Corticosteroids: sculptors of the hippocampal formation

Resilience to stress and sex-specific remodeling of microglia and neuronal morphology in a rat model of anxiety and anhedonia

Prenatal exposure to stress or glucocorticoids (GC) is associated with the appearance of psychiatric diseases later in life. Microglia, the immune cells of the brain, are altered in stress-related disorders.

Synthetic GC such as dexamethasone (DEX) are commonly prescribed in case of preterm risk labour in order to promote fetal lung maturation. Recently, we reported long-lasting differences in microglia morphology in a model of in utero exposure to DEX (iuDEX), that presents an anxious phenotype. However, it is still unclear if stress differentially affects iuDEX males and females.

In this work, we evaluated how iuDEX animals of both sexes cope with chronic mild stress for 2 weeks. We evaluated emotional behavior and microglia and neuronal morphology in the dorsal hippocampus (dHIP) and nucleus accumbens (NAc), two brain regions involved in emotion-related disorders. We report that males and females prenatally exposed to DEX have better performance in anxiety- and depression-related behavioral tests after chronic stress exposure in adulthood than non-exposed animals. Interestingly, iuDEX animals present sex-dependent changes in microglia morphology in the dHIP (hypertrophy in females) and in the NAc (atrophy in females and hypertrophy in males). After chronic stress, these cells undergo sex-specific morphological remodeling. Paralleled to these alterations in cytoarchitecture of microglia, we report inter-regional differences in dendritic morphology in a sex-specific manner. iuDEX females present fewer complex neurons in the NAc, whereas iuDEX males presented less complex neuronal morphology in the dHIP. Interestingly, these alterations were modified by stress exposure.

Our work shows that stressful events during pregnancy can exert a preserved sex-specific effect in adulthood. Although the role of the observed cellular remodeling is still unknown, sex-specific differences in microglia plasticity induced by long-term stress exposure may anticipate differences in drug efficacy in the context of stress-induced anxiety- or depression-related behaviors.

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iuDEX induces anxiety- and depression-related behavioral in both sexes.

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iuDEX induces sex dependent fine structural alterations in neurons and microglia morphology in the dHIP and in the NAc.

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uCMS in combination to iuDEX normalize the behavior as well the morphology of neurons in the NAc.

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Stressful events during pregnancy can exert a preserved sex-specific effect in adulthood.

The development of stress reactivity and regulation during human development

Adverse experiences during childhood can have long-lasting impacts on physical and mental health. At the heart of most theories of how these effects are transduced into health impacts is the activity of stress-mediating systems, most notably the hypothalamic-pituitary-adrenocortical (HPA) axis. Here we review the anatomy and physiology of the axis, models of stress and development, the development of the axis prenatally through adolescence, the role of experience and sensitive periods in shaping its regulation, the social regulation of the axis at different points in development, and finally conclude with suggestions for future research. We conclude that it is clear that early adversity sculpts the stress system, but we do not understand which dimensions have the most impact and at what points in early development. It is equally clear that secure attachment relationships buffer the developing stress system; however, the mechanisms of social buffering and how these may change with development are not yet clear. Another critical issue that is not understood is when and for whom adversity will result in hypo- vs hyperactivity of stress-mediating systems. These and other issues are important for advancing our understanding of how early adversity "gets under the skin" and shapes human physical and mental health.

Biochemical Mechanisms and Translational Relevance of Hippocampal Vulnerability to Distant Focal Brain Injury: The Price of Stress Response

Focal brain injuries (in particular, stroke and traumatic brain injury) induce with high probability the development of delayed (months, years) cognitive and depressive disturbances which are frequently comorbid. The association of these complications with hippocampal alterations (in spite of the lack of a primary injury of this structure), as well as the lack of a clear dependence between the probability of depression and dementia development and primary damage severity and localization served as the basis for a new hypothesis on the distant hippocampal damage as a key link in the pathogenesis of cognitive and psychiatric disturbances. According to this hypothesis, the excess of corticosteroids secreted after a focal brain damage, in particular in patients with abnormal stress-response due to hypothalamic-pituitary-adrenal axis (HPAA) dysfunction, interacts with corticosteroid receptors in the hippocampus inducing signaling pathways which stimulate neuroinflammation and subsequent events including disturbances in neurogenesis and hippocampal neurodegeneration. In this article, the molecular and cellular mechanisms associated with the regulatory role of the HPAA and multiple functions of brain corticosteroid receptors in the hippocampus are analyzed. Functional and structural damage to the hippocampus, a brain region selectively vulnerable to external factors and responding to them by increased cytokine secretion, forms the basis for cognitive function disturbances and psychopathology development. This concept is confirmed by our own experimental data, results of other groups and by prospective clinical studies of post-stroke complications. Clinically relevant biochemical approaches to predict the risks and probability of post-stroke/post-trauma cognitive and depressive disturbances are suggested using the evaluation of biochemical markers of patients' individual stress-response. Pathogenetically justified ways for preventing these consequences of focal brain damage are proposed by targeting key molecular mechanisms underlying hippocampal dysfunction.

Neuroplasticity-related correlates of environmental enrichment combined with physical activity differ between the sexes

Environmental enrichment (EE), comprising positive physical (exercise) and cognitive stimuli, influences neuronal structure and usually improves brain function. The promise of EE as a preventative strategy against neuropsychiatric disease is especially high during early postnatal development when the brain is still amenable to reorganization. Despite the fact that male and female brains differ in terms of connectivity and function that may reflect early life experiences, knowledge of the neural substrates and mechanisms by which such changes arise remains limited. This study compared the impact of EE combined with physical activity on neuroplasticity and its functional consequences in adult male and female rats; EE was provided during the first 3 months of life and our analysis focused on the hippocampus, an area implicated in cognitive behavior as well as the neuroendocrine response to stress. Both male and female rats reared in EE displayed better object recognition memory than their control counterparts. Interestingly, sex differences were revealed in the effects of EE on time spent exploring the objects during this test. Independently of sex, EE increased hippocampal turnover rates of dopamine and serotonin and reduced expression of 5-HT_1A receptors; in addition, EE upregulated expression of synaptophysin, a presynaptic protein, in the hippocampus. As compared to their respective controls, EE-exposed males exhibited parallel increases in phosphorylated Tau and the GluN2B receptor, whereas females responded to EE with reduced hippocampal levels of glutamate and GluN2B. Together, these observations provide further evidence on the differential effects of EE on markers of hippocampal neuroplasticity in males and females.

Region-specific control of microglia by adenosine A2A receptors: uncoupling anxiety and associated cognitive deficits in female rats

Epidemiologic studies have provided compelling evidence that prenatal stress, through excessive maternal glucocorticoids exposure, is associated with psychiatric disorders later in life. We have recently reported that anxiety associated with prenatal exposure to dexamethasone (DEX, a synthetic glucocorticoid) correlates with a gender-specific remodeling of microglia in the medial prefrontal cortex (mPFC), a core brain region in anxiety-related disorders. Gender differences in microglia morphology, the higher prevalence of anxiety in women and the negative impact of anxiety in cognition, led us to specifically evaluate cognitive behavior and associated circuits (namely mPFC-dorsal hippocampus, dHIP), as well as microglia morphology in female rats prenatally exposed to dexamethasone (in utero DEX, iuDEX). We report that iuDEX impaired recognition memory and deteriorated neuronal synchronization between mPFC and dHIP. These functional deficits are paralleled by microglia hyper-ramification in the dHIP and decreased ramification in the mPFC, showing a heterogeneous remodeling of microglia morphology, both postnatally and at adulthood in different brain regions, that differently affect mood and cognition. The chronic blockade of adenosine A2A receptors (A2A R), which are core regulators of microglia morphology and physiology, ameliorated the cognitive deficits, but not the anxiety-like behavior. Notably, A2A R blockade rectified both microglia morphology in the dHIP and the lack of mPFC-dHIP synchronization, further heralding their role in cognitive function.

Adenosine A2A receptor regulation of microglia morphological remodeling-gender bias in physiology and in a model of chronic anxiety

Developmental risk factors, such as the exposure to stress or high levels of glucocorticoids (GCs), may contribute to the pathogenesis of anxiety disorders. The immunomodulatory role of GCs and the immunological fingerprint found in animals prenatally exposed to GCs point towards an interplay between the immune and the nervous systems in the etiology of these disorders. Microglia are immune cells of the brain, responsive to GCs and morphologically altered in stress-related disorders. These cells are regulated by adenosine A_2A receptors, which are also involved in the pathophysiology of anxiety. We now compare animal behavior and microglia morphology in males and females prenatally exposed to the GC dexamethasone. We report that prenatal exposure to dexamethasone is associated with a gender-specific remodeling of microglial cell processes in the prefrontal cortex: males show a hyper-ramification and increased length whereas females exhibit a decrease in the number and in the length of microglia processes. Microglial cells re-organization responded in a gender-specific manner to the chronic treatment with a selective adenosine A_2A receptor antagonist, which was able to ameliorate microglial processes alterations and anxiety behavior in males, but not in females.

Metyrapone prevents brain damage induced by status epilepticus in the rat lithium-pilocarpine model

The status epilepticus (SE) induced by lithium-pilocarpine is a well characterized rodent model of the human temporal lobe epilepsy (TLE) which is accompanied by severe brain damage. Stress and glucocorticoids markedly contribute to exacerbate neuronal damage induced by seizures but the underlying mechanisms are poorly understood. Herein we sought to investigate whether a single administration of metyrapone (150 mg/kg, i.p.), an 11β-hydroxylase inhibitor, enzyme involved in the peripheral and central synthesis of corticosteroids, had neuroprotective properties in this model. Two experiments were carried out. In exp. 1, metyrapone was administered 3 h before pilocarpine injection whereas in exp. 2, metyrapone administration took place at the onset of the SE. In both experiments, 3 days after the insult, brain metabolism was assessed by in vivo 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG) positron emission tomography (PET). Brains were processed for analyses of markers of hippocampal integrity (Nissl staining), neurodegeneration (Fluoro-Jade C), astrogliosis (glial fibrillary acidic protein (GFAP) immunohistochemistry) and, for a marker of activated microglia by in vitro autoradiography with the TSPO (18 kDa translocator protein) radioligand [¹⁸F]GE180. The SE resulted in a consistent hypometabolism in hippocampus, cortex and striatum and neuronal damage, hippocampal neurodegeneration, neuronal death and gliosis. Interestingly, metyrapone had neuroprotective effects when administered before, but not after the insult. In summary, we conclude that metyrapone administration prior but not after the SE protected from brain damage induced by SE in the lithium-pilocarpine model. Therefore, it seems that the effect of metyrapone is preventive in nature and likely related to its antiseizure properties.

The impact of chronic stress on the rat brain lipidome

Chronic stress is a major risk factor for several human disorders that affect modern societies. The brain is a key target of chronic stress. In fact, there is growing evidence indicating that exposure to stress affects learning and memory, decision making and emotional responses, and may even predispose for pathological processes, such as Alzheimer's disease and depression. Lipids are a major constituent of the brain and specifically signaling lipids have been shown to regulate brain function. Here, we used a mass spectrometry-based lipidomic approach to evaluate the impact of a chronic unpredictable stress (CUS) paradigm on the rat brain in a region-specific manner. We found that the prefrontal cortex (PFC) was the area with the highest degree of changes induced by chronic stress. Although the hippocampus presented relevant lipidomic changes, the amygdala and, to a greater extent, the cerebellum presented few lipid changes upon chronic stress exposure. The sphingolipid and phospholipid metabolism were profoundly affected, showing an increase in ceramide (Cer) and a decrease in sphingomyelin (SM) and dihydrosphingomyelin (dhSM) levels, and a decrease in phosphatidylethanolamine (PE) and ether phosphatidylcholine (PCe) and increase in lysophosphatidylethanolamine (LPE) levels, respectively. Furthermore, the fatty-acyl profile of phospholipids and diacylglycerol revealed that chronic stressed rats had higher 38 carbon(38C)-lipid levels in the hippocampus and reduced 36C-lipid levels in the PFC. Finally, lysophosphatidylcholine (LPC) levels in the PFC were found to be correlated with blood corticosterone (CORT) levels. In summary, lipidomic profiling of the effect of chronic stress allowed the identification of dysregulated lipid pathways, revealing putative targets for pharmacological intervention that may potentially be used to modulate stress-induced deficits.

Stress, glucocorticoid hormones, and hippocampal neural progenitor cells: implications to mood disorders

The hypothalamic-pituitary-adrenal (HPA) axis and its end-effectors glucocorticoid hormones play central roles in the adaptive response to numerous stressors that can be either internal or external. Thus, this system has a strong impact on the brain hippocampus and its major functions, such as cognition, memory as well as behavior, and mood. The hippocampal area of the adult brain contains neural stem cells or more committed neural progenitor cells, which retain throughout the human life the ability of self-renewal and to differentiate into multiple neural cell lineages, such as neurons, astrocytes, and oligodendrocytes. Importantly, these characteristic cells contribute significantly to the above-indicated functions of the hippocampus, while various stressors and glucocorticoids influence proliferation, differentiation, and fate of these cells. This review offers an overview of the current understanding on the interactions between the HPA axis/glucocorticoid stress-responsive system and hippocampal neural progenitor cells by focusing on the actions of glucocorticoids. Also addressed is a further discussion on the implications of such interactions to the pathophysiology of mood disorders.

The place of corticosteroids in migraine attack management: A 65-year systematic review with pooled analysis and critical appraisal

BACKGROUND AND OBJECTIVES

Headaches recur in up to 87% of migraine patients visiting the emergency department (ED), making ED recidivism a management challenge. We aimed herein to determine the role of corticosteroids in the acute management of migraine in the ED and outpatient care.

METHODS

Advanced search strategies employing PubMed/MEDLINE, Web of Science, and Cochrane Library databases inclusive of a relevant gray literature search was employed for Clinical Studies and Systematic Reviews by combining the terms "migraine" and "corticosteroids" spanning all previous years since the production of synthetic corticosteroids ca. 1950 until August 30, 2014. Methods were in accordance with MOOSE guidelines.

RESULTS

Twenty-five studies (n = 3989, median age 37.5 years, interquartile range or IQR 35-41 years; median male:female ratio 1:4.23, IQR 1:2.1-6.14; 52% ED-based, 56% randomized-controlled) and four systematic reviews were included. International Classification of Headache Disorders criteria were applied in 64%. Nineteen studies (76%) indicated observed outcome differences favoring benefits of corticosteroids, while six (24%) studies indicated non-inferior outcomes for corticosteroids. Median absolute risk reduction was 30% (range 6%-48.2%), and 11% (6%-48.6%) for 24-, and 72-hour headache recurrence, respectively. Parenteral dexamethasone was the most commonly (56%) administered steroid, at a median single dose of 10 mg (range 4-24 mg). All meta-analyses revealed efficacy of adjuvant corticosteroids to various abortive medications-indicating generalizability. Adverse effects were tolerable. Higher disability, status migrainosus, incomplete pain relief, and previous history of headache recurrence predicted outcome favorability.

CONCLUSIONS

Our literature review suggests that with corticosteroid treatment, recurrent headaches become milder than pretreated headaches and later respond to nonsteroidal therapy. Single-dose intravenous dexamethasone is a reasonable option for managing resistant, severe, or prolonged migraine attacks.

Different patterns of morphological changes in the hippocampus and dentate gyrus accompany the differential expression of disability following nerve injury

Physical and psychological trauma which results in mood disorders and the disruption of complex behaviours is associated with reductions in hippocampal volume. Clinical evaluation of neuropathic pain reveals mood and behavioural change in a significant number of patients. A rat model of neuropathic injury results in complex behavioural changes in a subpopulation (~30%) of injured rats; these changes are co-morbid with a range of other 'disabilities'. The specific objective of this study was to determine in rats the morphology of the hippocampus and dentate gyrus in individuals with and without complex behavioural disruptions following a constriction injury of the sciatic nerve, and to determine whether rats that develop disabilities following nerve injury have a reduced hippocampal volume compared with injured rats with no disabilities. The social behaviours of nerve-injured rats were evaluated before and after nerve injury. The morphology of the hippocampus of rats with and without behavioural disruptions was compared in serial histological sections. Single-housing and repeated social-interaction testing had no effect on the morphology of either the hippocampus or the dentate gyrus. Rats with transient or ongoing disability identified by behavioural disruption following sciatic nerve injury, show bilateral reductions in hippocampal volume, and lateralised reduction in the dentate gyrus (left side). Disabled rats display a combination of behavioural and physiological changes, which resemble many of the criteria used clinically to diagnose mood disorders. They also show reductions in the volume of the hippocampus similar to people with clinically diagnosed mood disorders. The sciatic nerve injury model reveals a similarity to the human neuropathic pain presentation presenting an anatomically specific focus for the investigation of the neural mechanisms underpinning the co-morbidity of chronic pain and mood disorder.

Relationships between lead biomarkers and diurnal salivary cortisol indices in pregnant women from Mexico City: a cross-sectional study

BACKGROUND

Lead (Pb) exposure during pregnancy may increase the risk of adverse maternal, infant, or childhood health outcomes by interfering with hypothalamic-pituitary-adrenal-axis function. We examined relationships between maternal blood or bone Pb concentrations and features of diurnal cortisol profiles in 936 pregnant women from Mexico City.

METHODS

From 2007-11 we recruited women from hospitals/clinics affiliated with the Mexican Social Security System. Pb was measured in blood (BPb) during the second trimester and in mothers' tibia and patella 1-month postpartum. We characterized maternal HPA-axis function using 10 timed salivary cortisol measurements collected over 2-days (mean: 19.7, range: 14-35 weeks gestation). We used linear mixed models to examine the relationship between Pb biomarkers and cortisol area under the curve (AUC), awakening response (CAR), and diurnal slope.

RESULTS

After adjustment for confounders, women in the highest quintile of BPb concentrations had a reduced CAR (Ratio: -13%; Confidence Interval [CI]: -24, 1, p-value for trend < 0.05) compared to women in the lowest quintile. Tibia/patella Pb concentrations were not associated with CAR, but diurnal cortisol slopes were suggestively flatter among women in the highest patella Pb quantile compared to women in the lowest quantile (Ratio: 14%; CI: -2, 33). BPb and bone Pb concentrations were not associated with cortisol AUC.

CONCLUSIONS

Concurrent blood Pb levels were associated with cortisol awakening response in these pregnant women and this might explain adverse health outcomes associated with Pb. Further research is needed to confirm these results and determine if other environmental chemicals disrupt hypothalamic-pituitary-adrenal-axis function during pregnancy.

A novel point mutation of the human glucocorticoid receptor gene causes primary generalized glucocorticoid resistance through impaired interaction with the LXXLL motif of the p160 coactivators: dissociation of the transactivating and transreppressive activities

CONTEXT

Primary generalized glucocorticoid resistance is a rare genetic disorder characterized by generalized, partial, target-tissue insensitivity to glucocorticoids. The molecular basis of the condition has been ascribed to inactivating mutations in the human glucocorticoid receptor (hGR) gene.

OBJECTIVE

The objective of the study was to present three new cases caused by a novel mutation in the hGR gene and to delineate the molecular mechanisms through which the mutant receptor impairs glucocorticoid signal transduction.

DESIGN AND RESULTS

The index case (father) and his two daughters presented with increased urinary free cortisol excretion and resistance of the hypothalamic-pituitary-adrenal axis to dexamethasone suppression in the absence of clinical manifestations suggestive of Cushing syndrome. All subjects harbored a novel, heterozygous, point mutation (T→G) at nucleotide position 1724 of the hGR gene, which resulted in substitution of valine by glycine at amino acid 575 of the receptor. Compared with the wild-type receptor, the hGRαV575G demonstrated a significant (33%) reduction in its ability to transactivate the mouse mammary tumor virus promoter in response to dexamethasone, a 50% decrease in its affinity for the ligand, and a 2.5-fold delay in nuclear translocation. Although it did not exert a dominant negative effect on the wild-type receptor and preserved its ability to bind to DNA, hGRαV575G displayed significantly enhanced (∼80%) ability to transrepress the nuclear factor-κΒ signaling pathway. Finally, the mutant receptor hGRαV575G demonstrated impaired interaction with the LXXLL motif of the glucocorticoid receptor-interacting protein 1 coactivator in vitro and in computer-based structural simulation via its defective activation function-2 (AF-2) domain.

CONCLUSIONS

The natural mutant receptor hGRαV575G causes primary generalized glucocorticoid resistance by affecting multiple steps in the glucocorticoid signaling cascade, including the affinity for the ligand, the time required for nuclear translocation, and the interaction with the glucocorticoid-interacting protein-1 coactivator.

Steroids and injury to the developing brain: net harm or net benefit?

Deleterious effects result from both glucocorticoid insufficiency and excess glucocorticoid tissue exposure in the developing brain. Accumulating evidence suggests a net benefit of postnatal glucocorticoid therapy when administered shortly after the first week of life to premature infants with early and persistent pulmonary dysfunction, particularly in those with evidence of relative adrenal insufficiency. The decision to treat with steroids should ensure maximum respiratory benefit at the lowest possible neurologic risk, while avoiding serious systemic complications. Ongoing clinical trials must validate this approach.

Forced swim test induces divergent global transcriptomic alterations in the hippocampus of high versus low novelty-seeker rats

BACKGROUND

Many neuropsychiatric disorders, including stress-related mood disorders, are complex multi-parametric syndromes. Susceptibility to stress and depression is individually different. The best animal model of individual differences that can be used to study the neurobiology of affect regards spontaneous reactions to novelty. Experimentally, when naive rats are exposed to the stress of a novel environment, they display a highly variable exploratory activity and are classified as high or low responders (HR or LR, respectively). Importantly, HR and LR rats do not seem to exhibit a substantial differentiation in relation to their 'depressive-like' status in the forced swim test (FST), a widely used animal model of 'behavioral despair'. In the present study, we investigated whether FST exposure would be accompanied by phenotype-dependent differences in hippocampal gene expression in HR and LR rats.

RESULTS

HR and LR rats present a distinct behavioral pattern in the pre-test session but develop comparable depressive-like status in the second FST session. At 24 h following the second FST session, HR and LR rats (stressed and unstressed controls) were sacrificed and hippocampal samples were independently analyzed on whole rat genome Illumina arrays. Functional analysis into pathways and networks was performed using Ingenuity Pathway Analysis (IPA) software. Notably, hippocampal gene expression signatures between HR and LR rats were markedly divergent, despite their comparable depressive-like status in the FST. These molecular differences are reflected in both the extent of transcriptional remodeling (number of significantly changed genes) and the types of molecular pathways affected following FST exposure. A markedly higher number of genes (i.e., 2.28-fold) were statistically significantly changed following FST in LR rats, as compared to their HR counterparts. Notably, genes associated with neurogenesis and synaptic plasticity were induced in the hippocampus of LR rats in response to FST, whereas in HR rats, FST induced pathways directly or indirectly associated with induction of apoptotic mechanisms.

CONCLUSIONS

The markedly divergent gene expression signatures exposed herein support the notion that the hippocampus of HR and LR rats undergoes distinct transcriptional remodeling in response to the same stress regimen, thus yielding a different FST-related 'endophenotype', despite the seemingly similar depressive-like phenotype.

Nonhuman primate models of depression: effects of early experience and stress

Depression causes significant morbidity in the human population. The Diathesis-Stress/Two-Hit model of depression hypothesizes that stress interacts with underlying (probably genetic) predispositions to produce a central nervous system that is primed to express psychopathology when confronted with stressful experiences later in life. Nonhuman primate (NHP) studies have been extensively utilized to test this model. NHPs are especially useful for studying effects of early experience, because many aspects of NHP infancy are similar to humans, whereas development occurs at an accelerated rate and therefore allows for more rapid assessment of experimental variables. In addition, the ability to manipulate putative risk factors, including introducing experimental stress during development, allows inference of causality not possible with human studies. This manuscript reviews experimental paradigms that have been utilized to model early adverse experience in NHPs, including peer-rearing, maternal separation, and variable foraging. It also provides examples of how this model has been used to investigate the effects of early experience on later neurobiology, physiology, and behavior associated with depression. We conclude that the NHP offers an excellent model to research mechanisms contributing to the Diathesis-Stress/Two-Hit model of depression.

Spatial memory impairments in a prediabetic rat model

Diabetes is associated with an increased risk for brain disorders, namely cognitive impairments associated with hippocampal dysfunction underlying diabetic encephalopathy. However, the impact of a prediabetic state on cognitive function is unknown. Therefore, we now investigated whether spatial learning and memory deficits and the underlying hippocampal dysfunction were already present in a prediabetic animal model. Adult Wistar rats drinking high-sucrose (HSu) diet (35% sucrose solution during 9 weeks) were compared to controls' drinking water. HSu rats exhibited fasting normoglycemia accompanied by hyperinsulinemia and hypertriglyceridemia in the fed state, and insulin resistance with impaired glucose tolerance confirming them as a prediabetic rodent model. HSu rats displayed a poorer performance in hippocampal-dependent short- and long-term spatial memory performance, assessed with the modified Y-maze and Morris water maze tasks, respectively; this was accompanied by a reduction of insulin receptor-β density with normal levels of insulin receptor substrate-1 pSer636/639, and decreased hippocampal glucocorticoid receptor levels without changes of the plasma corticosterone levels. Importantly, HSu animals exhibited increased hippocampal levels of AMPA and NMDA receptor subunits GluA1 and GLUN1, respectively, whereas the levels of protein markers related to nerve terminals (synaptophysin) and oxidative stress/inflammation (HNE, RAGE, TNF-α) remained unaltered. These findings indicate that 9 weeks of sucrose consumption resulted in a metabolic condition suggestive of a prediabetic state, which translated into short- and long-term spatial memory deficits accompanied by alterations in hippocampal glutamatergic neurotransmission and abnormal glucocorticoid signaling.

Increased neuroplasticity may protect against cardiovascular disease

Neuroplasticity refers to the capacity of the nervous system to modify its organization such that the brain can be shaped by environmental input. Individuals exhibit different degrees of neuroplasticity because of their different courses of growth. Neuroplasticity may thus play a role in individual differences in the treatment of neuropsychiatric diseases. The nervous system monitors and coordinates internal organ function. Thus neuroplasticity may also be associated with the pathogenesis and the treatment of some other diseases besides neuropsychiatric diseases. The cardiovascular system is controlled by the nervous system, mainly by the autonomic nervous system. Stress may lead to depression and cardiovascular disease (CVD). CVD is associated with depression, which is a disorder of decreased neuroplasticity. And the mechanisms of depression and CVD are related. So we conclude that decreased neuroplasticity causes the coexistence of depression with CVD, and increased neuroplasticity may be beneficial against the development of CVD. This theory provides another angle that can explain some of the reported phenomena related to CVD and neuropsychiatry and provide a potential treatment to protect against CVD.

Expression profiles of the nuclear receptors and their transcriptional coregulators during differentiation of neural stem cells

Neural stem cells (NSCs) are pluripotent precursors with the ability to proliferate and differentiate into 3 neural cell lineages, neurons, astrocytes and oligodendrocytes. Elucidation of the mechanisms underlying these biologic processes is essential for understanding both physiologic and pathologic neural development and regeneration after injury. Nuclear hormone receptors (NRs) and their transcriptional coregulators also play crucial roles in neural development, functions and fate. To identify key NRs and their transcriptional regulators in NSC differentiation, we examined mRNA expression of 49 NRs and many of their coregulators during differentiation (0-5 days) of mouse embryonic NSCs induced by withdrawal of fibroblast growth factor-2 (FGF2). 37 out of 49 NRs were expressed in NSCs before induction of differentiation, while receptors known to play major roles in neural development, such as THRα, RXRs, RORs, TRs, and COUP-TFs, were highly expressed. CAR, which plays important roles in xenobiotic metabolism, was also highly expressed. FGF2 withdrawal induced mRNA expression of RORγ, RXRγ, and MR by over 20-fold. Most of the transcriptional coregulators examined were expressed basally and throughout differentiation without major changes, while FGF2 withdrawal strongly induced mRNA expression of several histone deacetylases (HDACs), including HDAC11. Dexamethasone and aldosterone, respectively a synthetic glucocorticoid and natural mineralocorticoid, increased NSC numbers and induced differentiation into neurons and astrocytes. These results indicate that the NRs and their coregulators are present and/or change their expression during NSC differentiation, suggesting that they may influence development of the central nervous system in the absence or presence of their ligands.

Stress Transiently Affects Pavlovian-to-Instrumental Transfer

Stress has a strong impact in the brain, impairing decision-making processes as a result of changes in circuits involving the prefrontal and orbitofrontal cortices and the striatum. Given that these same circuits are key for action control and outcome encoding, we hypothesized that adaptive responses to which these are essential functions, could also be targeted by stress. To test this hypothesis we herein assessed the impact of chronic stress in a Pavlovian-to-instrumental transfer (PIT) paradigm, a model of an adaptive response in which a previously conditioned cue biases an instrumental goal-directed action. Data reveals that rats submitted to chronic unpredictable stress did not display deficits in pavlovian conditioning nor on the learning of the instrumental task, but were impaired in PIT; importantly, after a stress-free period the PIT deficits were no longer observed. These results are relevant to understand how stress biases multiple incentive processes that contribute to instrumental performance.

New Neurons in Aging Brains: Molecular Control by Small Non-Coding RNAs

Adult neurogenesis generates functional neurons from neural stem cells present in specific brain regions. It is largely confined to two main regions: the subventricular zone of the lateral ventricle, and the subgranular zone of the dentate gyrus (DG), in the hippocampus. With age, the function of the hippocampus and particularly the DG is impaired. For instance, adult neurogenesis is decreased with aging, in both proliferating and differentiation of newborn cells, while in parallel an age-associated decline in cognitive performance is often seen. Surprisingly, the synaptogenic potential of adult-born neurons is only marginally influenced by aging. Therefore, although proliferation, differentiation, and synaptogenesis of adult-born new neurons in the DG are closely related to each other, they are differentially affected by aging. In this review we discuss the crucial roles of a novel class of recently discovered modulators of gene expression, the small non-coding RNAs, in the regulation of adult neurogenesis. Multiple small non-coding RNAs are differentially expressed in the hippocampus. In particular a subgroup of the small non-coding RNAs, the microRNAs, fine-tune the progression of adult neurogenesis. This makes small non-coding RNAs appealing candidates to orchestrate the functional alterations in adult neurogenesis and cognition associated with aging. Finally, we summarize observations that link changes in circulating levels of steroid hormones with alterations in adult neurogenesis, cognitive decline, and vulnerability to psychopathology in advanced age, and discuss a potential interplay between steroid hormone receptors and microRNAs in cognitive decline in aging individuals.

BAG-1 diversely affects steroid receptor activity

Part of the cellular and physiological functions of BAG-1 (Bcl-2-associated athanogene 1) has been ascribed to the ability of this hsp70 (heat-shock protein 70) co-chaperone to regulate steroid receptor activity. BAG-1 has been reported to inhibit the GR (glucocorticoid receptor) and stimulate the androgen receptor, but to leave the activity of the MR (mineralocorticoid receptor) unchanged. Given the high homology between the MR and GR, this disparity in the actions of BAG-1 is surprising. In the present study, we analysed the effect of BAG-1 on the activity of the closely related PR (progesterone receptor). Similarly to the GR, the transcriptional activity of the PR is inhibited by the long and middle isoforms of BAG-1, BAG-1L and BAG-1M, but not by the short isoform, BAG-1S. We found this inhibition to require the hsp70-binding domain of BAG-1. To shed light on the mechanisms that could explain BAG-1's differential actions on steroid receptors, we tested the binding of BAG-1M to the PR. Mutational analyses of the PR and BAG-1M revealed that the mode of interaction and BAG-1M-mediated inhibition of the PR differs from the reported scenario for the GR. Surprisingly, we also found binding of BAG-1M to the MR. In addition, BAG-1M was able to inhibit the transcriptional activity of the MR. These data entail a reappraisal of the physiological actions of BAG-1M on steroid receptor activity.

Opposite Effects of Cortisol on Consolidation of Temporal Sequence Memory during Waking and Sleep

Memory functions involve three stages: encoding, consolidation, and retrieval. Modulating effects of glucocorticoids (GCs) have been consistently observed for declarative memory with GCs enhancing encoding and impairing retrieval, but surprisingly, little is known on how GCs affect memory consolidation. Studies in rats suggest a beneficial effect of GCs that were administered during postlearning wake periods, whereas in humans, cortisol impaired memory consolidation when administered during postlearning sleep. These inconsistent results raise the question whether effects of GCs critically depend on the brain state during consolidation (sleep vs. wake). Here, we compare for the first time directly the effects of cortisol on memory consolidation during postlearning sleep and wakefulness in different measures of declarative memory. Cortisol (13 mg vs. placebo) was intravenously infused during a postlearning nap or a time-matched period of wakefulness after participants had encoded neutral and emotional text material. Memory for the texts was tested (a) by asking for the contents of the texts (“item” memory) and (b) for the temporal order of the contents within the texts (“relational” memory). Neither postlearning infusion of cortisol during sleep nor during wakefulness affected retention of content words of emotional or neutral texts. Critically, however, the retention of temporal order within the texts, known to rely most specifically on the hippocampus proper within the medial-temporal lobe memory system, was distinctly improved by cortisol infusion during the wake phase but impaired by cortisol during sleep. These results point toward fundamentally different mechanisms of hippocampal memory consolidation, depending on the brain state.

Mifepristone prevents stress-induced apoptosis in newborn neurons and increases AMPA receptor expression in the dentate gyrus of C57/BL6 mice

Chronic stress produces sustained elevation of corticosteroid levels, which is why it is considered one of the most potent negative regulators of adult hippocampal neurogenesis (AHN). Several mood disorders are accompanied by elevated glucocorticoid levels and have been linked to alterations in AHN, such as major depression (MD). Nevertheless, the mechanism by which acute stress affects the maturation of neural precursors in the dentate gyrus is poorly understood. We analyzed the survival and differentiation of 1 to 8 week-old cells in the dentate gyrus of female C57/BL6 mice following exposure to an acute stressor (the Porsolt or forced swimming test). Furthermore, we evaluated the effects of the glucocorticoid receptor (GR) antagonist mifepristone on the cell death induced by the Porsolt test. Forced swimming induced selective apoptotic cell death in 1 week-old cells, an effect that was abolished by pretreatment with mifepristone. Independent of its antagonism of GR, mifepristone also induced an increase in the percentage of 1 week-old cells that were AMPA⁺. We propose that the induction of AMPA receptor expression in immature cells may mediate the neuroprotective effects of mifepristone, in line with the proposed antidepressant effects of AMPA receptor potentiators.

Administration of a selective glucocorticoid antagonist attenuates electroconvulsive shock-induced retrograde amnesia

Mifepristone, a glucocorticoid and progesterone receptor antagonist, has been shown to attenuate retrograde amnesia induced by repeated electroconvulsive shocks (ECS). We examined the efficacy of CORT 108297, a selective glucocorticoid antagonist, in this regard. Adult, male, Wistar rats (n = 69) received either vehicle or CORT 108297 (1 mg/kg) 2 h before each of 5 once-daily true or sham 30 mC ECS. Recall of previous exposure to a noxious stimulus in a passive avoidance (step-through) paradigm was tested 1 day after the 5-ECS course. Analyses were conducted using recall operationalized in different ways: using the absolute final latency scores; defining adequate recall as a final latency of 30 s or greater; defining perfect recall as a final latency of 180 s; and using visual, subjective assessments of animal behavior. ECS was associated with significant impairment of recall, and this impairment was significantly attenuated by CORT 108297 on all outcome measures (with the exception of the perfect recall analyses, where outcomes narrowly missed statistical significance). In conclusion, these findings strengthen previous data from our laboratory implicating glucocorticoid mechanisms in ECS-induced retrograde amnesia. We suggest that the administration of a selective glucocorticoid receptor antagonist shortly before electroconvulsive therapy (ECT) treatments may attenuate the deleterious effect of ECT-induced acute hypercortisolemia on neural mechanisms involved in learning and memory.

Potential predictors of hippocampal atrophy in Alzheimer's disease

The hippocampus is a vulnerable and plastic brain structure that is damaged by a variety of stimuli, e.g. hypoxia, hypoperfusion, hypoglycaemia, stress and seizures. Alzheimer's disease is a common and important disorder in which hippocampal atrophy is reported. Indeed, the available evidence suggests that hippocampal atrophy is the starting point of the pathogenesis of Alzheimer's disease and a significant number of patients with hippocampal atrophy will develop Alzheimer's disease. Studies indicate that hippocampal atrophy has functional consequences, e.g. cognitive impairment. Deposition of tau protein, formation of neurofibrillary tangles and accumulation of β-amyloid (Aβ) contributes to hippocampal atrophy together with damage caused by several other factors. Some of the factors associated with the development of hippocampal atrophy in Alzheimer's disease have been identified, e.g. hypertension, diabetes mellitus, hyperlipidaemia, seizures, affective disturbances and stress, and more is being learnt about other factors. Hypertension can potentially damage the hippocampus through ischaemia caused by atherosclerosis and cerebral amyloid angiopathy. Diabetes can produce hippocampal lesions via both vascular and non-vascular pathologies and can reduce the threshold for hippocampal damage. Carriers of the apolipoprotein E (ApoE)-ε4 genotype have been shown to have greater mesial temporal atrophy and poorer memory functions than non-carriers. In addition to giving rise to abnormal lipid metabolism, the ApoE-ε4 allele can affect the course of Alzheimer's disease via both Aβ-dependent and -independent pathways. Repetitive seizures can increase Aβ-peptide production and cause neurotransmission dysfunction and cytoskeletal abnormalities or a combination of these. Affective disturbances and stress are proposed to increase corticosteroid-induced hippocampal damage in many different ways. In the absence of any specific markers for predicting Alzheimer's disease progression, it seems appropriate to learn more about the various predictors of hippocampal atrophy that determine the progression of Alzheimer's disease from mild cognitive impairment (MCI), and then attempt to address these. It would be interesting to know to what extent these predictors play a role in the development of MCI or hasten the conversion of MCI to full-blown Alzheimer's disease. Finally, it would be useful to know the extent to which these predictors can worsen or aggravate existing Alzheimer's disease. Of the clinically used drugs in Alzheimer's disease, anticholinesterases have been shown to slow down the rate of progression of hippocampal atrophy. One study observed that the neuroprotective effect of these agents is possibly due to an anti-Aβ effect produced by cholinergic stimulation. Similarly, antihypertensive and antihyperglycaemic drugs (pioglitazone and insulin) have been shown to reduce the risk of Alzheimer's disease or disease progression. Currently, there are no disease-modifying therapies available for Alzheimer's disease. It has been suggested that for treatment to be most effective, the regimen must be started before significant downstream damage has occurred (i.e. before the clinical diagnosis of Alzheimer's disease, at the stage of MCI or earlier). Since the hippocampus is a plastic structure and atrophy of this structure is closely related to the pathophysiology of Alzheimer's disease, if we could control blood pressure, regulate blood sugar, treat behavioural and psychological symptoms, achieve satisfactory lipid lowering and maintain a seizure-free state in patients with Alzheimer's disease, this may not only improve disease control but could also potentially affect the rate of disease progression.

The hypothalamic-pituitary-adrenal axis and serotonin abnormalities: a selective overview for the implications of suicide prevention

Suicidal behavior and mood disorders are one of the world's largest public health problems. The biological vulnerability for these problems includes genetic factors involved in the regulation of the serotonergic system and stress system. The hypothalamic-pituitary-adrenal (HPA) axis is a neuroendocrine system that regulates the body's response to stress and has complex interactions with brain serotonergic, noradrenergic and dopaminergic systems. Corticotropin-releasing hormone and vasopressin act synergistically to stimulate the secretion of ACTH that stimulates the biosynthesis of corticosteroids such as cortisol from cholesterol. Cortisol is a major stress hormone and has effects on many tissues, including on mineralocorticoid receptors and glucocorticoid receptors in the brain. Glucocorticoids produce behavioral changes, and one important target of glucocorticoids is the hypothalamus, which is a major controlling center of the HPA axis. Stress plays a major role in the various pathophysiological processes associated with mood disorders and suicidal behavior. Serotonergic dysfunction is a well-established substrate for mood disorders and suicidal behavior. Corticosteroids may play an important role in the relationship between stress, mood changes and perhaps suicidal behavior by interacting with 5-HT1A receptors. Abnormalities in the HPA axis in response to increased levels of stress are found to be associated with a dysregulation in the serotonergic system, both in subjects with mood disorders and those who engage in suicidal behavior. HPA over-activity may be a good predictor of mood disorders and perhaps suicidal behavior via abnormalities in the serotonergic system.

Effect of treadmill exercise on blood glucose, serum corticosterone levels and glucocorticoid receptor immunoreactivity in the hippocampus in chronic diabetic rats

Abnormal excess of glucocorticoid is one of feature characteristics in type 2 diabetes. In the present study, we investigated the effect of treadmill exercise at chronic diabetic stages on glucocorticoid receptor (GR) immunoreactivity in the hippocampal CA1 region and dentate gyrus, which are very vulnerable to diabetes. For this study, we used Zucker diabetic fatty (ZDF) rats and Zucker lean control (ZLC) rats. Twenty-three-week-old ZLC and ZDF rats were put on the treadmill with or without running for 7 weeks and sacrificed at 30 weeks of age. Treadmill exercise significantly decreased diabetes-induced blood glucose and serum corticosteroid levels although they did not drop to control levels. In sedentary ZLC rats, GR immunoreactivity was detected in pyramidal cells of the CA1 region as well as in granule cells of the dentate gyrus. In the sedentary ZDF rats, GR immunoreactivity was significantly increased in these regions. However, treadmill exercise significantly decreased GR immunoreactivity in these regions. These results indicate that treadmill exercise in chronic diabetic rats significantly decreased GR immunoreactivity in the hippocampal CA1 region and dentate gyrus, although blood glucose and serum corticosteroid levels did not fully recover to normal state.

How antidepressant drugs act: A primer on neuroplasticity as the eventual mediator of antidepressant efficacy

Depression is conventionally viewed as a state of chemical imbalance, and antidepressants are suggested to act through increasing monoaminergic neurotransmission. These views are currently considered simplistic. This article examines the animal and human literature on the neurohistological mechanisms underlying stress, depression and antidepressant treatment. Pathological stress and depression are associated with changes such as loss of dendritic spines, shrinkage of the dendritic tree and loss of synapses in the hippocampus and prefrontal cortex. There is also a decrease in glia. Apoptosis may occur under extreme circumstances. In contrast, there is increased dendritic arborization and synaptogenesis in the amygdala. Antidepressant treatment protects against and even reverses some but not all of these stress-induced neurohistological changes. Pathological stress results in an aberrant neuroplasticity response characterized by abnormally increased activity in the amygdala and by impaired functioning of the hippocampus, prefrontal cortex and downstream structures. This aberrant neuroplasticity response directly explains most of the clinical symptoms of depression. Antidepressant treatment protects against stress-induced pathoplastic neurohistological and neurocognitive changes. Antidepressant treatment also restores functional neuroplasticity in stressed organisms and, thereby, presumably, facilitates re-adaptation through learning and memory mechanisms. Thus, the stress-depression syndrome and the therapeutic and prophylactic efficacy of antidepressant treatments can be explained through a hardwiring analogy. In this context, glutamate is an important neurotransmitter.

Interaction of childhood stress with hippocampus and prefrontal cortex volume reduction in major depression

Early emotional stress is associated with a life-long burden of risk for later depression and stressful life events contribute to the development of depressive episodes. In this study we investigated whether childhood stress is associated with structural brain alterations in patients with major depression (MD). Forty-three patients with MD and 44 age as well as gender matched healthy control subjects were investigated using high-resolution magnetic resonance imaging (MRI). Region of interest analysis of the hippocampus, whole brain voxel-based morphometry (VBM) and assessment of childhood stress was carried out. Significantly smaller hippocampal white matter and prefrontal gray matter volume was observed in patients with MD compared to healthy controls. In particular left hippocampal white matter was smaller in patients, who had emotional childhood neglect, compared to those without neglect. For male patients this effect was seen in the left and right hippocampus. Moreover, physical neglect during childhood affected prefrontal gray matter volume in healthy subjects. Both emotional neglect and brain structural abnormalities predicted cumulative illness duration and there was a significant interaction between emotional neglect and prefrontal volumes as well as hippocampal white matter on the illness course. Childhood neglect resulted in hippocampal white matter changes in patients with major depression, pronounced at the left side and in males. Most interestingly, childhood stress and brain structure volumes independently predicted cumulative illness course. Subjects with both, structural brain changes and childhood emotional neglect seem to be at a very high risk to develop a more severe illness course.

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.

Is bigger always better? A critical appraisal of the use of volumetric analysis in the study of the hippocampus

A well-developed spatial memory is important for many animals, but appears especially important for scatter-hoarding species. Consequently, the scatter-hoarding system provides an excellent paradigm in which to study the integrative aspects of memory use within an ecological and evolutionary framework. One of the main tenets of this paradigm is that selection for enhanced spatial memory for cache locations should specialize the brain areas involved in memory. One such brain area is the hippocampus (Hp). Many studies have examined this adaptive specialization hypothesis, typically relating spatial memory to Hp volume. However, it is unclear how the volume of the Hp is related to its function for spatial memory. Thus, the goal of this article is to evaluate volume as a main measurement of the degree of morphological and physiological adaptation of the Hp as it relates to memory. We will briefly review the evidence for the specialization of memory in food-hoarding animals and discuss the philosophy behind volume as the main currency. We will then examine the problems associated with this approach, attempting to understand the advantages and limitations of using volume and discuss alternatives that might yield more specific hypotheses. Overall, there is strong evidence that the Hp is involved in the specialization of spatial memory in scatter-hoarding animals. However, volume may be only a coarse proxy for more relevant and subtle changes in the structure of the brain underlying changes in behaviour. To better understand the nature of this brain/memory relationship, we suggest focusing on more specific and relevant features of the Hp, such as the number or size of neurons, variation in connectivity depending on dendritic and axonal arborization and the number of synapses. These should generate more specific hypotheses derived from a solid theoretical background and should provide a better understanding of both neural mechanisms of memory and their evolution.

Exogenous corticosterone induces the expression of the clock protein, PERIOD2, in the oval nucleus of the bed nucleus of the stria terminalis and the central nucleus of the amygdala of adrenalectomized and intact rats

The cyclical expression of the clock protein PERIOD2 (PER2) in select regions of the limbic forebrain is contingent upon the rhythmic secretion of the adrenal glucocorticoid, corticosterone. Daily rhythmic PER2 expression in the oval nucleus of the bed nucleus of the stria terminalis (BNSTov) and the central nucleus of the amygdala (CEA) is abolished with the removal of the adrenal glands but restored with rhythmic hormone replacement via the drinking water at a time corresponding to the endogenous peak of circulating glucocorticoids. Here, we investigated the effects of serial or acute systemic injections of corticosterone on the expression of PER2 in the BNSTov and CEA of both adrenalectomized (ADX) and intact rats. We sought to determine whether there is a temporal window of corticosterone sensitivity by delivering the hormone at a time corresponding to trough levels of circulating glucocorticoids, at lights on. We found that daily morning injections of corticosterone induced PER2 expression in the BNSTov and CEA of ADX rats, with levels peaking 1 h after injection. In intact rats, daily morning injections significantly upregulated the expression of PER2 in the BNSTov and CEA 1 h after injection and dampened the evening peak, while a single injection abolished the rhythm of PER2 expression in the CEA but had no effect on PER2 in the BNSTov. Our findings suggest that despite the potential masking effect of signals from the light-entrained master clock, daytime chronic and acute corticosterone administration can alter the rhythmic expression of PER2 in the BNSTov and CEA, and that the response is region-specific and dependent on the duration of treatment.

Cyclin-dependent kinase 5 modulates the transcriptional activity of the mineralocorticoid receptor and regulates expression of brain-derived neurotrophic factor

Glucocorticoids, major end effectors of the stress response, play an essential role in the homeostasis of the central nervous system (CNS) and contribute to memory consolidation and emotional control through their intracellular receptors, the glucocorticoid and mineralocorticoid receptors. Cyclin-dependent kinase 5 (CDK5), on the other hand, plays important roles in the morphogenesis and functions of the central nervous system, and its aberrant activation has been associated with development of neurodegenerative disorders. We previously reported that CDK5 phosphorylated the glucocorticoid receptor and modulated its transcriptional activity. Here we found that CDK5 also regulated mineralocorticoid receptor-induced transcriptional activity by phosphorylating multiple serine and threonine residues located in its N-terminal domain through physical interaction. Aldosterone and dexamethasone, respectively, increased and suppressed mRNA/protein expression of brain-derived neurotrophic factor (BDNF) in rat cortical neuronal cells, whereas the endogenous glucocorticoid corticosterone showed a biphasic effect. CDK5 enhanced the effect of aldosterone and dexamethasone on BDNF expression. Because this neurotrophic factor plays critical roles in neuronal viability, synaptic plasticity, consolidation of memory, and emotional changes, we suggest that aberrant activation of CDK5 might influence these functions through corticosteroid receptors/BDNF.

Corticosteroids: way upstream

Studies into the mechanisms of corticosteroid action continue to be a rich bed of research, spanning the fields of neuroscience and endocrinology through to immunology and metabolism. However, the vast literature generated, in particular with respect to corticosteroid actions in the brain, tends to be contentious, with some aspects suffering from loose definitions, poorly-defined models, and appropriate dissection kits. Here, rather than presenting a comprehensive review of the subject, we aim to present a critique of key concepts that have emerged over the years so as to stimulate new thoughts in the field by identifying apparent shortcomings. This article will draw on experience and knowledge derived from studies of the neural actions of other steroid hormones, in particular estrogens, not only because there are many parallels but also because 'learning from differences' can be a fruitful approach. The core purpose of this review is to consider the mechanisms through which corticosteroids might act rapidly to alter neural signaling.

Sex-dependent alterations in response to maternal deprivation in rats

We review here our latest results regarding short- and long-term effects of a neonatal maternal deprivation (MD) stress [24h at postnatal day (PND) 9] on diverse psychoneuroimmunoendocrine parameters, pointing out the existence of numerous sexual dimorphisms. Behavioral changes observed in MD animals might be at least in part attributable to neurodevelopmental effects of MD-induced elevated corticosterone levels. Our findings of short-term effects of MD on hippocampal and cerebellar neurons and glial cells appear to support this hypothesis. However, it is important to note that these cellular effects were more marked in males than in females. Moreover, in analyzing the effects of this neonatal stress on the endocannabinoid system (hippocampal endocannabinoid levels and CB1 receptors) we have also found that males were more affected by MD. Since all these sexual dimorphisms were found at an early neonatal age (PND 13), they are attributable to organizational effects of gonadal steroids. We discuss the potential implications of the elevated corticosterone and decreased leptin levels shown by MD animals in their diverse functional alterations, including the above mentioned neural effects as well as the intriguing persistent deficit in their immunological system. We also emphasize the necessity of analyzing the important influence of sex as regards the specific consequences of early life stress.

Cortisol and 3,4-methylenedioxymethamphetamine: neurohormonal aspects of bioenergetic stress in ecstasy users

AIMS

3,4-Methylenedioxymethamphetamine (MDMA) can affect both neurotransmitter and neurohormonal activity. This review will debate the role of the metabolic activation hormone cortisol for the psychobiological effects of ecstasy/MDMA.

METHODS

The empirical literature on cortisol release following acute MDMA administration and cortisol functioning in drug-free recreational ecstasy/MDMA users will be reviewed. This will be followed by an overview of cortisol as a bioenergetic stress neurohormone, and a debate on how it could be modulating the acute and chronic psychobiological effects of MDMA.

RESULTS

Cortisol release is increased by stimulatory factors, including physical activity, thermal stress and stimulant drugs. In laboratory studies MDMA leads to an acute cortisol increase of around 150% in sedentary humans. In MDMA-using dance clubbers, the cortisol levels are increased by around 800%, possibly due to the combined factors of stimulant drug, physical exertion and psychosocial stimulation. Regular ecstasy/MDMA users also demonstrate changes in baseline cortisol levels and cortisol reactivity, with compromised hypothalamic-pituitary-adrenal activity. Nonpharmacological research has shown how cortisol is important for psychological aspects such as memory, cognition, sleep, impulsivity, depression and neuronal damage. These same functions are often impaired in recreational ecstasy/MDMA users, and cortisol may be an important modulatory co-factor.

CONCLUSIONS

The energizing hormone cortisol is involved in the psychobiology of MDMA, probably via its effects on energy metabolism. Acute cortisol release may potentiate the stimulating effects of MDMA in dance clubbers. Chronically, cortisol may contribute to the variance in functional and structural consequences of repeated ecstasy usage.

Apoptosis in subicular neurons: A comparison between suicide and Addison's disease

BACKGROUND

Stress and depression shows possible links to neuronal death in hippocampus. Subiculum plays a prominent role in limbic stress integration and direct effect of corticosteroids on subicular neurons needs to be defined to assess its subsequent impact on hippocampal plasticity.

AIM

This study was intended to assess apoptosis in subicular neurons of a young depressed suicide victim, where presumably stress induced excess of corticosteroids and a case of young Addison's disease with low level of corticosteroids.

MATERIALS AND METHOD

Both bilateral adrenal glands (Addison's) and subiculum (both cases) were initially stained with hematoxylin and eosin; subicular neurons of both cases were examined for the degree of apoptosis using 'ApopTag Kit'. Apoptotic cell counts were expressed as average number of labeled cells/mm 2 and the results were analysed statistically using a non-parametric Mann-Whitney U test.

RESULT

Apoptotic neurons were detected in the subicular region of both suicide and Addison victims, and it is statistically significant in both right and left between the cases (P < 0.05). In suicide victim, the neuronal apoptosis is considerably significant between the two hemispheres (P < 0.05), in contrast to Addison disease where the number of neuronal cell death between right and left was statistically insignificant (P > 0.05).

CONCLUSION

The present study confirms the vulnerability of the subicular neurons to apoptosis, possibly due to corticosteroids in both ends of spectrum.

Antinociception induced by chronic glucocorticoid treatment is correlated to local modulation of spinal neurotransmitter content

Background

While acute effects of stress on pain are well described, those produced by chronic stress are still a matter of dispute. Previously we demonstrated that chronic unpredictable stress results in antinociception in the tail-flick test, an effect that is mediated by increased levels of corticosteroids. In the present study, we evaluated nociception in rats after chronic treatment with corticosterone (CORT) and dexamethasone (DEX) in order to discriminate the role of each type of corticosteroid receptors in antinociception.

Results

Both experimental groups exhibited a pronounced antinociceptive effect after three weeks of treatment when compared to controls (CONT); however, at four weeks the pain threshold in CORT-treated animals returned to basal levels whereas in DEX-treated rats antinociception was maintained. In order to assess if these differences are associated with altered expression of neuropeptides involved in nociceptive transmission we evaluated the density of substance P (SP), calcitonin gene-related peptide (CGRP), somatostatin (SS) and _B2-γ-aminobutiric acid receptors (GABA_B2) expression in the spinal dorsal horn using light density measurements and stereological techniques. After three weeks of treatment the expression of CGRP in the superficial dorsal horn was significantly decreased in both CORT and DEX groups, while GABA_B2 was significantly increased; the levels of SP for both experimental groups remained unchanged at this point. At 4 weeks, CGRP and SP are reduced in DEX-treated animals and GABA_B2 unchanged, but all changes were restored to CONT levels in CORT-treated animals. The expression of SS remained unaltered throughout the experimental period.

Conclusion

These data indicate that corticosteroids modulate nociception since chronic corticosteroid treatment alters the expression of neuropeptides involved in nociceptive transmission at the spinal cord level. As previously observed in some supraspinal areas, the exclusive GR activation resulted in more profound and sustained behavioural and neurochemical changes, than the one observed with a mixed ligand of corticosteroid receptors. These results might be of relevance for the pharmacological management of certain types of chronic pain, in which corticosteroids are used as adjuvant analgesics.

Moving towards making social toxins mainstream in children's environmental health

PURPOSE OF REVIEW

Although traditional disciplinary research theory and methods have focused separately on how social and physical environmental factors affect children's health, evolving research underscores important integrated effects.

RECENT FINDINGS

This review outlines the specific reasons why social determinants should be considered mainstream in children's environmental health research with particular focus on interactive effects between social and physical hazards. These include sensitivity of overlapping physiological systems, via epigenesis, programming, and plasticity to social and physical environmental moderation that may impact health across the life span; ways in which social environmental vulnerabilities moderate the effects of physical environmental factors, providing specific examples related to respiratory health and neurodevelopment; overlapping exposure distribution profiles; and relevance to pediatric health disparities.

SUMMARY

Because of the covariance across exposures, and evidence that social stress and other environmental toxins (e.g., pollutants, tobacco smoke) may influence common physiological pathways (e.g., oxidative stress, proinflammatory immune pathways, autonomic disruption), understanding the potential synergistic effects promises to more completely inform children's environmental health risk. Although this discussion focuses around the respiratory and neurological systems, these concepts extend more broadly to children's psychological and physical development.

Glucocorticoids and lithium reciprocally regulate the proliferation of adult dentate gyrus-derived neural precursor cells through GSK-3beta and beta-catenin/TCF pathway

Adult hippocampal neurogenesis is decreased in rodent models for stress-related disorders at least partly through an elevated level of glucocorticoids. On the other hand, the mood stabilizer lithium (Li) commonly used for their treatment increases it. This effect is thought to be one of the therapeutic actions of Li, but the molecular mechanism has been poorly understood. Here we established the culture system of adult rat dentate gyrus-derived neural precursor cells (ADPs) and examined the effects of dexamethasone (DEX), an agonist of glucocorticoids receptor, and Li on ADP proliferation. It is possible for ADP to be a type 2a cell, which corresponds to the second stage in a model of four differentiation stages in adult hippocampal neural precursor cells. DEX decreased ADP proliferation, but Li did not have any effect on it. However, Li recovered ADP proliferation decreased by DEX. The recovery effect of Li was abolished by quercetin, an inhibitor of beta-catenin/TCF pathway. The intranuclear translocation of beta-catenin and expression of cyclin D1 are reciprocally regulated by DEX and Li in a way similar to proliferation. In addition, DEX increased the phosphorylation of Tyr(216), which renders glycogen synthase kinase-3beta (GSK-3beta) active on it. These results suggest that GSK-3beta and beta-catenin/TCF pathway might be important in the reciprocal effects between DEX and Li on ADP proliferation and are new targets of therapeutic agents for stress-related disorders.

The amyloidogenic potential and behavioral correlates of stress

Observations of elevated basal cortisol levels in Alzheimer's disease (AD) patients prompted the hypothesis that stress and glucocorticoids (GC) may contribute to the development and/or maintenance of AD. Consistent with that hypothesis, we show that stress and GC provoke misprocessing of amyloid precursor peptide in the rat hippocampus and prefrontal cortex, resulting in increased levels of the peptide C-terminal fragment 99 (C99), whose further proteolytic cleavage results in the generation of amyloid-beta (Abeta). We also show that exogenous Abeta can reproduce the effects of stress and GC on C99 production and that a history of stress strikingly potentiates the C99-inducing effects of Abeta and GC. Previous work has indicated a role for Abeta in disruption of synaptic function and cognitive behaviors, and AD patients reportedly show signs of heightened anxiety. Here, behavioral analysis revealed that like stress and GC, Abeta administration causes spatial memory deficits that are exacerbated by stress and GC; additionally, Abeta, stress and GC induced a state of hyperanxiety. Given that the intrinsic properties of C99 and Abeta include neuroendangerment and behavioral impairment, our findings suggest a causal role for stress and GC in the etiopathogenesis of AD, and demonstrate that stressful life events and GC therapy can have a cumulative impact on the course of AD development and progression.