Calorie restriction reduces psychological stress reactivity and its association with brain volume and microstructure in aged rhesus monkeys

Evaluating depression- and anxiety-like behaviors in non-human primates

Depression and anxiety are some of the most prevalent and debilitating mental health conditions in humans. They can present on their own or as co-morbidities with other disorders. Like humans, non-human primates (NHPs) can develop depression- and anxiety-like signs. Here, we first define human depression and anxiety, examine equivalent species-specific behaviors in NHPs, and consider models and current methods to identify and evaluate these behaviors. We also discuss knowledge gaps, as well as the importance of evaluating the co-occurrence of depression- and anxiety-like behaviors in animal models of human disease. Lastly, we consider ethical challenges in depression and anxiety research on NHPs in order to ultimately advance the understanding and the personalized treatment of these disorders.

Inverse Association between Dietary Diversity Score Calculated from the Diet Quality Questionnaire and Psychological Stress in Chinese Adults: A Prospective Study from China Health and Nutrition Survey

Specific nutrients or dietary patterns influence an individual’s psychological stress. As a major aspect of a healthy diet, the influence of dietary diversity on psychological stress remains uncertain. Within these contexts, we aimed to examine the association between the dietary diversity score and psychological stress, using prospective data from the China Health and Nutrition Survey (CHNS). We included 7434 adult participants, with complete dietary information, in the 2011 wave, and followed-up with perceived stress scale (PSS-14) in the 2015 wave. The dietary intake of foods was coded into 29 food groups, using the DQQ for China, and the dietary diversity scores were obtained, using DQQ, by calculating the number of food groups consumed during one 24-h dietary recall. The univariate analysis, and logistic regression model were used to examine the relationship between psychological stress and diet diversity. Approximately half of the participants (4204, 56.55%) perceived a higher level of stress (PSS-14 total score > 25). Dietary diversity was lower in the higher-stress group (p for trend <0.0001). Unconditional multivariate logistic regression demonstrated that participants with higher daily dietary diversity were less likely to experience higher-level psychological stress, compared with participants with lower daily dietary diversity (ORs range: 0.480−0.809). Dietary diversity was found to be inversely associated with psychological stress, in this prospective analysis of a national population. Further studies are required to figure out the mechanism and effectiveness of dietary diversity on psychological stress.

Horizons in Human Aging Neuroscience: From Normal Neural Aging to Mental (Fr)Agility

While aging is an important risk factor for neurodegenerative disorders such as Alzheimer’s disease and Parkinson’s disease, age-related cognitive decline can also manifest without apparent neurodegenerative changes. In this review, we discuss molecular, cellular, and network changes that occur during normal aging in the absence of neurodegenerative disease. Emerging findings reveal that these changes include metabolic alterations, oxidative stress, DNA damage, inflammation, calcium dyshomeostasis, and several other hallmarks of age-related neural changes that do not act on their own, but are often interconnected and together may underlie age-related alterations in brain plasticity and cognitive function. Importantly, age-related cognitive decline may not be reduced to a single neurobiological cause, but should instead be considered in terms of a densely connected system that underlies age-related cognitive alterations. We speculate that a decline in one hallmark of neural aging may trigger a decline in other, otherwise thus far stable subsystems, thereby triggering a cascade that may at some point also incur a decline of cognitive functions and mental well-being. Beyond studying the effects of these factors in isolation, considerable insight may be gained by studying the larger picture that entails a representative collection of such factors and their interactions, ranging from molecules to neural networks. Finally, we discuss some potential interventions that may help to prevent these alterations, thereby reducing cognitive decline and mental fragility, and enhancing mental well-being, and healthy aging.

Satiety Associated with Calorie Restriction and Time-Restricted Feeding: Central Neuroendocrine Integration

This review focuses on summarizing current knowledge on how time-restricted feeding (TRF) and continuous caloric restriction (CR) affect central neuroendocrine systems involved in regulating satiety. Several interconnected regions of the hypothalamus, brainstem, and cortical areas of the brain are involved in the regulation of satiety. Following CR and TRF, the increase in hunger and reduction in satiety signals of the melanocortin system [neuropeptide Y (NPY), proopiomelanocortin (POMC), and agouti-related peptide (AgRP)] appear similar between CR and TRF protocols, as do the dopaminergic responses in the mesocorticolimbic circuit. However, ghrelin and leptin signaling via the melanocortin system appears to improve energy balance signals and reduce hyperphagia following TRF, which has not been reported in CR. In addition to satiety systems, CR and TRF also influence circadian rhythms. CR influences the suprachiasmatic nucleus (SCN) or the primary circadian clock as seen by increased clock gene expression. In contrast, TRF appears to affect both the SCN and the peripheral clocks, as seen by phasic changes in the non-SCN (potentially the elusive food entrainable oscillator) and metabolic clocks. The peripheral clocks are influenced by the primary circadian clock but are also entrained by food timing, sleep timing, and other lifestyle parameters, which can supersede the metabolic processes that are regulated by the primary circadian clock. Taken together, TRF influences hunger/satiety, energy balance systems, and circadian rhythms, suggesting a role for adherence to CR in the long run if implemented using the TRF approach. However, these suggestions are based on only a few studies, and future investigations that use standardized protocols for the evaluation of the effect of these diet patterns (time, duration, meal composition, sufficiently powered) are necessary to verify these preliminary observations.

Potential associations between immune signaling genes, deactivated microglia, and oligodendrocytes and cortical gray matter loss in patients with long-term remitted Cushing's disease

INTRODUCTION

Cushing's disease (CD) is a rare and severe endocrine disease characterized by hypercortisolemia. Previous studies have found structural brain alterations in remitted CD patients compared to healthy controls, specifically in the anterior cingulate cortex (ACC). However, potential mechanisms through which these persistent alterations may have occurred are currently unknown.

METHODS

Structural 3T MRI's from 25 remitted CD patients were linked with gene expression data from neurotypical donors, derived from the Allen Human Brain Atlas. Differences in gene expression between the ACC and an unaffected control cortical region were examined, followed by a Gene Ontology (GO) enrichment analysis. A cell type enrichment analysis was conducted on the differentially expressed genes, and a disease association enrichment analysis was conducted to determine possible associations between differentially expressed genes and specific diseases. Subsequently, cortisol sensitivity of these genes in existing datasets was examined.

RESULTS

The gene expression analysis identified 300 differentially expressed genes in the ACC compared to the cortical control region. GO analyses found underexpressed genes to represent immune function. The cell type specificity analysis indicated that underexpressed genes were enriched for deactivated microglia and oligodendrocytes. Neither significant associations with diseases, nor evidence of cortisol sensitivity with the differentially expressed genes were found.

DISCUSSION

Underexpressed genes in the ACC, the area vulnerable to permanent changes in remitted CD patients, were often associated with immune functioning. The specific lack of deactivated microglia and oligodendrocytes implicates protective effects of these cell types against the long-term effects of cortisol overexposure.

Inflammation, negative affect, and amyloid burden in Alzheimer's disease: Insights from the kynurenine pathway

BACKGROUND

Depressive symptoms in Alzheimer's disease (AD) predict worse cognitive and functional outcomes. Both AD and major depression inflammatory processes are characterized by shunted tryptophan metabolism away from serotonin (5-HT) and toward the neuroinflammatory kynurenine (Kyn) pathway. The present study assessed associations between Kyn and behavioral, neuroanatomical, neuropathological, and physiological outcomes common to both AD and negative affect across the AD continuum.

METHODS

In 58 cognitively normal, 396 mild cognitive impairment, and 112 AD participants from the Alzheimer's Disease Neuroimaging Initiative-1 (ADNI1) cohort, serum markers of 5-HT, tryptophan, and Kyn were measured and their relationships investigated with immunologic markers, affect and functional outcomes, CSF markers of beta-amyloid (Aβ) and tau, and regional gray matter.

RESULTS

A higher Kyn/Tryptophan ratio was linked to many inflammatory markers, as well as lower functional independence and memory scores. A higher Kyn/5-HT ratio showed similar associations, but also strong relationships with negative affect and neuropsychiatric disturbance, executive dysfunction, and global cognitive decline. Further, gray matter atrophy was seen in hippocampus, anterior cingulate, and prefrontal cortices, as well as greater amyloid and total tau deposition. Finally, using moderated-mediation, several pro-inflammatory factors partially mediated Kyn/5-HT and negative affect scores in participants with subclinical Aβ (i.e., Aβ-), whereas such associations were fully mediated by Complement 3 in Aβ+ participants.

CONCLUSION

These findings suggest that inflammatory signaling cascades may occur during AD, which is associated with increased Kyn metabolism that influences the pathogenesis of negative affect. Aβ and the complement system may be critical contributing factors in this process.

Microglial heterogeneity in aging and Alzheimer's disease: Is sex relevant?

Neurodegenerative diseases and their associated cognitive decline are known to be more prevalent during aging. Recent evidence has uncovered the role of microglia, the immunocompetent cells of the brain, in dysfunctions linked to neurodegenerative diseases such as is Alzheimer's disease (AD). Similar to other pathologies, AD is shown to be sex-biased, with females being more at risk compared to males. While the mechanisms driving this prevalence are still unclear, emerging data suggest the sex differences present in microglia throughout life might lead to different responses of these cells in both health and disease. Furthermore, microglial cells have recently been recognized as a deeply heterogeneous population, with multiple subsets and/or phenotypes stemming from diverse parameters such as age, sex or state of health. Therefore, this review discusses microglial heterogeneity during aging in both basal conditions and AD with a focus on existing sex differences in this process.

Mini-review: Aging of the neuroendocrine system: Insights from nonhuman primate models

The neuroendocrine system (NES) plays a crucial role in synchronizing the physiology and behavior of the whole organism in response to environmental constraints. The NES consists of a hypothalamic-pituitary-target organ axis that acts in coordination to regulate growth, reproduction, stress and basal metabolism. The growth (or somatotropic), hypothalamic-pituitary-gonadal (HPG), hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-thyroid (HPT) axes are therefore finely tuned by the hypothalamus through the successive release of hypothalamic and pituitary hormones to control the downstream physiological functions. These functions rely on a complex set of mechanisms requiring tight synchronization between peripheral organs and the hypothalamic-pituitary complex, whose functionality can be altered during aging. Here, we review the results of research on the effects of aging on the NES of nonhuman primate (NHP) species in wild and captive conditions. A focus on the age-related dysregulation of the master circadian pacemaker, which, in turn, alters the synchronization of the NES with the organism environment, is proposed. Finally, practical and ethical considerations of using NHP models to test the effects of nutrition-based or hormonal treatments to combat the deterioration of the NES are discussed.

Odorants: a tool to provide nonpharmacological intervention to reduce anxiety during normal and pathological aging

Anxiety disorders represent 1 of the most common classes of psychiatric disorders. In the aging population and for patients with age-related pathology, the percentage of people suffering of anxiety is significantly elevated. Furthermore, anxiety carries with it an increased risk for a variety of age-related medical conditions, including cardiovascular disease, stroke, cognitive decline, and increased severity of motor symptoms in Parkinson's disease. A variety of anxiolytic compounds are available but often carry with them disturbing side effects that impact quality of life. Among nonmedicinal approaches to reducing anxiety, odor diffusion and aromatherapy are the most popular. In this review, we highlight the emerging perspective that the use of odorants may reduce anxiety symptoms or at least potentiate the effect of other anxiolytic approaches and may serve as an alternative form of therapy to deal with anxiety symptoms. Such approaches may be particularly beneficial in aging populations with elevated risk for these disorders. We also discuss potential neural mechanisms underlying the anxiolytic effects of odorants based on work in animal models.

Neural, Hormonal, and Cognitive Correlates of Metabolic Dysfunction and Emotional Reactivity

OBJECTIVE

Prediabetes and type 2 diabetes (i.e., hyperglycemia) are characterized by insulin resistance. These problems with energy metabolism may exacerbate emotional reactivity to negatively valenced stimuli and related phenomena such as predisposition toward negative affect, as well as cognitive deficits. Higher emotional reactivity is seen with hyperglycemia and insulin resistance. However, it is largely unknown how metabolic dysfunction correlates with related neural, hormonal, and cognitive outcomes.

METHODS

Among 331 adults from the Midlife in the United States study, eye-blink response (EBR) we cross sectionally examined to gauge reactivity to negative, positive, or neutrally valenced pictures from international affect picture system stimuli proximal to an acoustic startle probe. Increased EBR to negative stimuli was considered an index of stress reactivity. Frontal alpha asymmetry, a biomarker of negative affect predisposition, was determined using resting electroencephalography. Baseline urinary cortisol output was collected. Cognitive performance was gauged using the Brief Test of Adult Cognition by telephone. Fasting glucose and insulin characterized hyperglycemia or the homeostatic model assessment of insulin resistance.

RESULTS

Higher homeostatic model assessment of insulin resistance corresponded to an increased startle response, measured by EBR magnitude, for negative versus positive stimuli (R = 0.218, F(1,457) = 5.48, p = .020, euglycemia: M(SD) = .092(.776), hyperglycemia: M(SD) = .120(.881)). Participants with hyperglycemia versus euglycemia showed greater right frontal alpha asymmetry (F(1,307) = 6.62, p = .011, euglycemia: M(SD) = .018(.167), hyperglycemia: M(SD) = -.029(.160)), and worse Brief Test of Adult Cognition by telephone arithmetic performance (F(1,284) = 4.25, p = .040, euglycemia: M(SD) = 2.390(1.526), hyperglycemia: M(SD) = 1.920(1.462)). Baseline urinary cortisol (log10 μg/12 hours) was also dysregulated in individuals with hyperglycemia (F(1,324) = 5.09, p = .025, euglycemia: M(SD) = 1.052 ± .332, hyperglycemia: M(SD) = .961 (.362)).

CONCLUSIONS

These results suggest that dysmetabolism is associated with increased emotional reactivity, predisposition toward negative affect, and specific cognitive deficits.

Caloric restriction mitigates age-associated hippocampal differential CG and non-CG methylation

Brain aging is marked by cognitive decline and susceptibility to neurodegeneration. Calorie restriction (CR) increases neurogenesis, improves memory function, and protects from age-associated neurological disorders. Epigenetic mechanisms, including DNA methylation, are vital to normal central nervous system cellular and memory functions and are dysregulated with aging. The beneficial effects of CR have been proposed to work through epigenetic processes, but this is largely unexplored. We therefore tested whether life long CR prevents age-related hippocampal DNA methylation changes. Hippocampal DNA from young (3 months) and old (24 months) male mice fed ad libitum and 24-month-old mice fed a 40% calorie-restricted diet from 3 months of age were examined by genome-wide bisulfite sequencing to measure methylation with base specificity. Over 27 million CG and CH (non-CG) sites were examined. Of the ∼40,000 differentially methylated CG and ∼80,000 CH sites with aging, >1/3 were prevented by CR and were found across genomic regulatory regions and gene pathways. CR also caused alterations to CG and CH methylation at sites not differentially methylated with aging, and these CR-specific changes demonstrated a different pattern of regulatory element and gene pathway enrichment than those affected by aging. CR-specific DNA methyltransferase 1 and Tet methylcytosine dioxygenase 3 promoter hypermethylation corresponded to reduced gene expression. These findings demonstrate that CR attenuates age-related CG and CH hippocampal methylation changes, in combination with CR-specific methylation that may also contribute to the neuroprotective effects of CR. The prevention of age-related methylation alterations is also consistent with the prolongevity effects of CR working through an epigenetic mechanism.

Caloric restriction preserves memory and reduces anxiety of aging mice with early enhancement of neurovascular functions

Neurovascular integrity plays an important role in protecting cognitive and mental health in aging. Lifestyle interventions that sustain neurovascular integrity may thus be critical on preserving brain functions in aging and reducing the risk for age-related neurodegenerative disorders. Here we show that caloric restriction (CR) had an early effect on neurovascular enhancements, and played a critical role in preserving vascular, cognitive and mental health in aging. In particular, we found that CR significantly enhanced cerebral blood flow (CBF) and blood-brain barrier function in young mice at 5-6 months of age. The neurovascular enhancements were associated with reduced mammalian target of rapamycin expression, elevated endothelial nitric oxide synthase signaling, and increased ketone bodies utilization. With age, CR decelerated the rate of decline in CBF. The preserved CBF in hippocampus and frontal cortex were highly correlated with preserved memory and learning, and reduced anxiety, of the aging mice treated with CR (18-20 months of age). Our results suggest that dietary intervention started in the early stage (e.g., young adults) may benefit cognitive and mental reserve in aging. Understanding nutritional effects on neurovascular functions may have profound implications in human brain aging and age-related neurodegenerative disorders.

Non-human primates as a model for aging

There has been, and continues to be, a dramatic shift in the human population towards older ages necessitating biomedical research aimed at better understanding the basic biology of aging and age-related diseases and facilitating new and improved therapeutic options. As it is not practical to perform the breadth of this research in humans, animal models are necessary to recapitulate the complexity of the aging environment. The mouse model is most frequently chosen for these endeavors, however, they are frequently not the most appropriate model. Non-human primates, on the other hand, are more closely related to humans and recapitulate the human aging process and development of age-related diseases. Extensive aging research has been performed in the well-characterized rhesus macaque aging model. More recently, the common marmoset, a small non-human primate with a shorter lifespan, has been explored as a potential aging model. This model holds particular promise as an aging disease model in part due to the successful creation of transgenic marmosets. Limitations to the use of non-human primates in aging research exist but can be mitigated somewhat by the existence of available resources supported by the National Institutes of Health. This article is part of a Special Issue entitled: Animal models of aging - edited by "Houtkooper Riekelt".

Neuroimaging Biomarkers of Caloric Restriction on Brain Metabolic and Vascular Functions

PURPOSE OF REVIEW

Non-invasive neuroimaging methods have been developed as powerful tools for identifying in vivo brain functions for studies in humans and animals. Here we review the imaging biomarkers that are being used to determine the changes within brain metabolic and vascular functions induced by caloric restriction (CR), and their potential usefulness for future studies with dietary interventions in humans.

RECENT FINDINGS

CR causes an early shift in brain metabolism of glucose to ketone bodies, and enhances ATP production, neuronal activity and cerebral blood flow (CBF). With age, CR preserves mitochondrial activity, neurotransmission, CBF, and spatial memory. CR also reduces anxiety in aging mice. Neuroimaging studies in humans show that CR restores abnormal brain activity in the amygdala of women with obesity and enhances brain connectivity in old adults.

SUMMARY

Neuroimaging methods have excellent translational values and can be widely applied in future studies to identify dietary effects on brain functions in humans.

Microglia Priming with Aging and Stress

The population of aged individuals is increasing worldwide and this has significant health and socio-economic implications. Clinical and experimental studies on aging have discovered myriad changes in the brain, including reduced neurogenesis, increased synaptic aberrations, higher metabolic stress, and augmented inflammation. In rodent models of aging, these alterations are associated with cognitive decline, neurobehavioral deficits, and increased reactivity to immune challenges. In rodents, caloric restriction and young blood-induced revitalization reverses the behavioral effects of aging. The increased inflammation in the aged brain is attributed, in part, to the resident population of microglia. For example, microglia of the aged brain are marked by dystrophic morphology, elevated expression of inflammatory markers, and diminished expression of neuroprotective factors. Importantly, the heightened inflammatory profile of microglia in aging is associated with a 'sensitized' or 'primed' phenotype. Mounting evidence points to a causal link between the primed profile of the aged brain and vulnerability to secondary insults, including infections and psychological stress. Conversely, psychological stress may also induce aging-like sensitization of microglia and increase reactivity to secondary challenges. This review delves into the characteristics of neuroinflammatory signaling and microglial sensitization in aging, its implications in psychological stress, and interventions that reverse aging-associated deficits.

Adulthood stress responses in rats are variably altered as a factor of adolescent stress exposure

Stress exposure during development may influence adulthood stress response severity. The present study investigates persisting effects of two adolescent stressors upon adulthood response to predator exposure (PE). Rats were exposed to underwater trauma (UWT) or PE during adolescence, then to PE after reaching adulthood. Rats were then exposed to predator odor (PO) to test responses to predator cues alone. Behavioral and neuroendocrine assessments were conducted to determine acute effects of each stress experience. Adolescent stress altered behavioral response to adulthood PE. Acoustic startle response was blunted. Bidirectional changes in plus maze exploration were revealed as a factor of adolescent stress type. Neuroendocrine response magnitude did not predict severity of adolescent or adult stress response, suggesting that different adolescent stress events may differentially alter developmental outcomes regardless of acute behavioral or neuroendocrine response. We report that exposure to two different stressors in adolescence may differentially affect stress response outcomes in adulthood. Acute response to an adolescent stressor may not be consistent across all stressors or all dependent measures, and may not predict alterations in developmental outcomes pertaining to adulthood stress exposure. Further studies are needed to characterize factors underlying long-term effects of a developmental stressor.

Contributions of Nonhuman Primates to Research on Aging

Aging is the biological process of declining physiologic function associated with increasing mortality rate during advancing age. Humans and higher nonhuman primates exhibit unusually longer average life spans as compared with mammals of similar body mass. Furthermore, the population of humans worldwide is growing older as a result of improvements in public health, social services, and health care systems. Comparative studies among a wide range of organisms that include nonhuman primates contribute greatly to our understanding about the basic mechanisms of aging. Based on their genetic and physiologic relatedness to humans, nonhuman primates are especially important for better understanding processes of aging unique to primates, as well as for testing intervention strategies to improve healthy aging and to treat diseases and disabilities in older people. Rhesus and cynomolgus macaques are the predominant monkeys used in studies on aging, but research with lower nonhuman primate species is increasing. One of the priority topics of research about aging in nonhuman primates involves neurologic changes associated with cognitive decline and neurodegenerative diseases. Additional areas of research include osteoporosis, reproductive decline, caloric restriction, and their mimetics, as well as immune senescence and chronic inflammation that affect vaccine efficacy and resistance to infections and cancer. The purpose of this review is to highlight the findings from nonhuman primate research that contribute to our understanding about aging and health span in humans.

What is the effect of fasting on the lifespan of neurons?

Medical advancements have increased life expectancy but have consequently increased the incidence of age-related disease. Fasting or dietary restriction (DR) can help prevent these via anti-ageing effects; however, these effects in neurons are less well characterized. Here, a series of animal and human studies of the effects of DR on the structural and functional integrity of neurons and the underlying mechanisms are analyzed. DR improves the integrity of animal neurons via a wide range of possible mechanisms including changes in metabolism, oxidative damage, stress responses, growth factors, and gene expression. These mechanisms are extensively interlinked and point to an optimum range of calorie intake, above calorie deprivation and below burdensome calorie excess. Human studies also suggest that DR improves neuron integrity; however, due to ethical and methodological limitations, the most conclusive data on DR hinge upon on-going life-long monkey experiments. Rather than developing pharmacological mimetics of DR, our focus should be on educating the public about DR in order to minimize age-related disease.

Cardiovascular response to short-term fasting in menstrual phases in young women: an observational study

Background

Menstrual cycle-related symptoms are an important health issue for many women, and some may affect cardiac autonomic regulation. In the present study, we evaluated the cardiovascular and physiological stress response to 12-h short-term fasting in the menstrual phases of healthy young women.

Methods

We performed a randomized crossover study. Subjects were seven female university students (age: 22.3 ± 1.0 years). The experiments comprised four sessions: meal intake in the follicular phase, meal intake in the luteal phase, fasting in the follicular phase, and fasting in the luteal phase. All subjects participated in a total of four experimental sessions during two successive phases (follicular and luteal phase in the same menstrual cycle, or luteal phase and follicular phase in the next menstrual cycle) according to a randomized crossover design. R-R intervals were continuously recorded before and after meals, and power spectral analysis of heart rate variability was performed. Other physiological data were obtained before and 20, 40, 60, and 80 min after meal intake or after the corresponding time point of meal intake (fasting in the follicular or luteal phase).

Results

Heart rate decreased during fasting in the follicular and luteal phases. High frequency power increased during fasting in the follicular and luteal phases. In addition, salivary cortisol concentrations decreased during fasting in the luteal phase.

Conclusions

In the present study, short-term fasting resulted in higher parasympathetic activity and lower cortisol levels in the luteal phase in these young women. These results indicate a possibility to produce an anti-stress effect in the luteal phase, which may reduce menstrual symptoms.

Does the brain shrink as the waist expands?

Recent studies suggest that being overweight or obese is related to worse cognitive performance, particularly executive function. Obesity may also increase the risk of Alzheimer's disease. Consequently, there has been increasing interest in whether adiposity is related to gray or white matter (GM, WM) atrophy. In this review, we identified and critically evaluated studies assessing obesity and GM or WM volumes either globally or in specific regions of interest (ROIs). Across all ages, higher adiposity was consistently associated with frontal GM atrophy, particularly in prefrontal cortex. In children and adults <40 years of age, most studies found no relationship between adiposity and occipital or parietal GM volumes, whereas findings for temporal lobe were mixed. In middle-aged and aged adults, a majority of studies found that higher adiposity is associated with parietal and temporal GM atrophy, whereas results for precuneus, posterior cingulate, and hippocampus were mixed. Higher adiposity had no clear association with global or regional WM in any age group. We conclude that higher adiposity may be associated with frontal GM atrophy across all ages and parietal and temporal GM atrophy in middle and old age.

Links between white matter microstructure and cortisol reactivity to stress in early childhood: evidence for moderation by parenting

Activity of the hypothalamic–pituitary–adrenal axis (measured via cortisol reactivity) may be a biological marker of risk for depression and anxiety, possibly even early in development. However, the structural neural correlates of early cortisol reactivity are not well known, although these would potentially inform broader models of mechanisms of risk, especially if the early environment further shapes these relationships. Therefore, we examined links between white matter architecture and young girls' cortisol reactivity and whether early caregiving moderated these links. We recruited 45 6-year-old girls based on whether they had previously shown high or low cortisol reactivity to a stress task at age 3. White matter integrity was assessed by calculating fractional anisotropy (FA) of diffusion-weighted magnetic resonance imaging scans. Parenting styles were measured via a standardized parent–child interaction task. Significant associations were found between FA in white matter regions adjacent to the left thalamus, the right anterior cingulate cortex, and the right superior frontal gyrus (all ps < .001). Further, positive early caregiving moderated the effect of high cortisol reactivity on white matter FA (all ps ≤ .05), with high stress reactive girls who received greater parent positive affect showing white matter structure more similar to that of low stress reactive girls. Results show associations between white matter integrity of various limbic regions of the brain and early cortisol reactivity to stress and provide preliminary support for the notion that parenting may moderate associations.

•

We examined neural correlates of cortisol reactivity to stress in young girls.

•

DTI was performed in young girls to examine white matter fractional anisotropy (FA).

•

Lower FA was linked to high cortisol reactivity to stress.

•

Differences in neuronal fiber projections were linked to cortisol reactivity.

•

Parenting style buffered the effect of high cortisol reactivity on white matter FA.

Brain white matter integrity and cortisol in older men: the Lothian Birth Cohort 1936

Elevated glucocorticoid (GC) levels are hypothesized to be deleterious to some brain regions, including white matter (WM). Older age is accompanied by increased between-participant variation in GC levels, yet relationships between WM integrity and cortisol levels in older humans are underexplored. Moreover, it is unclear whether GC-WM associations might be general or pathway specific. We analyzed relationships between salivary cortisol (diurnal and reactive) and general measures of brain WM hyperintensity (WMH) volume, fractional anisotropy (g_FA), and mean diffusivity (g_MD) in 90 males, aged 73 years. Significant associations were predominantly found between cortisol measures and WMHs and g_MD but not g_FA. Higher cortisol at the start of a mild cognitive stressor was associated with higher WMH and g_MD. Higher cortisol at the end was associated with greater WMHs. A constant or increasing cortisol level during cognitive testing was associated with lower g_MD. Tract-specific bases of these associations implicated anterior thalamic radiation, uncinate, and arcuate and inferior longitudinal fasciculi. The cognitive sequelae of these relationships, above other covariates, are a priority for future study.

•

We correlated salivary cortisol and brain white matter (WM) measures in older males.

•

Cortisol was measured diurnally and in reaction to a cognitive challenge.

•

Diffusion tensor magnetic resonance imaging (fractional anisotropy and mean diffusivity) and total hyperintensity volume measured WM integrity.

•

WM-cortisol relations were found for mean diffusivity and hyperintensity volume but not fractional anisotropy.

•

Higher cortisol in response to cognitive stressor denoted lower WM integrity.

Effects of mild calorie restriction on anxiety and hypothalamic-pituitary-adrenal axis responses to stress in the male rat

Chronic calorie restriction (CR) is one of the few interventions to improve longevity and quality of life in a variety of species. It also reduces behavioral indices of anxiety and influences some stress hormones under basal conditions. However, it is not known how CR influences hypothalamic–pituitary–adrenal (HPA) axis function or if those on a CR diet have heightened HPA axis responses to stress. We hypothesized elevated basal glucocorticoid levels induced by CR would lead to exacerbated HPA axis responses to the psychological stress, restraint, in the male rat. We first confirmed rats fed 75% of their normal calorie intake for 3 weeks were less anxious than ad libitum‐fed (AD) rats in the elevated plus maze test for anxiety. The anxiolytic effect was mild, with only grooming significantly attenuated in the open field and no measured behavior affected in the light/dark box. Despite elevated basal glucocorticoids, CR rats had very similar hormonal and central responses to 15‐min restraint to the AD rats. Both CR and AD rats responded to restraint stress with a robust increase in glucocorticoids that was resolved by 60 min. Both groups also showed robust neuronal activation in the paraventricular nucleus of the hypothalamus and in other stress‐ and feeding‐sensitive brain regions that was not substantially affected by calorie intake. Our findings thus demonstrate chronic mild CR is subtly anxiolytic and is not likely to affect HPA axis responses to psychological stress. These findings support research suggesting a beneficial effect of mild CR.

Widespread reductions of white matter integrity in patients with long-term remission of Cushing's disease

BACKGROUND

Hypercortisolism leads to various physical, psychological and cognitive symptoms, which may partly persist after the treatment of Cushing's disease. The aim of the present study was to investigate abnormalities in white matter integrity in patients with long-term remission of Cushing's disease, and their relation with psychological symptoms, cognitive impairment and clinical characteristics.

METHODS

In patients with long-term remission of Cushing's disease (n = 22) and matched healthy controls (n = 22) we examined fractional anisotropy (FA) values of white matter in a region-of-interest (ROI; bilateral cingulate cingulum, bilateral hippocampal cingulum, bilateral uncinate fasciculus and corpus callosum) and the whole brain, using 3 T diffusion tensor imaging (DTI) and a tract-based spatial statistics (TBSS) approach. Psychological and cognitive functioning were assessed with validated questionnaires and clinical severity was assessed using the Cushing's syndrome Severity Index.

RESULTS

The ROI analysis showed FA reductions in all of the hypothesized regions, with the exception of the bilateral hippocampal cingulum, in patients when compared to controls. The exploratory whole brain analysis showed multiple regions with lower FA values throughout the brain. Patients reported more apathy (p = .003) and more depressive symptoms (p < .001), whereas depression symptom severity in the patient group was negatively associated with FA in the left uncinate fasciculus (p < 0.05). Post-hoc analyses showed increased radial and mean diffusivity in the patient group.

CONCLUSION

Patients with a history of endogenous hypercortisolism in present remission show widespread changes of white matter integrity in the brain, with abnormalities in the integrity of the uncinate fasciculus being related to the severity of depressive symptoms, suggesting persistent structural effects of hypercortisolism.

Dietary restriction and the pursuit of effective mimetics

Dietary restriction (DR) has been shown to extend both median and maximum lifespan in a range of animals, although recent findings suggest that these effects are not universally enjoyed across all animals. In particular, the lifespan effect following DR in mice is highly strain-specific and there is little current evidence that DR induces a positive effect on all-cause mortality in non-human primates. However, the positive effects of DR on health appear to be highly conserved across the vast majority of species, including human subjects. Despite these effects on health, it is highly unlikely that DR will become a realistic or popular life choice for most human subjects given the level of restraint required. Consequently significant research is focusing on identifying compounds that will bestow the benefits of DR without the obligation to adhere to stringent reductions in daily food intake. Several such compounds, including rapamycin, metformin and resveratrol, have been identified as potential DR mimetics. Although these compounds show significant promise, there is a need to properly understand the mechanisms through which these drugs act. This review will discuss the importance in understanding the role that genetic background and heterogeneity play in mediating the lifespan and healthspan effects of DR. It will also provide an overview of the most promising current DR mimetics and their effects on healthy lifespan.

Brain white matter microstructure alterations in adolescent rhesus monkeys exposed to early life stress: associations with high cortisol during infancy

BACKGROUND

Early adverse experiences, especially those involving disruption of the mother-infant relationship, are detrimental for proper socioemotional development in primates. Humans with histories of childhood maltreatment are at high risk for developing psychopathologies including depression, anxiety, substance abuse, and behavioral disorders. However, the underlying neurodevelopmental alterations are not well understood. Here we used a nonhuman primate animal model of infant maltreatment to study the long-term effects of this early life stress on brain white matter integrity during adolescence, its behavioral correlates, and the relationship with early levels of stress hormones.

METHODS

Diffusion tensor imaging and tract based spatial statistics were used to investigate white matter integrity in 9 maltreated and 10 control animals during adolescence. Basal plasma cortisol levels collected at one month of age (when abuse rates were highest) were correlated with white matter integrity in regions with group differences. Total aggression was also measured and correlated with white matter integrity.

RESULTS

We found significant reductions in white matter structural integrity (measured as fractional anisotropy) in the corpus callosum, occipital white matter, external medullary lamina, as well as in the brainstem of adolescent rhesus monkeys that experienced maternal infant maltreatment. In most regions showing fractional anisotropy reductions, opposite effects were detected in radial diffusivity, without changes in axial diffusivity, suggesting that the alterations in tract integrity likely involve reduced myelin. Moreover, in most regions showing reduced white matter integrity, this was associated with elevated plasma cortisol levels early in life, which was significantly higher in maltreated than in control infants. Reduced fractional anisotropy in occipital white matter was also associated with increased social aggression.

CONCLUSIONS

These findings highlight the long-term impact of infant maltreatment on brain white matter structural integrity, particularly in tracts involved in visual processing, emotional regulation, and somatosensory and motor integration. They also suggest a relationship between elevations in stress hormones detected in maltreated animals during infancy and long-term brain white matter structural effects.

Interleukin-8 and interleukin-10, brain volume and microstructure, and the influence of calorie restriction in old rhesus macaques

Higher systemic levels of the proinflammatory cytokine interleukin-6 (IL-6) were found to be associated with lower gray matter volume and tissue density in old rhesus macaques. This association between IL-6, and these brain indices were attenuated by long-term 30 % calorie restriction (CR). To extend these findings, the current analysis determined if a CR diet in 27 aged rhesus monkeys compared to 17 normally fed controls reduced circulating levels of another proinflammatory cytokine, interleukin-8 (IL-8), and raised levels of anti-inflammatory interleukin-10 (IL-10). Further, these cytokines were regressed onto imaged brain volume and microstructure using voxel-wise regression analyses. CR significantly lowered IL-8 and raised IL-10 levels. Across the two dietary conditions, higher IL-8 predicted smaller gray matter volumes in bilateral hippocampus. Higher IL-10 was associated with more white matter volume in visual areas and tracts. Consuming a CR diet reduced the association between systemic IL-8 and hippocampal volumes. Conversely, CR strengthened associations between IL-10 and microstructural tissue density in the prefrontal cortex and other areas, particularly in a region of dorsal prefrontal cortex, which concurred with our prior findings for IL-6. Consumption of a CR diet lowered proinflammatory and increased anti-inflammatory cytokine concentrations, which lessened the statistical association between systemic inflammation and the age-related alterations in important brain regions, including the hippocampus.

Social subordination stress and serotonin transporter polymorphisms: associations with brain white matter tract integrity and behavior in juvenile female macaques

We examined the relationship between social rank and brain white matter (WM) microstructure, and socioemotional behavior, and its modulation by serotonin (5HT) transporter (5HTT) polymorphisms in prepubertal female macaques. Using diffusion tensor imaging and tract-based spatial statistics, social status differences were found in medial prefrontal cortex (mPFC) WM and cortico-thalamic tracts, with subordinates showing higher WM structural integrity (measured as fractional anisotropy, FA) than dominant animals. 5HTT genotype-related differences were detected in the posterior limb of the internal capsule, where s-variants had higher FA than l/l animals. Status by 5HTT interaction effects were found in (1) external capsule (middle longitudinal fasciculus), (2) parietal WM, and (3) short-range PFC tracts, with opposite effects in dominant and subordinate animals. In most regions showing FA differences, opposite differences were detected in radial diffusivity, but none in axial diffusivity, suggesting that differences in tract integrity likely involve differences in myelin. These findings highlight that differences in social rank are associated with differences in WM structural integrity in juveniles, particularly in tracts connecting prefrontal, sensory processing, motor and association regions, sometimes modulated by 5HTT genotype. Differences in these tracts were associated with increased emotional reactivity in subordinates, particularly with higher submissive and fear behaviors.

White matter integrity is reduced in bulimia nervosa

OBJECTIVE

To investigate brain white matter (WM) functionality in bulimia nervosa (BN) in relation to anxiety.

METHOD

Twenty-one control women (CW, mean age 27 ± 7 years) and 20 BN women (mean age 25 ± 5 years) underwent brain diffusion tensor imaging to measure fractional anisotropy (FA; an indication of WM axon integrity) and the apparent diffusion coefficient (ADC; reflecting WM cell damage).

RESULTS

FA was decreased in BN in the bilateral corona radiata extending into the posterior limb of the internal capsule, the corpus callosum, the right sub-insular WM, and right fornix. In CW but not BN, trait anxiety correlated negatively with fornix, corpus callosum, and left corona radiata FA. ADC was increased in BN compared with CW in the bilateral corona radiata, corpus callosum, inferior fronto-occipital, and uncinate fasciculus. Alterations in BN WM functionality were not due to structural brain alterations.

DISCUSSION

WM integrity is disturbed in BN, especially in the corona radiata, which has been associated with taste and brain reward processing. Whether this is a premorbid condition or an effect from the illness is yet uncertain. The relationships between WM FA and trait anxiety in CW but not BN may suggest that altered WM functionality contributes to high anxious traits in BN.

Early life nutrient restriction impairs blood-brain metabolic profile and neurobehavior predisposing to Alzheimer's disease with aging

Prenatal nutrient restriction (NR) culminating in intra-uterine growth restriction (IUGR) with postnatal catch up growth leads to diabesity. In contrast, postnatal NR with growth restriction (PNGR) superimposed on IUGR (IPGR) protects young and aging adults from this phenotype. We hypothesized that PNGR/IPGR will compromise the blood-brain metabolic profile impairing neurobehavior and predisposing to Alzheimer's disease (AD). NR (50%) in late gestation followed by cross-fostering of rat pups to either ad lib fed (CON) or NR (50%) lactating mothers generated CON, IUGR, PNGR and IPGR male (M) and female (F) offspring that were examined through the life span. In PNGR/IPGR plasma/CSF glucose and lactate decreased while ketones increased in (M) and (F) (PN21, PN50). In addition increased brain glucose transporters, Glut1 & Glut3, greater brain derived neurotrophic factor (BDNF), reduced Glut4, with unchanged serotonin transporter concentrations were noted in (F) (PN50-60). While (F) displayed more hyperactivity, both (F) and (M) exhibited anxiety although socially and cognitively unimpaired (PN25-28&50). Aging (15-17 m) (F) not (M), expressed low plasma insulin, reduced brain IRS-2, pAkt, and pGSK-3β(Ser9), unchanged pPDK1, pTau or lipoprotein receptor related protein 1 (LRP1), higher glial fibrillary acidic protein (GFAP) and spinophilin but a 10-fold increased amyloid-β42. We conclude that therapeutically superimposing PNGR on IUGR (IPGR) should be carefully weighed in light of unintended consequences related to perturbed neurobehavior and potential predilection for AD.

Energy intake and exercise as determinants of brain health and vulnerability to injury and disease

Evolution favored individuals with superior cognitive and physical abilities under conditions of limited food sources, and brain function can therefore be optimized by intermittent dietary energy restriction (ER) and exercise. Such energetic challenges engage adaptive cellular stress-response signaling pathways in neurons involving neurotrophic factors, protein chaperones, DNA-repair proteins, autophagy, and mitochondrial biogenesis. By suppressing adaptive cellular stress responses, overeating and a sedentary lifestyle may increase the risk of Alzheimer's and Parkinson's diseases, stroke, and depression. Intense concerted efforts of governments, families, schools, and physicians will be required to successfully implement brain-healthy lifestyles that incorporate ER and exercise.