Stress Effects on Neuronal Structure: Hippocampus, Amygdala, and Prefrontal Cortex

Functional disruption of stress modulatory circuits in a model of temporal lobe epilepsy

Clinical data suggest that the neuroendocrine stress response is chronically dysregulated in a subset of patients with temporal lobe epilepsy (TLE), potentially contributing to both disease progression and the development of psychiatric comorbidities such as anxiety and depression. Whether neuroendocrine dysregulation and psychiatric comorbidities reflect direct effects of epilepsy-related pathologies, or secondary effects of disease burden particular to humans with epilepsy (i.e. social estrangement, employment changes) is not clear. Animal models provide an opportunity to dissociate these factors. Therefore, we queried whether epileptic mice would reproduce neuroendocrine and behavioral changes associated with human epilepsy. Male FVB mice were exposed to pilocarpine to induce status epilepticus (SE) and the subsequent development of spontaneous recurrent seizures. Morning baseline corticosterone levels were elevated in pilocarpine treated mice at 1, 7 and 10 weeks post-SE relative to controls. Similarly, epileptic mice had increased adrenal weight when compared to control mice. Exposure to acute restraint stress resulted in hypersecretion of corticosterone 30 min after the onset of the challenge. Anatomical analyses revealed reduced Fos expression in infralimbic and prelimbic prefrontal cortex, ventral subiculum and basal amygdala following restraint. No differences in Fos immunoreactivity were found in the paraventricular nucleus of the hypothalamus, hippocampal subfields or central amygdala. In order to assess emotional behavior, a second cohort of mice underwent a battery of behavioral tests, including sucrose preference, open field, elevated plus maze, 24h home-cage monitoring and forced swim. Epileptic mice showed increased anhedonic behavior, hyperactivity and anxiety-like behaviors. Together these data demonstrate that epileptic mice develop HPA axis hyperactivity and exhibit behavioral dysfunction. Endocrine and behavioral changes are associated with impaired recruitment of forebrain circuits regulating stress inhibition and emotional reactivity. Loss of forebrain control may underlie pronounced endocrine dysfunction and comorbid psychopathologies seen in temporal lobe epilepsy.

Multiplicative Effects of Social and Psychological Risk Factors on College Students' Suicidal Behaviors

Less is known about the multiplicative effects of social and psychological risk and protective factors of suicidality on college campuses. The current study aimed to investigate the multiplicative effects of social (identifying oneself as gay/lesbian, financial difficulty, violence victimization, and religiosity) and psychological (anxiety, depression, problem alcohol use, drug use) and risk/protective factors on suicidal behaviors among college students in the United States. Using a cross-sectional design, the Healthy Mind Study (HMS; 2016–2017), is a national online survey of college students in the United States. Social (identifying oneself as gay/lesbian, violence victimization, financial difficulty, and religiosity) and psychological (anxiety, depression, problem alcohol use, and drug use) risk/protective factors were assessed among 27,961 individuals. Three aspects of suicidality, including ideation, plan, and attempt, were also assessed. Logistic regression models were used for data analysis. Financial difficulty, violence victimization, identifying oneself as gay/lesbian, anxiety, depression, and drug use increased, while religiosity reduced the odds of suicidal behaviors. Multiplicative effects were found between the following social and psychological risk factors: (1) financial difficulty and anxiety; (2) financial difficulty and depression; (3) depression and drug use; (4) problem alcohol use and drug use; and (5) depression and problem alcohol use. There is a considerable overlap in the social and psychological processes, such as financial stress, mood disorders, and substance use problems, on risk of suicide in college students. As social and psychological risk factors do not operate independently, comprehensive suicidal risk evaluations that simultaneously address multiple social and psychological risk factors may be superior to programs that only address a single risk factor.

Stress and the psyche-brain-immune network in psychiatric diseases based on psychoneuroendocrineimmunology: a concise review

In the last decades, psychoneuroendocrineimmunology research has made relevant contributions to the fields of neuroscience, psychobiology, epigenetics, molecular biology, and clinical research by studying the effect of stress on human health and highlighting the close interrelations between psyche, brain, and bodily systems. It is now well recognized that chronic stress can alter the physiological cross-talk between brain and biological systems, leading to long-lasting maladaptive effects (allostatic overload) on the nervous, immune, endocrine, and metabolic systems, which compromises stress resiliency and health. Stressful conditions in early life have been associated with profound alterations in cortical and subcortical brain regions involved in emotion regulation and the salience network, showing relevant overlap with different psychiatric conditions. This paper provides a summary of the available literature concerning the notable effects of stress on the brain and immune system. We highlight the role of epigenetics as a mechanistic pathway mediating the influences of the social and physical environment on brain structure and connectivity, the immune system, and psycho-physical health in psychiatric diseases. We also summarize the evidence regarding the effects of stress management techniques (mainly psychotherapy and meditation practice) on clinical outcomes, brain neurocircuitry, and immune-inflammatory network in major psychiatric diseases.

Differential effects of acute versus chronic stress on ethanol sensitivity: Evidence for interactions on both behavioral and neuroimmune outcomes

Acute alcohol intoxication induces significant alterations in brain cytokines. Since stress challenges also profoundly impact central cytokine expression, these experiments examined the influence of acute and chronic stress on ethanol-induced brain cytokine responses. In Experiment 1, adult male rats were exposed to acute footshock. After a post-stress recovery interval of 0, 2, 4, or 24 h, rats were administered ethanol (4 g/kg; intragastric), with trunk blood and brains collected 3 h later. In non-stressed controls, acute ethanol increased expression of Il-6 and IκBα in the hippocampus. In contrast, rats exposed to footshock 24 h prior to ethanol demonstrated potentiation of hippocampal Il-6 and IκBα expression relative to ethanol-exposed non-stressed controls. Experiment 2 subsequently examined the effects of chronic stress on ethanol-related cytokine expression. Following a novel chronic escalating stress procedure, rats were intubated with ethanol. As expected, acute ethanol increased Il-6 expression in all structures examined, yet the Il-6 response was attenuated exclusively in the hippocampus in chronically stressed rats. Later experiments determined that neither acute nor chronic stress affected ethanol pharmacokinetics. When ethanol hypnosis was examined, however, rats exposed to chronic stress awoke at significantly lower blood ethanol levels compared to acutely stressed rats, despite similar durations of ethanol-induced sedation. These data indicate that chronic stress may increase sensitivity to ethanol hypnosis. Together, these experiments demonstrate an intriguing interaction between recent stress history and ethanol-induced increases in hippocampal Il-6, and may provide insight into novel pharmacotherapeutic targets for prevention and treatment of alcohol-related health outcomes based on stress susceptibility.

Gene regulatory mechanisms underlying sex differences in brain development and psychiatric disease

The sexual differentiation of the mammalian nervous system requires the precise coordination of the temporal and spatial regulation of gene expression in diverse cell types. Sex hormones act at multiple developmental time points to specify sex-typical differentiation during embryonic and early development and to coordinate subsequent responses to gonadal hormones later in life by establishing sex-typical patterns of epigenetic modifications across the genome. Thus, mutations associated with neuropsychiatric conditions may result in sexually dimorphic symptoms by acting on different neural substrates or chromatin landscapes in males and females. Finally, as stress hormone signaling may directly alter the molecular machinery that interacts with sex hormone receptors to regulate gene expression, the contribution of chronic stress to the pathogenesis or presentation of mental illness may be additionally different between the sexes. Here, we review the mechanisms that contribute to sexual differentiation in the mammalian nervous system and consider some of the implications of these processes for sex differences in neuropsychiatric conditions.

Effects of the Extremely Low Frequency Electromagnetic Fields on NMDA-Receptor Gene Expression and Visual Working Memory in Male Rhesus Macaques

Introduction

The present research aimed to examine Visual Working Memory (VWM) test scores, as well as hormonal, genomic, and brain anatomic changes in the male rhesus macaques exposed to Extremely Low Frequency Magnetic Field (ELF-MF).

Methods

Four monkeys were exposed to two different ELF-MF frequencies: 1 Hz (control) and 12 Hz (experiment) with 0.7 μT (magnitude) 4 h/d for 30 consecutive days. Before and after the exposure, VWM test was conducted using a coated devise on a movable stand. About 10 mL of the animals' blood was obtained from their femoral vain and used to evaluate their melatonin concentration. Blood lymphocytes were used for assaying the expressions of N-Methyl-D-aspartate NMDA-receptor genes expression before and after ELF exposure. Anatomical changes of hippocampus size were also assessed using MRI images.

Results

Results indicated that VWM scores in primates exposed to 12 Hz frequency ELF increased significantly. Plasma melatonin level was also increased in these animals. However, these variables did not change in the animals exposed to 1 Hz ELF. At last, expression of the NMDA receptors increased at exposure to 12 Hz frequency. However, hippocampal volume did not increase significantly in the animals exposed to both frequencies.

Conclusion

In short, these results indicate that ELF (12 Hz) may have a beneficial value for memory enhancement (indicated by the increase in VWM scores). This may be due to an increase in plasma melatonin and or expression of NMDA glutamate receptors. However, direct involvement of the hippocampus in this process needs more research.

Behavioral and structural adaptations to stress

Unpredictable aversive experiences, or stressors, lead to changes in depression- and anxiety-related behavior and to changes in hippocampal structure including decreases in adult neurogenesis, granule cell and pyramidal cell dendritic morphology, and volume. Here we review the relationship between these behavioral and structural changes and discuss the possibility that these changes may be largely adaptive. Specifically, we suggest that new neurons in the dentate gyrus enhance behavioral adaptability to changes in the environment, biasing behavior in novel situations based on previous experience with stress. Conversely, atrophy-like changes in the hippocampus and decreased adult neurogenesis following chronic stress may serve to limit stress responses and stabilize behavior during chronic stress.

Cerebrovascular dysfunction with stress and depression

Maintenance of adequate tissue perfusion through a dense network of cerebral microvessels is critical for the perseveration of normal brain function. Regulation of the cerebral blood flow has to ensure adequate delivery of nutrients and oxygen with moment-to-moment adjustments to avoid both hypo- and hyper-perfusion of the brain tissue. Even mild impairments of cerebral blood flow regulation can have significant implications on brain function. Evidence suggests that chronic stress and depression elicits multifaceted functional impairments to the cerebral microcirculation, which plays a critical role in brain health and the pathogenesis of stress-related cognitive impairment and cerebrovascular events. Identifying the functional and structural changes to the brain that are induced by stress is crucial for achieving a realistic understanding of how related illnesses, which are highly disabling and with a large economic cost, can be managed or reversed. This overview discusses the stress-induced alterations in neurovascular coupling with specific attention to cerebrovascular regulation (endothelial dependent and independent vasomotor function, microvessel density). The pathophysiological consequences of cerebral microvascular dysfunction with stress and depression are explored.

Importance of the brain corticosteroid receptor balance in metaplasticity, cognitive performance and neuro-inflammation

Bruce McEwen's discovery of receptors for corticosterone in the rat hippocampus introduced higher brain circuits in the neuroendocrinology of stress. Subsequently, these receptors were identified as mineralocorticoid receptors (MRs) that are involved in appraisal processes, choice of coping style, encoding and retrieval. The MR-mediated actions on cognition are complemented by slower actions via glucocorticoid receptors (GRs) on contextualization, rationalization and memory storage of the experience. These sequential phases in cognitive performance depend on synaptic metaplasticity that is regulated by coordinate MR- and GR activation. The receptor activation includes recruitment of coregulators and transcription factors as determinants of context-dependent specificity in steroid action; they can be modulated by genetic variation and (early) experience. Interestingly, inflammatory responses to damage seem to be governed by a similarly balanced MR:GR-mediated action as the initiating, terminating and priming mechanisms involved in stress-adaptation. We conclude with five questions challenging the MR:GR balance hypothesis.

Influences of photic stress on postsubicular head-directional processing

The stress response serves vital adaptive functions. However, acute stress episodes often negatively impact cognitive processing. Here, we aimed to elucidate whether stress detrimentally affects the head‐direction cells of the postsubiculum, which may in turn impair downstream spatial information processing. We recorded neurons in the rats’ postsubiculum during a pellet‐chasing task during baseline non‐stress conditions and after a 30‐min acute photic stress exposure. Based on their baseline firing rate, we identified a subpopulation of head‐direction cells that drastically decreased its firing rate as a response to stress while preserving their head directionality. The remaining population of head‐direction cells as well as other neurons recorded in the postsubiculum were unaffected. The observed altered activity in the subpopulation might be the basis for spatial processing deficits observed following acute stress episodes.

Stress, Depression, Resilience and Ageing: A Role for the LPA-LPA1 Pathway

BACKGROUND

Chronic stress affects health and the quality of life, with its effects being particularly relevant in ageing due to the psychobiological characteristics of this population. However, while some people develop psychiatric disorders, especially depression, others seem very capable of dealing with adversity. There is no doubt that along with the identification of neurobiological mechanisms involved in developing depression, discovering which factors are involved in positive adaptation under circumstances of extreme difficulty will be crucial for promoting resilience.

METHODS

Here, we review recent work in our laboratory, using an animal model lacking the LPA1 receptor, together with pharmacological studies and clinical evidence for the possible participation of the LPA1 receptor in mood and resilience to stress.

RESULTS

Substantial evidence has shown that the LPA1 receptor is involved in emotional regulation and in coping responses to chronic stress, which, if dysfunctional, may induce vulnerability to stress and predisposition to the development of depression. Given that there is commonality of mechanisms between those involved in negative consequences of stress and in ageing, this is not surprising, considering that the LPA1 receptor may be involved in coping with adversity during ageing.

CONCLUSION

Alterations in this receptor may be a susceptibility factor for the presence of depression and cognitive deficits in the elderly population. However, because this is only a promising hypothesis based on previous data, future studies should focus on the involvement of the LPA-LPA1 pathway in coping with stress and resilience in ageing.

Antenatal and Neonatal Antecedents of Executive Dysfunctions in Extremely Preterm Children

To find out why children born extremely preterm are at heightened risk of executive dysfunctions, the authors assessed 716 children who were 10 years old born extremely preterm whose IQ was ≥ 70. A working memory dysfunction (n = 169), an inhibition dysfunction (n = 360), a switching dysfunction (355), and all 3 (executive dysfunction; n = 107) were defined on the basis of Z-scores ≤ -1 on the Differential Ability Scales-II Working Memory composite, and/or on the NEPSY-II Inhibition-Inhibition and Inhibition-Switching subtests. All risk profiles include an indicator of socioeconomic disadvantage. The risk profile of each of the 3 individual dysfunctions includes an indicator of the newborn's immaturity, and the risk profiles of the inhibition dysfunction and switching dysfunction also include an indicator of inflammation. Only the switching dysfunction was associated with fetal growth restriction. The risk factors for executive dysfunction can be subsumed under the 4 themes of socioeconomic disadvantage, immaturity/vulnerability, inflammation, and fetal growth restriction.

Morphological and functional changes in the preweaning basolateral amygdala induced by early chronic stress associate with anxiety and fear behavior in adult male, but not female rats

Suboptimal maternal care is a form of chronic early-life stress (ELS) and a risk factor for mental illness and behavioral impairments throughout the life span. The amygdala, particularly the basolateral amygdala (BLA), exhibits exquisite sensitivity to ELS and could promote dysregulation of stress reactivity and anxiety-related disorders. While ELS has profound impacts on the adult or adolescent amygdala, less is known regarding the sensitivity of the preweaning BLA to ELS. We employed a naturalistic rodent model of chronic ELS that limits the amount of bedding/nesting material (LB) available to the mother between postnatal day (PND) 1-9 and examined the morphological and functional effects in the preweaning BLA on PND10 and 18-22. BLA neurons displayed dendritic hypertrophy and increased spine numbers in male, but not female, LB pups already by PND10 and BLA volume tended to increase after LB exposure in preweaning rats, suggesting an accelerated and long-lasting recruitment of the amygdala. Morphological changes seen in male LB pups were paralleled with increased evoked synaptic responses recorded from BLA neurons in vitro, suggesting enhanced excitatory inputs to these neurons. Interestingly, morphological and functional changes in the preweaning BLA were not associated with basal hypercorticosteronemia or enhanced stress responsiveness in LB pups, perhaps due to a differential sensitivity of the neuroendocrine stress axis to the effects of LB exposure. Early changes in the synaptic organization and excitability of the neonatal amygdala might contribute to the increased anxiety-like and fear behavior observed in adulthood, specifically in male offspring.

Pumilio2 regulates synaptic plasticity via translational repression of synaptic receptors in mice

PUMILIO 2 (PUM2) is a member of Pumilio and FBF (PUF) family, an RNA binding protein family with phylogenetically conserved roles in germ cell development. The Drosophila Pumilio homolog is also required for dendrite morphogenesis and synaptic function via translational control of synaptic proteins, such as glutamate receptors, and recent mammalian studies demonstrated a similar role in neuronal culture with associated motor and memory abnormalities in vivo. Importantly, transgenic mice with PUM2 knockout show prominent epileptiform activity, and patients with intractable temporal lobe epilepsy and mice with pilocarpine-induced seizures have decreased neuronal PUM2, possibly leading to further seizure susceptibility. However, how PUM2 influences synaptic function in vivo and, subsequently, seizures is not known. We found that PUM2 is highly expressed in the brain, especially in the temporal lobe, and knockout of Pum2 (Pum2^-/- ) resulted in significantly increased pyramidal cell dendrite spine and synapse density. In addition, multiple proteins associated with excitatory synaptic function, including glutamate receptor 2 (GLUR2), are up-regulated in Pum2^-/- mice. The expression of GLUR2 protein but not mRNA is increased in the Pum2^-/- mutant hippocampus, Glur2 transcripts are increased in mutant polysome fractions, and overexpression of PUM2 led to repression of reporter expression containing the 3'Untranslated Region (3'UTR) of Glur2, suggesting translation of GLUR2 was increased in the absence of Pum2. Overall, these studies provide a molecular mechanism for the increased temporal lobe excitability observed with PUM2 loss and suggest PUM2 might contribute to intractable temporal lobe epilepsy.

Cell-type-specific role for nucleus accumbens neuroligin-2 in depression and stress susceptibility

Behavioral coping strategies are critical for active resilience to stress and depression; here we describe a role for neuroligin-2 (NLGN-2) in the nucleus accumbens (NAc). Neuroligins (NLGN) are a family of neuronal postsynaptic cell adhesion proteins that are constituents of the excitatory and inhibitory synapse. Importantly, NLGN-3 and NLGN-4 mutations are strongly implicated as candidates underlying the development of neuropsychiatric disorders with social disturbances such as autism, but the role of NLGN-2 in neuropsychiatric disease states is unclear. Here we show a reduction in NLGN-2 gene expression in the NAc of patients with major depressive disorder. Chronic social defeat stress in mice also decreases NLGN-2 selectively in dopamine D1-positive cells, but not dopamine D2-positive cells, within the NAc of stress-susceptible mice. Functional NLGN-2 knockdown produces bidirectional, cell-type-specific effects: knockdown in dopamine D1-positive cells promotes subordination and stress susceptibility, whereas knockdown in dopamine D2-positive cells mediates active defensive behavior. These findings establish a behavioral role for NAc NLGN-2 in stress and depression; provide a basis for targeted, cell-type specific therapy; and highlight the role of active behavioral coping mechanisms in stress susceptibility.

Exposure to Ambient Air Particles Increases the Risk of Mental Disorder: Findings from a Natural Experiment in Beijing

Epidemiology studies indicated that air pollution has been associated with adverse neurological effects in human. Moreover, the secretion of glucocorticoid (GC) affects the mood regulation, and the negative feedback of hippocampal glucocorticoid receptors (GR) inhibits the GC secretion. Meanwhile, the over secretion of GC can interfere the immune system and induce neurotoxicity. In the present study, the human test showed that the secretion of the cortisol in plasma was elevated after exposure in heavy air pollution. In the mouse model, we found that breathing the highly polluted air resulted in the negative responses of the mood-related behavioral tests and morphology of hippocampus, as well as the over secretion of GC in plasma, down regulation of GR, and up-regulation of cytokine and chemokine in the hippocampus. When considering the interrelated trends between the hippocampal GR, inflammatory factors, and plasmatic GC, we speculated that PM_2.5 exposure could lead to the increased secretion of GC in plasma by decreasing the expression of GR in hippocampus, which activated the inflammation response, and finally induced neurotoxicity, suggesting that PM_2.5 exposure negatively affects mood regulation. When combined with the results of the human test, it indicated that exposure to ambient air particles increased the risk of mental disorder.

Anhedonia Following Early-Life Adversity Involves Aberrant Interaction of Reward and Anxiety Circuits and Is Reversed by Partial Silencing of Amygdala Corticotropin-Releasing Hormone Gene

BACKGROUND

Anhedonia, the diminished ability to experience pleasure, is an important dimensional entity linked to depression, schizophrenia, and other emotional disorders, but its origins and mechanisms are poorly understood. We have previously identified anhedonia, manifest as decreased sucrose preference and social play, in adolescent male rats that experienced chronic early-life adversity/stress (CES). Here we probed the molecular, cellular, and circuit processes underlying CES-induced anhedonia and tested them mechanistically.

METHODS

We examined functional brain circuits and neuronal populations activated by social play in adolescent CES and control rats. Structural connectivity between stress- and reward-related networks was probed using high-resolution diffusion tensor imaging, and cellular/regional activation was probed using c-Fos. We employed viral-genetic approaches to reduce corticotropin-releasing hormone (Crh) expression in the central nucleus of the amygdala in anhedonic rats, and tested for anhedonia reversal in the same animals.

RESULTS

Sucrose preference was reduced in adolescent CES rats. Social play, generally considered an independent measure of pleasure, activated brain regions involved in reward circuitry in both control and CES groups. In CES rats, social play activated Crh-expressing neurons in the central nucleus of the amygdala, typically involved in anxiety/fear, indicating aberrant functional connectivity of pleasure/reward and fear circuits. Diffusion tensor imaging tractography revealed increased structural connectivity of the amygdala to the medial prefrontal cortex in CES rats. Crh-short hairpin RNA, but not control short hairpin RNA, given into the central nucleus of the amygdala reversed CES-induced anhedonia without influencing other emotional measures.

CONCLUSIONS

These findings robustly demonstrate aberrant interactions of stress and reward networks after early-life adversity and suggest mechanistic roles for Crh-expressing amygdala neurons in emotional deficits portending major neuropsychiatric disorders.

Memory deficits following neonatal critical illness: a common neurodevelopmental pathway

Over the past decade, evidence has emerged that children growing up after neonatal critical illness, irrespective of underlying diagnosis, are at risk of memory impairment and academic problems. These difficulties are manifest even when intelligence is within the normal range. In this Review, we propose a common neurodevelopmental pathway following neonatal critical illness by showing that survivors of preterm birth, congenital heart disease, and severe respiratory failure share an increased risk of long-term memory deficits and associated hippocampal alterations. Rather than a consequence of underlying diagnosis, we suggest that this shared vulnerability is probably related to common conditions associated with neonatal critical illness, including hypoxia, neuroinflammation, stress, exposure to anaesthetics, or a complex interplay of these factors at different postconceptional ages. Future work should be aimed at improvement of early identification of patients at risk and evaluation of intervention modalities, such as exercise or cognitive training.

A-to-I RNA editing in the rat brain is age-dependent, region-specific and sensitive to environmental stress across generations

BACKGROUND

Adenosine-to-inosine (A-to-I) RNA editing is an epigenetic modification catalyzed by adenosine deaminases acting on RNA (ADARs), and is especially prevalent in the brain. We used the highly accurate microfluidics-based multiplex PCR sequencing (mmPCR-seq) technique to assess the effects of development and environmental stress on A-to-I editing at 146 pre-selected, conserved sites in the rat prefrontal cortex and amygdala. Furthermore, we asked whether changes in editing can be observed in offspring of stress-exposed rats. In parallel, we assessed changes in ADARs expression levels.

RESULTS

In agreement with previous studies, we found editing to be generally higher in adult compared to neonatal rat brain. At birth, editing was generally lower in prefrontal cortex than in amygdala. Stress affected editing at the serotonin receptor 2c (Htr2c), and editing at this site was significantly altered in offspring of rats exposed to prereproductive stress across two generations. Stress-induced changes in Htr2c editing measured with mmPCR-seq were comparable to changes measured with Sanger and Illumina sequencing. Developmental and stress-induced changes in Adar and Adarb1 mRNA expression were observed but did not correlate with editing changes.

CONCLUSIONS

Our findings indicate that mmPCR-seq can accurately detect A-to-I RNA editing in rat brain samples, and confirm previous accounts of a developmental increase in RNA editing rates. Our findings also point to stress in adolescence as an environmental factor that alters RNA editing patterns several generations forward, joining a growing body of literature describing the transgenerational effects of stress.

The dose makes the poison: from glutamate-mediated neurogenesis to neuronal atrophy and depression

Experimental evidence has demonstrated that glutamate is an essential factor for neurogenesis, whereas another line of research postulates that excessive glutamatergic neurotransmission is associated with the pathogenesis of depression. The present review shows that such paradox can be explained within the framework of hormesis, defined as biphasic dose responses. Low glutamate levels activate adaptive stress responses that include proteins that protect neurons against more severe stress. Conversely, abnormally high levels of glutamate, resulting from increased release and/or decreased removal, cause neuronal atrophy and depression. The dysregulation of the glutamatergic transmission in depression could be underlined by several factors including a decreased inhibition (γ-aminobutyric acid or serotonin) or an increased excitation (primarily within the glutamatergic system). Experimental evidence shows that the activation of N-methyl-D-aspartate receptor (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPAR) can exert two opposite effects on neurogenesis and neuron survival depending on the synaptic or extrasynaptic concentration. Chronic stress, which usually underlies experimental and clinical depression, enhances glutamate release. This overactivates NMDA receptors (NMDAR) and consequently impairs AMPAR activity. Various studies show that treatment with antidepressants decreases plasma glutamate levels in depressed individuals and regulates glutamate receptors by reducing NMDAR function by decreasing the expression of its subunits and by potentiating AMPAR-mediated transmission. Additionally, it has been shown that chronic treatment with antidepressants having divergent mechanisms of action (including tricyclics, selective serotonin reuptake inhibitors, and ketamine) markedly reduced depolarization-evoked glutamate release in the hippocampus. These data, taken together, suggest that the glutamatergic system could be a final common pathway for antidepressant treatments.

Adaptive Modifications of Maternal Hypothalamic-Pituitary-Adrenal Axis Activity during Lactation and Salsolinol as a New Player in this Phenomenon

Both basal and stress-induced secretory activities of the hypothalamic-pituitary-adrenal (HPA) axis are distinctly modified in lactating females. On the one hand, it aims to meet the physiological demands of the mother, and on the other hand, the appropriate and stable plasma cortisol level is one of the essential factors for the proper offspring development. Specific adaptations of HPA axis activity to lactation have been extensively studied in several animal species and humans, providing interesting data on the HPA axis plasticity mechanism. However, most of the data related to this phenomenon are derived from studies in rats. The purpose of this review is to highlight these adaptations, with a particular emphasis on stress reaction and differences that occur between species. Existing data on breastfeeding women are also included in several aspects. Finally, data from the experiments in sheep are presented, indicating a new regulatory factor of the HPA axis-salsolinol-which typical role was revealed in lactation. It is suggested that this dopamine derivative is involved in both maintaining basal and suppressing stress-induced HPA axis activities in lactating dams.

Brain-Derived Neurotrophic Factor Precursor in the Hippocampus Regulates Both Depressive and Anxiety-Like Behaviors in Rats

Depression and anxiety are two affective disorders that greatly threaten the mental health of a large population worldwide. Previous studies have shown that brain-derived neurotrophic factor precursor (proBDNF) is involved in the development of depression. However, it is still elusive whether proBDNF is involved in anxiety, and if so, which brain regions of proBDNF regulate these two affective disorders. The present study aims to investigate the role of proBDNF in the hippocampus in the development of depression and anxiety. Rat models of an anxiety-like phenotype and depression-like phenotype were established by complete Freund's adjuvant intra-plantar injection and chronic restraint stress, respectively. Both rat models developed anxiety-like behaviors as determined by the open field test and elevated plus maze test. However, only rats with depression-like phenotype displayed the lower sucrose consumption in the sucrose preference test and a longer immobility time in the forced swimming test. Sholl analysis showed that the dendritic arborization of granule cells in the hippocampus was decreased in rats with depression-like phenotype but was not changed in rats with anxiety-like phenotype. In addition, synaptophysin was downregulated in the rats with depression-like phenotype but upregulated in the rats with anxiety-like phenotype. In both models, proBDNF was greatly increased in the hippocampus. Intra-hippocampal injection anti-proBDNF antibody greatly ameliorated the anxiety-like and depressive behaviors in the rats. These findings suggest that despite some behavioral and morphological differences between depression and anxiety, hippocampal proBDNF is a common mediator to regulate these two mental disorders.

Mediators of the Effect of Childhood Socioeconomic Status on Late Midlife Cognitive Abilities: A Four Decade Longitudinal Study

BACKGROUND AND OBJECTIVES

Childhood socioeconomic status (cSES) is found to predict later-life cognitive abilities, yet the mechanisms underlying these associations remain unclear. The objective of this longitudinal study was to examine the direct and indirect paths through which cSES influences late midlife cognitive outcomes.

RESEARCH DESIGN AND METHODS

Participants were 1,009 male twins in the Vietnam Era Twin Study of Aging (VETSA). At mean ages 20 and 62, participants completed a standardized test for general cognitive ability (GCA). The age 62 cognitive assessment also included in-person tests of processing speed, episodic memory, abstract reasoning, working memory, verbal fluency, visual-spatial ability, and executive functions. At mean age 56, participants were interviewed regarding their own and their parents' education and occupation, and completed questionnaires about cognitive leisure activities and sociodemographic information. Multiple mediation analyses were conducted to examine the direct path effects and indirect path effects of cSES through age 20 GCA, adult SES, and cognitive leisure activities on seven cognitive outcomes at age 62, adjusting for age, ethnicity, and non-independence of observations.

RESULTS

Total (direct plus indirect) effects were significant for all measures with the exception of executive functions. Men from lower cSES backgrounds had poorer cognitive functioning in late midlife. The direct effect of cSES was partially mediated for abstract reasoning, and was fully mediated for the remaining six cognitive outcomes. Total indirect effects accounted for at least half of the total effects in each model, with paths through age 20 GCA explaining most of the total indirect effects.

DISCUSSION AND IMPLICATIONS

cSES predicted cognitive functioning in late middle age Using multiple mediation models, we show that lower cSES predicts poorer cognition in late midlife primarily through young adult cognitive ability and to a lesser extent through SES in adulthood and engagement in cognitively stimulating activities.

The behavioral and molecular evaluation of effects of social instability stress as a model of stress-related disorders in adult female rats

The study aimed to test the hypotheses that chronic social instability stress (CSIS) alters behavioral and physiological parameters and expression of selected genes important for stress response and social behaviors. Adult female Sprague-Dawley rats were subjected to the 4-week CSIS procedure, which involves unpredictable rotation between phases of isolation and overcrowding. Behavioral analyses (Experiment 1) were performed on the same rats before and after CSIS (n = 16) and physiological and biochemical measurements (Experiment 2) were made on further control (CON; n = 7) and stressed groups (CSIS; n = 8). Behaviors in the open field test (locomotor and exploratory activities) and elevated-plus maze (anxiety-related behaviors) indicated anxiety after CSIS. CSIS did not alter the physiological parameters measured, i.e. body weight gain, regularity of estrous cycles, and circulating concentrations of stress hormones and sex steroids. QRT-PCR analysis of mRNA expression levels was performed on amygdala, hippocampus, prefrontal cortex (PFC), and hypothalamus. The main finding is that CSIS alters the mRNA levels for the studied genes in a region-specific manner. Hence, expression of POMC (pro-opiomelanocortin), AVPR1a (arginine vasopressin receptor), and OXTR (oxytocin receptor) significantly increased in the amygdala following CSIS, while in PFC and/or hypothalamus, POMC, AVPR1a, AVPR1b, OXTR, and ERβ (estrogen receptor beta) expression decreased. CSIS significantly reduced expression of CRH-R1 (corticotropin-releasing hormone receptor type 1) in the hippocampus. The directions of change in gene expression and the genes and regions affected indicate a molecular basis for the behavior changes. In conclusion, CSIS may be valuable for further analyzing the neurobiology of stress-related disorders in females.

Genomic and epigenomic mechanisms of glucocorticoids in the brain

Following the discovery of glucocorticoid receptors in the hippocampus and other brain regions, research has focused on understanding the effects of glucocorticoids in the brain and their role in regulating emotion and cognition. Glucocorticoids are essential for adaptation to stressors (allostasis) and in maladaptation resulting from allostatic load and overload. Allostatic overload, which can occur during chronic stress, can reshape the hypothalamic-pituitary-adrenal axis through epigenetic modification of genes in the hippocampus, hypothalamus and other stress-responsive brain regions. Glucocorticoids exert their effects on the brain through genomic mechanisms that involve both glucocorticoid receptors and mineralocorticoid receptors directly binding to DNA, as well as by non-genomic mechanisms. Furthermore, glucocorticoids synergize both genomically and non-genomically with neurotransmitters, neurotrophic factors, sex hormones and other stress mediators to shape an organism's present and future responses to a stressful environment. Here, we discuss the mechanisms of glucocorticoid action in the brain and review how glucocorticoids interact with stress mediators in the context of allostasis, allostatic load and stress-induced neuroplasticity.

Corticosteroid-induced dendrite loss and behavioral deficiencies can be blocked by activation of Abl2/Arg kinase

Stressor exposure induces neuronal remodeling in specific brain regions. Given the persistence of stress-related illnesses, key next steps in determining the contributions of neural structure to mental health are to identify cell types that fail to recover from stressor exposure and to identify "trigger points" and molecular underpinnings of stress-related neural degeneration. We evaluated dendrite arbor structure on hippocampal CA1 pyramidal neurons before, during, and following prolonged exposure to one key mediator of the stress response - corticosterone (cortisol in humans). Basal dendrite arbors progressively simplified during a 3-week exposure period, and failed to recover when corticosterone was withdrawn. Corticosterone exposure decreased levels of the dendrite stabilization factor Abl2/Arg nonreceptor tyrosine kinase and phosphorylation of its substrates p190RhoGAP and cortactin within 11days, suggesting that disruption of Arg-mediated signaling may trigger dendrite arbor atrophy and, potentially, behavioral abnormalities resulting from corticosterone exposure. To test this, we administered the novel, bioactive Arg kinase activator, 5-(1,3-diaryl-1H-pyrazol-4-yl)hydantoin, 5-[3-(4-fluorophenyl)-1-phenyl-1H-pyrazol-4-yl]-2,4-imidazolidinedione (DPH), in conjunction with corticosterone. We found that repeated treatment corrected CA1 arbor structure, otherwise simplified by corticosterone. DPH also corrected corticosterone-induced errors in a hippocampal-dependent reversal learning task and anhedonic-like behavior. Thus, pharmacological compounds that target cytoskeletal regulators, rather than classical neurotransmitter systems, may interfere with stress-associated cognitive decline and mental health concerns.

Perceived stress is associated with smaller hippocampal volume in adolescence

Perceived stress has been associated with decreased hippocampal, amygdala, and prefrontal cortex volume, as well as decreased memory and executive functioning performance in adulthood. Parents' perceived stress has been linked to decreased hippocampal volume in young children. However, no studies have investigated the links between self-perceived stress and brain structure or function in adolescents. Additionally, findings from previous research with younger or older samples are inconsistent, likely in part due to inconsistencies in participants' age range. In this study, we investigated the associations among self-perceived stress, family socioeconomic factors (family income, parental education), subcortical (hippocampus, amygdala) volumes, prefrontal cortical thickness and surface area, and memory and executive functioning performance in adolescents. One hundred and forty-three participants (12-20 years old) were administered a cognitive battery, a questionnaire to assess perceived stress, and a structural MRI scan. Higher levels of perceived stress were associated with decreased adolescent hippocampal volume. This study provides empirical evidence of how experience may shape brain development in adolescence-a period of plasticity during which it may be possible to intervene and prevent negative developmental outcomes.

Role of the Astroglial Glutamate Exchanger xCT in Ventral Hippocampus in Resilience to Stress

We demonstrate that stress differentially regulates glutamate homeostasis in the dorsal and ventral hippocampus and identify a role for the astroglial xCT in ventral dentate gyrus (vDG) in stress and antidepressant responses. We provide an RNA-seq roadmap for the stress-sensitive vDG. The transcription factor REST binds to xCT promoter in co-occupancy with the epigenetic marker H3K27ac to regulate expression of xCT, which is also reduced in a genetic mouse model of inherent susceptibility to depressive-like behavior. Pharmacologically, modulating histone acetylation with acetyl-L-carnitine (LAC) or acetyl-N-cysteine (NAC) rapidly increases xCT and activates a network with mGlu2 receptors to prime an enhanced glutamate homeostasis that promotes both pro-resilient and antidepressant-like responses. Pharmacological xCT blockage counteracts NAC prophylactic effects. GFAP⁺-Cre-dependent overexpression of xCT in vDG mimics pharmacological actions in promoting resilience. This work establishes a mechanism by which vDG protection leads to stress resilience and antidepressant responses via epigenetic programming of an xCT-mGlu2 network.

microRNA-124 targets glucocorticoid receptor and is involved in depression-like behaviors

Dysregulation of microRNA (miRNA) has been shown to be involved in early observations of depression. MicroRNA-124-3p (miR-124) is the most abundant microRNA in the brain. Previous studies have shown that miR-124 plays a major role in depression. Here we showed that miR-124 directly targeted glucocorticoid receptor (GR) in HEK 293 cells. In addition, inhibition of miR-124 by its antagomir (2nmol/every two days) could reverse the decrease of sucrose preference and the increase of immobility time in mice exposed to chronic corticosterone (CORT, 40mg/kg) injection. Moreover, these effects on behavioral improvement were coupled to the activation of brain-derived neurotrophic factor (BDNF), TrkB, ERK, and CREB, as well as the induction of synaptogenesis and neuronal proliferation. Altogether, our study suggests that miR-124 can be served as a biomarker for depression and a novel target for drug development, and demonstrates that inhibition of miR-124 may be a strategy for treating depression by activating BDNF-TrkB signaling pathway in the hippocampus.

Neuroprotective effect of amantadine on corticosterone-induced abnormal glutamatergic synaptic transmission of CA3-CA1 pathway in rat's hippocampal slices

Depression is a psychiatric disorder and chronic stress, leading to altered glucocorticoid secretion patterns, is one of the factors that induce depression. Our previous study showed that amantadine significantly attenuated the impairments of synaptic plasticity and cognitive function a rat model of CUS. However, little is known regarding the underlying mechanism. In the present study, the whole-cell patch-clamp technique was applied to examine the protection effect of amantadine on the hippocampus CA3-CA1 pathway. Evoked excitatory postsynaptic currents (eEPSCs), miniature excitatory postsynaptic currents (mEPSCs), paired-pulse ratio (PPR) and the action potentials of CA3 neurons were recorded. Our data showed that corticosterone increased the amplitude of eEPSCs and decreased the value of paired-pulse ratio (PPR), but both of them were significantly reversed by amantadine. In addition, the frequency of mEPSC was considerably increased by corticosterone, but it was reduced by amantadine. Moreover, we used the Fluo-3/AM image to detect the Ca²⁺ influx in primary cultured hippocampal neurons. The results showed that the intracellular calcium levels were significantly decreased by amantadine in the corticosterone treated neurons. Additionally, the superoxide dismutase (SOD) and catalase (CAT) activities were reduced by corticosterone, while they were enhanced by either amantadine or low-calcium artificial cerebral spinal fluid (ACSF). These results suggest that amantadine significantly improves corticosterone-induced abnormal glutamatergic synaptic transmission of CA3-CA1 synapses presynaptically and alleviates the activities of antioxidant enzymes via regulating the calcium influx.

Enhanced ventral hippocampal synaptic transmission and impaired synaptic plasticity in a rodent model of alcohol addiction vulnerability

It has long been appreciated that adolescence represents a uniquely vulnerable period when chronic exposure to stressors can precipitate the onset of a broad spectrum of psychiatric disorders and addiction in adulthood. However, the neurobiological substrates and the full repertoire of adaptations within these substrates making adolescence a particularly susceptible developmental stage are not well understood. Prior work has demonstrated that a rodent model of adolescent social isolation (aSI) produces robust and persistent increases in phenotypes relevant to anxiety/stressor disorders and alcohol addiction, including anxiogenesis, deficits in fear extinction, and increased ethanol consumption. Here, we used extracellular field recordings in hippocampal slices to investigate adaptations in synaptic function and synaptic plasticity arising from aSI. We demonstrate that this early life stressor leads to enhanced excitatory synaptic transmission and decreased levels of long-term potentiation at hippocampal Schaffer collateral-CA1 synapses. Further, these changes were largely confined to the ventral hippocampus. As the ventral hippocampus is integral to neurocircuitry that mediates emotional behaviors, our results add to mounting evidence that aSI has profound effects on brain areas that regulate affective states. These studies also lend additional support to our recent proposal of the aSI model as a valid model of alcohol addiction vulnerability.

Cross Talk: The Microbiota and Neurodevelopmental Disorders

Humans evolved within a microbial ecosystem resulting in an interlinked physiology. The gut microbiota can signal to the brain via the immune system, the vagus nerve or other host-microbe interactions facilitated by gut hormones, regulation of tryptophan metabolism and microbial metabolites such as short chain fatty acids (SCFA), to influence brain development, function and behavior. Emerging evidence suggests that the gut microbiota may play a role in shaping cognitive networks encompassing emotional and social domains in neurodevelopmental disorders. Drawing upon pre-clinical and clinical evidence, we review the potential role of the gut microbiota in the origins and development of social and emotional domains related to Autism spectrum disorders (ASD) and schizophrenia. Small preliminary clinical studies have demonstrated gut microbiota alterations in both ASD and schizophrenia compared to healthy controls. However, we await the further development of mechanistic insights, together with large scale longitudinal clinical trials, that encompass a systems level dimensional approach, to investigate whether promising pre-clinical and initial clinical findings lead to clinical relevance.

Socially Housed Female Macaques: a Translational Model for the Interaction of Chronic Stress and Estrogen in Aging

PURPOSE OF REVIEW

Estrogen's role in cognitive aging remains unclear. Despite evidence implicating stress in pathological aging, the interaction of stress with estrogen on cognition in older women has received little attention, and few animal models exist with which to examine this interaction.

RECENT FINDINGS

We present evidence that aging socially subordinate female macaques that experience chronic psychosocial stress constitute a suitable model to investigate this. First, we review studies showing that estrogen modulates cognition in animal models, as well as studies demonstrating that estrogen's action on certain types of cognition is impaired by stress. Next, we discuss data showing that middle-aged socially subordinate female macaques exhibit distinct stress-induced phenotypes, and review our investigations indicating that estrogen modulates behavior and physiology differently in subordinate female monkeys. We conclude that socially housed female macaques represent a translational animal model for investigating the interplay of chronic stress and estrogen on cognitive aging in women.

Phenotypic plasticity and remodeling in the stress-induced Caenorhabditis elegans dauer

Organisms are often capable of modifying their development to better suit their environment. Under adverse conditions, the nematode Caenorhabditis elegans develops into a stress-resistant alternative larval stage called dauer. The dauer stage is the primary survival stage for C. elegans in nature. Large-scale tissue remodeling during dauer conveys resistance to harsh environments. The environmental and genetic regulation of the decision to enter dauer has been extensively studied. However, less is known about the mechanisms regulating tissue remodeling. Changes to the cuticle and suppression of feeding in dauers lead to an increased resistance to external stressors. Meanwhile reproductive development arrests during dauer while preserving the ability to reproduce once favorable environmental conditions return. Dramatic remodeling of neurons, glia, and muscles during dauer likely facilitate dauer-specific behaviors. Dauer-specific pulsation of the excretory duct likely mediates a response to osmotic stress. The power of C. elegans genetics has uncovered some of the molecular pathways regulating dauer tissue remodeling. In addition to genes that regulate single remodeling events, several mutants result in pleiotropic defects in dauer remodeling. This review details the individual aspects of morphological changes that occur during dauer formation and discusses molecular mechanisms regulating these processes. The dauer stage provides us with an excellent model for understanding phenotypic plasticity and remodeling from the individual cell to an entire animal. WIREs Dev Biol 2017, 6:e278. doi: 10.1002/wdev.278 For further resources related to this article, please visit the WIREs website.

Early life stress explains reduced positive memory biases in remitted depression

BACKGROUND

There is contradictory evidence regarding negative memory biases in major depressive disorder (MDD) and whether these persist into remission, which would suggest their role as vulnerability traits rather than correlates of mood state. Early life stress (ELS), common in patients with psychiatric disorders, has independently been associated with memory biases, and confounds MDD versus control group comparisons. Furthermore, in most studies negative biases could have resulted from executive impairments rather than memory difficulties per se.

METHODS

To investigate whether memory biases are relevant to MDD vulnerability and how they are influenced by ELS, we developed an associative recognition memory task for temporo-spatial contexts of social actions with low executive demands, which were matched across conditions (self-blame, other-blame, self-praise, other-praise). We included fifty-three medication-free remitted MDD (25 with ELS, 28 without) and 24 healthy control (HC) participants without ELS.

RESULTS

Only MDD patients with ELS showed a reduced bias (accuracy/speed ratio) towards memory for positive vs. negative materials when compared with MDD without ELS and with HC participants; attenuated positive biases correlated with number of past major depressive episodes, but not current symptoms. There were no biases towards self-blaming or self-praising memories.

CONCLUSIONS

This demonstrates that reduced positive biases in associative memory were specific to MDD patients with ELS rather than a general feature of MDD, and were associated with lifetime recurrence risk which may reflect a scarring effect. If replicated, our results would call for stratifying MDD patients by history of ELS when assessing and treating emotional memories.

Antidepressant Effects of Pharmacopuncture on Behavior and Brain-Derived Neurotrophic Factor (BDNF) Expression in Chronic Stress Model of Mice

OBJECTIVES

The present study aimed to investigate the antidepressant effect of the traditional Korean medical pharmacopuncture, Liver Qi Depression (HJ11), in a mouse model of depression induced by exposure to chronic immobilization stress (CIS).

METHODS

Mice were subjected to 2 hours of immobilization stress daily for 14 days. They were also injected with distilled water (DW) (CIS + DW) or HJ11 at the acupoints HT7, SP6, and GV20 (CIS + HJ11) an hour before stress. The positive control group (CIS + paroxetine) was intraperitoneally injected with paroxetine (10 mg/kg, 14 days). The tail suspension test and the forced swimming test were performed to assess depression-like behaviors. Western blotting was also conducted to seek the change in brain.

RESULTS

CIS + DW mice showed significantly longer immobile times in the tail suspension test and forced swimming test than sham mice that did not go through daily restraint. Immobility of CIS + HJ11 and that of CIS + paroxetine mice was significantly decreased compared with immobility of CIS + DW mice. Immunoblotting showed that HJ11 increased the expression of brain-derived neurotrophic factor both in the hippocampus and the amygdala.

CONCLUSION

HJ11 improves depressive-like behaviors in the stress-induced mouse model of depression, and the results indicate that the neuroprotective effect of HJ11, identified by brain-derived neurotrophic factor expression, may play a critical role in its antidepressant effect.

Trauma, PTSD, and the Developing Brain

PURPOSE OF REVIEW

PTSD in youth is common and debilitating. In contrast to adult PTSD, relatively little is known about the neurobiology of pediatric PTSD, nor how neurodevelopment may be altered. This review summarizes recent neuroimaging studies in pediatric PTSD and discusses implications for future study.

RECENT FINDINGS

Pediatric PTSD is characterized by abnormal structure and function in neural circuitry supporting threat processing and emotion regulation. Furthermore, cross-sectional studies suggest that youth with PTSD have abnormal frontolimbic development compared to typically developing youth. Examples include declining hippocampal volume, increasing amygdala reactivity, and declining amygdala-prefrontal coupling with age. Pediatric PTSD is characterized by both overt and developmental abnormalities in frontolimbic circuitry. Notably, abnormal frontolimbic development may contribute to increasing threat reactivity and weaker emotion regulation as youth age. Longitudinal studies of pediatric PTSD are needed to characterize individual outcomes and determine whether current treatments are capable of restoring healthy neurodevelopment.

Social isolation suppresses actin dynamics and synaptic plasticity through ADF/cofilin inactivation in the developing rat barrel cortex

Exposure to a stressful environment early in life can cause psychiatric disorders by disrupting circuit formation. Actin plays central roles in regulating neuronal structure and protein trafficking. We have recently reported that neonatal isolation inactivated ADF/cofilin, the actin depolymerizing factor, resulted in a reduced actin dynamics at spines and an attenuation of synaptic α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor delivery in the juvenile rat medial prefrontal cortex (mPFC), leading to altered social behaviours. Here, we investigated the impact of neonatal social isolation in the developing rat barrel cortex. Similar to the mPFC study, we detected an increase in stable actin fraction in spines and this resulted in a decreased synaptic AMPA receptor delivery. Thus, we conclude that early life social isolation affects multiple cortical areas with common molecular changes.

The ethanol extract of Aquilariae Lignum ameliorates hippocampal oxidative stress in a repeated restraint stress mouse model

Background

Chronic stress contributes to the development of brain disorders, such as neurodegenerative and psychiatric diseases. Oxidative damage is well known as a causative factor for pathogenic process in brain tissues. The aim of this study is to evaluate the neuroprotective effect of a 30% ethanol extract of Aquilariae Lignum (ALE) in repeated stress-induced hippocampal oxidative injury.

Methods

Fifty BALB/c male mice (12 weeks old) were randomly divided into five groups (n = 10). For 11 consecutive days, each group was orally administered with distilled water, ALE (20 or 80 mg/kg) or N-acetylcysteine (NAC; 100 mg/kg), and then all mice (except unstressed group) were subjected to restraint stress for 6 h. On the final day, brain tissues and sera were isolated, and stress hormones and hippocampal oxidative alterations were examined. We also treated lipopolysaccharide (LPS, 1 μg/mL)-stimulated BV2 microglial cells with ALE (1 and 5 μg/mL) or NAC (10 μM) to investigate the pharmacological mechanism.

Results

Restraint stress considerably increased the serum levels of corticosterone and adrenaline and the hippocampal levels of reactive oxygen species (ROS), nitric oxide (NO), and malondialdehyde (MDA). ALE administration significantly attenuated the above abnormalities. ALE also significantly normalized the stress-induced activation of astrocytes and microglial cells in the hippocampus as well as the elevation of pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β). The in vitro assay outcome supplemented ALE could dramatically block NF-κB activation in microglia. The anti-oxidative stress effects of ALE were supported by the results of antioxidant components, 4-hydroxynonenal (4-HNE), NADPH oxidase 2 (NOX2), inducible nitric oxide synthase (iNOS) and NFE2L2 (Nrf2) in the hippocampal tissues.

Conclusions

We firstly demonstrated the neuroprotective potentials of A. Lignum against hippocampal oxidative injury in repeated restraint stress. The corresponding mechanisms might involve modulations in the release of ROS, pro-inflammatory cytokines and stress hormones.

Blunted stress reactivity in chronic cannabis users

RATIONALE

One of the most commonly cited reasons for chronic cannabis use is to cope with stress. Consistent with this, cannabis users have shown reduced emotional arousal and dampened stress reactivity in response to negative imagery.

OBJECTIVES

To our knowledge, the present study represents the first to examine the effects of an acute stress manipulation on subjective stress and salivary cortisol in chronic cannabis users compared to non-users.

METHODS

Forty cannabis users and 42 non-users were randomly assigned to complete either the stress or no stress conditions of the Maastricht Acute Stress Test (MAST). The stress condition of the MAST manipulates both physiological (placing hand in ice bath) and psychosocial stress (performing math under conditions of social evaluation). Participants gave baseline subjective stress ratings before, during, and after the stress manipulation. Cortisol was measured from saliva samples obtained before and after the stress manipulation. Further, cannabis cravings and symptoms of withdrawal were measured.

RESULTS

Subjective stress ratings and cortisol levels were significantly higher in non-users in the stress condition relative to non-users in the no stress condition. In contrast, cannabis users demonstrated blunted stress reactivity; specifically, they showed no increase in cortisol and a significantly smaller increase in subjective stress ratings. The stress manipulation had no impact on cannabis users' self-reported cravings or withdrawal symptoms.

CONCLUSION

Chronic cannabis use is associated with blunted stress reactivity. Future research is needed to determine whether this helps to confer resiliency or vulnerability to stress-related psychopathology as well as the mechanisms underlying this effect.

Distinctive Mechanisms of Adversity and Socioeconomic Inequality in Child Development: A Review and Recommendations for Evidence-Based Policy

This review proposes separate and distinct biological mechanisms for the effects of adversity, more commonly experienced in poverty, and socioeconomic status (SES) on child development. Adversity affects brain and cognitive development through the biological stress response, which confers risk for pathology. Critically, we argue that a different mechanism, enrichment, shapes differences in brain and cognitive development across the SES spectrum. Distinguishing between adversity and SES allows for precise, evidence-based policy recommendations. We offer recommendations designed to ensure equity in children's experiences to help narrow the achievement gap and promote intergenerational mobility.