Immune status influences fear and anxiety responses in mice after acute stress exposure

The amino acid metabolism pathway of peripheral T lymphocytes and ketamine-induced schizophrenia-like phenotype

BACKGROUND

The intricate interplay between peripheral adaptive immune cells and the central nervous system (CNS) has garnered increasing recognition. Given that alterations in cell quantities often translate into modifications in metabolite profiles and that these metabolic changes can potentially traverse the bloodstream and enter the CNS, thereby modulating the progression of mental illnesses, we sought to explore the metabolic profiles of peripheral immune cells in a ketamine-treated mouse model of schizophrenia.

METHODS

We used flow cytometry to scrutinize the alterations in peripheral adaptive immune cells in a ketamine-induced schizophrenia mouse model. Subsequently, we implemented an untargeted metabolomic approach with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) to detect the metabolite profiles of peripheral abnormal lymphocytes and identify differential metabolites present in plasma. We then employed targeted metabolomics using UPLC-MS/MS to quantify the common differential metabolites detected in mouse plasma.

RESULTS

Flow cytometry analysis detected a notable increase in the count of peripheral CD3+ T cells in a ketamine-induced schizophrenia mouse model. Subsequent untargeted metabolomics analysis revealed that the amino acid metabolism pathway underwent substantial alterations. A detailed quantification of 22 amino acid profiles in the peripheral plasma indicated significant elevation in the levels of glycine, alanine, asparagine, and aspartic acid.

LIMITATIONS

Our ongoing research has yet to conclusively identify the precise amino acid metabolism pathway that serves as the pivotal factor in the manifestation of the schizophrenia-like phenotype induced by ketamine.

CONCLUSION

The peripheral amino acid metabolism pathway is involved in the ketamine-induced schizophrenia-like phenotype. The metabolic profile of peripheral immune cells could provide accurate biomarkers for the diagnosis and treatment of psychiatric diseases.

B cells and the stressed brain: emerging evidence of neuroimmune interactions in the context of psychosocial stress and major depression

The immune system has emerged as a key regulator of central nervous system (CNS) function in health and in disease. Importantly, improved understanding of immune contributions to mood disorders has provided novel opportunities for the treatment of debilitating stress-related mental health conditions such as major depressive disorder (MDD). Yet, the impact to, and involvement of, B lymphocytes in the response to stress is not well-understood, leaving a fundamental gap in our knowledge underlying the immune theory of depression. Several emerging clinical and preclinical findings highlight pronounced consequences for B cells in stress and MDD and may indicate key roles for B cells in modulating mood. This review will describe the clinical and foundational observations implicating B cell-psychological stress interactions, discuss potential mechanisms by which B cells may impact brain function in the context of stress and mood disorders, describe research tools that support the investigation of their neurobiological impacts, and highlight remaining research questions. The goal here is for this discussion to illuminate both the scope and limitations of our current understanding regarding the role of B cells, stress, mood, and depression.

Defensive responses: behaviour, the brain and the body

Most animals live under constant threat from predators, and predation has been a major selective force in shaping animal behaviour. Nevertheless, defence responses against predatory threats need to be balanced against other adaptive behaviours such as foraging, mating and recovering from infection. This behavioural balance in ethologically relevant contexts requires adequate integration of internal and external signals in a complex interplay between the brain and the body. Despite this complexity, research has often considered defensive behaviour as entirely mediated by the brain processing threat-related information obtained via perception of the external environment. However, accumulating evidence suggests that the endocrine, immune, gastrointestinal and reproductive systems have important roles in modulating behavioural responses to threat. In this Review, we focus on how predatory threat defence responses are shaped by threat imminence and review the circuitry between subcortical brain regions involved in mediating defensive behaviours. Then, we discuss the intersection of peripheral systems involved in internal states related to infection, hunger and mating with the neurocircuits that underlie defence responses against predatory threat. Through this process, we aim to elucidate the interconnections between the brain and body as an integrated network that facilitates appropriate defensive responses to threat and to discuss the implications for future behavioural research.

The Effect of Psychological Intervention on the Visual Quality of Patients with a Diffractive Multifocal Intraocular Lens Implant

OBJECTIVE

This study aimed to investigate the effect of psychological intervention on the visual quality of patients with a diffractive multifocal intraocular lens implant and its possible mechanism.

METHODS

Eighty-nine patients undergoing age-related cataract surgery were enrolled in the study at the Affiliated Hospital of Southwest Medical University between December 2015 and July 2017. They were randomly divided into two groups: multiple focus M1 group (n = 45) and multiple focus M2 group (n = 40). The M1 group was only given routine preoperative health education, treatment, and evaluation, while the M2 group also received psychological intervention.

RESULTS

After treatment, there was no statistical difference in the uncorrected distance and near visual acuity, corrected distance and near visual acuity, or the vision and near removal rate in either of the two groups (p > 0.05). However, postoperative glare was lower in the M2 group (p < 0.05), and patient satisfaction was higher in the M2 group (p < 0.05). The M2 group had a more obvious improvement in the Symptom Checklist-90 score (p < 0.05), the serum interleukin-6 (IL-6) was lower, and the serum brain-derived neurotrophic factor (BDNF) was higher in the M2 group (p < 0.05). In addition, serum IL-6 had a negative correlation with the depression score, and serum BDNF also showed a negative correlation with the anxiety score (p < 0.05).

CONCLUSIONS

Psychological intervention improved the stress state of patients with age-related cataracts and diffractive multifocal intraocular lens implants, reduced the level of inflammatory factors in the body, improved the level of BDNF, reduced postoperative visual interference, and improved postoperative satisfaction.

Mouse models of immune dysfunction: their neuroanatomical differences reflect their anxiety-behavioural phenotype

Extensive evidence supports the role of the immune system in modulating brain function and behaviour. However, past studies have revealed striking heterogeneity in behavioural phenotypes produced from immune system dysfunction. Using magnetic resonance imaging, we studied the neuroanatomical differences among 11 distinct genetically modified mouse lines (n = 371), each deficient in a different element of the immune system. We found a significant and heterogeneous effect of immune dysfunction on the brains of both male and female mice. However, by imaging the whole brain and using Bayesian hierarchical modelling, we were able to identify patterns within the heterogeneous phenotype. Certain structures-such as the corpus callosum, midbrain, and thalamus-were more likely to be affected by immune dysfunction. A notable brain-behaviour relationship was identified with neuroanatomy endophenotypes across mouse models clustering according to anxiety-like behaviour phenotypes reported in literature, such as altered volume in brains regions associated with promoting fear response (e.g., the lateral septum and cerebellum). Interestingly, genes with preferential spatial expression in the most commonly affected regions are also associated with multiple sclerosis and other immune-mediated diseases. In total, our data suggest that the immune system modulates anxiety behaviour through well-established brain networks.

Corticotropin-releasing factor induces functional and structural synaptic remodelling in acute stress

Biological responses to stress are complex and highly conserved. Corticotropin-releasing factor (CRF) plays a central role in regulating these lifesaving physiological responses to stress. We show that, in mice, CRF rapidly changes Schaffer Collateral (SC) input into hippocampal CA1 pyramidal cells (PC) by modulating both functional and structural aspects of these synapses. Host exposure to acute stress, in vivo CRF injection, and ex vivo CRF application all result in fast de novo formation and remodeling of existing dendritic spines. Functionally, CRF leads to a rapid increase in synaptic strength of SC input into CA1 neurons, e.g., increase in spontaneous neurotransmitter release, paired-pulse facilitation, and repetitive excitability and improves synaptic plasticity: long-term potentiation (LTP) and long-term depression (LTD). In line with the changes in synaptic function, CRF increases the number of presynaptic vesicles, induces redistribution of vesicles towards the active zone, increases active zone size, and improves the alignment of the pre- and postsynaptic compartments. Therefore, CRF rapidly enhances synaptic communication in the hippocampus, potentially playing a crucial role in the enhanced memory consolidation in acute stress.

Priorities in stress research: a view from the U.S. National Institute of Mental Health

The mission of the National Institute of Mental Health is to transform the understanding and treatment of mental illnesses through basic and clinical research, paving the way for prevention, recovery, and cure. In consultation with a broad range of experts, the NIMH has identified a set of priorities for stress biology research aimed squarely at creating the basic and clinical knowledge bases for reducing and alleviating mental health burden across the lifespan. Here, we discuss these priority areas in stress biology research, which include: understanding the heterogeneity of stressors and outcomes; refining and expanding the experimental systems used to study stress and its effects; embracing and exploiting the complexity of the stress response; and prioritizing translational studies that seek to test mechanistic hypotheses in human beings. We emphasize the challenge of establishing mechanistic links across levels of analysis to explain how and when specific and diverse stressors lead to enduring changes in neural systems and produce lasting functional deficits in mental health relevant behaviors. An improved understanding of mechanisms underlying stress responses and the functional consequences of stress can and will speed translation from basic research to predictive markers of risk and to improved, personalized interventions for mental illness.

Immuno-moodulin: A new anxiogenic factor produced by Annexin-A1 transgenic autoimmune-prone T cells

Patients suffering from autoimmune diseases are more susceptible to mental disorders yet, the existence of specific cellular and molecular mechanisms behind the co-morbidity of these pathologies is far from being fully elucidated. By generating transgenic mice overexpressing Annexin-A1 exclusively in T cells to study its impact in models of autoimmune diseases, we made the unpredicted observation of an increased level of anxiety. Gene microarray of Annexin-A1 CD4⁺ T cells identified a novel anxiogenic factor, a small protein of approximately 21 kDa encoded by the gene 2610019F03Rik which we named Immuno-moodulin. Neutralizing antibodies against Immuno-moodulin reverted the behavioral phenotype of Annexin-A1 transgenic mice and lowered the basal levels of anxiety in wild type mice; moreover, we also found that patients suffering from obsessive compulsive disorders show high levels of Imood in their peripheral mononuclear cells. We thus identify this protein as a novel peripheral determinant that modulates anxiety behavior. Therapies targeting Immuno-moodulin may lead to a new type of treatment for mental disorders through regulation of the functions of the immune system, rather than directly acting on the nervous system.

Loss of T cells influences sex differences in stress-related gene expression

Deficiencies in the adaptive immune system have been linked to anxiety-like behaviours and stress reactivity. Mice lacking T lymphocytes through knockout of the T cell receptor (TCR) β and δ chains were compared to wild type C57Bl/6 mice. Central stress circuitry gene expression was assessed following repeated restraint stress. TCRβ-/-δ-/- mice showed an increased baseline plasma corticosterone and exaggerated changes in stress-related gene expression after repeated restraint stress. Sexual dimorphic stress responses were observed in wild-type C57Bl/6 mice but not in TCRβ-/-δ-/- mice. These data suggest that T cell-brain interactions influence sex-differences in CNS stress circuitry and stress reactivity.

The Relationships Between Stress, Mental Disorders, and Epigenetic Regulation of BDNF

Brain-derived neurotrophic factor (BDNF), a critical member of the neurotrophic family, plays an important role in multiple stress-related mental disorders. Although alterations in BDNF in multiple brain regions of individuals experiencing stress have been demonstrated in previous studies, it appears that a set of elements are involved in the complex regulation. In this review, we summarize the specific brain regions with altered BDNF expression during stress exposure. How various environmental factors, including both physical and psychological stress, affect the expression of BDNF in specific brain regions are further summarized. Moreover, epigenetic regulation of BDNF, including DNA methylation, histone modification, and noncoding RNA, in response to diverse types of stress, as well as sex differences in the sensitivity of BDNF to the stress response, is also summarized. Clarification of the underlying role of BDNF in the stress process will promote our understanding of the pathology of stress-linked mental disorders and provide a potent target for the future treatment of stress-related illness.

T Cell Subpopulations in the Physiopathology of Fibromyalgia: Evidence and Perspectives

Fibromyalgia is one of the most important “rheumatic” disorders, after osteoarthritis. The etiology of the disease is still not clear. At the moment, the most defined pathological mechanism is the alteration of central pain pathways, and emotional conditions can trigger or worsen symptoms. Increasing evidence supports the role of mast cells in maintaining pain conditions such as musculoskeletal pain and central sensitization. Importantly, mast cells can mediate microglia activation through the production of proinflammatory cytokines such as IL-1β, IL-6, and TNFα. In addition, levels of chemokines and proinflammatory cytokines are enhanced in serum and could contribute to inflammation at systemic level. Despite the well-characterized relationship between the nervous system and inflammation, the mechanism that links the different pathological features of fibromyalgia, including stress-related manifestations, central sensitization, and dysregulation of the innate and adaptive immune responses is largely unknown. This review aims to provide an overview of the current understanding of the role of adaptive immune cells, in particular T cells, in the physiopathology of fibromyalgia. It also aims at linking the latest advances emerging from basic science to envisage new perspectives to explain the role of T cells in interconnecting the psychological, neurological, and inflammatory symptoms of fibromyalgia.

Treatment with a heat-killed preparation of Mycobacterium vaccae after fear conditioning enhances fear extinction in the fear-potentiated startle paradigm

The hygiene hypothesis or "Old Friends" hypothesis proposes that inflammatory diseases are increasing in modern urban societies, due in part to reduced exposure to microorganisms that drive immunoregulatory circuits and a failure to terminate inappropriate inflammatory responses. Inappropriate inflammation is also emerging as a risk factor for anxiety disorders, affective disorders, and trauma-and stressor-related disorders, including posttraumatic stress disorder (PTSD), which is characterized as persistent re-experiencing of the trauma after a traumatic experience. Traumatic experiences can lead to long-lasting fear memories and fear potentiation of the acoustic startle reflex. The acoustic startle reflex is an ethologically relevant reflex and can be potentiated in both humans and rats through Pavlovian conditioning. Mycobacterium vaccae is a soil-derived bacterium with immunoregulatory and anti-inflammatory properties that has been demonstrated to enhance fear extinction in the fear-potentiated startle paradigm when given prior to fear conditioning. To determine if immunization with M. vaccae after fear conditioning also has protective effects, adult male Sprague Dawley rats underwent fear conditioning on days -37 and -36 followed by immunizations (3x), once per week beginning 24 h following fear conditioning, with a heat-killed preparation of M. vaccae NCTC 11659 (0.1 mg, s.c., in 100 µl borate-buffered saline) or vehicle, and, then, 3 weeks following the final immunization, were tested in the fear-potentiated startle paradigm (n = 12 per group). Rats underwent fear extinction training on days 1 through 6 followed by spontaneous recovery 14 days later (day 20). Rats were euthanized on day 21 and brain tissue was sectioned for analysis of Tph2, Htr1a, Slc6a4, Slc22a3, and Crhr2 mRNA expression throughout the brainstem dorsal and median raphe nuclei. Immunization with M. vaccae did not affect fear expression on day 1. However, M. vaccae-immunized rats showed enhanced enhanced within-session fear extinction on day 1 and enhanced between-session fear extinction beginning on day 2, relative to vehicle-immunized controls. Immunization with M. vaccae and fear-potentiated startle had minimal effects on serotonergic gene expression when assessed 42 days after the final immunization. Together with previous studies, these data are consistent with the hypothesis that immunoregulatory strategies, such as immunization with M. vaccae, have potential for both prevention and treatment of trauma- and stressor-related psychiatric disorders.

A probabilistic model of startle response reveals opposite effects of acute versus chronic Methylphenidate treatment

BACKGROUND

The startle response is considered as the major physio-behavioral indication of anxiety in health and disease conditions. However, due to different protocols of stimulation and measurement, the magnitude as well as the appearance of the startle response is inconsistent.

NEW METHOD

We postulate that the startle probability and not merely the amplitude may bare information that will form a consistent physiological measure of anxiety.

RESULTS

To examine the proof-of-concept of our suggested probability model, we evaluated the effects of acute (single) versus chronic (14 days) MPH administration on both startle amplitude and probability. We found that both acute and chronic MPH administration has yielded similar effects on startle amplitude. However, acute MPH increased the startle's probability while chronic MPH decreased it. Next, we evaluated the effects of acute versus chronic stress on the startle's parameters and found a complementary effect. Explicitly, acute stress increased the startle's probability while chronic stress increased the startle amplitude. In contrast, enriched environment had no significant effects. Finally, to further validate the probability measure, we show that Midazolam had significant anxiolytic effects. In the second part, we investigated the acoustic startle response parameters (e.g. background noise and pulse duration), to better understand the interplay between these parameters and the startle amplitude versus probability.

CONCLUSIONS

We show that the probabilistic element of the startle response does not only point to deeper physiologic relationships but may also serve as "hidden variables" congruent but not entirely identical to the commonly researched amplitude of the startle response.

Autonomic and Redox Imbalance Correlates With T-Lymphocyte Inflammation in a Model of Chronic Social Defeat Stress

Patients diagnosed with post-traumatic stress disorder (PTSD) are at a significantly elevated risk of developing comorbid inflammatory conditions, but the mechanisms underlying this predilection remain unclear. Our previous work has shown that T-lymphocytes exposed to elevated levels of norepinephrine (NE) displayed a pro-inflammatory signature reminiscent of an autoreactive phenotype. With this, we hypothesized that the increased sympathetic tone observed during psychological trauma may be promoting pro-inflammatory T-lymphocytes, which causes a predisposition to comorbid inflammatory conditions. Here, we examined the consequences of psychological trauma on splenic T-lymphocytes using a mouse model of repeated social defeat stress. Social defeat led to anxiety-like and depression-like behavior as has been previously described. The spleens of socially-defeated mice showed significant elevations of NE, tyrosine hydroxylase (TH), and acetylcholinesterase (ACHE) levels, which appeared to be due in part to increased expression within T-lymphocytes. Additionally, T-lymphocytes from stressed animals showed higher levels of pro-inflammatory cytokines and mitochondrial superoxide. Interestingly, in this model system, close associations exist within splenic T-lymphocytes amid the autonomic, inflammatory, and redox environments, but these only weakly correlate with individual behavioral differences among animals suggesting the psychological and physiological manifestations of trauma may not be tightly coupled. Last, we describe, for the first time, elevations in calprotectin levels within T-lymphocytes and in circulation of psychologically stressed animals. Calprotectin correlated with both behavioral and physiological changes after social defeat, suggesting the potential for a new biological marker and/or therapeutic target for psychological trauma and its inflammatory comorbidities.

Neonatal adoptive transfer of lymphocytes rescues social behaviour during adolescence in immune-deficient mice

Accumulating evidence has shown that lymphocytes modulate behaviour and cognition by direct interactions with the central nervous system. Studies have shown that reconstitution by adoptive transfer of lymphocytes from wild type into immune-deficient mice restores a number of neurobehavioural deficits observed in these models. Moreover, it has been shown that these effects are mostly mediated by T lymphocytes. Studies of adoptive transfer thus far have employed adult mice, but whether lymphocytes may also modulate behaviour during development remains unknown. In this study, neonate lymphocyte-deficient Rag2^-/- mice were reconstituted within 48 hours after birth with lymphoid cells from transgenic donors expressing green fluorescent protein, allowing for their identification in various tissues in recipient mice while retaining all functional aspects. Adolescent Rag2^-/- and reconstituted Rag2^-/- along with C57BL/6J wild-type mice underwent a series of behavioural tests, including open field, social interaction and sucrose preference tests. At 12 weeks, they were evaluated in the Morris water maze (MWM). Reconstituted mice showed changes in almost all aspects of behaviour that were assessed, with a remarkable complete rescue of impaired social behaviour displayed by adolescent Rag2^-/- mice. Consistent with previous reports in adult mice, neonatal reconstitution in Rag2^-/- mice restored spatial memory in the MWM. The presence of donor lymphocytes in the brain of neonatally reconstituted Rag2^-/- mice was confirmed at various developmental points. These findings provide evidence that lymphocytes colonize the brain during post-natal development and modulate behaviour across the lifespan supporting a role for adaptive immunity during brain maturation.

Therapeutic effects of stress-programmed lymphocytes transferred to chronically stressed mice

Our group has recently provided novel insights into a poorly understood component of intercommunication between the brain and the immune system by showing that psychological stress can modify lymphocytes in a manner that may boost resilience to psychological stress. To demonstrate the influence of the adaptive immune system on mood states, we previously showed that cells from lymph nodes of socially defeated mice, but not from unstressed mice, conferred anxiolytic and antidepressant-like effects and elevated hippocampal cell proliferation when transferred into naïve lymphopenic Rag2(-/-) mice. In the present study, we asked whether similar transfer could be anxiolytic and antidepressant when done in animals that had been rendered anxious and depressed by chronic psychological stress. First, we demonstrated that lymphopenic Rag2(-/-) mice and their wild-type C57BL/6 mouse counterparts had similar levels of affect normally. Second, we found that following chronic (14days) restraint stress, both groups displayed an anxious and depressive-like phenotype and decreased hippocampal cell proliferation. Third, we showed that behavior in the open field test and light/dark box was normalized in the restraint-stressed Rag2(-/-) mice following adoptive transfer of lymph node cells from green fluorescent protein (GFP) expressing donor mice previously exposed to chronic (14days) of social defeat stress. Cells transferred from unstressed donor mice had no effect on behavior. Immunolabeling of GFP+ cells confirmed that tissue engraftment had occurred at 14days after transfer. We found GFP+ lymphocytes in the spleen, lymph nodes, blood, choroid plexus, and meninges of the recipient Rag2(-/-) mice. The findings suggest that the adaptive immune system may play a key role in promoting recovery from chronic stress. The data support using lymphocytes as a novel therapeutic target for anxiety states.

Expansion of brain T cells in homeostatic conditions in lymphopenic Rag2(-/-) mice

The concept of the brain as an immune privileged organ is rapidly evolving in light of new findings outlining the sophisticated relationship between the central nervous and the immune systems. The role of T cells in brain development and function, as well as modulation of behavior has been demonstrated by an increasing number of studies. Moreover, recent studies have redefined the existence of a brain lymphatic system and the presence of T cells in specific brain structures, such as the meninges and choroid plexus. Nevertheless, much information is needed to further the understanding of brain T cells and their relationship with the central nervous system under non-inflammatory conditions. In the present study we employed the Rag2(-/-) mouse model of lymphocyte deficiency and reconstitution by adoptive transfer to study the temporal and anatomical expansion of T cells in the brain under homeostatic conditions. Lymphopenic Rag2(-/-) mice were reconstituted with 10 million lymphoid cells and studied at one, two and four weeks after transfer. Moreover, lymphoid cells and purified CD4(+) and CD8(+) T cells from transgenic GFP expressing mice were used to define the neuroanatomical localization of transferred cells. T cell numbers were very low in the brain of reconstituted mice up to one week after transfer and significantly increased by 2weeks, reaching wild type values at 4weeks after transfer. CD4(+) T cells were the most abundant lymphocyte subtype found in the brain followed by CD8(+) T cells and lastly B cells. Furthermore, proliferation studies showed that CD4(+) T cells expand more rapidly than CD8(+) T cells. Lymphoid cells localize abundantly in meningeal structures, choroid plexus, and circumventricular organs. Lymphocytes were also found in vascular and perivascular spaces and in the brain parenchyma across several regions of the brain, in particular in structures rich in white matter content. These results provide proof of concept that the brain meningeal system, as well as vascular and perivascular spaces, are homing sites of lymphocytes and suggest the possibility of a brain specific T cell subtype.

CD4(+) T cells confer anxiolytic and antidepressant-like effects, but enhance fear memory processes in Rag2(-/-) mice

Accumulating evidence supports a role of T cells in behavioral stress responsiveness. Our laboratory previously reported that lymphocyte deficient Rag2(-/-) mice on a BALB/c background display resilience to maladaptive stress responses when compared with immune competent mice in the predator odor exposure (POE) paradigm, while exhibiting similar behavior in a cued fear-conditioning (FC) paradigm. In the present study, Rag2(-/-) mice on a C57BL/6 background were assessed in the same behavioral paradigms, as well as additional tests of anxiety and depressive-like behavior. Furthermore, the effects of naïve CD4(+ ) T cells were evaluated by adoptive transfer of functional cells from nonstressed, wild-type donors to Rag2(-/-) mice. Consistent with our prior results, Rag2(-/-) mice displayed an attenuated startle response after POE. Nevertheless, reconstitution of Rag2(-/-) mice with CD4(+ ) T cells did not modify startle reactivity. Additionally, in contrast with our previous findings, Rag2(-/-) mice showed attenuated fear responses in the FC paradigm compared to wild-type mice and reconstitution with CD4(+ ) T cells promoted fear learning and memory. Notably, reconstitution with CD4(+ ) T cells had anxiolytic and antidepressant-like effects in Rag2(-/-) mice that had not been previously stressed, but had no effect after POE. Taken together, our results support a role of CD4(+ ) T cells in emotionality, but also indicate that they may promote fear responses by enhancing learning and memory processes.

The influence of genes on "positive valence systems" constructs: A systematic review

In 2009, the U.S. National Institute of Mental Health (NIMH) proposed an approach toward the deconstruction of psychiatric nosology under the research domain criteria (RDoC) framework. The overarching goal of RDoC is to identify robust, objective measures of behavior, emotion, cognition, and other domains that are more closely related to neurobiology than are diagnoses. A preliminary framework has been constructed, which has connected molecules, genes, brain circuits, behaviors, and other elements to dimensional psychiatric constructs. Although the RDoC framework has salience in emerging studies, foundational literature that pre-dated this framework requires synthesis and translation to the evolving objectives and nomenclature of RDoC. Toward this end, we review the candidate-gene association, linkage, and genome-wide studies that have implicated a variety of loci and genetic polymorphisms in selected Positive Valence Systems (PVS) constructs. Our goal is to review supporting evidence to currently listed genes implicated in this domain and novel candidates. We systematically searched and reviewed literature based on keywords listed under the June, 2011, edition of the PVS matrix on the RDoC website (http://www.nimh.nih.gov/research-priorities/rdoc/positive-valence-systems-workshop-proceedings.shtml), which were supplemented with de novo keywords pertinent to the scope of our review. Several candidate genes linked to the PVS framework were identified from candidate-gene association studies. We also identified novel candidates with loose association to PVS traits from genome-wide studies. There is strong evidence suggesting that PVS constructs, as currently conceptualized under the RDoC initiative, index genetically influenced traits; however, future research, including genetic epidemiological, and psychometric analyses, must be performed.

Gene networks specific for innate immunity define post-traumatic stress disorder

The molecular factors involved in the development of Post-Traumatic Stress Disorder (PTSD) remain poorly understood. Previous transcriptomic studies investigating the mechanisms of PTSD apply targeted approaches to identify individual genes under a cross-sectional framework lack a holistic view of the behaviours and properties of these genes at the system-level. Here we sought to apply an unsupervised gene-network based approach to a prospective experimental design using whole-transcriptome RNA-Seq gene expression from peripheral blood leukocytes of U.S. Marines (N=188), obtained both pre- and post-deployment to conflict zones. We identified discrete groups of co-regulated genes (i.e., co-expression modules) and tested them for association to PTSD. We identified one module at both pre- and post-deployment containing putative causal signatures for PTSD development displaying an over-expression of genes enriched for functions of innate-immune response and interferon signalling (Type-I and Type-II). Importantly, these results were replicated in a second non-overlapping independent dataset of U.S. Marines (N=96), further outlining the role of innate immune and interferon signalling genes within co-expression modules to explain at least part of the causal pathophysiology for PTSD development. A second module, consequential of trauma exposure, contained PTSD resiliency signatures and an over-expression of genes involved in hemostasis and wound responsiveness suggesting that chronic levels of stress impair proper wound healing during/after exposure to the battlefield while highlighting the role of the hemostatic system as a clinical indicator of chronic-based stress. These findings provide novel insights for early preventative measures and advanced PTSD detection, which may lead to interventions that delay or perhaps abrogate the development of PTSD.

IL-4/10 prevents stress vulnerability following imipramine discontinuation

Background

Identifying stress vulnerability after antidepressant discontinuation may be useful in treating relapses in depression. Previous studies have suggested significant effects of the immune system as well as the central nervous system (CNS) on progression and induction of major depression. In the present study, we hypothesized that the factors that are not rescued by a tricyclic antidepressant imipramine may be associated with stress vulnerability and relapses in depression.

Methods

To address this issue, mice were exposed to 2 h of restraint stress for 21 consecutive days (chronic restraint stress (CRS)) with or without co-treatment of imipramine. These groups were exposed to an electronic foot shock (FS) as additional stress after imipramine washout. Main targets of stress and antidepressants were analyzed in the hippocampus, lymph node, and serum after a series of depression-like behavior analysis.

Results

In this study, we found for the first time that mice exposed to CRS with a tricyclic antidepressant imipramine co-treatment, which did not show depressive-like behaviors, were vulnerable to subsequent stressful stimuli compared to the non-stressed mice after imipramine washout. CRS mice with imipramine co-treatment did not show any difference in BDNF, serotonin receptors, pro-inflammatory cytokines, or kynurenine pathway in the hippocampus compared to the controls. However, peripheral IL-4, IL-10, and alternatively activated microglial phenotypes in the hippocampus were not restored with sustained reduction in CRS mice despite chronic imipramine administration. Supplementing recombinant IL-4 and IL-10 in co-Imi+CRS mice prevented the stress vulnerability on additional stress and restored factors related to alternatively activated microglia (M2) in the hippocampus.

Conclusion

Thus, our results suggest that the reduced IL-4 and IL-10 levels in serum with hippocampal M2 markers may be involved in the stress vulnerability after imipramine discontinuation, and the restoration and modulation of these factors may be useful to some forms of depression-associated conditions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0416-3) contains supplementary material, which is available to authorized users.

Effects of Habitat Complexity on Pair-Housed Zebrafish

Sexually mature zebrafish were housed as single male-female pairs with or without plastic vegetation for 1, 5, or 10 d for comparison of whole-body cortisol measured by radioimmunoassay. Individually housed male zebrafish were used as controls. In the fish that were pair-housed without vegetation (NVeg), one animal died in 5 of 24 pairs, and one animal was alive but wounded in an additional pair. No deaths or wounds occurred in the fish that were pair-housed with vegetation (Veg). Cortisol levels did not differ between the treatment groups on day 1. On day 5, cortisol values were higher in the Veg group than in the individually housed fish (P < 0.0005) and the NVeg fish (P = 0.004). On day 10, the relationships were inversed: cortisol levels had risen in the individually housed and NVeg groups and had fallen to baseline levels in the Veg group. Cortisol values on day 10 were lower in the Veg group than in the individually housed (P = 0.004) and NVeg (P = 0.05) groups. Cortisol levels in individually housed male zebrafish increased over time. Although this study did not demonstrate a reduction in cortisol levels associated with providing vegetation, this enrichment prevented injury and death from fighting. These findings show how commonly used housing situations may affect the wellbeing of laboratory zebrafish.

Asynchronous therapy targeting Nogo-A enhances neurobehavioral recovery by reducing neuronal loss and promoting neurite outgrowth after cerebral ischemia in mice

Therapeutics targeting the Nogo-A signal pathway hold promise to promote recovery following brain injury. Based on the temporal characteristics of Nogo-A expression in the process of cerebral ischemia and reperfusion, we tested a novel asynchronous treatment, in which TAT-M9 was used in the early stage to decrease neuronal loss, and TAT-NEP1-40 was used in the delayed stage to promote neurite outgrowth after bilateral common carotid artery occlusion (BCCAO) in mice. Both TAT-M9 and TAT-NEP1-40 were efficiently delivered into the brains of mice by intraperitoneal injection. TAT-M9 treatment promoted neuron survival and inhibited neuronal apoptosis. Asynchronous therapy with TAT-M9 and TAT-NEP1-40 increased the expression of Tau, GAP43 and MAP-2 proteins, and enhanced short-term and long-term cognitive functions. In conclusion, the asynchronous treatment had a long-term neuroprotective effect, which reduced neurologic injury and apoptosis, promoted neurite outgrowth and enhanced functional recovery after ischemia. It suggests that this asynchronous treatment could be a promising therapy for cerebral ischemia in humans.

Dissociation between sickness behavior and emotionality during lipopolysaccharide challenge in lymphocyte deficient Rag2(-/-) mice

Inflammatory diseases are highly associated with affective disorders including depression and anxiety. While the role of the innate immune system on emotionality has been extensively studied, the role of adaptive immunity is less understood. Considering that chronic inflammatory conditions are mediated largely by maladaptive lymphocyte function, the role of these cells on brain function and behavior during inflammation warrants investigation. In the present study we employed mice deficient in lymphocyte function and studied behavioral and inflammatory responses during challenge with bacterial lipopolysaccharides (LPS). Rag2(-/-) mice lacking mature lymphocytes were susceptible to death under sub-septic (5 mg/kg) doses of LPS and survived only to moderate (1 mg/kg) doses of LPS. Under these conditions, they displayed attenuated TNF-alpha responses and behavioral symptoms of sickness when compared with immunocompetent mice. Nevertheless, Rag2(-/-) mice had protracted motivational impairments after recovery from sickness suggesting a specific function for lymphocytes on the re-establishment of motivational states after activation of the innate immune system. The behavioral impairments in Rag2(-/-) mice were paralleled by an elevation in plasma corticosterone after behavioral tests. These results provide evidence that the absence of adaptive immunity may be associated with emotional deficits during inflammation and suggest that depressive states associated with medical illness may be mediated in part by impaired lymphocyte responses.