Eat less, live longer? New insights into the role of caloric restriction in the brain

Adult neural stem cells and neurogenesis are resilient to intermittent fasting

Intermittent fasting (IF) is a promising strategy to counteract ageing shown to increase the number of adult-born neurons in the dentate gyrus of mice. However, it is unclear which steps of the adult neurogenesis process are regulated by IF. The number of adult neural stem cells (NSCs) decreases with age in an activation-dependent manner and, to counteract this loss, adult NSCs are found in a quiescent state which ensures their long-term maintenance. We aimed to determine if and how IF affects adult NSCs in the hippocampus. To identify the effects of every-other-day IF on NSCs and all following steps in the neurogenic lineage, we combined fasting with lineage tracing and label retention assays. We show here that IF does not affect NSC activation or maintenance and, that contrary to previous reports, IF does not increase neurogenesis. The same results are obtained regardless of strain, sex, diet length, tamoxifen administration or new-born neuron identification method. Our data suggest that NSCs maintain homeostasis upon IF and that this intervention is not a reliable strategy to increase adult neurogenesis.

Effect of Avena sativa (Oats) on cognitive function: A systematic review of randomized controlled trials

BACKGROUND AND AIM

The effect of polyphenol-rich diets or supplements on cognitive function remains a contentious topic. The objective of this study was to investigate the effects of Avena sativa (oat extracts) on cognitive function among healthy adults.

METHODS

A structured literature search was undertaken using PubMed, Web of Science, and Scopus from the database's establishment until March 17, 2022. Data on cognitive function, regarding accuracy and speed of performance, were gathered from randomized controlled trials (RCTs) that investigated the acute or chronic effects of Avena sativa in healthy subjects. The Cochrane Collaboration risk-of-bias tool was used to assess the quality of included studies.

RESULTS

We included six RCTs, of which three were crossover designs, with a total of 287 individuals. Four studies investigated the acute effect of Avena sativa, while two investigated its chronic effect. Acute ingestion of Avena sativa appeared to positively influence the accuracy and speed of performance. While short-term chronic supplementation resulted in a significant improvement in cognitive function, long-term chronic supplementation did not. Overall, the evidence was of average quality.

CONCLUSION

Acute supplementation with Avena sativa may improve cognitive function in healthy volunteers. Given the small number of trials included and the disparity of the intervention dose, the conclusions of this study should be interpreted with caution. More high-quality, long-term studies are warranted.

Nutrition and adult neurogenesis in the hippocampus: Does what you eat help you remember?

Neurogenesis is a complex process by which neural progenitor cells (NPCs)/neural stem cells (NSCs) proliferate and differentiate into new neurons and other brain cells. In adulthood, the hippocampus is one of the areas with more neurogenesis activity, which is involved in the modulation of both emotional and cognitive hippocampal functions. This complex process is affected by many intrinsic and extrinsic factors, including nutrition. In this regard, preclinical studies performed in rats and mice demonstrate that high fats and/or sugars diets have a negative effect on adult hippocampal neurogenesis (AHN). In contrast, diets enriched with bioactive compounds, such as polyunsaturated fatty acids and polyphenols, as well as intermittent fasting or caloric restriction, can induce AHN. Interestingly, there is also growing evidence demonstrating that offspring AHN can be affected by maternal nutrition in the perinatal period. Therefore, nutritional interventions from early stages and throughout life are a promising perspective to alleviate neurodegenerative diseases by stimulating neurogenesis. The underlying mechanisms by which nutrients and dietary factors affect AHN are still being studied. Interestingly, recent evidence suggests that additional peripheral mediators may be involved. In this sense, the microbiota-gut-brain axis mediates bidirectional communication between the gut and the brain and could act as a link between nutritional factors and AHN. The aim of this mini-review is to summarize, the most recent findings related to the influence of nutrition and diet in the modulation of AHN. The importance of maternal nutrition in the AHN of the offspring and the role of the microbiota-gut-brain axis in the nutrition-neurogenesis relationship have also been included.

Neurogenesis in aging and age-related neurodegenerative diseases

Adult neurogenesis, the process by which neurons are generated in certain areas of the adult brain, declines in an age-dependent manner and is one potential target for extending cognitive healthspan. Aging is a major risk factor for neurodegenerative diseases and, as lifespans are increasing, these health challenges are becoming more prevalent. An age-associated loss in neural stem cell number and/or activity could cause this decline in brain function, so interventions that reverse aging in stem cells might increase the human cognitive healthspan. In this review, we describe the involvement of adult neurogenesis in neurodegenerative diseases and address the molecular mechanistic aspects of neurogenesis that involve some of the key aggregation-prone proteins in the brain (i.e., tau, Aβ, α-synuclein, …). We summarize the research pertaining to interventions that increase neurogenesis and regulate known targets in aging research, such as mTOR and sirtuins. Lastly, we share our outlook on restoring the levels of neurogenesis to physiological levels in elderly individuals and those with neurodegeneration. We suggest that modulating neurogenesis represents a potential target for interventions that could help in the fight against neurodegeneration and cognitive decline.

Nutrition and exercise interventions could ameliorate age-related cognitive decline: a meta-analysis of randomized controlled trials

OBJECTIVE

To evaluate the effect of nutrition combined physical exercise interventions on age-related cognitive decline by a systematic review and meta-analysis.

METHODS

We searched 9 databases, including PubMed, EMbase, The Cochrane Library, Web of Science, Science Direct, China National Knowledge Infrastructure (CNKI), VIP Information, China Biological Medical Database (CBM) and Wanfang for studies published until the end of December 2019. The selected trials should meet the following criteria, study objects: healthy adults aged 65 and over with cognitive dysfunction or diagnosed as MCI, but not meet the diagnostic criteria for dementia as well as no restriction on follow-up time, race or gender. Study interventions: multiple interventions including nutrition and exercise.

EXCLUSION CRITERIA

(1) studies included elderly people with any type of dementia or patients with cognitive impairment induced by secondary causes, including drug, alcohol, severe organic brain diseases, mental disorders. (2) Republished literature. (3) Studies with significant differences in baseline data between groups. (4) The data in the study cannot be converted into the required data format. We reviewed and extracted information and assessed the risk of bias of recruited studies independently. Meta-analysis was performed using STATA v.15.1 software. The bias of publication was estimated by Egger test.

RESULTS

A total of six RCTs representing 1039 participates were included in our meta-analysis. In terms of global cognitive function that has been assessed by neuropsychological test in different combinations, the result showed that the beneficial effect of nutrition combined exercise interventions was statistically significant [SMD = 0.23, 95% CI (0.1, 0.36), P = 0.0004]. There were no statistical differences from assays on MMSE scores, Memory, Executive Function, Attention, and Information Processing Speed across groups.

CONCLUSIONS

The current study shows that nutrition combined exercise interventions can improve global cognitive function in the aged with cognitive decline. Further researches emphasizing on longer follow-up time, experimental randomness, credibility and scale would better elucidate the effect of nutrition combined exercise interventions on cognitive function, particularly in older adults. (registration number: CRD42020159291, date of registration: 28/04/2020).

Hypothalamic neurogenesis and its implications for obesity-induced anxiety disorders

Obesity and anxiety are public health problems that have no effective cure. Obesity-induced anxiety is also the most common behavioural trait exhibited amongst obese patients, with the mechanisms linking these disorders being poorly understood. The hypothalamus and hippocampus are reciprocally connected, important neurogenic brain regions that could be vital to understanding these disorders. Dietary, physical activity and lifestyle interventions have been shown to be able to enhance neurogenesis within the hippocampus, while the effects thereof within the hypothalamus is yet to be ascertained. This review describes hypothalamic neurogenesis, its impairment in obesity as well as the effect of interventional therapies. Obesity is characterized by a neurogenic shift towards neuropeptide Y neurons, promoting appetite and weight gain. While, nutraceuticals and exercise promote proopiomelanocortin neuron proliferation, causing diminished appetite and reduced weight gain. Through the furthered development of multimodal approaches targeting both these brain regions could hold an even greater therapeutic potential.

Nutritional Factors Affecting Adult Neurogenesis and Cognitive Function

Adult neurogenesis, a complex process by which stem cells in the hippocampal brain region differentiate and proliferate into new neurons and other resident brain cells, is known to be affected by many intrinsic and extrinsic factors, including diet. Neurogenesis plays a critical role in neural plasticity, brain homeostasis, and maintenance in the central nervous system and is a crucial factor in preserving the cognitive function and repair of damaged brain cells affected by aging and brain disorders. Intrinsic factors such as aging, neuroinflammation, oxidative stress, and brain injury, as well as lifestyle factors such as high-fat and high-sugar diets and alcohol and opioid addiction, negatively affect adult neurogenesis. Conversely, many dietary components such as curcumin, resveratrol, blueberry polyphenols, sulforaphane, salvionic acid, polyunsaturated fatty acids (PUFAs), and diets enriched with polyphenols and PUFAs, as well as caloric restriction, physical exercise, and learning, have been shown to induce neurogenesis in adult brains. Although many of the underlying mechanisms by which nutrients and dietary factors affect adult neurogenesis have yet to be determined, nutritional approaches provide promising prospects to stimulate adult neurogenesis and combat neurodegenerative diseases and cognitive decline. In this review, we summarize the evidence supporting the role of nutritional factors in modifying adult neurogenesis and their potential to preserve cognitive function during aging.

Dietary Restriction Affects Neuronal Response Property and GABA Synthesis in the Primary Visual Cortex

Previous studies have reported inconsistent effects of dietary restriction (DR) on cortical inhibition. To clarify this issue, we examined the response properties of neurons in the primary visual cortex (V1) of DR and control groups of cats using in vivo extracellular single-unit recording techniques, and assessed the synthesis of inhibitory neurotransmitter GABA in the V1 of cats from both groups using immunohistochemical and Western blot techniques. Our results showed that the response of V1 neurons to visual stimuli was significantly modified by DR, as indicated by an enhanced selectivity for stimulus orientations and motion directions, decreased visually-evoked response, lowered spontaneous activity and increased signal-to-noise ratio in DR cats relative to control cats. Further, it was shown that, accompanied with these changes of neuronal responsiveness, GABA immunoreactivity and the expression of a key GABA-synthesizing enzyme GAD67 in the V1 were significantly increased by DR. These results demonstrate that DR may retard brain aging by increasing the intracortical inhibition effect and improve the function of visual cortical neurons in visual information processing. This DR-induced elevation of cortical inhibition may favor the brain in modulating energy expenditure based on food availability.

The Ever-Changing Morphology of Hippocampal Granule Neurons in Physiology and Pathology

Newborn neurons are continuously added to the hippocampal dentate gyrus throughout adulthood. In this review, we analyze the maturational stages that newborn granule neurons go through, with a focus on their unique morphological features during each stage under both physiological and pathological circumstances. In addition, the influence of deleterious (such as schizophrenia, stress, Alzheimer's disease, seizures, stroke, inflammation, dietary deficiencies, or the consumption of drugs of abuse or toxic substances) and neuroprotective (physical exercise and environmental enrichment) stimuli on the maturation of these cells will be examined. Finally, the regulation of this process by proteins involved in neurodegenerative and neurological disorders such as Glycogen synthase kinase 3β, Disrupted in Schizophrenia 1 (DISC-1), Glucocorticoid receptor, pro-inflammatory mediators, Presenilin-1, Amyloid precursor protein, Cyclin-dependent kinase 5 (CDK5), among others, will be evaluated. Given the recently acquired relevance of the dendritic branch as a functional synaptic unit required for memory storage, a full understanding of the morphological alterations observed in newborn neurons may have important consequences for the prevention and treatment of the cognitive and affective alterations that evolve in conjunction with impaired adult hippocampal neurogenesis.

Calorie restriction does not restore brain mitochondrial function in P301L tau mice, but it does decrease mitochondrial F0F1-ATPase activity

Calorie restriction (CR) has been shown to increase lifespan and delay aging phenotypes in many diverse eukaryotic species. In mouse models of Alzheimer's disease (AD), CR has been shown to decrease amyloid-beta and hyperphosphorylated tau levels and preserve cognitive function. Overexpression of human mutant tau protein has been shown to induce deficits in mitochondrial electron transport chain complex I activity. Therefore, experiments were performed to determine the effects of 4-month CR on brain mitochondrial function in Tg4510 mice, which express human P301L tau. Expression of mutant tau led to decreased ADP-stimulated respiratory rates, but not uncoupler-stimulated respiratory rates. The membrane potential was also slightly higher in mitochondria from the P301L tau mice. As shown previously, tau expression decreased mitochondrial complex I activity. The decreased complex I activity, decreased ADP-stimulated respiratory rate, and increased mitochondrial membrane potential occurring in mitochondria from Tg4510 mice were not restored by CR. However, the CR diet did result in a genotype independent decrease in mitochondrial F0F1-ATPase activity. This decrease in F0F1-ATPase activity was not due to lowered levels of the alpha or beta subunits of F0F1-ATPase. The possible mechanisms through which CR reduces the F0F1-ATPase activity in brain mitochondria are discussed.

Contrasting effects of chronic, systemic treatment with mTOR inhibitors rapamycin and metformin on adult neural progenitors in mice

The chronic and systemic administration of rapamycin extends life span in mammals. Rapamycin is a pharmacological inhibitor of mTOR. Metformin also inhibits mTOR signaling but by activating the upstream kinase AMPK. Here we report the effects of chronic and systemic administration of the two mTOR inhibitors, rapamycin and metformin, on adult neural stem cells of the subventricular region and the dendate gyrus of the mouse hippocampus. While rapamycin decreased the number of neural progenitors, metformin-mediated inhibition of mTOR had no such effect. Adult-born neurons are considered important for cognitive and behavioral health, and may contribute to improved health span. Our results demonstrate that distinct approaches of inhibiting mTOR signaling can have significantly different effects on organ function. These results underscore the importance of screening individual mTOR inhibitors on different organs and physiological processes for potential adverse effects that may compromise health span.

Brain response to calorie restriction

Calorie restriction extends longevity and delays ageing in model organisms and mammals, opposing the onset and progression of an array of age-related diseases. These beneficial effects also extend to the maintenance of brain cognitive functions at later age and to the prevention, at least in rodents, of brain senescence and associated neurodegenerative disorders. In recent years, the molecular mechanisms underlying brain response to calorie restriction have begun to be elucidated, revealing the unanticipated role of a number of key nutrient sensors and nutrient-triggered signaling cascades in the translation of metabolic cues into cellular and molecular events that ultimately lead to increased cell resistance to stress, enhanced synaptic plasticity, and improved cognitive performance. Of note, the brain's role in CR also includes the activation of nutrient-sensitive hypothalamic circuitries and the implementation of neuroendocrine responses that impact the entire organism. The present review addresses emerging molecular themes in brain response to dietary restriction, and the implications of this knowledge for the understanding and the prevention of brain disorders associated with ageing and metabolic disease.

High-intensity physical activity modulates diet effects on cerebrospinal amyloid-β levels in normal aging and mild cognitive impairment

We previously showed that amyloid-β 1-42 (Aβ(42)) levels in cerebrospinal fluid (CSF) were markedly altered in response to a 4-week dietary intervention in normal aging and mild cognitive impairment (MCI). Here, we re-examined the data to assess whether diet-induced effects on CSF Aβ(42) were modulated by high intensity physical activity (hi-PA). Normal older adults (n = 18, mean age = 68.6 ± 7.4 y) and adults with amnestic MCI (n = 23, mean age = 68.0 ± 6.5 y) received a low saturated fat/low glycemic index (LOW) diet or a high saturated fat/high glycemic index (HIGH) diet, and CSF levels of Aβ(42), tau, and IL-8 were measured at baseline and week 4. Pre-study activity levels were assessed using a 7-d questionnaire, and weekly duration of hi-PA was quantified. At baseline, increased hi-PA in normals predicted lower CSF levels of tau (r = -0.54, p = 0.020) and IL-8 (r = -0.70, p = 0.025). Diet-induced effects on CSF Aβ(42) during the intervention study were modulated by hi-PA, and the nature of this effect differed for normals and MCI (ANOVA, p = 0.039). That is, for normal adults, increased hi-PA attenuated the effects of the HIGH diet on CSF Aβ(42) whereas in MCI, increased hi-PA potentiated the effects of the LOW diet. Our results suggest that normal adults who engage in hi-PA are less vulnerable to the pathological effects of an unhealthy diet, while in MCI, the benefit of a healthy diet on Aβ modulation is greatest when paired with hi-PA. Exercise may thus interact with diet to alter pathological processes that ultimately modify risk of Alzheimer's disease.

Prevention of age-related changes in hippocampal levels of 5-methylcytidine by caloric restriction

Aberrant DNA methylation patterns have been linked to molecular and cellular alterations in the aging brain. Caloric restriction (CR) and upregulation of antioxidants have been proposed as interventions to prevent or delay age-related brain pathology. Previously, we have shown in large cohorts of aging mice, that age-related increases in DNA methyltransferase 3a (Dnmt3a) immunoreactivity in the mouse hippocampus were attenuated by CR, but not by overexpression of superoxide dismutase 1 (SOD1). Here, we investigated age-related alterations of 5-methylcytidine (5-mC), a marker of DNA methylation levels, in a hippocampal subregion-specific manner. Examination of 5-mC immunoreactivity in 12- and 24-month-old wild type (WT) mice on control diet, mice overexpressing SOD1 on control diet, wild type mice on CR, and SOD1 mice on CR, indicated an age-related increase in 5-mC immunoreactivity in the hippocampal dentate gyrus, CA3, and CA1-2 regions, which was prevented by CR but not by SOD1 overexpression. Moreover, positive correlations between 5-mC and Dnmt3a immunoreactivity were observed in the CA3 and CA1-2. These findings suggest a crucial role for DNA methylation in hippocampal aging and in the mediation of the beneficial effects of CR on aging.

Modeling mitochondrial dysfunctions in the brain: from mice to men

The biologist Lewis Thomas once wrote: "my mitochondria comprise a very large proportion of me. I cannot do the calculation, but I suppose there is almost as much of them in sheer dry bulk as there is the rest of me". As humans, or indeed as any mammal, bird, or insect, we contain a specific molecular makeup that is driven by vast numbers of these miniscule powerhouses residing in most of our cells (mature red blood cells notwithstanding), quietly replicating, living independent lives and containing their own DNA. Everything we do, from running a marathon to breathing, is driven by these small batteries, and yet there is evidence that these molecular energy sources were originally bacteria, possibly parasitic, incorporated into our cells through symbiosis. Dysfunctions in these organelles can lead to debilitating, and sometimes fatal, diseases of almost all the bodies' major organs. Mitochondrial dysfunction has been implicated in a wide variety of human disorders either as a primary cause or as a secondary consequence. To better understand the role of mitochondrial dysfunction in human disease, a multitude of pharmacologically induced and genetically manipulated animal models have been developed showing to a greater or lesser extent the clinical symptoms observed in patients with known and unknown causes of the disease. This review will focus on diseases of the brain and spinal cord in which mitochondrial dysfunction has been proven or is suspected and on animal models that are currently used to study the etiology, pathogenesis and treatment of these diseases.

Age-related cognitive decline: can neural stem cells help us?

Several studies suggest that an increase in adult neurogenesis has beneficial effects on emotional behavior and cognitive performance including learning and memory. The observation that aging has a negative effect on the proliferation of neural stem cells has prompted several laboratories to investigate new systems to artificially increase neurogenesis in senescent animals as a means to compensate for age-related cognitive decline. In this review we will discuss the systemic, cellular, and molecular changes induced by aging and affecting the neurogenic niche at the level of neural stem cell proliferation, their fate change, neuronal survival, and subsequent integration in the neuronal circuitry. Particular attention will be given to those manipulations that increase neurogenesis in the aged brain as a potential avenue towards therapy.

Caloric restriction attenuates age-related changes of DNA methyltransferase 3a in mouse hippocampus

Recent studies have suggested that DNA methylation is implicated in age-related changes in gene expression as well as in cognition. DNA methyltransferase 3a (Dnmt3a), which catalyzes DNA methylation, is essential for memory formation and underlying changes in neuronal and synaptic plasticity. Because caloric restriction (CR) and upregulation of antioxidants have been suggested as strategies to attenuate age-related alterations in the brain, we hypothesized that both a diet restricted in calories and transgenic overexpression of normal human Cu/Zn superoxide dismutase 1 (SOD) attenuate age-related changes in Dnmt3a in the aging mouse hippocampus. For this purpose, we performed qualitative and quantitative analyses of Dnmt3a-immunoreactivity (IR) for the hippocampal dentate gyrus (DG), CA3 and CA1-2 regions in 12- and 24-month-old mice from 4 groups, i.e. (1) wild-type (WT) mice on a control diet (WT-CD), (2) SOD-CD mice, (3) WT mice on CR (WT-CR), and (4) SOD-CR. Qualitative analyses revealed two types of Dnmt3a immunoreactive cells: type I cells--present throughout all hippocampal cell layers showing moderate levels of nuclear Dnmt3a-IR, and type II cells--a subpopulation of hippocampal cells showing very intense nuclear Dnmt3a-IR, and colocalization with Bromodeoxyuridine. Quantitative analyses indicated that the age-related increase in Dnmt3a-IR within the CA3 and CA1-2 in type I cells was attenuated by CR, but not by SOD overexpression. In contrast, the density of type II Dnmt3a immunoreactive cells showed an age-related reduction, without significant effects of both CR and SOD. These changes in Dnmt3a levels in the mouse hippocampus may have a significant impact on gene expression and associated cognitive functioning.

Caloric restriction experience reprograms stress and orexigenic pathways and promotes binge eating

Long-term weight management by dieting has a high failure rate. Pharmacological targets have focused on appetite reduction, although less is understood as to the potential contributions of the stress state during dieting in long-term behavioral modification. In a mouse model of moderate caloric restriction in which a 10-15% weight loss similar to human dieting is produced, we examined physiological and behavioral stress measures. After 3 weeks of restriction, mice showed significant increases in immobile time in a tail suspension test and stress-induced corticosterone levels. Increased stress was associated with brain region-specific alterations of corticotropin-releasing factor expression and promoter methylation, changes that were not normalized with refeeding. Similar outcomes were produced by high-fat diet withdrawal, an additional component of human dieting. In examination of long-term behavioral consequences, previously restricted mice showed a significant increase in binge eating of a palatable high-fat food during stress exposure. Orexigenic hormones, melanin-concentrating hormone (MCH) and orexin, were significantly elevated in response to the high-fat diet only in previously restricted mice. Furthermore, administration of the MCH receptor-1 antagonist GSK-856464 [4-(4-ethyl-5-methylsulfanyl-1,2,4-triazol-3-yl)pyridine] significantly reduced total caloric intake in these mice during high-fat access. These results reveal reprogramming of key central pathways involved in regulating stress responsivity and orexigenic drives by moderate caloric restriction experience. In humans, such changes would be expected to reduce treatment success by promoting behaviors resulting in weight regain, and suggest that management of stress during dieting may be beneficial in long-term maintenance.

Regulation of mRNA translation as a conserved mechanism of longevity control

Appropriate regulation of mRNA translation is essential for growth and survival and the pathways that regulate mRNA translation have been highly conserved throughout eukaryotic evolution. Translation is controlled by a complex set of mechanisms acting at multiple levels, ranging from global protein synthesis to individual mRNAs. Recently, several mutations that perturb regulation of mRNA translation have also been found to increase longevity in three model organisms: the buddingyeast Saccharomyces cerevisiae, the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster. Many of these translation control factors can be mapped to a single pathway downstream of the nutrient responsive target of rapamycin (TOR) kinase. In this chapter, we will review the data suggesting that mRNA translation is an evolutionarily conserved modifier of longevity and discuss potential mechanisms by which mRNA translation could influence aging and age-associated disease in different species.

Neuronutrition and Alzheimer's disease

Alzheimer's disease (AD) is a complex neurological disorder resulting from both genetic and environmental factors with the latter being particularly important for the sporadic form of the disease. As such, diets rich in saturated fatty acids and alcohol, and deficient in antioxidants and vitamins appear to promote the onset of the disease, while diets rich in unsaturated fatty acids, vitamins, antioxidants, and wine likely suppress its onset. In addition, evidence suggests that diets rich in polyphenols and some spices suppress the onset of AD by scavenging free radicals and preventing oxidative damage. Metal ions are known to catalyze the production of free radicals and induce mental retardation or dementia, and several studies have also identified metals such as Pb, Fe, Al, Cu, and Zn in AD pathogenesis. While specific metal chelators have been tested for therapy, they have not been very successful, probably due to their late administration, i.e., after brain damage has been triggered. Since several dietary polyphenols are known to chelate metals, their routine use may also be protective against the onset of AD. In this review, we summarize beneficial dietary techniques in the fight against AD.

Neurodegenerative diseases: exercising toward neurogenesis and neuroregeneration

Currently, there is still no effective therapy for neurodegenerative diseases (NDD) such as Alzheimer's disease (AD) and Parkinson's disease (PD) despite intensive research and on-going clinical trials. Collectively, these diseases account for the bulk of health care burden associated with age-related neurodegenerative disorders. There is therefore an urgent need to further research into the molecular pathogenesis, histological differentiation, and clinical management of NDD. Importantly, there is also an urgency to understand the similarities and differences between these two diseases so as to identify the common or different upstream and downstream signaling pathways. In this review, the role iron play in NDD will be highlighted, as iron is key to a common underlying pathway in the production of oxidative stress. There is increasing evidence to suggest that oxidative stress predisposed cells to undergo damage to DNA, protein and lipid, and as such a common factor involved in the pathogenesis of AD and PD. The challenge then is to minimize elevated and uncontrolled oxidative stress levels while not affecting basal iron metabolism, as iron plays vital roles in sustaining cellular function. However, overload of iron results in increased oxidative stress due to the Fenton reaction. We discuss evidence to suggest that sustained exercise and diet restriction may be ways to slow the rate of neurodegeneration, by perhaps promoting neurogenesis or antioxidant-related pathways. It is also our intention to cover NDD in a broad sense, in the context of basic and clinical sciences to cater for both clinician's and the scientist's needs, and to highlight current research investigating exercise as a therapeutic or preventive measure.

Caloric restriction attenuates amyloid deposition in middle-aged dtg APP/PS1 mice

Caloric restriction (CR) mitigates neurological damage arising from aging and a variety of other sources, including neuropathology in young adult mice that express single and double transgenic (tg) mutations associated with Alzheimer disease (AD). To evaluate the potential of CR to protect against relatively heavy AD-type pathology, middle-aged (13-14-month-old) mice that co-express two mutations related to familial AD, amyloid precursor protein (APP) and presenilin 1 (PS1), were fed balanced diets with 40% fewer calories than ad libitum-fed controls. Following 18 weeks of treatment, mice were killed and brains were processed for quantification of total volume of amyloid-beta (Abeta) in the hippocampal formation and the overlying neocortex. Computerized stereology confirmed that CR reduced the total Abeta volume by about one-third compared to that in age-matched controls. Thus, CR appears to attenuate the accumulation of AD-type neuropathology in two cortical brain regions of middle-aged dtg APP/PS1 mice. These findings support the view that CR could be a potentially effective, non-pharmacology strategy for reducing relatively heavy Abeta deposition in older adult dtg APP/PS1 mice, and possibly afford similar protection against the onset and progression of AD in older adult humans.

The TOR pathway comes of age

Studies in a variety of model organisms indicate that nutrient signaling is tightly coupled to longevity. In nutrient replete conditions, organisms develop, grow, and age quickly. When nutrients become sparse as with dietary restriction, growth and development decline, stress response pathways become induced and organisms live longer. Considerable effort has been devoted to understanding the molecular events mediating lifespan extension by dietary restriction. One central focus has been on nutrient-responsive signal transduction pathways including insulin/IGF-1, AMP kinase, protein kinase A and the TOR pathway. Here we describe the increasingly prominent links between TOR signaling and aging in invertebrates. Longevity studies in mammals are not published to date. Instead, we highlight studies in mouse models, which indicate that dampening the TOR pathway leads to widespread protection from an array of age-related diseases.

Caloric restriction increases hippocampal glutamate uptake and glutamine synthetase activity in Wistar rats

Recent studies indicate that caloric restriction (CR) protects the central nervous system from several pathological conditions. The impairment of astroglial cell function, including glutamate uptake, glutamine synthetase (GS) activity and S100B secretion, may contribute to the progression of neurological disorders. The present study aimed to evaluate hippocampal astrocytic changes in response to CR diet, measuring astroglial parameters, such as glutamate uptake, GS activity and the immunocontent of GFAP and S100B. Blood biochemical parameters were also analyzed. Rats (60-day old) were fed ad libitum or on CR diets for 12 weeks. CR-fed rats showed approximately 16% less body weight gain than control rats. The CR diet was able to induce a significant increase in glutamate uptake (23%) and in GS activity (26%). There were no statistically significant differences in the immunocontent of either GFAP or S100B. In summary, the present study indicates that CR also modulates astrocyte functions by increasing glutamate uptake and GS activity, suggesting that CR might exert its neuroprotective effects against brain illness by modulation of astrocytic functions.

Should obesity be the main game? Or do we need an environmental makeover to combat the inflammatory and chronic disease epidemics?

There is a link between obesity and chronic disease. However, the causal relationship is complicated. Some forms of obesity are associated with low-level systemic inflammation, which is linked to disease. But lifestyle behaviours that may not necessarily cause obesity (poor diet, inadequate sleep, smoking, etc.) can independently cause inflammation and consequent disease. It is proposed here that it is the environment driving modern lifestyles, which is the true cause of much chronic disease, rather than obesity per se, and that obesity may be a marker of environmental derangement, rather than the primary cause of the problem. Attempts to clinically manage obesity alone on a large scale are therefore unlikely to be successful at the population level without significant lifestyle or environmental change. Environmental factors influencing obesity and health have now also been implicated in ecological perturbations such as climate change, through the shift to positive energy balance in humans caused by the exponential use of fossil fuels in such areas as transport, and consequent rises in carbon emissions into the atmosphere. It is proposed therefore that a more policy-based approach to dealing with obesity, which attacks the common causes of both biological and ecological 'dis-ease', could have positive effects on both chronic disease and environmental problems. A plea is thus made for a greater health input into discussions on environmental regulation for chronic disease control, as well as climate change.

A diet for dopaminergic neurons?

Parkinson's disease (PD) is the second most common neurodegenerative disease, which unfortunately is still fatal. Since the discovery of dopamine (DA) neuronal cell loss within the substantia nigra in PD, the past decades have seen the understanding of the pathophysiological mechanisms underlying the degenerative process advance at a very impressive rate. Nevertheless, there is at present no cure for PD. Although there are no proven therapies for prevention, a large body of evidence from animal studies has highlighted the paramount role of dietary factors in counteracting DA degeneration. Consistently, associations between the risk of developing PD and the intake of nutrients, individual foods, and dietary patterns have been recently shown. Therefore, promoting healthy lifestyle choices such as a Mediterranean diet might be the key to reducing the risk of PD.

Caloric restriction and brain function

PURPOSE OF REVIEW

In addition to extending lifespan, animal research shows that specific diets benefit brain functioning. Indeed, it has been proven that caloric restriction prevents age-related neuronal damage. What are those mechanisms involved in the effects of caloric restriction on brain functioning? Could caloric restriction be proposed in the future to prevent or treat neurodegenerative disorders such as Alzheimer's disease? Is there a future for caloric restriction interventions in adults?

RECENT FINDINGS

Hypotheses linking caloric restriction to cognitive capability include anti-inflammatory mechanisms, reduction of neural oxidative stress, promotion of synaptic plasticity, induction of various stress and neurotrophic/neuroprotective factors. Caloric restriction may also prevent beta-amyloid neuropathology in Alzheimer transgenic models. Finally, both exercise and caloric restriction enhance neurogenesis via different mechanisms suggesting that their combination may decrease the risk of neurodegenerative disease.

SUMMARY

It is now well established that caloric restriction could be used to promote successful brain aging. Data from randomized controlled trials in humans are limited. No positive effect on cognitive impairment was found probably due to methodological limitations. The long-term effects of caloric restriction in adults must be clarified before engaging in such preventive strategy. Additional animal studies must be conducted in the future to test the effects of 'multidomain' interventions (caloric restriction plus regular exercise) on age-related cognitive decline.

Strain differences in proliferation of progenitor cells in the dentate gyrus of the adult rat and the response to fluoxetine are dependent on corticosterone

This paper investigates the role of differences in adrenal cortical function on the proliferation rate of progenitor cells in the dentate gyrus of the hippocampus in adult Sprague–Dawley (SD) and Lister-Hooded (LH) male rats. SD rats had around 60% more cells labeled with Ki67 (an index of mitosis) than LH rats under basal conditions. Bilateral adrenalectomy (ADX) increased levels in both strains, but by unequal amounts, such that post-ADX numbers of Ki67-labeled cells were similar in both strains. Daily injections of 5 mg/kg corticosterone for 7 days reduced levels to similar values in ADX rats of both strains. The activity of progenitor cells in either strain did not respond to daily i.p. injections of fluoxetine (10 mg/kg) for 14 days, but an equivalent dose administered by osmotic minipump stimulated proliferation in both by a similar proportional amount, such that strain differences persisted. S.c. implantation of a corticosterone pellet (75 mg), which flattens the diurnal rhythm in corticosterone, prevented fluoxetine delivered by minipump from activating progenitor cell mitosis in SD rats, as it had in the LH strain in a previous study. These results show that much, if not all, of the marked strain differences between SD and LH rats in progenitor cell activity, and hence rates of neurogenesis in the dentate gyrus may be ascribed to corresponding differences in adrenal cortical activity.