Effect of chronic psychosocial stress and long-term cortisol treatment on hippocampus-mediated memory and hippocampal volume: a pilot-study in tree shrews

Personal Mastery Attenuates the Association between Greater Perceived Discrimination and Lower Amygdala and Anterior Hippocampal Volume in a Diverse Sample of Older Adults

There is limited research investigating whether perceived discrimination influences brain structures that subserve episodic memory, namely the hippocampus and amygdala. Our rationale for examining these regions build on their known sensitivity to stress and functional differences along the long-axis of the hippocampus, with the anterior hippocampus and amygdala implicated in emotional and stress regulation. We defined perceived discrimination as the unfair treatment of one group by a dominant social group without the agency to respond to the event. A potential moderator of perceived discrimination is personal mastery, which we operationally defined as personal agency. Our primary goals were to determine whether perceived discrimination correlated with amygdala and anterior hippocampal volume, and if personal mastery moderated these relationships. Using FreeSurfer 7.1.0, we processed T1-weighted images to extract bilateral amygdala and hippocampal volumes. Discrimination and personal mastery were assessed via self-report (using the Experiences of Discrimination and Sense of Control questionnaires, respectively). Using multiple regression, greater perceived discrimination correlated with lower bilateral amygdala and anterior hippocampal volume, controlling for current stress, sex, education, age, and intracranial volume. Exploratory subfield analyses showed these associations were localized to the anterior hippocampal CA1 and subiculum. As predicted, using a moderation analysis, personal mastery attenuated the relationship between perceived discrimination and amygdala and anterior hippocampal volume. Here, we extend our knowledge on perceived discrimination as a salient psychosocial stressor with a neurobiological impact on brain systems implicated in stress, memory, and emotional regulation, and provide evidence for personal mastery as a moderating factor of these relationships.

Adverse childhood experiences (ACEs) relate to blunted cardiovascular and cortisol reactivity to acute laboratory stress: A systematic review and meta-analysis

Adverse childhood experiences (ACEs) are associated with poor future mental and physical health. Altered biological reactivity to mental stress may be a possible mechanism linking ACEs to poor health. However, it is not clear if ACEs relate to blunted or exaggerated stress reactivity. This meta-analysis aimed to determine whether exposure to ACEs is associated with cardiovascular and cortisol stress reactivity. A systematic review yielded 37 sources. Random-effects modelling tested the aggregate effects of 83 studies of the association between ACEs and stress reactivity. Exposure to ACEs was associated with relatively blunted cardiovascular and cortisol stress reactivity. Effect sizes did not vary as a function of sample sex or reactivity measure (e.g., heart rate, blood pressure, or cortisol). Meta-regression revealed preliminary evidence of greater blunting in samples of a younger age and samples reporting greater ACE exposure. Subgroup analyses for stress task, ACE measurement instrument, and sample race were not conducted because of a lack of between-study variability. Exposure to ACEs is associated with dysregulation of multiple components of the human stress response system.

Psychosocial stress has weaker than expected effects on episodic memory and related cognitive abilities: A meta-analysis

The impact of stress on episodic memory and related cognitive abilities is well documented in both animal and human literature. However, it is unclear whether the same cognitive effects result from all forms of stress - in particular psychosocial stress. This review systematically explored the effects of psychosocial stress on episodic memory and associated cognitive abilities. PubMed, PsycInfo, and Web of Science databases were searched. Fifty-one studies were identified and compared based on the timing of stress induction. A small positive effect of post-learning psychosocial stress with a long retention interval was shown. No other effects of psychosocial stress were seen. Re-analysis of previous meta-analyses also showed no significant effect of psychosocial stress on episodic memory, highlighting potentially different effects between stressor types. Psychosocial stress also had a moderately different effect when emotional vs. neutral stimuli were compared. Finally, psychosocial stress also decreased performance on executive function, but not working memory tasks. Our findings demonstrate that psychosocial stress may not have the clear effects on episodic memory previously ascribed to it.

Macro- and Microscale Stress-Associated Alterations in Brain Structure: Translational Link With Depression

Major depressive disorder (MDD) is a stress-related disorder associated with many cytoarchitectural and neurochemical changes. However, the majority of these changes cannot be reliably detected in the living brain. The examination of animal stress models and postmortem human brain tissue has significantly contributed to our understanding of the pathophysiology of MDD. Ronald Duman's work in humans and in rodent models was critical to the investigation of the contribution of synaptic deficits to MDD and chronic stress pathology, their role in the development and expression of depressive-like behavior, and reversal by novel drugs. Here, we review evidence from magnetic resonance imaging in humans and animals that suggests that corticolimbic alterations are associated with depression symptomatology. We also discuss evidence of cytoarchitectural alterations affecting neurons, astroglia, and synapses in MDD and highlight how similar changes are described in rodent chronic stress models and are linked to the emotion-related behavioral deficits. Finally, we report on the latest approaches developed to measure the synaptic and astroglial alterations in vivo, using positron emission tomography, and how it can inform on the contribution of MDD-associated cytoarchitectural alterations to the symptomatology and the treatment of stress-related disorders.

Understanding stress: Insights from rodent models

Through incorporating both physical and psychological forms of stressors, a variety of rodent models have provided important insights into the understanding of stress physiology. Rodent models also have provided significant information with regards to the mechanistic basis of the pathophysiology of stress-related disorders such as anxiety disorders, depressive illnesses, cognitive impairment and post-traumatic stress disorder. Additionally, rodent models of stress have served as valuable tools in the area of drug screening and drug development for treatment of stress-induced conditions. Although rodent models do not accurately reproduce the biochemical or physiological parameters of stress response and cannot fully mimic the natural progression of human disorders, yet, animal research has provided answers to many important scientific questions. In this review article, important studies utilizing a variety of stress models are described in terms of their design and apparatus, with specific focus on their capabilities to generate reliable behavioral and biochemical read-out. The review focusses on the utility of rodent models by discussing examples in the literature that offer important mechanistic insights into physiologically relevant questions. The review highlights the utility of rodent models of stress as important tools for advancing the mission of scientific research and inquiry.

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Stressful life events may lead to the onset of severe psychopathologies in humans.

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Rodents may model many features of stress exposure in human populations.

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Induction of stress via pharmacological and psychological manipulations alter rodent behavior.

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Mechanistic rodent studies reveal key molecular targets critical for new therapeutic targets.

Evidence for Better Lives Study: a comparative birth-cohort study on child exposure to violence and other adversities in eight low- and middle-income countries - foundational research (study protocol)

INTRODUCTION

Violence against children is a health, human rights and social problem affecting approximately half of the world's children. Its effects begin at prenatal stages with long-lasting impacts on later health and well-being. The Evidence for Better Lives Study (EBLS) aims to produce high-quality longitudinal data from cities in eight low- and middle-income countries-Ghana, Jamaica, Pakistan, the Philippines, Romania, South Africa, Sri Lanka and Vietnam-to support effective intervention to reduce violence against children. EBLS-Foundational Research (EBLS-FR) tests critical aspects of the planned EBLS, including participant recruitment and retention, data collection and analysis. Alongside epidemiological estimates of levels and predictors of exposure to violence and adversity during pregnancy, we plan to explore mechanisms that may link exposure to violence to mothers' biological stress markers and subjective well-being.

METHODS AND ANALYSES

EBLS-FR is a short longitudinal study with a sample of 1200 pregnant women. Data are collected during the last trimester of pregnancy and 2 to 6 months after birth. The questionnaire for participating women has been translated into nine languages. Measures obtained from mothers will include, among others, mental and physical health, attitudes to corporal punishment, adverse childhood experiences, prenatal intimate partner violence, substance use and social/community support. Hair and dry blood spot samples are collected from the pregnant women to measure stress markers. To explore research participation among fathers, EBLS-FR is recruiting 300 fathers in the Philippines and Sri Lanka.

ETHICS AND DISSEMINATION

The study received ethical approvals at all recruiting sites and universities in the project. Results will be disseminated through journal publications, conferences and seminar presentations involving local communities, health services and other stakeholders. Findings from this work will help to adjust the subsequent stages of the EBLS project.

Functional polymorphisms of the mineralocorticoid receptor gene NR3C2 are associated with diminished memory decline: Results from a longitudinal general-population study

BACKGROUND

The mineralocorticoid receptor (MR) in the brain has a key role in the regulation of the central stress response and is associated with memory performance. We investigated whether the genetic polymorphisms rs5522 and rs2070951 of NR3C2 showed main and interactive effects with childhood trauma on memory decline.

METHODS

Declarative memory was longitudinally assessed in 1,318 participants from the community-dwelling Study of Health in Pomerania using the Verbal Learning and Memory Test (VLMT). In a subsample of 377 participants aged 60 and older, the Mini-Mental Status Examination (MMSE) was additionally applied. Mean follow-up time for the VLMT and MMSE were 6.4 and 10.7 years, respectively.

RESULTS

Homozygous carriers of the G allele of rs2070951 (p < .01) and of the A allele of rs5522 (p < .001) showed higher immediate recall of words as compared to carriers of C allele (rs2070951) or the G allele (rs5522). The CG haplotype was associated with decreased recall (p < .001). Likewise, in the subsample of older patients, the AA genotype of rs5522 was associated with higher MMSE scores (p < .05). CG haplotypes showed significantly reduced MMSE scores in comparison to the reference haplotype (β = -0.60; p < .01).

CONCLUSIONS

Our results indicate that the GG genotype of rs2070951 as well as the AA genotype of rs5522 are associated with diminished memory decline.

Prospective study of hippocampal volume and function in human subjects treated with corticosteroids

Purpose.

Decreased hippocampal volume reported in neuropsychiatric and endocrine disorders is considered a result of putative neuronal damage mediated by corticosteroids. This is the first prospective study of hippocampal volume and function in patients treated with corticosteroids.

Methods.

14 subjects treated systemically with prednisone or betamethasone for dermatological or rheumatic disorders underwent prospective neurocognitive testing (Auditory Verbal Learning Test—AVLT, Trail Making Test—TMT, Digit Span—DS) and nine of them also repeated magnetic resonance volumetry.

Results.

The mean duration of treatment between the first and the second assessment was 73 ± 38 days with mean daily dose of 37 ± 17 mg prednisone and 193 ± 29 days, with mean daily dose of 24 ± 15 mg prednisone between the first and the third assessment. There was a trend towards decreases in total AVLT scores and an improvement in the TMT and DS, but no significant changes in the volumes of the right or the left hippocampi between the assessments. Prednisone dose did not correlate with the hippocampal volume change.

Conclusion.

We observed a trend for decline in verbal memory despite improvement in psychomotor speed, attention/working memory and no macroscopic hippocampal volume changes during 36–238 days of treatment with therapeutic doses of corticosteroids.

Stress-related deficits of older adults' spatial working memory: an EEG investigation of occipital alpha and frontal-midline theta activities

Studies highlight cumulative life stress as a significant predictor of accelerated cognitive aging. This study paired electrophysiological with behavioral measures to explore how cumulative stress affects attentional and maintenance processes underpinning working memory retention. We collected electroencephalographic recordings from 60 individuals (30 older, 30 younger) reporting high or low levels of cumulative stress during the performance of a spatial Sternberg task. We measured mid-occipital alpha (8-12 Hz) and frontal-midline theta (4-6 Hz) as indicators of attentional and maintenance processes. Older, high-stress participants' behavioral performance lay significantly below than that of younger adults and low-stress older individuals. Impaired task performance coincided with reduced event-related synchronization in alpha and theta frequency ranges during memory maintenance. Electrophysiological findings suggest that older adults' reduced performance results from a stress-related impact on their ability to retain a stimulus in working memory and inhibit extraneous information from interfering with maintenance. Our results demonstrate the wide-ranging impact of cumulative stress on cognitive health and provide insight into the functional mechanisms disrupted by its influence.

Delayed effects of combined stress and Aβ infusion on L-LTP of the dentate gyrus: Prevention by nicotine

Alzheimer's Disease (AD) is a progressive dementia hallmarked by the presence in the brain of extracellular beta-amyloid (Aβ) plaques and intraneuronal fibrillary tangles. Chronic stress is associated with heightened Aβ buildup and acceleration of development of AD, however, stress alone has no significant effect on synaptic plasticity in the dentate gyrus (DG) area. Previously, we have reported that the combination of stress and AD causes more severe inhibition of synaptic plasticity of hippocampal area CA1 than chronic stress or AD alone, and that chronic nicotine treatment prevents this impairment. To investigate the effect of stress and nicotine on synaptic plasticity in the relatively injury-resistant DG area, the present experiments analyzed the effect of chronic stress and the neuroprotective effect of nicotine on LTP in the DG area of a rat model of AD. Wistar rats were chronically stressed and treated with nicotine (1 mg/kg/twice daily; s.c.) for six weeks. Then, at weeks 5-6, AD model was generated by 14-day i.c.v osmotic pump infusion of Aβ peptides (300 pmol/day) into the brains of these rats. Field potential recordings from the DG area of anesthetized rats, revealed that while chronic stress did not accentuate Aβ-induced impairments of E-LTP, it markedly augmented Aβ effect on L-LTP that was only seen 100 min after multiple high frequency stimulation. This delayed action is likely to be due to impairment of process of de novo protein synthesis required for maintenance phase of L-LTP. Chronic nicotine treatment prevented stress-enhanced suppression of synaptic plasticity.

Perinatal stress and human hippocampal volume: Findings from typically developing young adults

The main objective of this study was to investigate the impact of prenatal and early postnatal stress on hippocampal volume in young adulthood. In sharp contrast to numerous results in animal models, our data from a neuroimaging follow-up (n = 131) of a community-based birth cohort from the Czech Republic (European Longitudinal Study of Pregnancy and Childhood) showed that in typically developing young adults, hippocampal volume was not associated with birth weight, stressful life events during the prenatal or early postnatal period, or dysregulated mood and wellbeing in the mother during the early postnatal period. Interestingly, mother’s anxiety/co-dependence during the first weeks after birth did show long-lasting effects on the hippocampal volume in young adult offspring irrespective of sex. Further analyses revealed that these effects were subfield-specific; present in CA1, CA2/3, CA4, GC-DG, subiculum, molecular layer, and HATA, hippocampal subfields identified by translational research as most stress- and glucocorticoid-sensitive, but not in the remaining subfields. Our findings provide evidence that the type of early stress is critical when studying its effects on the human brain.

Characterization of the anterior cingulate cortex in adult tree shrew

The anterior cingulate cortex (ACC) is a key brain region for the perception of pain and emotion. Cellular and molecular mechanisms of the ACC are usually investigated in rodents such as mice and rats. Studies of synaptic mechanisms in primates are limited. To facilitate the translation of basic results from rodents to humans, it is critical to use a primate-like animal model for the investigation of the ACC. The tree shrew presents a great opportunity for this as they have similar genome sequences to primates and are considered to have many similarities to primates. In the present study, by combining anatomy, immunostaining and micro-optical sectioning tomography methods, we examined the morphological properties of the ACC in the tree shrew and compared them with the mouse and rat. We found that the ACC in the tree shrew is significantly larger than those found in the mouse and rat. The sizes of cell bodies of ACC pyramidal cells in tree shrew are also larger than that found in the mouse or rat. Furthermore, there are significantly more apical/basal dendritic branches and apical dendritic spines of ACC pyramidal neurons in tree shrew. These results demonstrate that pyramidal cells of the ACC in tree shrews are more advanced than those found in rodents (mice and rats), indicating that the tree shrew can be used as a useful animal model for studying the cellular mechanism for ACC-related physiological and pathological changes in humans.

Chronic administration of ellagic acid improved the cognition in middle-aged overweight men

This study aimed to investigate if ellagic acid has beneficial effects on cognitive deficits in middle-aged overweight individuals and to propose a possible mechanism. A total of 150 middle-aged male participants, including 76 normal-weight and 74 overweight men, aged between 45 to 55 years, were recruited for this study. Both normal-weight and overweight participants were administered either 50 mg ellagic acid or placebo cellulose daily for 12 weeks. Blood lipids, peripheral brain-derived neurotrophic factor (BDNF), and saliva cortisol were assessed on the last day of the procedure to investigate the effects induced by ellagic acid. The results revealed that ellagic acid treatment improved the levels of blood lipid metabolism with a 4.7% decline in total cholesterol, 7.3% decline in triglycerides, 26.5% increase in high-density lipoprotein, and 6.5% decline in low-density lipoprotein. Additionally, ellagic acid increased plasma BDNF by 21.2% in the overweight group and showed no effects on normal-weight participants. Moreover, the increased saliva cortisol level in overweight individuals was inhibited by 22.7% in a 12-week ellagic acid treatment. Also, compared with placebo, overweight individuals who consumed ellagic acid showed enhanced cognitive function as measured by the Wechsler Adult Intelligence Scale-Revised and the Montreal Cognitive Assessment. To the best of our knowledge, this is the first report showing that ellagic acid prevents cognitive deficits through normalization of lipid metabolism, increase in plasma BDNF level, and reduction of saliva cortisol concentration. These results indicate that ellagic acid has a potential to restore cognitive performance related to mild age-related declines.

CA3 hippocampal field: Cellular changes and its relation with blood nitro-oxidative stress reveal a balancing function of CA3 area in rats exposed to repetead restraint stress

Rats exposed to repeated restraint stress exhibit structural and functional deficits in hippocampus that are similar to those observed in patients with depressive illnesses. Blood corticosterone concentrations are proportionally increased with catalase and glutathione-peroxidase activity and are inversely proportional with 3-nitrotyrosine concentrations.Cytochrome c oxidase, adenosin tryphosphatase and monoamine oxidase activities of CA3 hippocampal field mark a stress-time dependent decrease. Acridine-orange labeling of the CA3 field reveals an enhancing green fluorescence of glyocites in stress conditions. After three days of restraint stress, the secretory activity of CA3 neurons did not show significant decrease, and neurons appeared with normal shapes and distribution. CA3 neurons after seven days of restraint stress have marked a slight decrease of secretory activity. In contrast to a well-preserved histological appearance of the CA3 neurons, local and blood stress-related reactions are observed. CA3-glial activation and disturbance of blood oxidative homeostasis are tandem processes during three and seven days of RS. This study depicts the balancing role of CA3 area in time-varying stress conditions.

A diffusion tensor imaging atlas of white matter in tree shrew

Tree shrews are small mammals now commonly classified in the order of Scandentia, but have relatively closer affinity to primates than rodents. The species has a high brain-to-body mass ratio and relatively well-differentiated neocortex, and thus has been frequently used in neuroscience research, especially for studies on vision and neurological/psychiatric diseases. The available atlases on tree shrew brain provided only limited information on white matter (WM) anatomy. In this study, diffusion tensor imaging (DTI) was used to study the WM anatomy of tree shrew, with the goal to establish an image-based WM atlas. DTI and T₂-weighted anatomical images were acquired in vivo and from fixed brain samples. Deterministic tractography was used for three-dimensional reconstruction and rendering of major WM tracts. Myelin and neurofilaments staining were used to study the microstructural properties of certain WM tracts. Taking into account prior knowledge on tree shrew neuroanatomy, tractography results, and comparisons to the homologous structures in rodents and primates, an image-based WM atlas of tree shrew brain was constructed, which is available to research community upon request.

Animal models of major depression and their clinical implications

Major depressive disorder is a common, complex, and potentially life-threatening mental disorder that imposes a severe social and economic burden worldwide. Over the years, numerous animal models have been established to elucidate pathophysiology that underlies depression and to test novel antidepressant treatment strategies. Despite these substantial efforts, the animal models available currently are of limited utility for these purposes, probably because none of the models mimics this complex disorder fully. It is presumable that psychiatric illnesses, such as affective disorders, are related to the complexity of the human brain. Here, we summarize the animal models that are used most commonly for depression, and discuss their advantages and limitations. We discuss genetic models, including the recently developed optogenetic tools and the stress models, such as the social stress, chronic mild stress, learned helplessness, and early-life stress paradigms. Moreover, we summarize briefly the olfactory bulbectomy model, as well as models that are based on pharmacological manipulations and disruption of the circadian rhythm. Finally, we highlight common misinterpretations and often-neglected important issues in this field.

Tree shrews at the German Primate Center

Abstract. For many years, Tupaia (family Tupaiidae), most commonly known as tree shrews, have been studied almost exclusively by zoologists resulting in a controversial debate on their taxonomic status among mammals. Today, tree shrews are placed in the order Scandentia; they are valuable, widely accepted and increasingly used model animals as an alternative to rodents and non-human primates in biomedical research. After a brief description on how tree shrews entered science and their taxonomic odyssey, the present article describes the history of the tree shrew (Tupaia belangeri) colony at the German Primate Center and selected aspects of our work with special emphasis on the psychosocial stress model in these animals.

The impact of experienced stress on aged spatial discrimination: Cortical overreliance as a result of hippocampal impairment

A large body of neuroscientific work indicates that exposure to experienced stress causes damage to both cortical and hippocampal cells and results in impairments to cognitive abilities associated with these structures. Similarly, work within the domain of cognitive aging demonstrates that elderly participants who report experiencing greater amounts of stress show reduced levels of cognitive functioning. The present article attempted to combine both findings by collecting data from elderly and young participants who completed a spatial discrimination paradigm developed by Reagh and colleagues [Reagh et al. (2013) Hippocampus 24:303-314] to measure hippocampal-mediated cognitive processes. In order to investigate the effect of stress on the cortex and, indirectly, the hippocampus, it paired the paradigm with electroencephalographic recordings of the theta frequency band, which is thought to reflect cortical/hippocampal interactions. Findings revealed that elderly participants with high levels of experienced stress performed significantly worse on target recognition and lure discrimination and demonstrated heightened levels of cortical theta synchronization compared with young and elderly low stress counterparts. Results therefore provided further evidence for the adverse effect of stress on cognitive aging and indicate that impaired behavioral performance among high stress elderly may coincide with an overreliance on cortical cognitive processing strategies as a result of early damage to the hippocampus.

Astroglial Plasticity Is Implicated in Hippocampal Remodelling in Adult Rats Exposed to Antenatal Dexamethasone

The long-term effects of antenatal dexamethasone treatment on brain remodelling in 3-month-old male Sprague Dawley rats whose mothers had been treated with dexamethasone were investigated in the present study. Dorsal hippocampus, basolateral amygdala and nucleus accumbens volume, cell numbers, and GFAP-immunoreactive astroglial cell morphology were analysed using stereology. Total brain volume as assessed by micro-CT was not affected by the treatment. The relative volume of the dorsal hippocampus (% of total brain volume) showed a moderate, by 8%, but significant reduction in dexamethasone-treated versus control animals. Dexamethasone had no effect on the total and GFAP-positive cell numbers in the hippocampal subregions, basolateral amygdala, and nucleus accumbens. Morphological analysis indicated that numbers of astroglial primary processes were not affected in any of the hippocampal subregions analysed but significant reductions in the total primary process length were observed in CA1 by 32%, CA3 by 50%, and DG by 25%. Mean primary process length values were also significantly decreased in CA1 by 25%, CA3 by 45%, and DG by 25%. No significant astroglial morphological changes were found in basolateral amygdala and nucleus accumbens. We propose that the dexamethasone-dependent impoverishment of hippocampal astroglial morphology is the case of maladaptive glial plasticity induced prenatally.

The effect of childhood trauma on spatial cognition in adults: a possible role of sex

Although animal evidence indicates that early life trauma results in pervasive hippocampal deficits underlying spatial and cognitive impairment, visuo-spatial data from adult humans with early childhood adversity are lacking. We administered 4 tests of visuo-spatial ability from the Cambridge Neuorpsychological Test Automated Battery (CANTAB) to adults with a history of childhood trauma (measured by the Childhood Trauma Questionnaire) and a matched sample of healthy controls (trauma/control = 27/28). We observed a significant effect of trauma history on spatial/pattern learning. These effects could not be accounted for by adverse adult experiences, and were sex-specific, with prior adversity improving performance in men but worsening performance in women, relative to controls. Limitations include the small sample size and reliance of our study design on a retrospective, self report measure. Our results suggest that early adversity can lead to specific and pervasive deficits in adult cognitive function.

The impact of stress and glucocorticoids on memory

Responses to stress are mediated by a complex network of the nervous and endocrine systems. Glucocorticoids, which are among the most important “players” in stress resilience, may have important implications in the cognitive functions, particularly in the modulation of memory. Declarative memory, the memory for facts, events and word meaning is the most studied type of memory on which glucocorticoids exert an influence, both positively through consolidation and negatively through impairment. These effects depend on the receptor type, dose, time of exposure, memory component and the salience of stimuli, retrieval being generally affected and storage being facilitated, especially for emotionally relevant events. Glucocorticoids also induce hippocampal atrophy, which is a hallmark seen in various diseases accompanied by a chronic high level of cortisol, such as the Cushing syndrome, major depression, post-traumatic stress disorder. Also, chronic stress might be a risk factor for the development of Alzheimer’s disease, especially when a genetic background and other environmental influences are present.

Anatomical MRI templates of tree shrew brain for volumetric analysis and voxel-based morphometry

BACKGROUND

Tree shrews are close relatives of primates, and are increasingly used as models in the research of vision, social stress and neurological/psychiatric diseases. However, neuroimaging techniques, for example magnetic resonance (MR) imaging, are only rarely applied to this species to study the structure and function of the brain. A template MR image set, which is essential for morphometry/volumetric analysis, of tree shrew brain has been lacking in the literature.

NEW METHOD

High-resolution anatomical MR images and diffusion tensor images of the brain were acquired from male Chinese tree shrews (Tupaia belangeri chinensis), and resampled to an isotropic resolution of 200 μm × 200 μm × 200 μm. Population-based image templates of tree shrew brain, including gray matter/white matter/cerebrospinal fluid probability maps and a fractional anisotropy template, were constructed at this spatial resolution, all in a reference space. Digital masks of representative anatomical structures, including hippocampus, amygdala and cingulum bundle, were created.

RESULT

With the templates constructed, the volumes of bilateral hippocampus and amygdala were measured using a template-facilitated semi-automated approach to be 59.8 ± 8.3 and 64.3 ± 3.4 mm(3), respectively.

COMPARISON WITH EXISTING METHOD(S)

For the first time, high-resolution MR image templates of tree shrew brain were reported. The average volume of bilateral hippocampus measured with the template-facilitated semi-automated approach was found to be similar to the result obtained by the much more labor-intensive manual approach.

CONCLUSIONS

The MR image templates obtained in this study are useful for analyzing neuroimage data of tree shrew brain. The templates are freely available to the scientific community upon request.

Brain Physiology and Pathophysiology in Mental Stress

Exposure to various forms of stress is a common daily occurrence in the lives of most individuals, with both positive and negative effects on brain function. The impact of stress is strongly influenced by the type and duration of the stressor. In its acute form, stress may be a necessary adaptive mechanism for survival and with only transient changes within the brain. However, severe and/or prolonged stress causes overactivation and dysregulation of the hypothalamic pituitary adrenal (HPA) axis thus inflicting detrimental changes in the brain structure and function. Therefore, chronic stress is often considered a negative modulator of the cognitive functions including the learning and memory processes. Exposure to long-lasting stress diminishes health and increases vulnerability to mental disorders. In addition, stress exacerbates functional changes associated with various brain disorders including Alzheimer’s disease and Parkinson’s disease. The primary purpose of this paper is to provide an overview for neuroscientists who are seeking a concise account of the effects of stress on learning and memory and associated signal transduction mechanisms. This review discusses chronic mental stress and its detrimental effects on various aspects of brain functions including learning and memory, synaptic plasticity, and cognition-related signaling enabled via key signal transduction molecules.

Brain-derived neurotrophic factor Val66Met polymorphism and early life adversity affect hippocampal volume

The interaction between adverse life events during childhood and genetic factors is associated with a higher risk to develop major depressive disorder (MDD). One of the polymorphisms found to be associated with MDD is the Val66MET polymorphism of brain-derived neurotrophic factor (BDNF). The aim of our two-center study was to determine how the BDNF Val66Met polymorphism and childhood adversity affect the volumetric measures of the hippocampus in healthy individuals and people with MDD. In this two-center study, 62 adult patients with MDD and 71 healthy matched controls underwent high-resolution magnetic resonance imaging. We used manual tracing of the bilateral hippocampal structure with help of the software BRAINS2, assessed childhood adversity using the Childhood Trauma Questionnaire and genotyped Val66Met BDNF SNP (rs6265). MDD patients had smaller hippocampal volumes, both in the left and right hemispheres (F = 5.4, P = 0.022). We also found a significant interaction between BDNF allele and history of childhood adversity (F = 6.1, P = 0.015): Met allele carriers in our samples showed significantly smaller hippocampal volumes when they did have a history of childhood adversity, both in patients and controls. Our results highlight how relevant stress-gene interactions are for hippocampal volume reductions. Subjects exposed to early life adversity developed smaller hippocampal volumes when they carry the Met-allele of the BDNF polymorphism.

The Effects of Sex and Chronic Restraint on Instrumental Learning in Rats

Chronic stress has been shown to impact learning, but studies have been sparse or nonexistent examining sex or task differences. We examined the effects of sex and chronic stress on instrumental learning in adult rats. Rats were tested in an aversive paradigm with or without prior appetitive experience, and daily body weight data was collected as an index of stress. Relative to control animals, reduced body weight was maintained across the stress period for males (−7%, P ≤ .05) and females (−5%, P ≤ .05). For males, there were within-subject day-by-day differences after asymptotic transition, and all restrained males were delayed in reaching asymptotic performance. In contrast, stressed females were facilitated in appetitive and aversive-only instrumental learning but impaired during acquisition of the aversive transfer task. Males were faster than females in reaching the appetitive shaping criterion, but females were more efficient in reaching the appetitive tone-signaled criterion. Finally, an effect of task showed that while females reached aversive shaping criterion at a faster rate when they had prior appetitive learning, they were impaired in tone-signaled avoidance learning only when they had prior appetitive learning. These tasks reveal important nuances on the effect of stress and sex differences on goal-directed behavior.

Dendritic morphology of hippocampal and amygdalar neurons in adolescent mice is resilient to genetic differences in stress reactivity

Many studies have shown that chronic stress or corticosterone over-exposure in rodents leads to extensive dendritic remodeling, particularly of principal neurons in the CA3 hippocampal area and the basolateral amygdala. We here investigated to what extent genetic predisposition of mice to high versus low stress reactivity, achieved through selective breeding of CD-1 mice, is also associated with structural plasticity in Golgi-stained neurons. Earlier, it was shown that the highly stress reactive (HR) compared to the intermediate (IR) and low (LR) stress reactive mice line presents a phenotype, with respect to neuroendocrine parameters, sleep architecture, emotional behavior and cognition, that recapitulates some of the features observed in patients suffering from major depression. In late adolescent males of the HR, IR, and LR mouse lines, we observed no significant differences in total dendritic length, number of branch points and branch tips, summated tip order, number of primary dendrites or dendritic complexity of either CA3 pyramidal neurons (apical as well as basal dendrites) or principal neurons in the basolateral amygdala. Apical dendrites of CA1 pyramidal neurons were also unaffected by the differences in stress reactivity of the animals; marginally higher length and complexity of the basal dendrites were found in LR compared to IR but not HR mice. In the same CA1 pyramidal neurons, spine density of distal apical tertiary dendrites was significantly higher in LR compared to IR or HR animals. We tentatively conclude that the dendritic complexity of principal hippocampal and amygdala neurons is remarkably stable in the light of a genetic predisposition to high versus low stress reactivity, while spine density seems more plastic. The latter possibly contributes to the behavioral phenotype of LR versus HR animals.

Recurrent long-lasting tethering reduces BDNF protein levels in the dorsal hippocampus and frontal cortex in pigs

Brain-derived neurotrophic factor (BDNF) signaling has been implicated in the onset of depression and in antidepressant efficacy, although the exact role of this neurotrophin in the pathophysiology of depression remains to be elucidated. Also, the interaction between chronic stress, which may precede depression, corticosteroids and BDNF is not fully understood. The present study aimed at investigating whether long-lasting, recurrent tethering of sows during a period of 1.5 or 4.5 years leads to enduring effects on measures that may be indicative of chronic stress, compared with animals kept in a group housing system ('loose' sows). Immediately after slaughter, the frontal cortex, dorsal and ventral hippocampus were dissected and protein levels of BDNF and its receptors were analyzed and compared with plasma cortisol levels and adrenal weights. Results indicate that tethering stress reduced BDNF protein levels in the dorsal hippocampus and the frontal cortex, but not in the ventral hippocampus. In addition, levels of TrkB, the high affinity receptor for BDNF, were increased in the dorsal hippocampus. Plasma cortisol levels and adrenal weight were increased after tethering. These stress effects on BDNF levels were more pronounced after 4.5 years of recurrent tethering and negatively correlated in particular in the frontal cortex with cortisol levels and adrenal weight. This suggests that the stress effect of tethered housing on neurotrophin levels may be mediated via cortisol. Taken together, these data indicate that recurrent tethering stress in sows over 4.5 years results in a loss of neurotrophic support by BDNF, mediated by an overactive neuroendocrine system.

Impact of chronic hypercortisolemia on affective processing

Cushing syndrome (CS) is the classic condition of cortisol dysregulation, and cortisol dysregulation is the prototypic finding in Major Depressive Disorder (MDD). We hypothesized that subjects with active CS would show dysfunction in frontal and limbic structures relevant to affective networks, and also manifest poorer facial affect identification accuracy, a finding reported in MDD. Twenty-one patients with confirmed CS (20 ACTH-dependent and 1 ACTH-independent) were compared to 21 healthy control subjects. Identification of affective facial expressions (Facial Emotion Perception Test) was conducted in a 3 Tesla GE fMRI scanner using BOLD fMRI signal. The impact of disease (illness duration, current hormone elevation and degree of disruption of circadian rhythm), performance, and comorbid conditions secondary to hypercortisolemia were evaluated. CS patients made more errors in categorizing facial expressions and had less activation in left anterior superior temporal gyrus, a region important in emotion processing. CS patients showed higher activation in frontal, medial, and subcortical regions relative to controls. Two regions of elevated activation in CS, left middle frontal and lateral posterior/pulvinar areas, were positively correlated with accuracy in emotion identification in the CS group, reflecting compensatory recruitment. In addition, within the CS group, greater activation in left dorsal anterior cingulate was related to greater severity of hormone dysregulation. In conclusion, cortisol dysregulation in CS patients is associated with problems in accuracy of affective discrimination and altered activation of brain structures relevant to emotion perception, processing and regulation, similar to the performance decrements and brain regions shown to be dysfunctional in MDD. This article is part of a Special Issue entitled 'Anxiety and Depression'.

The hippocampus in major depression: evidence for the convergence of the bench and bedside in psychiatric research?

Major depressive disorder (MDD) has until recently been conceptualized as an episodic disorder associated with 'chemical imbalances' but no permanent brain changes. Evidence has emerged in the past decade that MDD is associated with small hippocampal volumes. This paper reviews the clinical and biological correlates of small hippocampal volumes based on literature searches of PubMed and EMBASE and discusses the ways in which these data force a re-conceptualization of MDD. Preclinical data describe the molecular and cellular effects of chronic stress and antidepressant treatment on the hippocampus, providing plausible mechanisms through which MDD might be associated with small hippocampal volumes. Small hippocampal volumes are associated with poor clinical outcome and may be a mechanism through which MDD appears to be a risk factor for Alzheimer's disease. The pathways through which stress may be linked to MDD, the emergence of chronicity or treatment resistance in MDD and the association between MDD and memory problems may be at least partially understood by dissecting the association with depression and changes in the hippocampus. MDD must be re-conceived as a complex illness, associated with persistent morphological brain changes that are detectable before illness onset and which may be modified by clinical and treatment variables.

A critical review of chronic stress effects on spatial learning and memory

The purpose of this review is to evaluate the effects of chronic stress on hippocampal-dependent function, based primarily upon studies using young, adult male rodents and spatial navigation tasks. Despite this restriction, variability amongst the findings was evident and how or even whether chronic stress influenced spatial ability depended upon the type of task, the dependent variable measured and how the task was implemented, the type and duration of the stressors, housing conditions of the animals that include accessibility to food and cage mates, and duration from the end of the stress to the start of behavioral assessment. Nonetheless, patterns emerged as follows: For spatial memory, chronic stress impairs spatial reference memory and has transient effects on spatial working memory. For spatial learning, however, chronic stress effects appear to be task-specific: chronic stress impairs spatial learning on appetitively motivated tasks, such as the radial arm maze or holeboard, tasks that evoke relatively mild to low arousal components from fear. But under testing conditions that evoke moderate to strong arousal components from fear, such as during radial arm water maze testing, chronic stress appears to have minimal impairing effects or may even facilitate spatial learning. Chronic stress clearly impacts nearly every brain region and thus, how chronic stress alters hippocampal spatial ability likely depends upon the engagement of other brain structures during behavioral training and testing.

Prenatal stress causes dendritic atrophy of pyramidal neurons in hippocampal CA3 region by glutamate in offspring rats

A substantial number of human epidemiological data, as well as experimental studies, suggest that adverse maternal stress during gestation is involved in abnormal behavior, mental, and cognition disorder in offspring. To explore the effect of prenatal stress (PS) on hippocampal neurons, in this study, we observed the dendritic field of pyramidal neurons in hippocampal CA3, examined the concentration of glutamate (Glu), and detected the expression of synaptotagmin-1 (Syt-1) and N-methyl-D-aspartate receptor 1 (NR1) in hippocampus of juvenile female offspring rats. Pregnant rats were divided into two groups: control group (CON) and PS group. Female offspring rats used were 30-day old. The total length of the apical dendrites of pyramidal neurons in hippocampal CA3 of offspring was significantly shorter in PS than that in CON (p < 0.01). The number of branch points of the apical dendrites of pyramidal neurons in hippocampal CA3 of offspring was significantly less in PS (p < 0.01). PS offspring had a higher concentration of hippocampal Glu compared with CON (p < 0.05). PS offspring displayed increased expression of Syt-1 and decreased NR1 in hippocampus compared with CON (p < 0.001 and p < 0.01, respectively). The expression of NR1 in different hippocampus subfields of offspring was significantly decreased in PS than that in CON (p < 0.05-0.01). This study shows that PS increases the Glu in hippocampus and causes apical dendritic atrophy of pyramidal neurons of hippocampal CA3 in offspring rats. The decline of NR1 in hippocampus may be an adaptive response to the increased Glu.

Chronic stress selectively reduces hippocampal volume in rats: a longitudinal magnetic resonance imaging study

The notion of uncontrollable stress causing reduced hippocampal size remains controversial in the posttraumatic stress disorder literature, because human studies cannot discern the causality of effect. Here, we addressed this issue by using structural magnetic resonance imaging in rats to measure the hippocampus and other brain regions before and after stress. Chronic restraint stress produced approximately 3% reduction in hippocampal volume, which was not observed in control rats. This decrease was not signficantly correlated with baseline hippocampal volume or body weight. Total forebrain volume and the sizes of the other brain regions and adrenal glands were all unaffected by stress. This longitudinal, within-subjects design study provides direct evidence that the hippocampus is differentially vulnerable and sensitive to chronic stress.

The influence of pre-deployment neurocognitive functioning on post-deployment PTSD symptom outcomes among Iraq-deployed Army soldiers

This study evaluated associations between pre-deployment neurocognitive performance and post-deployment posttraumatic stress disorder (PTSD) symptoms in a sample of deployed active duty Army soldiers. As part of a larger longitudinal study, each participant completed baseline measures of memory, executive attention, and response inhibition, and baseline and post-deployment self-report measures of PTSD symptom severity. Data were subjected to multiple regression analyses that examined associations between baseline neurocognitive performances and longitudinal PTSD symptom outcome. Results revealed that pre-trauma immediate recall of visual information was associated with post-deployment PTSD symptom severity, even after controlling for pre-deployment PTSD symptom levels, combat intensity, age, gender, and test-retest interval. There was also an interaction between pre-deployment PTSD symptom severity and pre-deployment immediate visual recall and verbal learning, indicating that neurocognitive performances were more strongly (and negatively) associated with residualized post-deployment PTSD symptoms at higher levels of pre-deployment PTSD symptoms. These findings highlight the potential role of pre-trauma neurocognitive functioning in moderating the effects of trauma exposure on PTSD symptoms

Anterior hippocampal volume is reduced in behaviorally depressed female cynomolgus macaques

Hippocampal (HC) function and morphology have been implicated in the pathophysiology of depression. Reduced HC volume has been observed in depressed humans, although the effect is not always significant. Studies of functional differentiation of the HC have revealed that the anterior portion is associated with emotional and anxiety-related functioning, and the posterior portion with memory processing. As such, measuring whole HC volume may mask differences seen only in the anterior or posterior HC. We used unbiased stereology to measure whole, anterior, and posterior HC volumes in 12 adult female cynomolgus macaques, half of which exhibited spontaneously occurring depressive behavior defined as a slumped/collapsed body posture with open eyes, and a relative lack of responsivity to environmental stimuli. The two groups were otherwise matched on circulating estradiol, progesterone, and cortisol levels, social status, estimated age, and body weight. Frozen postmortem HC tissue from depressed and nondepressed monkeys was serially sectioned and thionin-stained. According to established neuroanatomical guidelines and with the aid of Neurolucida software (MBF Bioscience), every 10th section throughout the extent of the HC was manually traced and used to reconstruct the 3D models used to determine volumes. Anterior and posterior HC were delineated by the presence or absence of the uncus. No significant differences were found between depressed and nondepressed monkeys for whole or posterior HC volume, although the average HC volume was 4% smaller in depressed than nondepressed monkeys. Anterior HC volumes were significantly smaller (15.4%) in depressed compared to nondepressed monkeys. These results indicate that reduced volume in the anterior HC, an area previously implicated in emotional functioning, may be associated with a depressive phenotype in female cynomolgus macaques.

Stress and the hypothalamic pituitary adrenal axis in the developmental course of schizophrenia

Diathesis-stress models of schizophrenia and other psychotic disorders have dominated theorizing about etiology for over three decades. More recently, with advances in our understanding of the biological processes mediating the effects of stress, these models have incorporated mechanisms to account for the adverse impact of stress on brain function. This review examines recent scientific findings on the role of the hypothalamic-pituitary-adrenal (HPA) axis, one of the primary neural systems triggered by stress exposure, in the expression of vulnerability for schizophrenia. The results indicate that psychotic disorders are associated with elevated baseline and challenge-induced HPA activity, that antipsychotic medications reduce HPA activation, and that agents that augment stress hormone (cortisol) release exacerbate psychotic symptoms. The cumulative findings are discussed in light of a neural diathesis-stress model that postulates that cortisol has the potential to increase activity of dopamine pathways that have been implicated in schizophrenia and other psychotic disorders.

The potential role of a corticotropin-releasing factor receptor-1 antagonist in psychiatric disorders

The hypothalamic-pituitary-adrenal axis is a key mediator of the stress response in humans. The corticotropin-releasing factor (CRF) type 1 receptor (CRFR-1) in the pituitary gland is a gatekeeper for that response, and the CRFR-1 receptor is also present in many other mood- and cognition-related neural structures. Behaviorally, a number of relationships between stress and psychiatric disorders can be observed: chronic or repeated stress is associated with onset of depression; stressors can cause a recovering alcoholic to relapse; overactive stress responses mark many anxiety disorders; and insomnia can arise from an overactive stress response. Thus, a CRFR-1 antagonist could be useful for treating or preventing the consequences of CRF-mediated stress in depression, anxiety, insomnia, and substance abuse.

Glucocorticoids in the treatment of children with acute lymphoblastic leukemia and hodgkin's disease: a pilot study on the adverse psychological reactions and possible associations with neurobiological, endocrine, and genetic markers

PURPOSE

We did a controlled study to assess adverse psychological reactions (APR) associated with high-dose glucocorticoid therapy and tried to detect somatic correlates for the observed reactions.

PATIENTS AND METHODS

Our study included 37 patients with acute lymphoblastic leukemia (ALL) and 11 patients with Morbus Hodgkin (MH) disease, who were treated with high-dose glucocorticoid therapy, and 26 control patients with other types of malignancies. APRs were assessed with a standardized measure via parent-report. Patients with ALL and MH were further analyzed for signs of neuronal cell death in the cerebrospinal fluid, polymorphisms of the glucocorticoid receptor gene, as well as cortisol, adrenocorticorticotropic hormone, and dehydroepiandrosterone sulfate blood levels.

RESULTS

Fifty-four percent of ALL, 36% of MH, and 23% of control patients developed APR in the first few weeks of therapy. Approximately 3.5 months later, the majority of patients with ALL showed no APR, similar to control patients. Patients demonstrating a higher, nonsuppressible secretion of cortisol and/or adrenocorticorticotropic hormone during glucocorticoid therapy were found to be more likely to develop APR. No sign of neuronal cell destruction and no correlation of APR with specific glucocorticoid receptor polymorphisms were found.

CONCLUSION

Our results suggest that the development of APR due to glucocorticoid therapy is measurable and correlates with hormonal reaction patterns.

Modulation of stress consequences by hippocampal monoaminergic, glutamatergic and nitrergic neurotransmitter systems

Several findings relate the hippocampal formation to the behavioural consequences of stress. It contains a high concentration of corticoid receptors and undergoes plastic modifications, including decreased neurogenesis and cellular remodelling, following stress exposure. Various major neurotransmitter systems in the hippocampus are involved in these effects. Serotonin (5-HT) seems to exert a protective role in the hippocampus and attenuates the behavioural consequences of stress by activating 5-HT1A receptors in this structure. These effects may mediate the therapeutic actions of several antidepressants. The role of noradrenaline is less clear and possibly depends on the specific hippocampal region (dorsal vs. ventral). The deleterious modifications induced in the hippocampus by stress might involve a decrease in neurotrophic factors such as brain derived neurotrophic factor (BDNF) following glutamate N-methyl-D-aspartate (NMDA) receptor activation. In addition to glutamate, nitric oxide (NO) could also be related to these effects. Systemic and intra-hippocampal administration of nitric oxide synthase (NOS) inhibitors attenuates stress-induced behavioural consequences. The challenge for the future will be to integrate results related to these different neurotransmitter systems in a unifying theory about the role of the hippocampus in mood regulation, depressive disorder and antidepressant effects.

The effects of stress and stress hormones on human cognition: Implications for the field of brain and cognition

In this review, we report on studies that have assessed the effects of exogenous and endogenous increases in stress hormones on human cognitive performance. We first describe the history of the studies on the effects of using exogenous stress hormones such as glucocorticoids as anti-inflammatory medications on human cognition and mental health. Here, we summarize the cases that led to the diagnosis of glucocorticoid-induced 'steroid psychosis' in human populations and which demonstrated that these stress hormones could thus cross the blood-brain barrier and access the brain where they could influence cognition and mental health. We then summarize studies that assessed the effects of the exogenous administration of glucocorticoids on cognitive performance supported by the hippocampus, the frontal lobes and amygdala. In the second section of the paper, we summarize the effects of the endogenous release of glucocorticoids induced by exposure to a stressful situation on human cognition and we further dissociate the effects of emotion from those of stress on human learning and memory. Finally, in the last section of the paper, we discuss the potential impact that the environmental context to which we expose participants when assessing their memory could have on their reactivity to stress and subsequent cognitive performance. In order to make our point, we discuss the field of memory and aging and we suggest that some of the 'age-related memory impairments' observed in the literature could be partly due to increased stress reactivity in older adults to the environmental context of testing. We also discuss the inverse negative correlations reported between hippocampal volume and memory for young and older adults and suggest that these inverse correlations could be partly due to the effects of contextual stress in young and older adults, as a function of age-related differences in hippocampal volume.

Stress, the hippocampus and the hypothalamic-pituitary-adrenal axis: implications for the development of psychotic disorders

OBJECTIVE

The experience of stress is commonly implicated in models of the onset of psychotic disorders. However, prospective studies investigating associations between biological markers of stress and the emergence of psychotic disorders are limited and inconclusive. One biological system proposed as the link between the psychological experience of stress and the development of psychosis is the Hypothalamic-Pituitary-Adrenal (HPA) axis. This paper summarizes and discusses evidence supporting a role for HPA-axis dysfunction in the early phase of schizophrenia and related disorders.

METHOD

A selective review of psychiatric and psychological research on stress, coping, HPA-axis, the hippocampus and psychotic disorders was performed, with a particular focus on the relationship between HPA-axis dysfunction and the onset of psychotic disorders.

RESULTS

Individual strands of past research have suggested that the HPA-axis is dysfunctional in at least some individuals with established psychotic disorders; that the hippocampus is an area of the brain that appears to be implicated in the onset and maintenance of psychotic disorders; and that an increase in the experience of stress precedes the onset of a psychotic episode in some individuals. Models of the onset and maintenance of psychotic disorders that link these individual strands of research and strategies for examining these models are proposed in this paper.

CONCLUSIONS

The current literature provides some evidence that the onset of psychotic disorders may be associated with a higher rate of stress and changes to the hippocampus. It is suggested that future research should investigate whether a relationship exists between psychological stress, HPA-axis functioning and the hippocampus in the onset of these disorders. Longitudinal assessment of these factors in young people at 'ultra' high risk of psychosis and first-episode psychosis cohorts may enhance understanding of the possible interaction between them in the early phases of illness.