Effects of corticosterone treatment and rehabilitation on the hippocampal formation of neonatal and adult rats. An unbiased stereological study

Social isolation during adolescence differentially affects spatial learning in adult male and female mice

Social isolation is a risk factor for cognitive impairment. Adolescents may be particularly vulnerable to these effects, because they are in a critical period of development marked by significant physical, hormonal, and social changes. However, it is unclear if the effects of social isolation on learning and memory are similar in both sexes or if they persist into adulthood after a period of recovery. We socially isolated male and female 129Sv/Ev mice throughout adolescence (postnatal days 29-56), provided a 2-week resocialization recovery period, and then tested spatial learning and cognitive flexibility in the active place avoidance task. After behavioral testing, mice were injected with 5'-bromo-2'-deoxyuridine (BrdU) so that lasting effects of social isolation on cell proliferation in the dentate gyrus could be examined. Tissue was also stained for doublecortin (DCX). We found that in males, isolation led to a modest impairment in the rate of initial spatial learning, whereas in females, initial learning was unaffected. However, when the location of the shock zone was switched during the conflict variant of the task, cognitive flexibility was impaired in females only. Similarly, social isolation reduced cell proliferation and the number of immature neurons in the ventral dentate gyrus only in females. Together, these findings indicate that social isolation during adolescence differentially impairs spatial processing in males and females, with effects that persist into adulthood.

Neurochemical Anatomy of Cushing's Syndrome

The neurochemical anatomy underlying Cushing's syndrome is examined for regional brain metabolism as well as neurotransmitter levels and receptor binding of biogenic amines and amino acids. Preliminary studies generally indicate that glucose uptake, blood flow, and activation on fMRI scans decreased in neocortical areas and increased in subcortical areas of patients with Cushing's syndrome or disease. Glucocorticoid-mediated increases in hippocampal metabolism occurred despite in vitro evidence of glucocorticoid-induced decreases in glucose uptake or consumption, indicating that in vivo increases are the result of indirect, compensatory, or preliminary responses. In animal studies, glucocorticoid administration decreased 5HT levels and 5HT1A receptor binding in several brain regions while adrenalectomy increased such binding. Region-specific effects were also obtained in regard to the dopaminergic system, with predominant actions of glucocorticoid-induced potentiation of reuptake blockers and releasing agents. More in-depth neuroanatomical analyses are warranted of these and amino acid-related neurotransmission.

The Development of Stress Reactivity and Regulation in Children and Adolescents

Adversity experienced in early life can have detrimental effects on physical and mental health. One pathway in which these effects occur is through the hypothalamic-pituitary-adrenal (HPA) axis, a key physiological stress-mediating system. In this review, we discuss the theoretical perspectives that guide stress reactivity and regulation research, the anatomy and physiology of the axis, developmental changes in the axis and its regulation, brain systems regulating stress, the role of genetic and epigenetics variation in axis development, sensitive periods in stress system calibration, the social regulation of stress (i.e., social buffering), and emerging research areas in the study of stress physiology and development. Understanding the development of stress reactivity and regulation is crucial for uncovering how early adverse experiences influence mental and physical health.

Corticosterone effects on postnatal cerebellar development in mice

Glucocorticoids administered early in infancy can affect the architectonic organization of brain structures, particularly those with a postnatal development and resulting in long-term deficits of neuromotor function and cognition. The present study was undertaken to study the effects of daily corticosterone (CORT) injections at a pharmacological dose from postnatal days 8-15 on cerebellar and hippocampal development in mouse pups. Gene expression status for trophic factors involved in synaptic development and function as well as measures of layer thickness associated with cytochrome oxidase labelling were analyzed in the hippocampus, hypothalamus, and specific cerebellar lobules involved in motor control. Repeated CORT injections dysregulated the HPA axis with increased Crh and Nr3c1 mRNA levels in the hypothalamus and a resulting higher serum corticosterone level. The CORT treatment altered the morphology of the hippocampus and down-regulated gene transcription for corticotropin-releasing hormone (Crh) and its type-1 receptor (Crhr1), glucocorticoid receptor (Nr3c1), and brain-derived neurotrophic factor Bdnf and its receptor Ntrk2 (neurotrophic receptor tyrosine kinase 2). Similar mRNA expression decreases were found in the cerebellum for Crhr1, Crhr2, Nr3c1, and Grid2 (glutamatergic δ2 receptor). Morphological alterations and metabolic activity variations were observed in specific cerebellar lobules involved in motor control. The paramedian lobule, normally characterized by mitotic activity in the external germinative layer during the second postnatal week, was atrophic but metabolically hyperactive in its granule cell and molecular layers. On the contrary, lobules with an earlier cell proliferation displayed neurogenesis but a hypoactivated granule cell layer, suggesting a developmental delay in synaptogenesis. The results indicate that glucocorticoid, administered daily during the second postnatal week modulated the developmental programming of the hippocampus and cerebellum. These growth and metabolic alterations may lead possibly to morphological and functional changes later in life.

Acute or Chronic Exposure to Corticosterone Promotes Wakefulness in Mice

Elevated glucocorticoid levels triggered by stress potentially contribute to sleep disturbances in stress-induced depression. However, sleep changes in response to elevated corticosterone (CORT), the major glucocorticoid in rodents, remain unclear. Here, we investigated the effects of acute or chronic CORT administration on sleep using electroencephalogram (EEG) and electromyography (EMG) recordings in freely moving mice. Acute CORT exposure rapidly promoted wakefulness, marked by increased episodes and enhanced EEG delta power, while simultaneously suppressing rapid eye movement (REM) and non-rapid eye movement (NREM) sleep, with the latter marked by decreased mean duration and reduced delta power. Prolonged 28-day CORT exposure led to excessive wakefulness and REM sleep, characterized by higher episodes, and decreased NREM sleep, characterized by higher episodes and reduced mean duration. EEG theta activity during REM sleep and delta activity during NREM sleep were attenuated following 28-day CORT exposure. These effects persisted, except for REM sleep amounts, even 7 days after the drug withdrawal. Elevated plasma CORT levels and depressive phenotypes were identified and correlated with observed sleep changes during and after administration. Fos expression significantly increased in the lateral habenula, lateral hypothalamus, and ventral tegmental area following acute or chronic CORT treatment. Our findings demonstrate that CORT exposure enhanced wakefulness, suppressed and fragmented NREM sleep, and altered EEG activity across all stages. This study illuminates sleep alterations during short or extended periods of heightened CORT levels in mice, providing a neural link connecting insomnia and depression.

Acute and long-term effects of adolescence stress exposure on rodent adult hippocampal neurogenesis, cognition, and behaviour

Adolescence represents a critical period for brain and behavioural health and characterised by the onset of mood, psychotic and anxiety disorders. In rodents, neurogenesis is very active during adolescence, when is particularly vulnerable to stress. Whether stress-related neurogenesis changes influence adolescence onset of psychiatric symptoms remains largely unknown. A systematic review was conducted on studies investigating changes in hippocampal neurogenesis and neuroplasticity, hippocampal-dependent cognitive functions, and behaviour, occurring after adolescence stress exposure in mice both acutely (at post-natal days 21-65) and in adulthood. A total of 37 studies were identified in the literature. Seven studies showed reduced hippocampal cell proliferation, and out of those two reported increased depressive-like behaviours, in adolescent rodents exposed to stress. Three studies reported a reduction in the number of new-born neurons, which however were not associated with changes in cognition or behaviour. Sixteen studies showed acutely reduced hippocampal neuroplasticity, including pre- and post-synaptic plasticity markers, dendritic spine length and density, and long-term potentiation after stress exposure. Cognitive impairments and depressive-like behaviours were reported by 11 of the 16 studies. Among studies who looked at adolescence stress exposure effects into adulthood, seven showed that the negative effects of stress observed during adolescence on either cell proliferation or hippocampal neuroplasticity, cognitive deficits and depressive-like behaviour, had variable impact in adulthood. Treating adolescent mice with antidepressants, glutamate receptor inhibitors, glucocorticoid antagonists, or healthy diet enriched in omega-3 fatty acids and vitamin A, prevented or reversed those detrimental changes. Future research should investigate the translational value of these preclinical findings. Developing novel tools for measuring hippocampal neurogenesis in live humans, would allow assessing neurogenic changes following stress exposure, investigating relationships with psychiatric symptom onset, and identifying effects of therapeutic interventions.

An evolutionary perspective on stress responses, damage and repair

Variation in stress responses has been investigated in relation to environmental factors, species ecology, life history and fitness. Moreover, mechanistic studies have unravelled molecular mechanisms of how acute and chronic stress responses cause physiological impacts ('damage'), and how this damage can be repaired. However, it is not yet understood how the fitness effects of damage and repair influence stress response evolution. Here we study the evolution of hormone levels as a function of stressor occurrence, damage and the efficiency of repair. We hypothesise that the evolution of stress responses depends on the fitness consequences of damage and the ability to repair that damage. To obtain some general insights, we model a simplified scenario in which an organism repeatedly encounters a stressor with a certain frequency and predictability (temporal autocorrelation). The organism can defend itself by mounting a stress response (elevated hormone level), but this causes damage that takes time to repair. We identify optimal strategies in this scenario and then investigate how those strategies respond to acute and chronic exposures to the stressor. We find that for higher repair rates, baseline and peak hormone levels are higher. This typically means that the organism experiences higher levels of damage, which it can afford because that damage is repaired more quickly, but for very high repair rates the damage does not build up. With increasing predictability of the stressor, stress responses are sustained for longer, because the animal expects the stressor to persist, and thus damage builds up. This can result in very high (and potentially fatal) levels of damage when organisms are exposed to chronic stressors to which they are not evolutionarily adapted. Overall, our results highlight that at least three factors need to be considered jointly to advance our understanding of how stress physiology has evolved: (i) temporal dynamics of stressor occurrence; (ii) relative mortality risk imposed by the stressor itself versus damage caused by the stress response; and (iii) the efficiency of repair mechanisms.

Adolescent cadmium exposure impairs cognition and hippocampal neurogenesis in C57BL/6 mice

Cadmium (Cd) is a toxic heavy metal and a significant public health concern. Epidemiological studies suggest that Cd is a potential neurotoxicant, and its exposure is associated with cognitive deficits in children, adults, and seniors. Our previous study has found that adulthood-only Cd exposure can impair cognition in mice. However, few studies have addressed the effects of Cd exposure during adolescence on cognitive behavior in animals later in life. In the present study, we exposed 4-week-old male C57BL/6 mice to 3 mg/L Cd via drinking water for 28 weeks and assessed their hippocampus-dependent learning and memory. Cd did not affect anxiety or locomotor activity in the open field test. However, Cd exposure impaired short-term spatial memory and contextual fear memory in mice. A separate cohort of 4-week-old mice was similarly exposed to Cd for 13 weeks to investigate the potential mechanism of Cd neurotoxicity on cognition. We observed that Cd-treated mice had fewer adult-born cells, adult-born neurons, and a reduced proportion of adult-born cells that differentiated into mature neurons in the subgranular zone of the dentate gyrus. These results suggest that Cd exposure from adolescence to adulthood is sufficient to cause cognitive deficits and impair key processes of hippocampal neurogenesis in mice.

Current Views on the Role of Stress in the Pathogenesis of Chronic Neurodegenerative Diseases

The review summarizes the results of studies on the cellular and molecular mechanisms mediating the impact of stress on the pathogenesis of neurodegenerative brain pathologies (Alzheimer's disease, Parkinson's disease, etc.) and presents current information on the role of stress in the hyperphosphorylation of tau protein, aggregation of beta-amyloid, and hyperactivation of the hypothalamic-pituitary-adrenal axis involved in the hyperproduction of factors that contribute to the pathogenetic role of stress in neurodegeneration. The data on the participation of microglia in the effects of stress on the pathogenesis of neurodegenerative diseases are presented.

Stress-induced cortisol response is associated with right amygdala volume in early childhood

Rodent research suggests that dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and the resulting cortisol stress response can alter the structure of the hippocampus and amygdala. Because early-life changes in brain structure can produce later functional impairment and potentially increase risk for psychiatric disorder, it is critical to understand the relationship between the cortisol stress response and brain structure in early childhood. However, no study to date has characterized the concurrent association between cortisol stress response and hippocampal and amygdala volume in young children. In the present study, 42 young children (M age  = 5.97, SD = 0.76), completed a frustration task and cortisol response to stress was measured. Children also underwent magnetic resonance imaging (MRI), providing structural scans from which their hippocampal and amygdala volumes were extracted. Greater cortisol stress response was associated with reduced right amygdala volume, controlling for whole brain volume, age, sex, and number of cortisol samples. There were no significant associations between cortisol stress response and bilateral hippocampus or left amygdala volumes. The association between right amygdala volume and cortisol stress response raises the non-mutually exclusive possibilities that the function of the HPA axis may shape amygdala structure and/or that amygdala structure may shape HPA axis function. As both cortisol stress response and amygdala volume have been associated with risk for psychopathology, it is possible that the relationship between cortisol stress response and amygdala volume is part of a broader pathway contributing to psychiatric risk.

Nono-titanium dioxide exposure during the adolescent period induces neurotoxicities in rats: Ameliorative potential of bergamot essential oil

INTRODUCTION

In adolescence, the brain is still maturing, and disorders in maturation may affect the normal development of the brain. Exposure to titanium dioxide nanoparticles (TiO₂ NPs) has various potential negative effects on the central nervous system. Bergamot essential oil (BEO) has been found to be effective for neuroprotection.

METHODS

The rats were injected intraperitoneally with TiO₂ NPs (20 mg/kg) and/or BEO (200 mg/kg). The endogenous antioxidant state and inflammatory parameters were estimated using ELISA kits, and then the memory ability and anxiety-like behavior in rats were assessed.

RESULTS

TiO₂ NPs exposure during the adolescent period induced anxiety-like behavior, cognitive impairment, neuroinflammation and oxidative damage in hippocampus, and BEO treatment could significantly ameliorate the neurotoxicities induced by TiO₂ NPs exposure.

CONCLUSION

Our results suggest that the negative effects of TiO₂ NPs exposure during the adolescent period on anxiety-like behavior and cognitive function may be related to oxidative stress and neuroinflammation induced by TiO₂ NPs exposure. In addition, BEO may ameliorate the neurotoxicities induced by TiO2 NPs exposure in adolescent rats through the antioxidant and anti-inflammatory activity of BEO.

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 Immunopathogenesis of Alzheimer's Disease Is Related to the Composition of Gut Microbiota

The microbiota-gut-brain axis plays an important role in the development of neurodegenerative diseases. Commensal and pathogenic enteric bacteria can influence brain and immune system function by the production of lipopolysaccharides and amyloid. Dysbiosis of the intestinal microbiome induces local and consecutively systemic immune-mediated inflammation. Proinflammatory cytokines then trigger neuroinflammation and finally neurodegeneration. Immune-mediated oxidative stress can lead to a deficiency of vitamins and essential micronutrients. Furthermore, the wrong composition of gut microbiota might impair the intake and metabolization of nutrients. In patients with Alzheimer's disease (AD) significant alterations of the gut microbiota have been demonstrated. Standard Western diet, infections, decreased physical activity and chronic stress impact the composition and diversity of gut microbiota. A higher abundancy of "pro-inflammatory" gut microbiota goes along with enhanced systemic inflammation and neuroinflammatory processes. Thus, AD beginning in the gut is closely related to the imbalance of gut microbiota. Modulation of gut microbiota by Mediterranean diet, probiotics and curcumin can slow down cognitive decline and alter the gut microbiome significantly. A multi-domain intervention approach addressing underlying causes of AD (inflammation, infections, metabolic alterations like insulin resistance and nutrient deficiency, stress) appears very promising to reduce or even reverse cognitive decline by exerting positive effects on the gut microbiota.

Operations Research Methods for Estimating the Population Size of Neuron Types

Understanding brain computation requires assembling a complete catalog of its architectural components. Although the brain is organized into several anatomical and functional regions, it is ultimately the neurons in every region that are responsible for cognition and behavior. Thus, classifying neuron types throughout the brain and quantifying the population sizes of distinct classes in different regions is a key subject of research in the neuroscience community. The total number of neurons in the brain has been estimated for multiple species, but the definition and population size of each neuron type are still open questions even in common model organisms: the so called "cell census" problem. We propose a methodology that uses operations research principles to estimate the number of neurons in each type based on available information on their distinguishing properties. Thus, assuming a set of neuron type definitions, we provide a solution to the issue of assessing their relative proportions. Specifically, we present a three-step approach that includes literature search, equation generation, and numerical optimization. Solving computationally the set of equations generated by literature mining yields best estimates or most likely ranges for the number of neurons in each type. While this strategy can be applied towards any neural system, we illustrate its usage on the rodent hippocampus.

Corticosterone Induces Depressive-Like Behavior in Female Peri-Pubescent Rats, but Not in Pre-Pubescent Rats

Background

There are no data on the effect of exogenous corticosterone on depressive-like behavior in juvenile rats. Furthermore, it has not been tested whether the effects of corticosterone in female rats is different before or after puberty.

Objective

We tested the effect of corticosterone treatment on female pre- and peri-pubescent juvenile rats on depressive-like behavior.

Methods

Female juvenile rats were divided into pre-pubescent (post-natal day 7–27) or peri-pubescent (post-natal day 28–48) groups and administered daily corticosterone (40 mg kg⁻¹day⁻¹) for 21 days. Depressive-like behavior was assessed using a modified forced swim test and the sucrose preference test. After behavioral assessment, brains were analyzed to determine if there were changes in cell proliferation and newborn neuron survival in the dentate gyrus of the dorsal hippocampus.

Results

Chronic corticosterone treatment did not affect behavior or neurogenesis in female pre-pubescent juvenile rats. However, female peri-pubescent rats injected with corticosterone showed increased depressive-like behavior as well as a decrease in cell proliferation in the subgranular zone. Furthermore, there was an inverse correlation between time spent immobile in the forced swim test and cell proliferation in the granule cell layer in peri-pubescent rats.

Conclusions

Corticosterone induces depressive-like behavior in peri-pubescent, but not in pre-pubescent female rats. Finally, our results suggest that depressive-like behavior may be associated with a decrease in hippocampal cell proliferation in female peri-pubescent rats.

Cell numbers, distribution, shape, and regional variation throughout the murine hippocampal formation from the adult brain Allen Reference Atlas

Quantifying the distribution of cells in every brain region is fundamental to attaining a comprehensive census of distinct neuronal and glial types. Until recently, estimating neuron numbers involved time-consuming procedures that were practically limited to stereological sampling. Progress in open-source image recognition software, growth in computing power, and unprecedented neuroinformatics developments now offer the potentially paradigm-shifting alternative of comprehensive cell-by-cell analysis in an entire brain region. The Allen Brain Atlas provides free digital access to complete series of raw Nissl-stained histological section images along with regional delineations. Automated cell segmentation of these data enables reliable and reproducible high-throughput quantification of regional variations in cell count, density, size, and shape at whole-system scale. While this strategy is directly applicable to any regions of the mouse brain, we first deploy it here on the closed-loop circuit of the hippocampal formation: the medial and lateral entorhinal cortices; dentate gyrus (DG); areas Cornu Ammonis 3 (CA3), CA2, and CA1; and dorsal and ventral subiculum. Using two independent image processing pipelines and the adult mouse reference atlas, we report the first cellular-level soma segmentation in every sub-region and non-principal layer of the left hippocampal formation through the full rostral-caudal extent. It is important to note that our techniques excluded the layers with the largest number of cells, DG granular and CA pyramidal, due to dense packing. The numerical estimates for the remaining layers are corroborated by traditional stereological sampling on a data subset and well match sparse published reports.

In vivo Calcium Imaging Reveals That Cortisol Treatment Reduces the Number of Place Cells in Thy1-GCaMP6f Transgenic Mice

The hippocampus, a structure essential for spatial navigation and memory undergoes anatomical and functional changes during chronic stress. Here, we investigate the effects of chronic stress on the ability of place cells to encode the neural representation of a linear track. To model physiological conditions of chronic stress on hippocampal function, transgenic mice expressing the genetically encoded calcium indicator GCaMP6f in CA1 pyramidal neurons were chronically administered with 40 μg/ml of cortisol for 8 weeks. Cortisol-treated mice exhibited symptoms typically observed during chronic stress, including diminished reward seeking behavior and reduced adrenal gland and spleen weights. In vivo imaging of hippocampal cellular activity during linear track running behavior revealed a reduced number of cells that could be recruited to encode spatial position, despite an unchanged overall number of active cells, in cortisol-treated mice. The properties of the remaining place cells that could be recruited to encode spatial information, however, was unperturbed. Bayesian decoders trained to estimate the mouse’s position on the track using single neuron activity data demonstrated reduced performance in a cue richness-dependent fashion in cortisol-treated animals. The performance of decoders utilizing data from the entire neuronal ensemble was unaffected by cortisol treatment. Finally, to test the hypothesis that an antidepressant drug could prevent the effects of cortisol, we orally administered a group of mice with 10 mg/kg citalopram during cortisol administration. Citalopram prevented the cortisol-induced decrease in single-neuron decoder performance but failed to significantly prevent anhedonia and the cortisol-induced reduction in the proportion place cells. The dysfunction observed at the single-neuron level indicates that chronic stress may impair the ability of the hippocampus to encode individual neural representations of the mouse’s spatial position, a function pivotal to forming an accurate navigational map of the mouse’s external environment; however, the hippocampal ensemble as a whole is resilient to any cortisol-induced insults to single neuronal place cell function on the linear track.

Restraint stress exacerbates cell degeneration induced by acute binge ethanol in the adolescent, but not in the adult or middle-aged, brain

Restraint stress (RS) induces neurotoxicity in the hippocampus, yet most of the studies have employed protracted RS (i.e., ≈ 21 days). Binge ethanol can induce brain toxicity, an effect affected by age. It could be postulated that RS may facilitate ethanol-induced neurotoxicity, perhaps to a greater extent in adolescent vs. older subjects. We analyzed whether adolescent, adult or middle-aged male rats exposed to five episodes of RS followed, 72h later, by binge ethanol (i.e., two administrations of 2.5 g/kg ethanol) exhibited hippocampal neurotoxicity. Adolescents, but not adult or middle-aged rats, exhibited sensitivity to the neurotoxic effects of ethanol at dorsal CA2, ventral CA3 and ventral DG, and a neurotoxic effect of stress at dorsal CA1. Moreover, the combination of ethanol and stress exerted a synergistic effect upon cell degeneration at ventral CA1 and CA2, which was restricted to adolescents. Ethanol also increased cell degeneration, irrespective of age or stress, in dorsal CA3 and in dorsal DG; and ethanol and stress had, across all ages, a synergistic effect upon cell degeneration at the dorsal CA1. The greater neurotoxic response of adolescents to ethanol, stress, or ethanol+stress can put them at risk for the development of alcohol problems.

The Ca2+-Binding S100B Protein: An Important Diagnostic and Prognostic Neurobiomarker in Pediatric Laboratory Medicine

In recent decades a significant scientific effort has focused on projects regarding the use of neurobiomarkers in perinatal medicine with a view to understanding the mechanisms that interfere with physiological patterns of brain development and lead to ominous effects in several human diseases. Numerous potential neurobiomarkers have been proposed for use in monitoring high-risk fetuses and newborns, including markers of oxidative stress, neuroproteins, and vasoactive agents. Nonetheless, the use of these markers in clinical practice remains a matter of debate. Recently, the calcium-binding S100B protein has been proposed as being an ideal neurobiomarker, thanks to its simple availability and easy reproducibility, to the possibility of detecting it noninvasively in biological fluids with good reproducibility, and to the possibility of a longitudinal evaluation in relation to reference curves. The present chapter contains an overview of the most significant studies on the assessment of S100B in different biological fluids as a trophic factor and/or marker of brain damage in high-risk fetuses and newborns.

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.

Differential effects of adolescent and adult-initiated exercise on cognition and hippocampal neurogenesis

Adolescence is a critical period for postnatal brain maturation and thus a time when environmental influences may affect cognitive processes in later life. Exercise during adulthood has been shown to increase hippocampal neurogenesis and enhance cognition. However, the impact of exercise initiated in adolescence on the brain and behavior in adulthood is not fully understood. The aim of this study was to compare the impact of voluntary exercise that is initiated during adolescence or early adulthood on cognitive performance in hippocampal-dependent and -independent processes using both object-based and touchscreen operant paradigms. Adult (8 week) and adolescent (4 week) male Sprague-Dawley rats had access to a running wheel (exercise) or were left undisturbed (sedentary control) for 4 weeks prior to behavioral testing and for the duration of the experiment. Results from touchscreen-based tasks showed that reversal learning was enhanced by both adult and adolescent-initiated exercise, while only exercise that began in adolescence induced a subtle but transient increase in performance on a location discrimination task. Spontaneous alternation in the Y-maze was impaired following adolescent onset exercise, while object memory was unaffected by either adult or adolescent-initiated exercise. Adolescent-initiated exercise increased the number of hippocampal DCX cells, an indicator of neurogenesis. It also promoted the complexity of neurites on DCX cells, a key process for synaptic integration, to a greater degree than adult-initiated exercise. Together the data here show that exercise during the adolescent period compared to adulthood differentially affects cognitive processes and the development of new hippocampal neurons in later life.

Could a blood test for PTSD and depression be on the horizon?

INTRODUCTION

Depression and posttraumatic stress disorder (PTSD) are two complex and debilitating psychiatric disorders that result in poor life and destructive behaviors against self and others. Currently, diagnosis is based on subjective rather than objective determinations leading to misdiagnose and ineffective treatments. Advances in novel neurobiological methods have allowed assessment of promising biomarkers to diagnose depression and PTSD, which offers a new means of appropriately treating patients. Areas covered: Biomarkers discovery in blood represents a fundamental tool to predict, diagnose, and monitor treatment efficacy in depression and PTSD. The potential role of altered HPA axis, epigenetics, NPY, BDNF, neurosteroid biosynthesis, the endocannabinoid system, and their function as biomarkers for mood disorders is discussed. Insofar, we propose the identification of a biomarker axis to univocally identify and discriminate disorders with large comorbidity and symptoms overlap, so as to provide a base of support for development of targeted treatments. We also weigh in on the feasibility of a future blood test for early diagnosis. Expert commentary: Potential biomarkers have already been assessed in patients' blood and need to be further validated through multisite large clinical trial stratification. Another challenge is to assess the relation among several interdependent biomarkers to form an axis that identifies a specific disorder and secures the best-individualized treatment. The future of blood-based tests for PTSD and depression is not only on the horizon but, possibly, already around the corner.

Differential effects of adolescent and adult-initiated voluntary exercise on context and cued fear conditioning

Adolescence is a critical period for postnatal brain maturation and a time during which there is increased susceptibility to developing emotional and cognitive-related disorders. Exercise during adulthood has been shown to increase hippocampal plasticity and enhance cognition. However, the impact of exercise initiated in adolescence, on brain and behaviour in adulthood is not yet fully explored or understood. The aim of this study was to compare the impact of voluntary exercise that was initiated either during adolescence or early adulthood on cognitive performance in hippocampal and amygdala-dependent fear conditioning tasks in adulthood. Adult (eight weeks old) and adolescent (four weeks old) male Sprague Dawley rats had access to a running wheel (exercise) or were left undisturbed (sedentary control) for seven weeks. Adult-initiated exercise enhanced both contextual and cued fear conditioning, while conversely, exercise that began in adolescence did not affect performance in these tasks. These behaviours were accompanied by differential expression of plasticity-related genes in the hippocampus and amygdala in adulthood. Specifically, adolescent-initiated exercise increased the expression of an array of plasticity related genes in the hippocampus including BDNF, synaptophysin, Creb, PSD-95, Arc, TLX and DCX, while adult-initiated exercise did not affect hippocampal plasticity related genes. Together results show that exercise initiated during adolescence has a differential effect on hippocampal and amygdala-dependent behaviour and neuronal plasticity compared to when exercise was initiated in adulthood. These findings reinforce adolescence as a period during which environmental influences have a distinct impact on neuronal plasticity and cognition. This article is part of the Special Issue entitled "Neurobiology of Environmental Enrichment".

Hippocampal astrocyte atrophy in a mouse depression model induced by corticosterone is reversed by fluoxetine instead of benzodiazepine diazepam

Astrocytes have become promising new agents against major depressive disorders (MDD) primarily due to the crucial role they play in the pathogenesis of such disorders. However, a simple and reliable animal model that can be used to screen for astrocyte-targeting antidepressants has not yet been developed. In this study, we utilized a repeated corticosterone (CORT) injection paradigm to develop a mouse depression model wherein we examined the occurrence of alterations in hippocampal astrocyte population by using two astrocytic markers, namely, glial fibrillary acidic protein (GFAP) and S100β. Moreover, we determined the effects of fluoxetine and diazepam on CORT-induced astrocytic alterations to assess the predictive validity. Results showed that repeated CORT injections showed no effects on the number of GFAP⁺ and S100β⁺ astrocytes, but they decreased the protrusion length of GFAP⁺ astrocytes and GFAP protein expression in the hippocampus. Furthermore, repeated CORT injections produced a sustained increase of S100β protein levels in the entire hippocampus of male mice. CORT-induced hippocampal astrocyte disruption was antagonized by chronic fluoxetine treatment. By contrast, the anxiolytic drug diazepam was ineffective in the same experimental setting. All these findings suggest that the repeated CORT injection paradigm produces the astrocytic alterations similar to those in MDD and can serve as a useful mouse model to screen antidepressants meant to target astrocytes. These observations can also help in further discussing the underlying mechanisms of CORT-induced astrocytic alterations.

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.

Influence of postnatal glucocorticoids on hippocampal-dependent learning varies with elevation patterns and administration methods

Recent interest in the lasting effects of early-life stress has expanded to include effects on cognitive performance. An increase in circulating glucocorticoids is induced by stress exposure and glucocorticoid effects on the hippocampus likely underlie many of the cognitive consequences. Here we review studies showing that corticosterone administered to young rats at the conclusion of the stress-hyporesponsiveness period affects later performance in hippocampally-mediated trace eyeblink conditioning. The nature and even direction of these effects varies with the elevation patterns (level, duration, temporal fluctuation) achieved by different administration methods. We present new time course data indicating that constant glucocorticoid elevations generally corresponded with hippocampus-mediated learning deficits, whereas acute, cyclical elevations corresponded with improved initial acquisition. Sensitivity was greater for males than for females. Further, changes in hippocampal neurogenesis paralleled some but not all effects. The findings demonstrate that specific patterns of glucocorticoid elevation produced by different drug administration procedures can have markedly different, sex-specific consequences on basic cognitive performance and underlying hippocampal physiology. Implications of these findings for glucocorticoid medications prescribed in childhood are discussed.

Stress and adolescent hippocampal neurogenesis: diet and exercise as cognitive modulators

Adolescence is a critical period for brain maturation. Deciphering how disturbances to the central nervous system at this time affect structure, function and behavioural outputs is important to better understand any long-lasting effects. Hippocampal neurogenesis occurs during development and continues throughout life. In adulthood, integration of these new cells into the hippocampus is important for emotional behaviour, cognitive function and neural plasticity. During the adolescent period, maturation of the hippocampus and heightened levels of hippocampal neurogenesis are observed, making alterations to neurogenesis at this time particularly consequential. As stress negatively affects hippocampal neurogenesis, and adolescence is a particularly stressful time of life, it is important to investigate the impact of stressor exposure at this time on hippocampal neurogenesis and cognitive function. Adolescence may represent not only a time for which stress can have long-lasting effects, but is also a critical period during which interventions, such as exercise and diet, could ameliorate stress-induced changes to hippocampal function. In addition, intervention at this time may also promote life-long behavioural changes that would aid in fostering increased hippocampal neurogenesis and cognitive function. This review addresses both the acute and long-term stress-induced alterations to hippocampal neurogenesis and cognition during the adolescent period, as well as changes to the stress response and pubertal hormones at this time which may result in differential effects than are observed in adulthood. We hypothesise that adolescence may represent an optimal time for healthy lifestyle changes to have a positive and long-lasting impact on hippocampal neurogenesis, and to protect against stress-induced deficits. We conclude that future research into the mechanisms underlying the susceptibility of the adolescent hippocampus to stress, exercise and diet and the consequent effect on cognition may provide insight into why adolescence may be a vital period for correct conditioning of future hippocampal function.

Chronic stress and hippocampal dendritic complexity: Methodological and functional considerations

The current understanding of how chronic stress impacts hippocampal dendritic arbor complexity and the subsequent relationship to hippocampal-dependent spatial memory is reviewed. A surge in reports investigating hippocampal dendritic morphology is occurring, but with wide variations in methodological detail being reported. Consequently, this review systematically outlines the basic neuroanatomy of relevant hippocampal features to help clarify how chronic stress or glucocorticoids impact hippocampal dendritic complexity and how these changes occur in parallel with spatial cognition. Chronic stress often leads to hippocampal CA3 apical dendritic retraction first with other hippocampal regions (CA3 basal dendrites, CA1, dentate gyrus, DG) showing dendritic retraction when chronic stress is sufficiently robust or long lasting. The stress-induced reduction in hippocampal CA3 apical dendritic arbor complexity often coincides with impaired hippocampal function, such as spatial learning and memory. Yet, when chronic stress ends and a post-stress recovery period ensues, the atrophied dendritic arbors and poor spatial abilities often improve. However, this process differs from a simple reversal of chronic stress-induced deficits. Recent reports suggest that this return to baseline-like functioning is uniquely different from non-stressed controls, emphasizing the need for further studies to enhance our understanding of how a history of stress subsequently alters an organism's spatial abilities. To provide a consistent framework for future studies, this review concludes with an outline for a quick and easy reference on points to consider when planning chronic stress studies with the goal of measuring hippocampal dendritic complexity and spatial ability.

Administration of the TrkB receptor agonist 7,8-dihydroxyflavone prevents traumatic stress-induced spatial memory deficits and changes in synaptic plasticity

Post-traumatic stress disorder (PTSD) occurs after exposure to traumatic situations and it is characterized by cognitive deficits that include impaired explicit memory. The neurobiological bases of such PTSD-associated memory alterations are yet to be elucidated and no satisfactory treatment for them exists. To address this issue, we first studied whether a single exposure of young adult rats (60 days) to immobilization on boards (IMO), a putative model of PTSD, produces long-term behavioral effects (2-8 days) similar to those found in PTSD patients. Subsequently, we investigated whether the administration of the TrkB agonist 7,8-dihydroxyflavone (DHF) 8 h after stress (therapeutic window) ameliorated the PTSD-like effect of IMO and the associated changes in synaptic plasticity. A single IMO exposure induced a spatial memory impairment similar to that found in other animal models of PTSD or in PTSD patients. IMO also increased spine density and long-term potentiation (LTP) in the CA3-CA1 pathway. Significantly, DHF reverted both spatial memory impairment and the increase in LTP, while it produced no effect in the controls. These data provide novel insights into the possible neurobiological substrate for explicit memory impairment in PTSD patients, supporting the idea that the activation of the BDNF/TrkB pathway fulfils a protective role after severe stress. Administration of DHF in the aftermath of a traumatic experience might be relevant to prevent its long-term consequences. © 2016 Wiley Periodicals, Inc.

A critical evaluation of the activity-regulated cytoskeleton-associated protein (Arc/Arg3.1)'s putative role in regulating dendritic plasticity, cognitive processes, and mood in animal models of depression

Major depressive disorder (MDD) is primarily conceptualized as a mood disorder but cognitive dysfunction is also prevalent, and may limit the daily function of MDD patients. Current theories on MDD highlight disturbances in dendritic plasticity in its pathophysiology, which could conceivably play a role in the production of both MDD-related mood and cognitive symptoms. This paper attempts to review the accumulated knowledge on the basic biology of the activity-regulated cytoskeleton-associated protein (Arc or Arg3.1), its effects on neural plasticity, and how these may be related to mood or cognitive dysfunction in animal models of MDD. On a cellular level, Arc plays an important role in modulating dendritic spine density and remodeling. Arc also has a close, bidirectional relationship with postsynaptic glutamate neurotransmission, since it is stimulated by multiple glutamatergic receptor mechanisms but also modulates α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor internalization. The effects on AMPA receptor trafficking are likely related to Arc's ability to modulate phenomena such as long-term potentiation, long-term depression, and synaptic scaling, each of which are important for maintaining proper cognitive function. Chronic stress models of MDD in animals show suppressed Arc expression in the frontal cortex but elevation in the amygdala. Interestingly, cognitive tasks depending on the frontal cortex are generally impaired by chronic stress, while those depending on the amygdala are enhanced, and antidepressant treatments stimulate cortical Arc expression with a timeline that is reminiscent of the treatment efficacy lag observed in the clinic or in preclinical models. However, pharmacological treatments that stimulate regional Arc expression do not universally improve relevant cognitive functions, and this highlights a need to further refine our understanding of Arc on a subcellular and network level.

Short-term, high-dose administration of corticosterone by injection facilitates trace eyeblink conditioning in young male rats

Glucocorticoids released as part of the physiological response to stress are known to affect cognitive function, presumably via effects on the hippocampus. Trace classical eyeblink conditioning is an associative learning task which depends on the hippocampus and has been used to examine the development of learning processes in young mammals. Previously, we demonstrated deficits in trace eyeblink conditioning associated with postnatal administration of the glucocorticoid corticosterone by creating a sustained elevation with methods such as subcutaneous timed-release pellets and osmotic mini-pumps which were active over several days. In the present study, we examined the effects of an oscillating pattern of corticosterone elevation on subsequent trace eyeblink conditioning. Twice daily corticosterone injections (high, low, or vehicle) were administered over a 3-day period, starting at postnatal day 15. Then, on postnatal day 28, animals underwent trace classical eyeblink conditioning to examine the possible influence of earlier corticosterone elevations on the development of learning and memory. Eyeblink conditioning was affected by corticosterone treatments, but only for males, and only very early in acquisition; Males receiving the high dose of corticosterone exhibited facilitation of learning relative to controls. These data demonstrate that oscillating corticosterone elevations produce opposite effects on this associative learning task than do sustained elevations.

Hypothalamic-pituitary-adrenal (HPA) axis and aging

Human aging is associated with increasing frailty and morbidity which can result in significant disability. Dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis may contribute to aging-related diseases like depression, cognitive deficits, and Alzheimer's disease in some older individuals. In addition to neuro-cognitive dysfunction, it has also been associated with declining physical performance possibly due to sarcopenia. This article reviews the pathophysiology of HPA dysfunction with respect to increased basal adrenocorticotropic hormone (ACTH) and cortisol secretion, decreased glucocorticoid (GC) negative feedback at the level of the paraventricular nucleus (PVN) of the hypothalamus, hippocampus (HC), and prefrontal cortex (PFC), and flattening of diurnal pattern of cortisol release. It is possible that the increased cortisol secretion is secondary to peripheral conversion from cortisone. There is a decline in pregnolone secretion and C-19 steroids (DHEA) with aging. There is a small decrease in aldosterone with aging, but a subset of the older population have a genetic predisposition to develop hyperaldosteronism due to the increased ACTH stimulation. The understanding of the HPA axis and aging remains a complex area with conflicting studies leading to controversial interpretations.

Interaction of basal forebrain cholinergic neurons with the glucocorticoid system in stress regulation and cognitive impairment

A substantial number of studies on basal forebrain (BF) cholinergic neurons (BFCN) have provided compelling evidence for their role in the etiology of stress, cognitive aging, Alzheimer’s disease (AD), and other neurodegenerative diseases. BFCN project to a broad range of cortical sites and limbic structures, including the hippocampus, and are involved in stress and cognition. In particular, the hippocampus, the primary target tissue of the glucocorticoid stress hormones, is associated with cognitive function in tandem with hypothalamic-pituitary-adrenal (HPA) axis modulation. The present review summarizes glucocorticoid and HPA axis research to date in an effort to establish the manner in which stress affects the release of acetylcholine (ACh), glucocorticoids, and their receptor in the context of cognitive processes. We attempt to provide the molecular interactive link between the glucocorticoids and cholinergic system that contributes to BFCN degeneration in stress-induced acceleration of cognitive decline in aging and AD. We also discuss the importance of animal models in facilitating such studies for pharmacological use, to which could help decipher disease states and propose leads for pharmacological intervention.

A novel 2-decenoic acid thioester ameliorates corticosterone-induced depression- and anxiety-like behaviors and normalizes reduced hippocampal signal transduction in treated mice

We characterized mice administered corticosterone (CORT) at a dose of 20 mg/kg for 3 weeks to determine their suitability as a model of mood disorders and found that the time immobilized in the tail suspension test was longer and the time spent in the open arms of the elevated plus-maze test was shorter than those of the vehicle-treated group, findings demonstrating that chronic CORT induced both depression-like and anxiety-like behaviors. Furthermore, the levels of phosphorylated extracellular signal-regulated kinase (pERK) 1/2 in the hippocampus and cerebral cortex were reduced in the CORT-treated group. Using this model, we investigated the protective effect of the ester, thioester, and amide compounds of 2-decenoic acid derivatives (termed compounds A, B, and C, respectively). The potency of the protective activity against the CORT-induced depression-like or anxiety-like behaviors and the reduction in pERK1/2 level were found to be in the following order: compound B > compound C > compound A. Therefore, we further investigated the therapeutic activity of only compound B, and its effect on depression-like behavior was observed after oral administration for 1 or 2 weeks, and its effect on anxiety-like behavior was observed after oral administration for 3 weeks. The ratios of phosphorylated ERK1/2, Akt, and cAMP-response element-binding protein to their respective nonphosphorylated forms were smaller in the CORT-treated group than in the vehicle-treated group; however, subsequent treatment with compound B at either 0.3 or 1.5 mg/kg significantly ameliorated this reduction. Compound B appeared to elicit intracellular signaling, similar to that elicited by brain-derived neurotrophic factor, and its mode of action was shown to be novel and different from that of fluvoxamine, a currently prescribed drug for mood disorders.

Stereological estimation of neuron number and plaque load in the hippocampal region of a transgenic rat model of Alzheimer's disease

The main hallmarks of Alzheimer's disease (AD) are senile plaques, neurofibrillary tangles and neuronal death. The McGill-R-Thy1-APP rat is one of the few transgenic rat models of AD that displays progressive amyloid pathology. This study aimed to further characterise this rat model, focusing on the pathological changes in the hippocampal formation and the parahippocampal region. These structures, that are important for episodic memory and spatial navigation, are affected in the early stages of the disease. This study used unbiased stereology to investigate possible neuronal loss in the CA1, subiculum and entorhinal cortex of 18-month-old homozygous McGill-R-Thy1-APP rats, and also quantified the plaque load in all the areas of the hippocampal formation and parahippocampal region from 9 to 18 months old. A significant reduction of neurons at 18 months was only seen in the subiculum. The first plaque pathology was seen at 9 months in the subiculum. Although the quantified plaque load was variable between animals, the pattern of spatiotemporal progression was similar for all animals. The spread of plaque pathology mainly affected anatomically connected regions. Overall, the plaque pathology observed in the transgenic rats was similar to the early phases of amyloid beta (Aβ)-deposition described in human patients. The findings here thus indicate that the McGill-R-Thy1-APP rat could be a good model of the Aβ pathology in AD, but less so with respect to neuron loss.

β-Alanine supplemented diets enhance behavioral resilience to stress exposure in an animal model of PTSD

This study investigated the effects of β-alanine (BA) ingestion on the behavioral and neuroendocrine response of post-traumatic stress disorder (PTSD) in a murine model. Animals were fed a normal diet with or without (PL) BA supplementation (100 mg kg(-1)) for 30 days. Animals were then exposed to a predator-scent stress (PSS) or a sham (UNEX). Behaviors were evaluated using an elevated plus maze (EPM) and acoustic startle response (ASR) 7 days following exposure to the PSS. Corticosterone concentrations (CS), expression of brain-derived neurotrophic factor (BDNF), and brain carnosine concentrations were analyzed a day later. Animals in PSS+PL spent significantly less time in the open arms and in the number of entries in the EPM than PSS+BA, UNEX+BA, or UNEX+PL. Animals in PSS+BA had comparable scores to UNEX+BA. Anxiety index was higher (p < 0.05) in PSS+PL compared to PSS+BA or animals that were unexposed. ASR and freezing were greater (p < 0.05) in animals exposed to PSS compared to animals unexposed. CS expression was higher (p < 0.05) in animals exposed to PSS compared to unexposed animals. Brain carnosine concentrations in the hippocampus and other brain sections were significantly greater in animals supplemented with BA compared to PL. BDNF expression in the CA1 and DG subregions of the hippocampus was lower (p < 0.05) in animals exposed and fed a normal diet compared to animals exposed and supplemented with BA, or animals unexposed. In conclusion, BA supplementation in rats increased brain carnosine concentrations and resulted in a reduction in PTSD-like behavior, which may be mediated in part by maintaining BDNF expression in the hippocampus.

Depression and antidepressant use moderate association between widowhood and Alzheimer's disease

OBJECTIVE

In recent decades, biological evidence has implicated chronic stress in the etiology of Alzheimer's disease (AD). As a result, the relationship between widowhood, one of the most stressful life events, and AD has also received attention. This study extends this literature by investigating whether depression, which may indicate proneness to distress, and antidepressant use, which can protect against hippocampal shrinkage, moderate the relationship between widowhood and increased risk for AD.

METHODS

To investigate this, this study utilized data from the Cache County Memory Study, a large population-based epidemiological study of AD, and the Utah Population Database, one of the world's foremost linked genealogical databases, to regress AD on the interaction between widowhood and history of depression and antidepressant use.

RESULTS

In Cox regression analyses, history of depression and antidepressant use moderated the association between widowhood and AD (p = 0.007 and p = 0.006, respectively), in that widowhood was associated with 73% and 94% increased hazard of AD among those reporting depression (hazard ratio [HR] = 1.73, 95% confidence interval [CI]: 1.001 to 2.99) and those reporting antidepressant use (HR = 1.94, 95% CI: 1.13 to 3.33). A significant three-way interaction between widowhood, depression, and antidepressant use was also found (p = 0.02), showing depression to moderate the association between widowhood and AD only among those not using antidepressants (p = 0.02).

CONCLUSIONS

These findings advance clinical and scientific knowledge concerning the effects of widowhood on risk for AD and underscore the importance of depression and antidepressant use in understanding vulnerability to and protection from these effects.

Stress and glucocorticoids promote oligodendrogenesis in the adult hippocampus

Stress can exert long-lasting changes on the brain that contribute to vulnerability to mental illness, yet mechanisms underlying this long-term vulnerability are not well understood. We hypothesized that stress may alter the production of oligodendrocytes in the adult brain, providing a cellular and structural basis for stress-related disorders. We found that immobilization stress decreased neurogenesis and increased oligodendrogenesis in the dentate gyrus (DG) of the adult rat hippocampus and that injections of the rat glucocorticoid stress hormone corticosterone (cort) were sufficient to replicate this effect. The DG contains a unique population of multipotent neural stem cells (NSCs) that give rise to adult newborn neurons, but oligodendrogenic potential has not been demonstrated in vivo. We used a nestin-CreER/YFP transgenic mouse line for lineage tracing and found that cort induces oligodendrogenesis from nestin-expressing NSCs in vivo. Using hippocampal NSCs cultured in vitro, we further showed that exposure to cort induced a pro-oligodendrogenic transcriptional program and resulted in an increase in oligodendrogenesis and decrease in neurogenesis, which was prevented by genetic blockade of glucocorticoid receptor (GR). Together, these results suggest a novel model in which stress may alter hippocampal function by promoting oligodendrogenesis, thereby altering the cellular composition and white matter structure.

Association between glucocorticoid receptor methylation and hippocampal subfields in major depressive disorder

Background

DNA methylation in the promoter region of the glucocorticoid receptor gene (NR3C1) is closely associated with childhood adversity and suicide. However, few studies have examined NR3C1 methylation in relation to major depressive disorder (MDD) and hippocampal subfield volumes. We investigated the possible association between NR3C1 methylation and structural brain alterations in MDD in comparison with healthy controls.

Methods

We compared the degree of NR3C1 promoter methylation in the peripheral blood of non-psychotic outpatients with MDD and that of healthy controls. Correlations among NR3C1 promoter methylation, structural abnormalities in hippocampal subfield volumes and whole-brain cortical thickness, and clinical variables were also analyzed.

Results

In total, 117 participants (45 with MDD and 72 healthy controls) were recruited. Patients with MDD had significantly lower methylation than healthy controls at 2 CpG sites. In MDD, methylations had positive correlations with the bilateral cornu ammonis (CA) 2–3 and CA4-dentate gyrus (DG) subfields. However, in healthy controls, methylations had positive correlation with the subiculum and presubiculum. There were no differences in total and subfield volumes of the hippocampus between patients with MDD and healthy controls. Compared with healthy controls, patients with MDD had a significantly thinner cortex in the left rostromiddle frontal, right lateral orbitofrontal, and right pars triangularis areas.

Conclusions

Lower methylation in the NR3C1 promoter, which might have compensatory effects relating to CA2-3 and CA4-DG, is a distinct epigenetic characteristic in non-psychotic outpatients with MDD. Future studies with a longitudinal design and a comprehensive neurobiological approach are warranted in order to elucidate the effects of NR3C1 methylation.

Effects of postnatal hyperoxia exposure on the rat dentate gyrus and subventricular zone

Premature newborns may be exposed to hyperoxia in the first postnatal period, but clinical and experimental works have raised the question of oxygen toxicity for the developing brain. However, specific analysis of hyperoxia exposure on neurogenesis is still lacking. Thus, the aim of the present study was to evaluate possible changes in the morphometric parameters of the main neurogenic sites in newborn rats exposed to 60 or 95 % oxygen for the first 14 postnatal days. The optical disector, a morphometric method based upon unbiased sampling principles of stereology, was applied to analyse cell densities, total volumes, and total cell numbers of the dentate gyrus (DG) and subventricular zone (SVZ). Apoptosis and proliferation were also studied by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling method and anti-ki67 immunohistochemistry, respectively. Severe hyperoxia increased the percentage of apoptotic cells in the DG. Moderate and severe hyperoxia induced a proliferative response both in the DG and SVZ, but the two neurogenic sites showed different changes in their morphometric parameters. The DG of both the hyperoxic groups showed lower volume and total cell number than that of the normoxic one. Conversely, the SVZ of newborn rats exposed to 95 % hyperoxia showed statistically significant higher volume and total cell number than SVZ of rats raised in normoxia. Our findings indicate that hyperoxia exposure in the first postnatal period affects both the neurogenic areas, although in different ways, i.e. reduction of DG and expansion of SVZ.

Microarray-assisted fine mapping of quantitative trait loci on chromosome 15 for susceptibility to seizure-induced cell death in mice

Prior studies with crosses of the FVB/NJ (FVB; seizure-induced cell death-susceptible) mouse and the C57BL/6J (B6; seizure-induced cell death-resistant) mouse revealed the presence of a quantitative trait locus (QTL) on chromosome 15 that influenced susceptibility to kainic acid-induced cell death (Sicd2). In an earlier study, we confirmed that the Sicd2 interval harbors gene(s) conferring strong protection against seizure-induced cell death through the creation of the FVB.B6-Sicd2 congenic strain, and created three interval-specific congenic lines (ISCLs) that encompass Sicd2 on chromosome 15 to fine-map this locus. To further localise this Sicd2 QTL, an additional congenic line carrying overlapping intervals of the B6 segment was created (ISCL-4), and compared with the previously created ISCL-1-ISCL-3 and assessed for seizure-induced cell death phenotype. Whereas all of the ISCLs showed reduced cell death associated with the B6 phenotype, ISCL-4, showed the most extensive reduction in seizure-induced cell death throughout all hippocampal subfields. In order to characterise the susceptibility loci on Sicd2 by use of this ISCL and identify compelling candidate genes, we undertook an integrative genomic strategy of comparing exon transcript abundance in the hippocampus of this newly developed chromosome 15 subcongenic line (ISCL-4) and FVB-like littermates. We identified 10 putative candidate genes that are alternatively spliced between the strains and may govern strain-dependent differences in susceptibility to seizure-induced excitotoxic cell death. These results illustrate the importance of identifying transcriptomics variants in expression studies, and implicate novel candidate genes conferring susceptibility to seizure-induced cell death.

Cholesterol and perhaps estradiol protect against corticosterone-induced hippocampal CA3 dendritic retraction in gonadectomized female and male rats

Chronic stress or glucocorticoid exposure simplifies hippocampal Cornu Ammonis region 3 (CA3) apical dendritic arbors in male rats. In contrast to males, chronic stress either reduces CA3 basal branching or exerts no observable morphological effects in gonadally intact female rats. Under conditions that females display stress-induced CA3 dendritic retraction, such as that following ovariectomy, chronic exposure to 17β-estradiol or cholesterol can negate these changes. Whether glucocorticoids produce CA3 dendritic retraction in ovariectomized females and whether neuroprotection from 17β-estradiol or cholesterol is sex-specific remains unknown. The current study examined the effects of chronic glucocorticoid exposure, in conjunction with 17β-estradiol or cholesterol administration, on hippocampal CA3 dendritic complexity. Adult male and female Sprague-Dawley rats were gonadectomized and implanted with 25% 17β-estradiol in cholesterol, 100% cholesterol, or blank Silastic capsules. Rats were then assigned to either a 21-day corticosterone (CORT) drink (400μg/ml CORT, 2.4% ethanol in tap water) or tap water (Tap, 2.4% ethanol in tap water) treatment. Brains were processed for Golgi staining, and hippocampal CA3 dendritic architecture was quantified. Results showed 21-day CORT administration reduced hippocampal CA3 apical dendritic branch points, CA3 apical dendritic length, body weight gain, and adrenal weights compared to male and female control counterparts. Furthermore, male and female rats implanted with Silastic capsules containing cholesterol or 25% 17β-estradiol in cholesterol were protected from CORT-induced CA3 apical dendritic branch reduction. No effects were observed in the CA3 basal dendritic arbors. The present results demonstrate that CORT produces hippocampal CA3 dendritic retraction in gonadectomized male and female rats and that cholesterol and 25% 17β-estradiol in cholesterol prevent this dendritic simplification.

The effects of glycemic control on seizures and seizure-induced excitotoxic cell death

Background

Epilepsy is the most common neurological disorder after stroke, affecting more than 50 million persons worldwide. Metabolic disturbances are often associated with epileptic seizures, but the pathogenesis of this relationship is poorly understood. It is known that seizures result in altered glucose metabolism, the reduction of intracellular energy metabolites such as ATP, ADP and phosphocreatine and the accumulation of metabolic intermediates, such as lactate and adenosine. In particular, it has been suggested that the duration and extent of glucose dysregulation may be a predictor of the pathological outcome of status. However, little is known about neither the effects of glycemic control on brain metabolism nor the effects of managing systemic glucose concentrations in epilepsy.

Results

In this study, we examined glycemic modulation of kainate-induced seizure sensitivity and its neuropathological consequences. To investigate the relationship between glycemic modulation, seizure susceptibility and its neuropathological consequences, C57BL/6 mice (excitotoxin cell death resistant) were subjected to hypoglycemia or hyperglycemia, followed by systemic administration of kainic acid to induce seizures. Glycemic modulation resulted in minimal consequences with regard to seizure severity but increased hippocampal pathology, irrespective of whether mice were hypoglycemic or hyperglycemic prior to kainate administration. Moreover, we found that exogenous administration of glucose following kainic acid seizures significantly reduced the extent of hippocampal pathology in FVB/N mice (excitotoxin cell death susceptible) following systemic administration of kainic acid.

Conclusion

These findings demonstrate that modulation of the glycemic index can modify the outcome of brain injury in the kainate model of seizure induction. Moreover, modulation of the glycemic index through glucose rescue greatly diminishes the extent of seizure-induced cell death following kainate administration. Our data support the hypothesis that deficient insulin signaling may represent a critical contributing factor in the susceptibility to seizure-induced cell death and this may be an important therapeutic target.

Stress and inflammation reduce brain-derived neurotrophic factor expression in first-episode psychosis: a pathway to smaller hippocampal volume

BACKGROUND

Reduced brain-derived neurotrophic factor (BDNF) levels have been reported in the serum and plasma of patients with psychosis. The aim of this cross-sectional case-control study was to investigate potential causes and consequences of reduced BDNF expression in these patients by examining the association between BDNF levels and measures of stress, inflammation, and hippocampal volume in first-episode psychosis.

METHOD

Brain-derived neurotrophic factor, interleukin (IL)-6, and tumor necrosis factor (TNF)-α messenger RNA levels were measured in the leukocytes of 49 first-episode psychosis patients (DSM-IV criteria) and 30 healthy controls, all aged 18 to 65 years, recruited between January 2006 and December 2008. Patients were recruited from inpatient and outpatient units of the South London and Maudsley National Health Service Foundation Trust in London, United Kingdom, and the healthy controls were recruited from the same catchment area via advertisement and volunteer databases. In these same subjects, we measured salivary cortisol levels and collected information about psychosocial stressors (number of childhood traumas, number of recent stressors, and perceived stress). Finally, hippocampal volume was measured using brain magnetic resonance imaging in a subsample of 19 patients.

RESULTS

Patients had reduced BDNF (effect size, d = 1.3; P < .001) and increased IL-6 (effect size, d = 1.1; P < .001) and TNF-α (effect size, d = 1.7; P < .001) gene expression levels when compared with controls, as well as higher levels of psychosocial stressors. A linear regression analysis in patients showed that a history of childhood trauma and high levels of recent stressors predicted lower BDNF expression through an inflammation-mediated pathway (adjusted R(2) = 0.23, P = .009). In turn, lower BDNF expression, increased IL-6 expression, and increased cortisol levels all significantly and independently predicted a smaller left hippocampal volume (adjusted R(2) = 0.71, P < .001).

CONCLUSIONS

Biological changes activated by stress represent a significant factor influencing brain structure and function in first-episode psychosis through an effect on BDNF.