What do we know about the long-term consequences of stress on ageing and the progression of age-related neurodegenerative disorders?

Acute stress impacts reaction times in older but not in young adults in a flanker task

Acute psychosocial stress effects on inhibition have been investigated in young adults, but little is known about these effects in older adults. The present study investigated effects of the Trier Social Stress Test on cognitive inhibition (i.e., ability to ignore distracting information) using a cross-over (stress vs. control) design in healthy young (N = 50; 18-30 years; Mage = 23.06) versus older adults (N = 50; 65-84 years; Mage = 71.12). Cognitive inhibition was measured by a letter flanker task and psychophysiological measures (cortisol, heart rate, subjective stress) validated the stress induction. The results showed that while stress impaired overall accuracy across age groups and sessions, stress (vs. control) made older adults' faster in session 1 and slower in session 2. Given that session 2 effects were likely confounded by practice effects, these results suggest that acute psychosocial stress improved older adults' RTs on a novel flanker task but impaired RTs on a practiced flanker task. That is, the interaction between stress and learning effects might negatively affect response execution when testing older adults on flanker tasks. If confirmed by future research, these results might have important implications especially in settings where repeated cognitive testing is performed under acute stress.

Family history of FXTAS is associated with age-related cognitive-linguistic decline among mothers with the FMR1 premutation

BACKGROUND

Women who carry a premutation allele of the FMR1 gene are at increased vulnerability to an array of age-related symptoms and disorders, including age-related decline in select cognitive skills. However, the risk factors for age-related decline are poorly understood, including the potential role of family history and genetic factors. In other forms of pathological aging, early decline in syntactic complexity is observed and predicts the later onset of neurodegenerative disease. To shed light on the earliest signs of degeneration, the present study characterized longitudinal changes in the syntactic complexity of women with the FMR1 premutation across midlife, and associations with family history of fragile X-associated tremor/ataxia syndrome (FXTAS) and CGG repeat length.

METHODS

Forty-five women with the FMR1 premutation aged 35-64 years at study entry participated in 1-5 longitudinal assessments spaced approximately a year apart (130 observations total). All participants were mothers of children with confirmed fragile X syndrome. Language samples were analyzed for syntactic complexity and participants provided information on family history of FXTAS. CGG repeat length was determined via molecular genetic testing.

RESULTS

Hierarchical linear models indicated that women who reported a family history of FXTAS exhibited faster age-related decline in syntactic complexity than those without a family history, with that difference emerging as the women reached their mid-50 s. CGG repeat length was not a significant predictor of age-related change.

CONCLUSIONS

Results suggest that women with the FMR1 premutation who have a family history of FXTAS may be at increased risk for neurodegenerative disease, as indicated by age-related loss of syntactic complexity. Thus, family history of FXTAS may represent a personalized risk factor for age-related disease. Follow-up study is needed to determine whether syntactic decline is an early indicator of FXTAS specifically, as opposed to being a more general age-related cognitive decline associated with the FMR1 premutation.

Does older adults' cognition particularly suffer from stress? A systematic review of acute stress effects on cognition in older age

This literature review provides the first comprehensive qualitative and quantitative systematic synthesis of acute laboratory stress effects on older adults' cognition by specifying the direction and magnitude of those effects both overall and for different cognitive processes separately. A systematic literature search was performed, and effect sizes estimated whenever possible. We found meta-analytical evidence that stress has negative effects on older adults' verbal fluency (g_adj = -0.53, 95 % CI [-2.70, 1.63]), null-to-negative effects on episodic memory (g_adj = -0.26, 95 % CI [-0.44, -0.08]), null effects on executive functions (g_adj = 0.07, 95 % CI [-0.31, 0.46]), and enhancing effects on working memory (g_adj = 0.16, 95 % CI [-0.01, 0.33]). Relating these findings to those in young adults, notable differences emerged for some cognitive functions, such as opposing effects on working memory between age groups. Our review further reveals that stress effects on older adults' memory retention, associative memory, prospective memory, interference control or cognitive flexibility are heavily understudied. We provide a conceptual and methodological framework for future studies in older adults.

In vivo biomarkers of structural and functional brain development and aging in humans

Brain aging is a major determinant of aging. Along with the aging population, prevalence of neurodegenerative diseases is increasing, therewith placing economic and social burden on individuals and society. Individual rates of brain aging are shaped by genetics, epigenetics, and prenatal environmental. Biomarkers of biological brain aging are needed to predict individual trajectories of aging and the risk for age-associated neurological impairments for developing early preventive and interventional measures. We review current advances of in vivo biomarkers predicting individual brain age. Telomere length and epigenetic clock, two important biomarkers that are closely related to the mechanistic aging process, have only poor deterministic and predictive accuracy regarding individual brain aging due to their high intra- and interindividual variability. Phenotype-related biomarkers of global cognitive function and brain structure provide a much closer correlation to age at the individual level. During fetal and perinatal life, autonomic activity is a unique functional marker of brain development. The cognitive and structural biomarkers also boast high diagnostic specificity for determining individual risks for neurodegenerative diseases.

Spatial Learning Is Impaired in Male Pubertal Rats Following Neonatal Daily but Not Randomly Spaced Maternal Deprivation

Severe early life stress has long been associated with neuropsychological disorders in adulthood, including depression, schizophrenia, post-traumatic stress disorder, and memory dysfunction. To some extent, all of these conditions involve dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and reduced negative feedback inhibition of cortisol release in adulthood. However, the time course for mental health and hormonal outcomes across life stages and the attributes of early life stress that direct the behavioral and biological alterations is not fully understood. We designed our studies to compare outcomes of the two most common maternal deprivation schedules on cognitive ability prior to adulthood. We exposed rat pups to daily or randomly spaced maternal separation bouts within the first 3 weeks of life and examined cognitive performance, neurotrophic signaling, and stress and immune system markers during puberty. We found that the daily separation schedule impaired spatial learning while the randomly spaced schedule did not alter maze performance relative to normally reared control animals. Animals that underwent daily separation showed a tendency for reduced body weight compared to the randomly spaced condition, but there were no differences in adrenal weight. Thymus weight normalized by body weight was increased following daily separation compared to random separation and control conditions. Plasma corticosterone levels measured after behavior testing did not differ amongst experimental groups and there was no impact of TrKB receptor inhibition. Combined, the results show that different early life stress schedules produce different behavioral and biological outcomes when measured at puberty. Combined with prior findings from more mature animals, the results presented here suggest that daily neonatal stress produces varied alterations in spatial cognition at different life stages with a transient learning deficit at puberty preceding a more persistent and a progressive memory impairment through adulthood and into aging.

[Age-related changes in the immune system and cognitive disorders in vascular dementia and Alzheimer's disease]

The immune mechanisms of cognitive impairment are considered. Various causal relationships of the development of immune and neurodegenerative disorders, including vascular dementia (VD) and Alzheimer's disease (AD), are analyzed. It has been shown that age-related adaptive restructuring of immunity leads to the fact that lymphocytic immunity as a whole begins to work in an intermediate metastable state. The dominant role of immune factors in the development of VD and AD is highlighted. It is concluded that the pathogenesis of neurodegenerative diseases is associated with a decrease in antibody activity. The number of cytokines in aging animals is significantly reduced which leads to a decrease in the level of the immune response of the cell.

From Healthy Aging to Frailty: In Search of the Underlying Mechanisms

Population aging is accelerating rapidly worldwide, from 461 million people older than 65 years in 2004 to an estimated 2 billion people by 2050, leading to critical implications for the planning and delivery of health and social care. The most problematic expression of population aging is the clinical condition of frailty, which is a state of increased vulnerability that develops as a consequence of the accumulation of microscopic damages in many physiological systems that lead to a striking and disproportionate change in health state, even after an apparently small insult. Since little is known about the biology of frailty, an important perspective to understand this phenomenon is to establish how the alterations that physiologically occur during a condition of healthy aging may instead promote cumulative decline with subsequent depletion of homoeostatic reserve and increase the vulnerability also after minor stressor events. In this context, the present review aims to provide a description of the molecular mechanisms that, by having a critical impact on behavior and neuronal function in aging, might be relevant for the development of frailty. Moreover, since these biological systems are also involved in the coping strategies set in motion to respond to environmental challenges, we propose a role for lifestyle stress as an important player to drive frailty in aging.

Environment-dependent striatal gene expression in the BACHD rat model for Huntington disease

Huntington disease (HD) is an autosomal dominant neurodegenerative disorder caused by a mutation in the huntingtin (HTT) gene which results in progressive neurodegeneration in the striatum, cortex, and eventually most brain areas. Despite being a monogenic disorder, environmental factors influence HD characteristics. Both human and mouse studies suggest that mutant HTT (mHTT) leads to gene expression changes that harbor potential to be modulated by the environment. Yet, the underlying mechanisms integrating environmental cues into the gene regulatory program have remained largely unclear. To better understand gene-environment interactions in the context of mHTT, we employed RNA-seq to examine effects of maternal separation (MS) and environmental enrichment (EE) on striatal gene expression during development of BACHD rats. We integrated our results with striatal consensus modules defined on HTT-CAG length and age-dependent co-expression gene networks to relate the environmental factors with disease progression. While mHTT was the main determinant of expression changes, both MS and EE were capable of modulating these disturbances, resulting in distinctive and in several cases opposing effects of MS and EE on consensus modules. This bivalent response to maternal separation and environmental enrichment may aid in explaining their distinct effects observed on disease phenotypes in animal models of HD and related neurodegenerative disorders.

Sex differences in chronic stress responses and Alzheimer's disease

Clinical studies indicate that Alzheimer's disease (AD) disproportionately affects women in both disease prevalence and severity, but the mechanisms underlying this sex divergence are unknown. Though some have suggested this difference in risk is a reflection of known differences in longevity between men and women, mounting clinical and preclinical evidence supports women also having intrinsic susceptibilities towards the disease. While a number of potential risk factors have been hypothesized to affect these differences in risks, none have been definitively verified. In this review, we discuss a novel hypothesis whereby women's susceptibility to chronic stress also mediates increased risk for AD. As stress is a risk factor for AD, and women are twice as likely to develop mood disorders where stress is a major etiology, it is possible that sex dimorphisms in stress responses contribute to the increase in women with AD. In line with this, sex divergence in biochemical responses to stress have been noted along the hypothalamic-pituitary-adrenal (HPA) axis and among known molecular effectors of AD, with crosstalk between these processes also being likely. In addition, activation of the cortical corticotrophin-releasing factor receptor 1 (CRF1) signaling pathway leads to distinct female-biased increases in molecules associated with AD pathogenesis. Therefore, the different biochemical responses to stress between women and men may represent an intrinsic, sex-dependent risk factor for AD.

Targeting psychologic stress signaling pathways in Alzheimer's disease

Alzheimer's Disease (AD) is the most prevalent progressive neurodegenerative disease; to date, no AD therapy has proven effective in delaying or preventing the disease course. In the search for novel therapeutic targets in AD, it has been shown that increased chronic psychologic stress is associated with AD risk. Subsequently, biologic pathways underlying psychologic stress have been identified and shown to be able to exacerbate AD relevant pathologies. In this review, we summarize the literature relevant to the association between psychologic stress and AD, focusing on studies investigating the effects of stress paradigms on transgenic mouse models of Amyloid-β (Aβ) and tau pathologies. In recent years, a substantial amount of research has been done investigating a key stress-response mediator, corticotropin-releasing hormone (CRH), and its interactions with AD relevant processes. We highlight attempts to target the CRH signaling pathway as a therapeutic intervention in these transgenic mouse models and discuss how targeting this pathway is a promising avenue for further investigation.

Child mortality, hypothalamic-pituitary-adrenal axis activity and cellular aging in mothers

Psychological challenges, including traumatic events, have been hypothesized to increase the age-related pace of biological aging. Here we test the hypothesis that psychological challenges can affect the pace of telomere attrition, a marker of cellular aging, using data from an ongoing longitudinal-cohort study of Kaqchikel Mayan women living in a population with a high frequency of child mortality, a traumatic life event. Specifically, we evaluate the associations between child mortality, maternal telomere length and the mothers’ hypothalamic-pituitary-adrenal axis (HPAA), or stress axis, activity. Child mortality data were collected in 2000 and 2013. HPAA activity was assessed by quantifying cortisol levels in first morning urinary specimens collected every other day for seven weeks in 2013. Telomere length (TL) was quantified using qPCR in 55 women from buccal specimens collected in 2013. Results: Shorter TL with increasing age was only observed in women who experienced child mortality (p = 0.015). Women with higher average basal cortisol (p = 0.007) and greater within-individual variation (standard deviation) in basal cortisol (p = 0.053) presented shorter TL. Non-parametric bootstrapping to estimate mediation effects suggests that HPAA activity mediates the effect of child mortality on TL. Our results are, thus, consistent with the hypothesis that traumatic events can influence cellular aging and that HPAA activity may play a mediatory role. Future large-scale longitudinal studies are necessary to confirm our results and further explore the role of the HPAA in cellular aging, as well as to advance our understanding of the underlying mechanisms involved.

The Effect of Neonatal Maternal Stress on Plasma Levels of Adrenocorticotropic Hormone, Corticosterone, Leptin, and Ghrelin in Adult Male Rats Exposed to Acute Heterotypic Stressor

Activation of the hypothalamic-pituitary-adrenal (HPA) axis is important for maintenance of homeostasis during stress. Recent studies have shown a connection between the HPA axis and adipose tissue. The present study investigated the effect of acute heterotypic stress on plasma levels of adrenocorticotropic hormone (ACTH), corticosterone (CORT), leptin, and ghrelin in adult male rats with respect to neonatal maternal social and physical stressors. Thirty rat mothers and sixty of their male progeny were used. Pups were divided into three groups: unstressed control (C), stressed by maternal social stressor (S), stressed by maternal social and physical stressors (SW). Levels of hormones were measured in adult male progeny following an acute swimming stress (10 min) or no stress. ELISA immunoassay was used to measured hormones. The ACTH and CORT levels were significantly increased in all groups of adult progeny after acute stress; however, CORT levels were significantly lower in both neonatally stressed groups compared to controls. After acute stress, plasma leptin levels were decreased in the C and SW groups but increased in the S group. The data suggest that long-term neonatal stressors lead to lower sensitivity of ACTH receptors in the adrenal cortex, which could be a sign of stress adaptation in adulthood. Acute stress in adult male rats changes plasma levels of leptin differently relative to social or physical neonatal stressors.

Early-life stress changes expression of GnRH and kisspeptin genes and DNA methylation of GnRH3 promoter in the adult zebrafish brain

Early-life stress can cause long-term effects in the adulthood such as alterations in behaviour, brain functions and reproduction. DNA methylation is a mechanism of epigenetic change caused by early-life stress. Dexamethasone (DEX) was administered to zebrafish larvae to study its effect on reproductive dysfunction. The level of GnRH2, GnRH3, Kiss1 and Kiss2 mRNAs were measured between different doses of DEX treatment groups in adult zebrafish. Kiss1 and GnRH2 expression were increased in the 200mg/L DEX treated while Kiss2 and GnRH3 mRNA levels were up-regulated in the 2mg/L DEX-treated zebrafish. The up-regulation may be related to programming effect of DEX in the zebrafish larvae, causing overcompensation mechanism to increase the mRNA levels. Furthermore, DEX treatment caused negative impact on the development and maturation of the testes, in particular spermatogenesis. Therefore, immature gonadal development may cause positive feedback by increasing GnRH and Kiss. This indicates that DEX can alter the regulation of GnRH2, GnRH3, Kiss1 and Kiss2 in adult zebrafish, which affects maturation of gonads. Computer analysis of 1.5 kb region upstream of the 5' UTR of Kiss1, Kiss2, GnRH2 and GnRH3 promoter showed that there are putative binding sites of glucocorticoid response element and transcription factors involved in stress response. GnRH3 promoter analysed from pre-optic area, ventral telencephalon and ventral olfactory bulb showed higher methylation at CpG residues located on -1410, -1377 and -1355 between control and 2mg/L DEX-treated groups. Hence, early-life DEX treatment can alter methylation of GnRH3 gene promoter, which subsequently affects gene regulation and reproductive functions.

Prenatal restraint stress decreases the expression of alpha-7 nicotinic receptor in the brain of adult rat offspring

Prenatal stress (PS) strongly impacts fetal brain development and function in adulthood. In normal aging and Alzheimer's disease, there is hypothalamic-pituitary-adrenal axis dysfunction and loss of cholinergic neurons and neuronal nicotinic acetylcholine receptors (nAChRs). This study investigated whether prenatal restraint stress affects nAChR expression in the brain of adult offspring. For PS, pregnant dams were placed in a plastic restrainer for 45 min, three times daily during the last week of pregnancy; controls were undisturbed. Male offspring were analyzed at postnatal day (PND) 60 (n = 4 rats per group). Western blot (WB) and fluorescence microscopy showed that PS decreased α7-AChR subunit expression (∼50%) in the frontal cortex in the adult offspring. PS decreased significantly the number of α7-AChR-expressing cells in the medial prefrontal cortex (by ∼25%) and in the sensory-motor cortex (by ∼20%) without affecting the total cell number in those areas. No alterations were found in the hippocampus by quantitative polymerase chain reaction (qPCR), or WB analysis, but a detailed fluorescence microscopy analysis showed that PS affected α7-AChR mainly in the CA3 and dentate gyrus subfields: PS decreased α7-AChR subunit expression by ∼25 and ∼30%, respectively. Importantly, PS decreased the number of α7-AChR-expressing cells and the total cell number (by ∼15 and 20%, respectively) in the dentate gyrus. PS differently affected α4-AChR: PS impaired its mRNA expression in the frontal cortex (by ∼50%), without affecting protein levels. These results demonstrate that disturbances during gestation produce long-term alterations in the expression pattern of α7-AChR in rat brain.

Organismal stress, telomeres and life histories

Most organisms, including ourselves, are exposed to environmental stressors at various points during life, and responses to such stressors have been optimised by evolution to give the best fitness outcomes. It is expected that environmental change will substantially increase long-term stress exposure in many animal groups in the coming decades. A major challenge for biologists is to understand and predict how this will influence individuals, populations and ecosystems, and over what time scale such effects will occur. This requires a multi-disciplinary approach, combining studies of mechanisms with studies of fitness consequences for individuals and their descendants. In this review, I discuss the positive and negative fitness consequences of responses to stressful environments, particularly during early life, and with an emphasis on studies in birds. As many of the mechanisms underlying stress responses are highly conserved across the vertebrate groups, the findings from these studies have general applicability when interpreted in a life history context. One important route that has recently been identified whereby chronic stress exposure can affect health and longevity over long time frames is via effects on telomere dynamics. Much of this work has so far been done on humans, and is correlational in nature, but studies on other taxa, and experimental work, are increasing. I summarise the relevant aspects of vertebrate telomere biology and critically appraise our current knowledge with a view to pointing out important future research directions for our understanding of how stress exposure influences life histories.

Security of attachment to spouses in late life: Concurrent and prospective links with cognitive and emotional wellbeing

Social ties are powerful predictors of late-life health and wellbeing. Although many adults maintain intimate partnerships into late life, little is known about mental models of attachment to spouses and how they influence aging. Eighty-one elderly heterosexual couples (162 individuals) were interviewed to examine the structure of attachment security to their partners and completed measures of cognition and wellbeing concurrently and 2.5 years later. Factor analysis revealed a single factor for security of attachment. Higher security was linked concurrently with greater marital satisfaction, fewer depressive symptoms, better mood, and less frequent marital conflicts. Greater security predicted lower levels of negative affect, less depression, and greater life satisfaction 2.5 years later. For women, greater security predicted better memory 2.5 years later and attenuated the link between frequency of marital conflict and memory deficits. Late in life, mental models of attachment to partners are linked to wellbeing concurrently and over time.

Transgenerational effects of maternal care interact with fetal growth and influence attention skills at 18 months of age

BACKGROUND

Evidence suggests that there is an association between being born small for gestational age (SGA) and an increased risk of internalizing and externalizing problems, such as ADHD. Additionally, individuals who report having received a lower quality of maternal care show an increased prevalence of depression and anxiety, and they are generally worse caregivers of their offspring. Therefore, an interaction between the birth weight status and the quality of maternal care perceived by the mother could affect behavioral outcomes of the children.

AIMS

Evaluate the influence of being born SGA and parental bonding, as perceived by the mother during her infancy, on the children's behavior at 18 months of age.

STUDY DESIGN

Nested cross-sectional study within a Canadian prenatal cohort (MAVAN, Maternal Adversity, Vulnerability and Neurodevelopment) recruited from 2003 to 2010.

SUBJECTS

Data from 305 children who were evaluated at 18 months of age.

OUTCOME MEASURES

Early Childhood Behavior Questionnaire--ECBQ and Infant-Toddler Social and Emotional Assessment--ITSEA) were included.

RESULTS

Children born SGA whose mothers reported low maternal care during her infancy (using the Parental Bonding Instrument--PBI) showed lower scores in the attentional set shifting trait (ECBQ, p=0.002) and attention construct (ITSEA, p=0.05) at 18 months of age. We also found that SGA increases decreases cuddliness (p=0.011) and poor perceived maternal care decreases low intensity pleasure (p=0.016) on the ECBQ.

CONCLUSIONS

These findings suggest a complex transgenerational transmission whereby mother's own care interacts with the fetal growth of her offspring to predict its attentional skills at 18 months of age.

A robust and reliable non-invasive test for stress responsivity in mice

Stress and an altered stress response have been associated with many multifactorial diseases, such as psychiatric disorders or neurodegenerative diseases. As currently mouse mutants for each single gene are generated and phenotyped in a large-scale manner, it seems advisable also to test these mutants for alterations in their stress responses. Here we present the determinants of a robust and reliable non-invasive test for stress-responsivity in mice. Stress is applied through restraining the mice in tubes and recording behavior in the Open Field 20 min after cessation of the stress. Two hours, but not 15 or 50 min of restraint lead to a robust and reproducible increase in distance traveled and number of rearings during the first 5 min in the Open Field in C57BL/6 mice. This behavioral response is blocked by the corticosterone synthesis inhibitor metyrapone, but not by RU486 treatment, indicating that it depends on corticosteroid secretion, but is not mediated via the glucocorticoid receptor type II. We assumed that with a stress duration of 15 min one could detect hyper-responsivity, and with a stress duration of 2 h hypo-responsivity in mutant mouse lines. This was validated with two mutant lines known to show opposing effects on corticosterone secretion after stress exposure, corticotropin-releasing hormone (CRH) over-expressing mice and CRH receptor 1 knockout (KO) mice. Both lines showed the expected phenotype, i.e., increased stress responsivity in the CRH over-expressing mouse line (after 15 min restraint stress) and decreased stress responsivity in the CRHR1-KO mouse line (after 2 h of restraint stress). It is possible to repeat the acute stress test several times without the stressed animal adapting to it, and the behavioral response can be robustly evoked at different ages, in both sexes and in different mouse strains. Thus, locomotor and rearing behavior in the Open Field after an acute stress challenge can be used as reliable, non-invasive indicators of stress responsivity and corticosterone secretion in mice.

Stress exposure in early post-natal life reduces telomere length: an experimental demonstration in a long-lived seabird

Exposure to stressors early in life is associated with faster ageing and reduced longevity. One important mechanism that could underlie these late life effects is increased telomere loss. Telomere length in early post-natal life is an important predictor of subsequent lifespan, but the factors underpinning its variability are poorly understood. Recent human studies have linked stress exposure to increased telomere loss. These studies have of necessity been non-experimental and are consequently subjected to several confounding factors; also, being based on leucocyte populations, where cell composition is variable and some telomere restoration can occur, the extent to which these effects extend beyond the immune system has been questioned. In this study, we experimentally manipulated stress exposure early in post-natal life in nestling European shags (Phalacrocorax aristotelis) in the wild and examined the effect on telomere length in erythrocytes. Our results show that greater stress exposure during early post-natal life increases telomere loss at this life-history stage, and that such an effect is not confined to immune cells. The delayed effects of increased telomere attrition in early life could therefore give rise to a ‘time bomb’ that reduces longevity in the absence of any obvious phenotypic consequences early in life.

Correlations of behavioral deficits with brain pathology assessed through longitudinal MRI and histopathology in the R6/1 mouse model of Huntington's disease

Huntington's disease (HD) is caused by the expansion of a CAG repeat in the huntingtin (HTT) gene. The R6 mouse models of HD express a mutant version of exon 1 HTT and typically develop motor and cognitive impairments, a widespread huntingtin (HTT) aggregate pathology and brain atrophy. Unlike the more commonly used R6/2 mouse line, R6/1 mice have fewer CAG repeats and, subsequently, a less rapid pathological decline. Compared to the R6/2 line, fewer descriptions of the progressive pathologies exhibited by R6/1 mice exist. The association between the molecular and cellular neuropathology with brain atrophy, and with the development of behavioral phenotypes remains poorly understood in many models of HD. In attempt to link these factors in the R6/1 mouse line, we have performed detailed assessments of behavior and of regional brain abnormalities determined through longitudinal, in vivo magnetic resonance imaging (MRI), as well as an end-stage, ex vivo MRI study and histological assessment. We found progressive decline in both motor and non-motor related behavioral tasks in R6/1 mice, first evident at 11 weeks of age. Regional brain volumes were generally unaffected at 9 weeks, but by 17 weeks there was significant grey matter atrophy. This age-related brain volume loss was validated using a more precise, semi-automated Tensor Based morphometry assessment. As well as these clear progressive phenotypes, mutant HTT (mHTT) protein, the hallmark of HD molecular pathology, was widely distributed throughout the R6/1 brain and was accompanied by neuronal loss. Despite these seemingly concomitant, robust pathological phenotypes, there appeared to be little correlation between the three main outcome measures: behavioral performance, MRI-detected brain atrophy and histopathology. In conclusion, R6/1 mice exhibit many features of HD, but the underlying mechanisms driving these clear behavioral disturbances and the brain volume loss, still remain unclear.

Adenosine A(2A) receptor blockade reverts hippocampal stress-induced deficits and restores corticosterone circadian oscillation

Maternal separation (MS) is an early life stress model that induces permanent changes in the central nervous system, impairing hippocampal long-term potentiation (LTP) and spatial working memory. There are compelling evidences for a role of hippocampal adenosine A(2A) receptors in stress-induced modifications related to cognition, thus opening a potential window for therapeutic intervention. Here, we submitted rats to MS and evaluated the long-lasting molecular, electrophysiological and behavioral impairments in adulthood. We then assessed the therapeutic potential of KW6002, a blocker of A(2A) receptors, in stress-impaired animals. We report that the blockade of A(2A) receptors was efficient in reverting the behavior, electrophysiological and morphological impairments induced by MS. In addition, this effect is associated with restoration of the hypothalamic-pituitary-adrenal axis (HPA-axis) activity, as both the plasma corticosterone levels and hippocampal glucocorticoid receptor expression pattern returned to physiological-like status after the treatment. These results reveal the involvement of A(2A) receptors in the stress-associated impairments and directly in the stress response system by showing that the dysfunction of the HPA-axis as well as the long-lasting synaptic and behavioral effects of MS can be reverted by targeting adenosine A(2A) receptors. These findings provide a novel evidence for the use of adenosine A(2A) receptor antagonists as potential therapy against psychopathologies.

Cognitive ability and decline after early life stress exposure

We examined the effects of early life stress on cognitive ability and decline among men of the Helsinki Birth Cohort Study, 10% of whom were separated temporarily (mean age at separation = 4.1 years) from their parent(s) during World War II. The men underwent the Finnish Defense Forces Basic Intellectual Ability Test twice, at 20 years and retest at 70 years. Compared with the men without childhood separation and matched for year of birth (n = 186), men separated from their parents (n = 93) scored lower by 5.5 (95% confidence interval [CI], -9.2 to -1.7), 4.2 (95% CI, -8.1 to -0.3), 3.1 (95% CI, -7.0 to 0.8), and 4.5 (95% CI, -10.5 to -1.4) standardized points (SD = 15) on verbal, visuospatial, arithmetic, and general cognitive ability, respectively, at 70 years. Longer duration of separation was associated with lower test scores. Though early life stress was also associated significantly with weaker cognitive performance at the ages 20 and 70 years, it was not associated with cognitive decline over the 50-year period within this sample.

Exploiting the diversity of the heat-shock protein family for primary and secondary tauopathy therapeutics

The heat shock protein (Hsp) family is an evolutionarily conserved system that is charged with preventing unfolded or misfolded proteins in the cell from aggregating. In Alzheimer’s disease, extracellular accumulation of the amyloid β peptide (Aβ) and intracellular aggregation of the microtubule associated protein tau may result from mechanisms involving chaperone proteins like the Hsps. Due to the ability of Hsps to regulate aberrantly accumulating proteins like Aβ and tau, therapeutic strategies are emerging that target this family of chaperones to modulate their pathobiology. This article focuses on the use of Hsp-based therapeutics for treating primary and secondary tauopathies like Alzheimer’s disease. It will particularly focus on the pharmacological targeting of the Hsp70/90 system and the value of manipulating Hsp27 for treating Alzheimer’s disease.

Closing the gap between clinic and cage: sensori-motor and cognitive behavioural testing regimens in neurotoxin-induced animal models of Parkinson's disease

Animal models that make use of chemical toxins to adversely affect the nigrostriatal dopaminergic pathway of rodents and primates have contributed significantly towards the development of symptomatic therapies for Parkinson's disease (PD) patients. Although their use in developing neuro-therapeutic and -regenerative compounds remains to be ascertained, toxin-based mammalian and a range of non-mammalian models of PD are important tools in the identification and validation of candidate biomarkers for earlier diagnosis, as well as in the development of novel treatments that are currently working their way into the clinic. Toxin models of PD have and continue to be important models to use for understanding the consequences of nigrostriatal dopamine cell loss. Functional assessment of these models is also a critical component for eventual translational success. Sensitive behavioural testing regimens for assessing the extent of dysfunction exhibited in the toxin models, the degree of protection or improvement afforded by potential treatment modalities, and the correlation of these findings with what is observed clinically in PD patients, ultimately determines whether a potential treatment moves to clinical trials. Here, we review existing published work that describes the use of such behavioural outcome measures associated with toxin models of parkinsonism. In particular, we focus on tests assessing sensorimotor and cognitive function, both of which are significantly and progressively impaired in PD.

Gestational restraint stress and the developing dopaminergic system: an overview

Prenatal stress exerts a strong impact on fetal brain development in rats impairing adaptation to stressful conditions, subsequent vulnerability to anxiety, altered sexual function, and enhanced propensity to self-administer drugs. Most of these alterations have been attributed to changes in the neurotransmitter dopamine (DA). In humans; dysfunction of dopaminergic system is associated with development of several neurological disorders, such as Parkinson disease, schizophrenia, attention-deficit hyperactivity disorder, and depression. Evidences provided by animal research, as well as retrospective studies in humans, pointed out that exposure to adverse events in early life can alter adult behaviors and neurochemical indicators of midbrain DA activity, suggesting that the development of the DA system is sensitive to disruption by exposure to early stressors. The purpose of this article is to provide a general overview of published studies and our own study related to the effect of prenatal insults on the development of DA metabolism and biology, focusing mainly in articles involving prenatal-restraint stress protocols in rats. We will also attempt to make a correlation between theses alterations and DA-related pathological processes in humans.

Prenatal excess glucocorticoid exposure and adult affective disorders: a role for serotonergic and catecholamine pathways

Fetal glucocorticoid exposure is a key mechanism proposed to underlie prenatal 'programming' of adult affective behaviours such as depression and anxiety. Indeed, the glucocorticoid metabolising enzyme 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2), which is highly expressed in the placenta and the developing fetus, acts as a protective barrier from the high maternal glucocorticoids which may alter developmental trajectories. The programmed changes resulting from maternal stress or bypass or from the inhibition of 11β-HSD2 are frequently associated with alterations in the hypothalamic-pituitary-adrenal (HPA) axis. Hence, circulating glucocorticoid levels are increased either basally or in response to stress accompanied by CNS region-specific modulations in the expression of both corticosteroid receptors (mineralocorticoid and glucocorticoid receptors). Furthermore, early-life glucocorticoid exposure also affects serotonergic and catecholamine pathways within the brain, with changes in both associated neurotransmitters and receptors. Indeed, global removal of 11β-HSD2, an enzyme that inactivates glucocorticoids, increases anxiety- and depressive-like behaviour in mice; however, in this case the phenotype is not accompanied by overt perturbation in the HPA axis but, intriguingly, alterations in serotonergic and catecholamine pathways are maintained in this programming model. This review addresses one of the potential adverse effects of glucocorticoid overexposure in utero, i.e. increased incidence of affective behaviours, and the mechanisms underlying these behaviours including alteration of the HPA axis and serotonergic and catecholamine pathways.

11β-hydroxysteroid dehydrogenases and the brain: from zero to hero, a decade of progress

Glucocorticoids have profound effects on brain development and adult CNS function. Excess or insufficient glucocorticoids cause myriad abnormalities from development to ageing. The actions of glucocorticoids within cells are determined not only by blood steroid levels and target cell receptor density, but also by intracellular metabolism by 11β-hydroxysteroid dehydrogenases (11β-HSD). 11β-HSD1 regenerates active glucocorticoids from their inactive 11-keto derivatives and is widely expressed throughout the adult CNS. Elevated hippocampal and neocortical 11β-HSD1 is observed with ageing and causes cognitive decline; its deficiency prevents the emergence of cognitive defects with age. Conversely, 11β-HSD2 is a dehydrogenase, inactivating glucocorticoids. The major central effects of 11β-HSD2 occur in development, as expression of 11β-HSD2 is high in fetal brain and placenta. Deficient feto-placental 11β-HSD2 results in a life-long phenotype of anxiety and cardiometabolic disorders, consistent with early life glucocorticoid programming.

Interaction between Diazepam and Hippocampal Corticosterone after Acute Stress: Impact on Memory in Middle-Aged Mice

Benzodiazepines (BDZ) are widely prescribed in the treatment of anxiety disorders associated to aging. Interestingly, whereas a reciprocal interaction between the GABAergic system and HPA axis has been evidenced, there is to our knowledge no direct evaluation of the impact of BDZ on both hippocampus (HPC) corticosterone concentrations and HPC-dependent memory in stressed middle-aged subjects. We showed previously that an acute stress induced in middle-aged mice severe memory impairments in a hippocampus-dependent task, and increased in parallel hippocampus corticosterone concentrations, as compared to non-stressed middle-aged controls (Tronche et al., 2010). Based on these findings, the aims of the present study were to evidence the impact of diazepam (a positive allosteric modulator of the GABA-A receptor) on HPC glucocorticoids concentrations and in parallel on HPC-dependent memory in acutely stressed middle-aged mice. Microdialysis experiments showed an interaction between diazepam doses and corticosterone concentrations into the HPC. From 0.25 to 0.5 mg/kg, diazepam dose-dependently reduces intra-HPC corticosterone concentrations and in parallel, dose-dependently increased hippocampal-dependent memory performance. In contrast, the highest (1.0 mg/kg) diazepam dose induces a reduction in HPC corticosterone concentration, which was of greater magnitude as compared to the two other diazepam doses, but however decreased the hippocampal-dependent memory performance. In summary, our study provides first evidence that diazepam restores in stressed middle-aged animals the hippocampus-dependent response, in relation with HPC corticosterone concentrations. Overall, our data illustrate how stress and benzodiazepines could modulate cognitive functions depending on hippocampus activity.

Potential benefits and limitations of enriched environments and cognitive activity on age-related behavioural decline

The main aim of this chapter is to review preclinical studies that have evaluated interventions which may aid in preventing or delaying age-related behavioural decline. Animal models of Environmental Enrichment (EE) are useful for evaluating the influence of cognitive, physical and social stimulation in mitigating cognitive decline at different ages. The EE paradigm has been proposed as a non-invasive treatment for alleviating age-related memory impairment and neurodegenerative diseases. While in this complex environment, rodents can be stimulated at different levels (physical, social, cognitive and sensorial), although a synergism between all these components is likely to play an important role. We will summarize available data relating to EE as a potential therapeutic strategy that slows down or counteracts age-related cognitive and behavioural changes. EE also alters physiological responses and induces neurobiological changes such as stimulation of neurogenesis and neural plasticity. At the behavioural level, EE improves learning and memory tasks and reduces anxiety. Several variables seem to influence the behavioural and cognitive benefits induced by EE, including the age at which animals are first exposed to EE, total period during which animals are submitted to EE, gender, the cognitive task evaluated, the drug administered and individual factors. Cognitive and physical stimulation of animals in enriched experimental environments may lead to a better understanding of factors that promote the formation of cognitive reserve (CR) and a healthier life in humans. In the present chapter we review the potential benefits of EE in aged rodents and in animal models of Alzheimer Disease (AD). Results obtained in preclinical models of EE may be relevant to future research into mental and neurodegenerative diseases, stress, aging and development of enviromimetics. Finally, we outline the main limitations of EE studies (variability between laboratories, difficulty of separating the different components of EE, gender of experimental subjects, individual differences in the response to EE), evaluating the potential benefits of enriched environments and the neurobiological mechanisms that underlie them. We conclude that there are experimental data which demonstrate the cognitive benefits of rearing rodents in enriched environments and discuss their implication for clarifying which variables contribute to the formation of the CR.

Effect by acupuncture on hypothalamic expression of maternally separated rats: proteomic approach

OBJECTIVES

Early stressors can influence the development of biological and neurological systems. Maternal separation (social isolation) in early life may increase vulnerability to neurodegenerative diseases and neuropsychiatric disorders over the lifespan. To identify new proteins on acupuncture effects in maternally separated rats, an animal model for study of early environmental insults, proteomic approach on the expression of the hypothalamic proteins was performed.

METHODS

On post-natal day 14, rat pups were randomly divided into four groups: pups kept with their mothers for 7 days; pups kept with their mothers with acupuncture daily to HT8 (Sobu); maternally separated pups; maternally separated pups with acupuncture. The hypothalamic proteins were analysed by two-dimensional electrophoresis coupled with matrix assisted laser desorption/ionization time-of-flight mass spectrometer.

RESULTS

The results showed that 27 spots were differentially and commonly expressed. Of 27 spots, 21 spots were identified while six spots were not, and 15 proteins were known proteins. In maternally separated group, the expressions of 14 proteins were down-regulated, compared to control group. In group of maternally separation with acupuncture, five proteins were down-regulated and nine were up-regulated, compared to the maternally separated group. Among nine proteins up-regulated by acupuncture treatment, we found four proteins (dihydropyrimidinase-like 2, dystrophin-related protein 2, tubulin, alpha 1a and syntaxin 1b) related to neurodevelopment.

DISCUSSION

The result suggests that acupuncture to HT8 may affect neurodevelopment, and acupuncture may be a possible therapy for neurodevelopmental disorders.

Hormesis, adaptive epigenetic reorganization, and implications for human health and longevity

Hormesis is a common phenomenon in a number of biomedical areas. However, the basic nature of this phenomenon remains largely unknown. Therefore, significant uncertainty is inevitable in attempts to apply hormesis as a pro-health and anti-aging tool. Evidence supporting that hormetic-like effects may be the result of a generalized whole-organism adaptive epigenetic response is reviewed. Specific hormesis-inducing interventions during development would allow to achieve an optimal balance between activation and repression of various genes and thus to prevent age-related degenerative diseases and slow aging. The reasons that oscillating temperature mild stress could potentially be used for human application are discussed.

Chronic stress-mutated presenilin 1 gene interaction perturbs neurogenesis and accelerates neurodegeneration

Recent evidence suggests that supplemental factors coincident with aging and genetic determinants might be involved in the initial progression of Alzheimer's disease (AD). Early studies also indicate that chronic stress decreases hippocampal neurogenesis. Here, we investigate the effect of chronic stress on hippocampal neurogenesis using a transgenic mouse line (Tg) that overexpresses human presenilin 1 (PS1) with a familial AD (FAD)-related mutation in order to elucidate how the combination of chronic stress and mutated genes affects the cytoarchitecture in the hippocampal granule cell layer (GCL), which contributes to spatial learning and memory. Using an original chronic intermittent restraint stress (CIRS) protocol, we examined the effect of stress on hippocampal neurogenesis and neurodegeneration by immunohistochemical analysis. After short-term CIRS, neurodegeneration in Tg mice was significantly increased in the hippocampus with an earlier onset and progression than in the non-stressed Tg mice. Moreover, after long-term CIRS, transitional neurodegeneration appeared to proceed along the neuronal circuit involved in cognitive function in stressed Tg mice. Although the number of Pax6-positive (+) cells (mostly granule neuron precursors) did not significantly decrease during CIRS in both non-Tg and Tg mice, doublecortin (DCX) + neuronal progenitor cells in the GCL were markedly influenced in Tg mice; they were significantly reduced without stress compared with non-stressed non-Tg mice and significantly increased by CIRS compared with non-stressed Tg mice. We conclude from these results that diverse responses against stressful experiences among genetically predisposed individuals could lead to cognitive dysfunction through retardation of neuronal maturation and neurodegeneration.

Bladder cancer in the elderly

INTRODUCTION

Age is now widely accepted as the greatest single risk factor for developing bladder cancer, and bladder cancer is considered as primarily a disease of the elderly. Because of the close link between age and incidence of bladder cancer, it can be expected that this disease will become an enormous challenge with the growth of an aging population in the years ahead.

METHODS

Using MEDLINE, a search of the literature between January 1966 and July 2007 was performed to describe normative physiologic changes associated with aging, elucidate genetic and epigenetic alterations that associate aging with bladder cancer and its phenotypes; and to characterize how aging influences efficacies, risks, side effects, and potential complications of the treatments needed for the various stages of bladder cancer.

RESULTS

We discuss influence of aging on host physiology, genetic and epigenetic changes, environmental influences, and host factors in the development and treatment of bladder cancer. Treatments with intravesical bacille Calmette Guerin, radical cystectomy, and perioperative chemotherapy are less well tolerated and have poorer response in elderly patients compared with their younger counterparts. Elderly patients face both clinical and broader institutional barriers to appropriate treatment and may receive less aggressive treatment and sub-therapeutic dosing. However, when appropriately selected, elderly patients tolerate and respond well to cancer treatments.

CONCLUSIONS

The decision to undergo treatment for cancer is a tradeoff between loss of function and/or independence and extension of life, which is complicated by a host of concomitant issues such as comorbid medical conditions, functional declines and "frailty", family dynamics, and social and psychologic issues. Chronological age should not preclude definitive surgical therapy. It is imperative that healthcare practitioners and researchers from disparate disciplines collectively focus efforts towards gaining a better understanding of what the consequences of bladder cancer and its treatments are for older adults and how to appropriately meet the multifaceted medical and psychosocial needs of this growing population.

Neuroticism in adolescence and cognitive function in midlife in the British 1946 birth cohort: The HALCyon program

We examined whether higher levels of neuroticism in adolescence were associated with poorer cognitive function in midlife in 2,071 members of the British 1946 birth cohort. Higher neuroticism at age 13 was associated with poorer performance on tests of verbal ability, verbal fluency, and verbal memory at age 53 in sex-adjusted analyses. However, higher neuroticism was also associated with poorer cognitive performance at age 8. After adjustment for childhood cognition or educational attainment, the associations between neuroticism at age 13 and midlife cognition ceased to be statistically significant. The link between neuroticism and subsequent cognitive ability may be a reflection of a long-standing correlation between the stable aspects of these traits since childhood, but further measurements of both traits are needed to confirm this.

Chronic stress- and sex-specific neuromorphological and functional changes in limbic structures

Chronic stress produces sex-specific neuromorphological changes in a variety of brain regions, which likely contribute to the gender differences observed in stress-related illnesses and cognitive ability. Here, we review the literature investigating the relationship between chronic stress and sex differences on brain plasticity and function, with an emphasis on morphological changes in dendritic arborization and spines in the hippocampus, prefrontal cortex, and amygdala. These brain structures are highly interconnected and sensitive to stress and gonadal hormones, and influence a variety of cognitive abilities. Although much less work has been published using female subjects than with male subjects, the findings suggest that the relationship between brain morphology and function is very different between the sexes. After reviewing the literature, we present a model showing how chronic stress influences the morphology of these brain regions and changes the dynamic of how these limbic structures interact with each other to produce altered behavioral outcomes in spatial ability, behavioral flexibility/executive function, and emotional arousal.

Delirium and long-term cognitive impairment

Delirium is a severe, acute neuropsychiatric syndrome that is highly prevalent in acute hospital populations. Delirium has noticeable effects on length of hospitalization, cost of care, mortality and morbidity. In addition to these well-established adverse consequences, there is increasing evidence linking delirium and a higher risk of long-term cognitive impairment (LTCI), including dementia. A prior review (Jackson, Gordon, Hart, Hopkins, & Ely, 2004), in which nine studies (total N = 1,885, years 1989-2003) were considered, concluded that there was evidence for an association between delirium and LTCI. Here we provide a review of studies published since Jackson's review. We included nine reports, with a total of 2,025 patients. The studies show diverse sample sizes, methodologies, designs and patient populations. However, taken together, the results of these new studies broadly confirm that there is a link between delirium and LTCI. We go on to discuss putative mechanisms and explanations. These include (1) delirium as a marker of chronic progressive pathology, but unrelated to any progression, (2) delirium as a consequence of acute brain damage which is also responsible for a 'single hit' or triggering of active processes causing LTCI, (3) delirium itself as a cause of LTCI, and (4) drug treatment of delirium or other conditions as a cause of LTCI. We conclude with suggestions for future research.