in the etiology of many common chronic diseases and mental health disorders. Recent research suggests that inflammation may be a key biological mediator linking stress and health. Nevertheless, the neurocognitive pathways underlying stress-related increases in inflammatory activity are largely unknown. The present study thus examined associations between neural and inflammatory responses to an acute laboratory-based social stressor. Healthy female participants (n=31) were exposed to a brief episode of stress while they underwent an fMRI scan. Blood samples were taken before and after the stressor, and plasma was assayed for markers of inflammatory activity. Exposure to the stressor was associated with significant increases in feelings of social evaluation and rejection, and with increases in levels of inflammation. Analyses linking the neural and inflammatory data revealed that heightened neural activity in the amygdala in response to the stressor was associated with greater increases in inflammation. Functional connectivity analyses indicated that individuals who showed stronger coupling between the amygdala and the dorsomedial prefrontal cortex (DMPFC) also showed a heightened inflammatory response to the stressor. Interestingly, activity in a different set of neural regions was related to increases in feelings of social rejection. These data show that greater amygdala activity in response to a stressor, as well as tighter coupling between the amygdala and the DMPFC, are associated with greater increases in inflammatory activity. Results from this study begin to identify neural mechanisms that might link stress with increased risk for inflammation-related disorders such as cardiovascular disease and depression.

Is Postpartum Depression a Disease of Modern Civilization?

Access to calorie-dense foods, medicine, and other comforts has made modern humans healthier than our prehistoric ancestors in many respects. However, the epidemics of obesity, diabetes, and cardiovascular disease suggest that there are also drawbacks to modern living. Here, we address the question of whether the dramatic cultural changes that have occurred over the past century have inflated rates of postpartum depression, adding postpartum depression to the list of "diseases of modern civilization." We review evidence from cross-cultural, epidemiological, and experimental studies documenting associations between postpartum depression and modern patterns of early weaning, diets deficient in essential fatty acids, low levels of physical activity, low levels of sun exposure, and isolation from kin support networks, all of which mark significant divergences from lifestyles believed to have been typical throughout human evolutionary history. This "mismatch hypothesis" of postpartum depression integrates research across diverse research areas and generates novel predictions.

Type I interferon signaling genes in recurrent major depression: increased expression detected by whole-blood RNA sequencing

A study of genome-wide gene expression in major depressive disorder (MDD) was undertaken in a large population-based sample to determine whether altered expression levels of genes and pathways could provide insights into biological mechanisms that are relevant to this disorder. Gene expression studies have the potential to detect changes that may be because of differences in common or rare genomic sequence variation, environmental factors or their interaction. We recruited a European ancestry sample of 463 individuals with recurrent MDD and 459 controls, obtained self-report and semi-structured interview data about psychiatric and medical history and other environmental variables, sequenced RNA from whole blood and genotyped a genome-wide panel of common single-nucleotide polymorphisms. We used analytical methods to identify MDD-related genes and pathways using all of these sources of information. In analyses of association between MDD and expression levels of 13 857 single autosomal genes, accounting for multiple technical, physiological and environmental covariates, a significant excess of low P-values was observed, but there was no significant single-gene association after genome-wide correction. Pathway-based analyses of expression data detected significant association of MDD with increased expression of genes in the interferon α/β signaling pathway. This finding could not be explained by potentially confounding diseases and medications (including antidepressants) or by computationally estimated proportions of white blood cell types. Although cause-effect relationships cannot be determined from these data, the results support the hypothesis that altered immune signaling has a role in the pathogenesis, manifestation, and/or the persistence and progression of MDD.

Inflammation and lithium: clues to mechanisms contributing to suicide-linked traits

Suicide is one of the leading causes of death in the United States, yet it remains difficult to understand the mechanistic provocations and to intervene therapeutically. Stress is recognized as a frequent precursor to suicide. Psychological stress is well established to cause activation of the inflammatory response, including causing neuroinflammation, an increase of inflammatory molecules in the central nervous system (CNS). Neuroinflammation is increasingly recognized as affecting many aspects of CNS functions and behaviors. In particular, much evidence demonstrates that inflammatory markers are elevated in traits that have been linked to suicidal behavior, including aggression, impulsivity and depression. Lithium is recognized as significantly reducing suicidal behavior, is anti-inflammatory and diminishes aggression, impulsivity and depression traits, each of which is associated with elevated inflammation. The anti-inflammatory effects of lithium result from its inhibition of glycogen synthase kinase-3 (GSK3). GSK3 has been demonstrated to strongly promote inflammation, aggressive behavior in rodents and depression-like behaviors in rodents, whereas regulation of impulsivity by GSK3 has not yet been investigated. Altogether, evidence is building supporting the hypothesis that stress activates GSK3, which in turn promotes inflammation, and that inflammation is linked to behaviors associated with suicide, including particularly aggression, impulsivity and depression. Further investigation of these links may provide a clearer understanding of the causes of suicidal behavior and provide leads for the development of effective preventative interventions, which may include inhibitors of GSK3.

Glycogen synthase kinase-3 (GSK3): regulation, actions, and diseases

Glycogen synthase kinase-3 (GSK3) may be the busiest kinase in most cells, with over 100 known substrates to deal with. How does GSK3 maintain control to selectively phosphorylate each substrate, and why was it evolutionarily favorable for GSK3 to assume such a large responsibility? GSK3 must be particularly adaptable for incorporating new substrates into its repertoire, and we discuss the distinct properties of GSK3 that may contribute to its capacity to fulfill its roles in multiple signaling pathways. The mechanisms regulating GSK3 (predominantly post-translational modifications, substrate priming, cellular trafficking, protein complexes) have been reviewed previously, so here we focus on newly identified complexities in these mechanisms, how each of these regulatory mechanism contributes to the ability of GSK3 to select which substrates to phosphorylate, and how these mechanisms may have contributed to its adaptability as new substrates evolved. The current understanding of the mechanisms regulating GSK3 is reviewed, as are emerging topics in the actions of GSK3, particularly its interactions with receptors and receptor-coupled signal transduction events, and differential actions and regulation of the two GSK3 isoforms, GSK3α and GSK3β. Another remarkable characteristic of GSK3 is its involvement in many prevalent disorders, including psychiatric and neurological diseases, inflammatory diseases, cancer, and others. We address the feasibility of targeting GSK3 therapeutically, and provide an update of its involvement in the etiology and treatment of several disorders.

Microbiota, immunoregulatory old friends and psychiatric disorders

Regulation of the immune system is an important function of the gut microbiota. Increasing evidence suggests that modern living conditions cause the gut microbiota to deviate from the form it took during human evolution. Contributing factors include loss of helminth infections, encountering less microbial biodiversity, and modulation of the microbiota composition by diet and antibiotic use. Thus the gut microbiota is a major mediator of the hygiene hypothesis (or as we prefer, "Old Friends" mechanism), which describes the role of organisms with which we co-evolved, and that needed to be tolerated, as crucial inducers of immunoregulation. At least partly as a consequence of reduced exposure to immunoregulatory Old Friends, many but not all of which resided in the gut, high-income countries are undergoing large increases in a wide range of chronic inflammatory disorders including allergies, autoimmunity and inflammatory bowel diseases. Depression, anxiety and reduced stress resilience are comorbid with these conditions, or can occur in individuals with persistently raised circulating levels of biomarkers of inflammation in the absence of clinically apparent peripheral inflammatory disease. Moreover poorly regulated inflammation during pregnancy might contribute to brain developmental abnormalities that underlie some cases of autism spectrum disorders and schizophrenia. In this chapter we explain how the gut microbiota drives immunoregulation, how faulty immunoregulation and inflammation predispose to psychiatric disease, and how psychological stress drives further inflammation via pathways that involve the gut and microbiota. We also outline how this two-way relationship between the brain and inflammation implicates the microbiota, Old Friends and immunoregulation in the control of stress resilience.

Insights from interferon-α-related depression for the pathogenesis of depression associated with inflammation

Interferon-α (IFN-α) is a pleiotropic cytokine that is administered as a therapeutic in highly prevalent medical conditions such as chronic hepatitis C and B virus infection, melanoma and lymphoma. IFN-α induces, to a clinically relevant degree, concentration, memory, drive and mood disturbances in almost half of all patients. For this reason, IFN-α is increasingly being replaced by more specifically acting drugs. In the past decades, IFN-α has offered a valuable insight into the pathogenesis of major depression, particularly in settings associated with inflammation. IFN-α triggers immune responses, hypothalamo-pituitary-adrenal axis abnormalities and disturbances of brain metabolism resembling those in other depression states. IFN-α stimulates indoleamine-2,3 dioxygenase-1, activating the kynurenine pathway with reduced formation of the neurotransmitters serotonin and dopamine, excessive formation of the NMDA agonist quinolinic acid, and reduced formation of the NMDA antagonist kynurenic acid. In addition, IFN-α disturbs neurotrophic signaling and impedes neurite outgrowth, synaptic plasticity, endogenous neurogenesis and neuronal survival. Consequently, IFN-α-related depression may represent a model for the neurodegenerative changes that are noticed in late-life major depression. Indeed, the observation that brain responses in IFN-α-related depression resemble idiopathic depression is supported by the existence of common genetic signatures, among which of note, a number of neuronal survival and plasticity genes have been identified. In view of the high incidence of depressive symptoms, IFN-α-related depression is an attractive model for studying links between neuronal plasticity, neurodegeneration and depression. We predict that in the latter areas new targets for anti-depressant therapies could be identified, which may deepen our understanding of idiopathic major depression.

Sick in the Head? Pathogen Concerns Bias Implicit Perceptions of Mental Illness

Biases against the mentally ill are historically and cross-culturally pervasive, suggesting they may have an evolutionary basis. The prevailing view is that people seek to distance themselves from the mentally ill because they are perceived as dangerous, violent, and incompetent. However, because of similarities between sickness behaviors and symptoms of some mental disorders, it was hypothesized that mental illness stigma could be partially explained as a function of behavioral immune system biases designed to avoid potential sources of contagion. In two experiments, it was found that mental illness was implicitly associated more with disease than danger. In Experiment 1, this implicit association was exacerbated among people who have had their biological immune system activated by a recent illness. In Experiment 2, experimentally priming disease salience increased implicit association between mental illness and disease. Implications for the evolutionary origins of prejudice and the prevention of mental illness stigma are discussed.

Pediatric inflammatory bowel disease and depression: treatment implications

PURPOSE OF REVIEW

Depression in pediatric inflammatory bowel disease is increasingly recognized to be a heterogeneous condition with diverse underlying predisposing and precipitating factors. Although there is a growing awareness regarding the benefits of integrating behavioral health into medical care, the way psychiatric treatments can best target different aspects of depression and related dysfunction has not been systematically explored.

RECENT FINDINGS

This review discusses neurobiological risk factors for depression in inflammatory bowel disease including inflammation, associated anti-inflammatory treatment with corticosteroids, pain, and sleep disturbance, as well as psychosocial factors including reactions to illness, illness perception, and disease and environmental stressors with an emphasis on how these factors can influence treatment decisions. Empirically supported psychosocial and psychopharmacological interventions are discussed within this context.

SUMMARY

Understanding the diverse pathways that can lead to depression in youths with inflammatory bowel disease can lead to the development of more targeted interventions and better integration of psychosocial care into the medical treatment of inflammatory bowel disease.

Darwinian depression

BACKGROUND

The standard evolutionary explanation for depression is that being in an emotionally depressed state is adaptive.

METHOD

The article first undertakes a critical review of the extant literature. It then provides an alternative evolutionary explanation for event-based depression and elation. It argues that being in a depressed state is not adaptive (indeed, quite the opposite), but that the threat of depression for bad outcomes and the promise of pleasure for good outcomes are adaptive because they motivate the individual toward undertaking effort that increases fitness. The article then explains reasons for failure in the motivation system and the mood disorders that arise as a consequence.

RESULTS

The article explains why motivation depends on both elation and depression and why individual happiness is not permanently improved by winning the lottery (or permanently reduced by becoming wheelchair bound). It explains the comorbidity of bipolar disorder and panic disorder, why mood stabilizers tend to reduce motivation, and when anti-depressants are unlikely to cure "laziness."

LIMITATIONS

The evolutionary explanation for depression does not directly provide clinical criteria for determining when major depressive disorder is present nor has it yet provided new treatment strategies for mood disorders.

CONCLUSIONS

The theory presented here provides a coherent explanation for depression and elation and leads research in a different direction from previous evolutionary explanations.

Effects of oxidative stress on fatty acid- and one-carbon-metabolism in psychiatric and cardiovascular disease comorbidity

OBJECTIVE

Cardiovascular disease (CVD) is the leading cause of death in severe psychiatric disorders (depression, schizophrenia). Here, we provide evidence of how the effects of oxidative stress on fatty acid (FA) and one-carbon (1-C) cycle metabolism, which may initially represent adaptive responses, might underlie comorbidity between CVD and psychiatric disorders.

METHOD

We conducted a literature search and integrated data in a narrative review.

RESULTS

Oxidative stress, mainly generated in mitochondria, is implicated in both psychiatric and cardiovascular pathophysiology. Oxidative stress affects the intrinsically linked FA and 1-C cycle metabolism: FAs decrease in chain length and unsaturation (particularly omega-3 polyunsaturated FAs), and lipid peroxidation products increase; the 1-C cycle shifts from the methylation to transsulfuration pathway (lower folate and higher homocysteine and antioxidant glutathione). Interestingly, corresponding alterations were reported in psychiatric disorders and CVD. Potential mechanisms through which FA and 1-C cycle metabolism may be involved in brain (neurocognition, mood regulation) and cardiovascular system functioning (inflammation, thrombosis) include membrane peroxidizability and fluidity, eicosanoid synthesis, neuroprotection and epigenetics.

CONCLUSION

While oxidative-stress-induced alterations in FA and 1-C metabolism may initially enhance oxidative stress resistance, persisting chronically, they may cause damage possibly underlying (co-occurrence of) psychiatric disorders and CVD. This might have implications for research into diagnosis and (preventive) treatment of (CVD in) psychiatric patients.

Personality change associated with chronic diseases: pooled analysis of four prospective cohort studies

BACKGROUND

Common chronic conditions, such as heart disease and cancer, are associated with increased psychological distress, functional limitations and shortened life expectancy, but whether these diseases alter aspects of personality remains unclear.

METHOD

To examine whether the onset of heart disease, stroke, diabetes, cancer, hypertension, arthritis and respiratory disease is associated with subsequent changes in personality traits of the five-factor model, we pooled data from the Health and Retirement Study, the Midlife in the United States Survey, and the graduate and sibling samples of the Wisconsin Longitudinal Study for an individual-participant meta-analysis (total n=17,493; mean age at baseline 55.8 years).

RESULTS

After adjustment for age, we observed consistent decreases in extraversion [-0.25 T-scores per one disease; 95% confidence interval (CI) -0.40 to -0.10], emotional stability (-0.40, 95% CI -0.61 to -0.19), conscientiousness (-0.44, 95% CI -0.57 to -0.30) and openness to experience (-0.25, 95% CI -0.37 to -0.13) but not in agreeableness (-0.05, 95% CI -0.19 to 0.08) after the onset of chronic diseases. The onset of each additional chronic disease accelerated the average age-related personality change by 2.5 years in decreasing extraversion, 5.5 years in decreasing conscientiousness, and 1.6 years in decreasing openness to experience, and attenuated the increasing levels of emotional stability by 1.9 years. Co-morbid conditions were associated with larger changes than single diseases, suggesting a dose-response association between morbidity and personality change.

CONCLUSIONS

These results support the hypothesis that chronic diseases influence personality development in adulthood.

Association of metabolically healthy obesity with depressive symptoms: pooled analysis of eight studies

The hypothesis of metabolically healthy obesity posits that adverse health effects of obesity are largely avoided when obesity is accompanied by a favorable metabolic profile. We tested this hypothesis with depressive symptoms as the outcome using cross-sectional data on obesity, metabolic health and depressive symptoms. Data were extracted from eight studies and pooled for individual-participant meta-analysis with 30,337 men and women aged 15-105 years (mean age=46.1). Clinic measures included height, weight and metabolic risk factors (high blood pressure, high triglycerides, low high-density lipoprotein cholesterol, high C-reactive protein and high glycated hemoglobin). Depressive symptoms were assessed using clinical interview or standardized rating scales. The pooled sample comprised 7673 (25%) obese participants (body mass index ⩾30 kg m(-2)). Compared to all non-obese individuals, the OR for depressive symptoms was higher in metabolically unhealthy obese individuals with two or more metabolic risk factors (1.45; 95% confidence interval (CI)=1.30, 1.61) and for metabolically healthy obese with ⩽1 metabolic risk factor (1.19; 95% CI=1.03, 1.37), adjusted for sex, age and race/ethnicity. Metabolically unhealthy obesity was associated with higher depression risk (OR=1.23; 95% CI=1.05, 1.45) compared with metabolically healthy obesity. These associations were consistent across studies with no evidence for heterogeneity in estimates (all I(2)-values<4%). In conclusion, obese persons with a favorable metabolic profile have a slightly increased risk of depressive symptoms compared with non-obese, but the risk is greater when obesity is combined with an adverse metabolic profile. These findings suggest that metabolically healthy obesity is not a completely benign condition in relation to depression risk.

Molecular and cellular neuroinflammatory status of mouse brain after systemic lipopolysaccharide challenge: importance of CCR2/CCL2 signaling

Background

Genetic and environmental factors are critical elements influencing the etiology of major depression. It is now accepted that neuroinflammatory processes play a major role in neuropsychological disorders. Neuroinflammation results from the dysregulation of the synthesis and/or release of pro- and anti-inflammatory cytokines with central or peripheral origin after various insults. Systemic bacterial lipopolysaccharide (LPS) challenge is commonly used to study inflammation-induced depressive-like behaviors in rodents. In the present study, we investigated immune-to-brain communication in mice by examining the effects of peripheral LPS injection on neuroinflammation encompassing cytokine and chemokine production, microglia and central nervous system (CNS)-associated phagocyte activation, immune cell infiltration and serotonergic neuronal function.

Methods

LPS was administered to C57BL/6 J mice by intraperitoneal injection; brains were collected and pro-inflammatory cytokine mRNA and proteins were measured. To examine the relative contribution of the different populations of brain immune cells to the occurrence of neuroinflammation after acute systemic inflammation, we precisely characterized them by flow cytometry, studied changes in their proportions and level of activation, and measured the amount of cytokines they released by Cytometric Bead Array™ after cell sorting and ex vivo culture. Because of the central role that the chemokine CCL2 seems to play in our paradigm, we studied the effect of CCL2 on the activity of serotonergic neurons of the raphe nucleus using electrophysiological recordings.

Results

We report that systemic LPS administration in mice caused a marked increase in pro-inflammatory IL-1β, IL-6, TNFα and CCL2 (monocyte chemoattractant protein-1) mRNA and protein levels in the brain. Moreover, we found that LPS caused microglia and CNS-associated phagocyte activation characterized by upregulation of CCR2, TLR4/CD14, CD80 and IL-4Rα, associated with overproduction of pro-inflammatory cytokines and chemokines, especially CCL2. LPS also induced a marked and selective increase of CCR2⁺ inflammatory monocytes within the brain. Finally, we showed that CCL2 hyperpolarized serotonergic raphe neurons in mouse midbrain slices, thus probably reducing the serotonin tone in projection areas.

Conclusion

Together, we provide a detailed characterization of the molecular and cellular players involved in the establishment of neuroinflammation after systemic injection of LPS. This highlights the importance of the CCL2/CCR2 signaling and suggests a possible link with depressive disorders.

Sick in the head? Pathogen concerns bias implicit perceptions of mental illness

Biases against the mentally ill are historically and cross-culturally pervasive, suggesting they may have an evolutionary basis. The prevailing view is that people seek to distance themselves from the mentally ill because they are perceived as dangerous, violent, and incompetent. However, because of similarities between sickness behaviors and symptoms of some mental disorders, it was hypothesized that mental illness stigma could be partially explained as a function of behavioral immune system biases designed to avoid potential sources of contagion. In two experiments, it was found that mental illness was implicitly associated more with disease than danger. In Experiment 1, this implicit association was exacerbated among people who have had their biological immune system activated by a recent illness. In Experiment 2, experimentally priming disease salience increased implicit association between mental illness and disease. Implications for the evolutionary origins of prejudice and the prevention of mental illness stigma are discussed.

Serotonin 2A receptor gene (HTR2A) regulatory variants: possible association with severity of depression symptoms in children with autism spectrum disorder

OBJECTIVE AND BACKGROUND

Our aim was to characterize the association of 2 functional single nucleotide polymorphisms (rs6311 and rs6314) in the serotonin 2A receptor gene (HTR2A) with severity of depression symptoms in children with autism spectrum disorder. These polymorphisms have been shown to be associated with depression symptom severity and response to selective serotonin reuptake inhibitor drugs in adults with diagnosed depressive disorder.

METHODS

Parents of 104 children with autism spectrum disorder rated their children's depressive symptoms using a validated scale based on criteria from the Diagnostic and Statistical Manual of Mental Disorders, 4th edition. We compared severity of depression symptoms across the rs6311 and rs6314 genotypes, measured from the children's genomic DNA.

RESULTS

Children homozygous for the G allele of rs6311 had significantly more severe depression symptoms than those with G/A or A/A genotypes (P=0.025). The effect size (partial eta-squared) was small (ηp=0.047) but was somewhat larger when we controlled for severity of generalized anxiety disorder symptoms (P=0.006, ηp=0.072). When we restricted our analyses to white participants, our results were essentially the same as for the entire sample (P=0.004, ηp=0.086). There was no significant association between rs6314 (C/C versus T carriers) and severity of depression.

CONCLUSIONS

Our findings suggest that the HTR2A functional rs6311 polymorphism, which other studies have associated with differential HTR2A mRNA expression, may modulate the severity of depression symptoms in children with autism spectrum disorder. These tentative, hypothesis-generating findings need replication with larger, independent samples.

Early stress and human behavioral development: emerging evolutionary perspectives

Stress experienced early in life exerts a powerful, lasting influence on development. Converging empirical findings show that stressful experiences become deeply embedded in the child’s neurobiology, with an astonishing range of long-term effects on cognition, emotion, and behavior. In contrast with the prevailing view that such effects are the maladaptive outcomes of ‘toxic’ stress, adaptive models regard them as manifestations of evolved developmental plasticity. In this paper, I offer a brief introduction to adaptive models of early stress and human behavioral development, with emphasis on recent theoretical contributions and emerging concepts in the field. I begin by contrasting dysregulation models of early stress with their adaptive counterparts; I then introduce life history theory as a unifying framework, and review recent work on predictive adaptive responses (PARs) in human life history development. In particular, I discuss the distinction between forecasting the future state of the environment (external prediction) and forecasting the future state of the organism (internal prediction). Next, I present the adaptive calibration model, an integrative model of individual differences in stress responsivity based on life history concepts. I conclude by examining how maternal–fetal conflict may shape the physiology of prenatal stress and its adaptive and maladaptive effects on postnatal development. In total, I aim to show how theoretical work from evolutionary biology is reshaping the way we think about the role of stress in human development, and provide researchers with an up-to-date conceptual map of this fascinating and rapidly evolving field.

Competing targets of microRNA-608 affect anxiety and hypertension

MicroRNAs (miRNAs) can repress multiple targets, but how a single de-balanced interaction affects others remained unclear. We found that changing a single miRNA-target interaction can simultaneously affect multiple other miRNA-target interactions and modify physiological phenotype. We show that miR-608 targets acetylcholinesterase (AChE) and demonstrate weakened miR-608 interaction with the rs17228616 AChE allele having a single-nucleotide polymorphism (SNP) in the 3'-untranslated region (3'UTR). In cultured cells, this weakened interaction potentiated miR-608-mediated suppression of other targets, including CDC42 and interleukin-6 (IL6). Postmortem human cortices homozygote for the minor rs17228616 allele showed AChE elevation and CDC42/IL6 decreases compared with major allele homozygotes. Additionally, minor allele heterozygote and homozygote subjects showed reduced cortisol and elevated blood pressure, predicting risk of anxiety and hypertension. Parallel suppression of the conserved brain CDC42 activity by intracerebroventricular ML141 injection caused acute anxiety in mice. We demonstrate that SNPs in miRNA-binding regions could cause expanded downstream effects changing important biological pathways.

Depression and type 2 diabetes: a causal association?

There is a controversy regarding whether depression and type 2 diabetes are causally linked. To assess this issue, we review key findings for the association between depression and diabetes, and its underlying mechanisms. Findings from meta-analyses of cohort studies show a modestly sized bidirectional association between depression and type 2 diabetes (ie, depression predicts diabetes onset and diabetes predicts future depression). However, depression-related biological alterations in the hypothalamic-pituitary-adrenal cortex axis and the sympathetic nervous system, and subclinical inflammation, are not consistently linked with increased diabetes risk. The evidence for an association between depression and glycaemic traits (eg, glucose, insulin, insulin sensitivity, and insulin secretion) is also mixed. Diabetes increases the risk of depression to the same extent as do other chronic disorders (eg, cardiac diseases, osteoarthritis, lung disease, and poor hearing). At present, the available evidence suggests that pathophysiological changes preceding the onset of type 2 diabetes might not cause depression, nor might depression directly increase the risk of developing type 2 diabetes. Despite insufficient robust causal evidence, treating physicians should be aware of the co-occurrence of depression and type 2 diabetes.

Understanding heterogeneity in PTSD: fear, dysphoria, and distress

Fear, dysphoria, and distress are prominent components in the conceptualization of posttraumatic stress disorder (PTSD). However, because our diagnostic categories are open concepts, relying on observed patterns of symptoms for classification, it is unclear whether these components represent core or auxiliary features of the disorder. Convergence across multiple indices is critical for this understanding. In this paper, we examine these components of PTSD across observed symptom patterns, broader theoretical conceptualizations, underlying information processing mechanisms of attention and memory, and underlying learning and neurobiological mechanisms. For each, evidence for similarity or distinctiveness of PTSD with other anxiety disorders and depression is examined. Throughout the review, key points of similarity to the anxiety disorders and divergence with depression argue for a distinction between core fear symptoms and auxiliary dysphoria and distress symptoms. Implications are discussed, noting that, as heterogeneity increases, core characteristics will become more diffused and ancillary constructs will gain an inflated degree of importance.

Glycogen synthase kinase-3 inhibitors: Rescuers of cognitive impairments

Impairment of cognitive processes is a devastating outcome of many diseases, injuries, and drugs affecting the central nervous system (CNS). Most often, very little can be done by available therapeutic interventions to improve cognitive functions. Here we review evidence that inhibition of glycogen synthase kinase-3 (GSK3) ameliorates cognitive deficits in a wide variety of animal models of CNS diseases, including Alzheimer's disease, Fragile X syndrome, Down syndrome, Parkinson's disease, spinocerebellar ataxia type 1, traumatic brain injury, and others. GSK3 inhibitors also improve cognition following impairments caused by therapeutic interventions, such as cranial irradiation for brain tumors. These findings demonstrate that GSK3 inhibitors are able to ameliorate cognitive impairments caused by a diverse array of diseases, injury, and treatments. The improvements in impaired cognition instilled by administration of GSK3 inhibitors appear to involve a variety of different mechanisms, such as supporting long-term potentiation and diminishing long-term depression, promotion of neurogenesis, reduction of inflammation, and increasing a number of neuroprotective mechanisms. The potential for GSK3 inhibitors to repair cognitive deficits associated with many conditions warrants further investigation of their potential for therapeutic interventions, particularly considering the current dearth of treatments available to reduce loss of cognitive functions.

Immunology of schizophrenia

Increased proinflammatory markers like cytokines have been described in the blood and cerebrospinal fluid of patients suffering from schizophrenia. Animal models have shown that a hit in early life to the immune system might trigger a lifelong increased immune reactivity. Many epidemiological and clinical studies show the role of various infectious agents as risk factors for schizophrenia with overlap to other psychoses. The first large-scale epidemiological study in psychiatry from Denmark clearly demonstrates severe infections and autoimmune disorders during lifetime to be risk factors for schizophrenia. Genetic studies have shown the strongest signal for schizophrenia on chromosome 6p22.1, in a region related to the major histocompatibility complex and other immune functions. The vulnerability-stress-inflammation model is important as stress may increase proinflammatory cytokines and even contribute to a lasting proinflammatory state. The immune system itself is considered an important further piece in the puzzle, as in autoimmune disorders in general, which are always linked to three factors: genes, the environment and the immune system. Alterations of dopaminergic, serotonergic, noradrenergic and glutamatergic neurotransmission have been shown with low-level neuroinflammation and may directly be involved in the generation of schizophrenic symptoms. Loss of central nervous system volume and microglial activation has been demonstrated in schizophrenia in neuroimaging studies, which supports the assumption of a low-level neuroinflammatory process. Further support comes from the therapeutic benefit of anti-inflammatory medications in specific studies and the anti-inflammatory and immunomodulatory intrinsic effects of antipsychotics.

The evolutionary puzzle of suicide

Mechanisms of self-destruction are difficult to reconcile with evolution’s first rule of thumb: survive and reproduce. However, evolutionary success ultimately depends on inclusive fitness. The altruistic suicide hypothesis posits that the presence of low reproductive potential and burdensomeness toward kin can increase the inclusive fitness payoff of self-removal. The bargaining hypothesis assumes that suicide attempts could function as an honest signal of need. The payoff may be positive if the suicidal person has a low reproductive potential. The parasite manipulation hypothesis is founded on the rodent—Toxoplasma gondii host-parasite model, in which the parasite induces a “suicidal” feline attraction that allows the parasite to complete its life cycle. Interestingly, latent infection by T. gondii has been shown to cause behavioral alterations in humans, including increased suicide attempts. Finally, we discuss how suicide risk factors can be understood as nonadaptive byproducts of evolved mechanisms that malfunction. Although most of the mechanisms proposed in this article are largely speculative, the hypotheses that we raise accept self-destructive behavior within the framework of evolutionary theory.

Associations between change in sleep duration and inflammation: findings on C-reactive protein and interleukin 6 in the Whitehall II Study

Cross-sectional evidence suggests associations between sleep duration and levels of the inflammatory markers, C-reactive protein and interleukin-6. This longitudinal study uses data from the London-based Whitehall II study to examine whether changes in sleep duration are associated with average levels of inflammation from 2 measures 5 years apart. Sleep duration (≤5, 6, 7, 8, ≥9 hours on an average week night) was assessed in 5,003 middle-aged women and men in 1991/1994 and 1997/1999. Fasting levels of C-reactive protein and interleukin-6 were measured in 1997/1999 and 2002/2004. Cross-sectional analyses indicated that shorter sleep is associated with higher levels of inflammatory markers. Longitudinal analyses showed that each hour per night decrease in sleep duration between 1991/1994 and 1997/1999 was associated with higher levels of C-reactive protein (8.1%) and interleukin-6 (4.5%) averaged across measures in 1997/1999 and 2002/2004. Adjustment for longstanding illness and major cardiometabolic risk factors indicated that disease processes may partially underlie these associations. An increase in sleep duration was not associated with average levels of inflammatory markers. These results suggest that both short sleep and reductions in sleep are associated with average levels of inflammation over a 5-year period.

Do cytokines really sing the blues?

The World Health Organization predicts that depression, which already affects about 10 percent of the population in the United States, will be the world’s leading medical condition by 2030. Evidence suggests several causes for depression, including traumatic life events, disease, poison, and nutritional deficiencies. Many of these causes are associated with elevated levels of inflammatory biomarkers in the blood, which may in turn lead to inflammatory changes in the brain. Our authors examine what the latest research reveals about link between inflammation in the brain and depression, and how a better understanding of that link can play a critical first step in the personalization of care.

Malaise, melancholia and madness: the evolutionary legacy of an inflammatory bias

Evolutionary imperatives bred a vigorous and highly orchestrated behavioral and immune response to the microbial world that served to promote species survival and propagation. The resultant legacy is an inflammatory bias which goes largely unchecked in the modern world and is provoked not only by pathogens but also now by people. In this commentary, the authors' contributions to the special issue on Inflammation and Mental Health are described, beginning with the origins of the inflammatory bias, its roots in genetic predispositions to behavioral adaptations and ultimately maladaptations, and its consequences on the developing brain. In addition, the mechanisms by which the immune system engages behavior are described including a central role for the inflammasome which may serve to link psychological stress with inflammatory and behavioral responses. Neurotransmitter systems that mediate effects of the immune system on behavior are also described along with interactions of the inflammatory bias with depression and their convergent impact on the response to stress and medical illness. Finally, translational implications are discussed including data from a clinical trial using a cytokine antagonist in depressed patients, which suggests an interaction of the inflammatory bias with other evolutionary legacies including those related to food consumption and their modern consequences of obesity and the metabolic syndrome. Taken together, the articles offer a sampling of the rich literature that has evolved regarding the role of the immune system in behavioral disorders. The grounding of this relationship in our evolutionary past may serve to inform future research both theoretically and therapeutically.