Food restriction reduces brain damage and improves behavioral outcome following excitotoxic and metabolic insults

Dietary restriction started after spinal cord injury improves functional recovery

Spinal cord injury typically results in limited functional recovery. Here we investigated whether therapeutic dietary restriction, a multi-faceted, safe, and clinically-feasible treatment, can improve outcome from cervical spinal cord injury. The well-established notion that dietary restriction increases longevity has kindled interest in its potential benefits in injury and disease. When followed for several months prior to insult, prophylactic dietary restriction triggers multiple molecular responses and improves outcome in animal models of stroke and myocardial infarction. However, the efficacy of the clinically-relevant treatment of post-injury dietary restriction is unknown. Here we report that "every-other-day fasting" (EODF), a form of dietary restriction, implemented after rat cervical spinal cord injury was neuroprotective, promoted plasticity, and improved behavioral recovery. Without causing weight loss, EODF improved gait-pattern, forelimb function during ladder-crossing, and vertical exploration. In agreement, EODF preserved neuronal integrity, dramatically reduced lesion volume by >50%, and increased sprouting of corticospinal axons. As expected, blood beta-hydroxybutyrate levels, a ketone known to be neuroprotective, were increased by 2-3 fold on the fasting days. In addition, we found increased ratios of full-length to truncated trkB (receptor for brain-derived neurotrophic factor) in the spinal cord by 2-6 folds at both 5 days (lesion site) and 3 weeks after injury (caudal to lesion site) which may further enhance neuroprotection and plasticity. Because EODF is a safe, non-invasive, and low-cost treatment, it could be readily translated into the clinical setting of spinal cord injury and possibly other insults.

Starvation-dependent differential stress resistance protects normal but not cancer cells against high-dose chemotherapy

Strategies to treat cancer have focused primarily on the killing of tumor cells. Here, we describe a differential stress resistance (DSR) method that focuses instead on protecting the organism but not cancer cells against chemotherapy. Short-term starved S. cerevisiae or cells lacking proto-oncogene homologs were up to 1,000 times better protected against oxidative stress or chemotherapy drugs than cells expressing the oncogene homolog Ras2(val19). Low-glucose or low-serum media also protected primary glial cells but not six different rat and human glioma and neuroblastoma cancer cell lines against hydrogen peroxide or the chemotherapy drug/pro-oxidant cyclophosphamide. Finally, short-term starvation provided complete protection to mice but not to injected neuroblastoma cells against a high dose of the chemotherapy drug/pro-oxidant etoposide. These studies describe a starvation-based DSR strategy to enhance the efficacy of chemotherapy and suggest that specific agents among those that promote oxidative stress and DNA damage have the potential to maximize the differential toxicity to normal and cancer cells.

The influences of diet and exercise on mental health through hormesis

It is likely that the capacity of the brain to remain healthy during aging depends upon its ability to adapt and nurture in response to environmental challenges. In these terms, main principles involved in hormesis can be also applied to understand relationships at a higher level of complexity such as those existing between the CNS and the environment. This review emphasizes the ability of diet, exercise, and other lifestyle adaptations to modulate brain function. Exercise and diet are discussed in relationship to their aptitude to impact systems that sustain synaptic plasticity and mental health, and are therefore important for combating the effects of aging. Mechanisms that interface energy metabolism and synaptic plasticity are discussed, as these are the frameworks for the actions of cellular stress on cognitive function. In particular, neurotrophins are emerging as main factors in the equation that may connect lifestyle factors and mental health.

Adult-onset calorie restriction attenuates kainic acid excitotoxicity in the rat hippocampal slice

Lifelong calorie restriction is the only known intervention that has been shown to consistently increase life span and reduce the effects of aging on the brain. Given the difficulties of replicating lifelong calorie restriction within human populations, we have sought to assess the effects of short-term adult-onset calorie restriction upon acute excitotoxic insults in the rat hippocampus. Adult animals (approximately 6 months of age) underwent calorie restriction (alternate day feeding) for 7-10 weeks. Utilizing both electrophysiological and immunocytochemical techniques, we report that calorie restriction had no effect upon long-term potentiation (LTP), a measure of neuronal function. In control animals, application of kainic acid (20 microM) resulted in only 35% recovery of CA1 population spikes post-insult. However calorie-restricted animals showed significantly improved recovery after kainic acid treatment (64%). This data was supported by immunocytochemical studies which noted widespread loss of microtubule-associated protein (MAP 2) immunoreactivity in control slices following treatment with kainic acid; however MAP 2 staining was preserved in the CA1 and CA3 regions of calorie-restricted animals. Interestingly there was no significant difference in the recovery of population spikes between groups when slices were treated with N-methyl-d-aspartate (15 microM). We conclude that short-term adult-onset calorie restriction does not alter normal neuronal function and serves to protect the hippocampus from acute kainic acid excitotoxicity.

Dietary restriction modulates alpha-synuclein expression in the aging rat cortex and hippocampus

Dietary restriction (DR) is one of the promising environmental interventions known to attenuate aging and decrease risk of age-related neurodegenerative disorders. The aim of this study was to assess the effects of DR on expression of alpha-synuclein, a presynaptic protein involved in pathogenesis of Parkinson's and some other neurodegenerative diseases, in the cortex and hippocampus of adult, middle-aged, late middle-aged, and aged rats. Using Real Time RT-PCR, the authors report that aging regulates the expression of alpha-synuclein in a tissue-specific manner and that long-term DR reverts the late age-related changes of alpha-synuclein expression.

Curiosity and cure: translational research strategies for neural repair-mediated rehabilitation

Clinicians who seek interventions for neural repair in patients with paralysis and other impairments may extrapolate the results of cell culture and rodent experiments into the framework of a preclinical study. These experiments, however, must be interpreted within the context of the model and the highly constrained hypothesis and manipulation being tested. Rodent models of repair for stroke and spinal cord injury offer examples of potential pitfalls in the interpretation of results from developmental gene activation, transgenic mice, endogeneous neurogenesis, cellular transplantation, axon regeneration and remyelination, dendritic proliferation, activity-dependent adaptations, skills learning, and behavioral testing. Preclinical experiments that inform the design of human trials ideally include a lesion of etiology, volume and location that reflects the human disease; examine changes induced by injury and by repair procedures both near and remote from the lesion; distinguish between reactive molecular and histologic changes versus changes critical to repair cascades; employ explicit training paradigms for the reacquisition of testable skills; correlate morphologic and physiologic measures of repair with behavioral measures of task reacquisition; reproduce key results in more than one laboratory, in different strains or species of rodent, and in a larger mammal; and generalize the results across several disease models, such as axonal regeneration in a stroke and spinal cord injury platform. Collaborations between basic and clinical scientists in the development of translational animal models of injury and repair can propel experiments for ethical bench-to-bedside therapies to augment the rehabilitation of disabled patients.

Food restriction attenuates ischemia-induced spatial learning and memory deficits despite extensive CA1 ischemic injury

The purpose of the present study was to examine whether short-term food restriction (40% less food over a 3-month period) can attenuate ischemia-induced CA1 neuronal degeneration, and whether this attenuation translated into improved recovery of functional impairments following global ischemia. There was a significant loss of pyramidal CA1 neurons in ischemic compared to sham-operated rats but no difference between the ad lib and food-restricted ischemic animals. Although the diet did not influence neuronal damage in ischemic animals, the performance of food-restricted ischemic rats in spatial task such as the radial arm maze was significantly better than that of ad lib fed ischemic rats. Food-restricted ischemic rats made equivalent numbers of working memory errors as sham-operated animals and took the same time to complete a standard 8-arm radial arm maze task. They also displayed higher activity level in the open field compared to ad libitum fed ischemic rats, and spent considerably more time in the open arms of the elevated plus maze compared to the other groups, suggesting decreased anxiety in these ischemic rats. The relative sparing of spatial memory performance in food-restricted ischemic animals suggests that food restriction facilitates functional recovery.

Dietary factors, hormesis and health

The impact of dietary factors on health and longevity is increasingly appreciated. The most prominent dietary factor that affects the risk of many different chronic diseases is energy intake -- excessive calorie intake increases the risk. Reducing energy intake by controlled caloric restriction or intermittent fasting increases lifespan and protects various tissues against disease, in part, by hormesis mechanisms that increase cellular stress resistance. Some specific dietary components may also exert health benefits by inducing adaptive cellular stress responses. Indeed, recent findings suggest that several heavily studied phytochemicals exhibit biphasic dose responses on cells with low doses activating signaling pathways that result in increased expression of genes encoding cytoprotective proteins including antioxidant enzymes, protein chaperones, growth factors and mitochondrial proteins. Examples include: activation of the Nrf-2 -- ARE pathway by sulforaphane and curcumin; activation of TRP ion channels by allicin and capsaicin; and activation of sirtuin-1 by resveratrol. Research that establishes dose response and kinetic characteristics of the effects of dietary factors on cells, animals and humans will lead to a better understanding of hormesis and to improvements in dietary interventions for disease prevention and treatment.

Calorie restriction ameliorates neurodegenerative phenotypes in forebrain-specific presenilin-1 and presenilin-2 double knockout mice

Conditional double knockout of presenilin-1 and presenilin-2 (cDKO) in forebrain of mice led to brain atrophy, tau hyperphosphorylation, synaptic dysfunction and cognitive deficit. These brain changes recapitulated most of the neurodegenerative phenotypes of Alzheimer's disease (AD). In this report, we have investigated the effects of 4-month calorie restriction (CR) regimen on different phenotypes in cDKO mice. We found that CR improved novel object recognition and contextual fear conditioning memory in the cDKO mice. Histological and biochemical analysis showed that CR attenuated ventricle enlargement, caspase-3 activation and astrogliosis. In addition, the induction of tau hyperphosphorylation in the cDKO mice was reduced by CR, possibly through reduction of p25 accumulation and aberrant CDK5 activation. Finally, DNA microarray analysis demonstrated that CR could increase the expression of neurogenesis related genes and decrease the expression of inflammation related genes in the hippocampus of cDKO mice. The possible molecular mechanisms of the CR effects on alleviating AD pathogenesis have been discussed.

Intermittent fasting and caloric restriction ameliorate age-related behavioral deficits in the triple-transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive decline in cognitive function associated with the neuropathological hallmarks amyloid beta-peptide (Abeta) plaques and neurofibrillary tangles. Because aging is the major risk factor for AD, and dietary energy restriction can retard aging processes in the brain, we tested the hypothesis that two different energy restriction regimens, 40% calorie restriction (CR) and intermittent fasting (IF) can protect against cognitive decline in the triple-transgenic mouse model of AD (3xTgAD mice). Groups of 3xTgAD mice were maintained on an ad libitum control diet, or CR or IF diets, beginning at 3 months of age. Half of the mice in each diet group were subjected to behavioral testing (Morris swim task and open field apparatus) at 10 months of age and the other half at 17 months of age. At 10 months 3xTgAD mice on the control diet exhibited reduced exploratory activity compared to non-transgenic mice and to 3xTgAD mice on CR and IF diets. Overall, there were no major differences in performance in the water maze among genotypes or diets in 10-month-old mice. In 17-month-old 3xTgAD mice the CR and IF groups exhibited higher levels of exploratory behavior, and performed better in both the goal latency and probe trials of the swim task, compared to 3xTgAD mice on the control diet. 3xTgAD mice in the CR group showed lower levels of Abeta1-40, Abeta1-42 and phospho-tau in the hippocampus compared to the control diet group, whereas Abeta and phospho-tau levels were not decreased in 3xTgAD mice in the IF group. IF may therefore protect neurons against adverse effects of Abeta and tau pathologies on synaptic function. We conclude that CR and IF dietary regimens can ameliorate age-related deficits in cognitive function by mechanisms that may or may not be related to Abeta and tau pathologies.

Neuroprotective potential of the Bahadori leanness program: A “mini-fast with exercise” strategy

The Bahadori Leanness Program (BLP) is a multi-step strategy for weight control, the most innovative feature of which is "mini-fast with exercise" - every 24h includes a fast of 12-14 h duration within which is nested a session of aerobic exercise. Low-fat, low-glycemic-index foods choices help to insure that diurnal levels of glucose and insulin remain relatively low. Clinical experience demonstrates that clients can achieve good compliance with this protocol, and the long term impact on body weight is gratifying. Rodent studies demonstrate that alternate-day feeding is even more effective than caloric restriction for promoting neuroprotection, suggesting that intermittent periods of mild metabolic stress induce protective adaptations in the brain; exercise training is also neuroprotective in these models. Mattson has raised the possibility that regular meal-skipping might be a feasible strategy for achieving similar - though perhaps less potent - protection in humans. Thus, it is suggested that exercise superimposed on regular short-term fasts, as in the BLP, might provide meaningful neuroprotection. Studies assessing CSF levels of brain neurotrophic hormones might be useful for evaluating the impact of such a strategy on brain neurochemistry. It should not be overlooked that leanness, good insulin sensitivity, and regular exercise are likely to be neuroprotective in their own right. The episodic metabolic stress associated with BLP may also have potential for prevention and therapy of cancer, inasmuch as down-regulation of systemic IGF-I activity during the mini-fasts would be expected to boost the rate of apoptosis in IGF-I-responsive neoplastic or pre-neoplastic tissues. Moreover, the relatively low-diurnal insulin levels and exercise training associated with BLP would be expected to down-regulate sympathetic activity while boosting cardiac parasympathetic tone - effects that should decrease risk for hypertension and sudden-death arrhythmias. Thus, it is conceivable that BLP will provide a range of health benefits extending beyond those attributable to its favorable impact on body composition.

Calorie restriction up-regulates the plasma membrane redox system in brain cells and suppresses oxidative stress during aging

The plasma membrane (PM) contains redox enzymes that provide electrons for energy metabolism and recycling of antioxidants such as coenzyme Q and alpha-tocopherol. Brain aging and neurodegenerative disorders involve impaired energy metabolism and oxidative damage, but the involvement of the PM redox system (PMRS) in these processes is unknown. Caloric restriction (CR), a manipulation that protects the brain against aging and disease, increased activities of PMRS enzymes (NADH-ascorbate free radical reductase, NADH-quinone oxidoreductase 1, NADH-ferrocyanide reductase, NADH-coenzyme Q10 reductase, and NADH-cytochrome c reductase) and antioxidant levels (alpha-tocopherol and coenzyme Q10) in brain PM during aging. Age-related increases in PM lipid peroxidation, protein carbonyls, and nitrotyrosine were attenuated by CR, levels of PMRS enzyme activities were higher, and markers of oxidative stress were lower in cultured neuronal cells treated with CR serum compared with those treated with ad libitum serum. These findings suggest important roles for the PMRS in protecting brain cells against age-related increases in oxidative and metabolic stress.

Neuronal life-and-death signaling, apoptosis, and neurodegenerative disorders

When subjected to excessive oxidative stress, neurons may respond adaptively to overcome the stress, or they may activate a programmed cell death pathway called apoptosis. Apoptosis is characterized by alterations in mitochondria and the endoplasmic reticulum and activation of cysteine proteases called caspases. Increasing evidence suggests that apoptotic biochemical cascades are involved in the dysfunction and death of neurons in neurodegenerative disorders such as Alzheimer's, Parkinson, and Huntington's diseases. Studies of normal aging, of genetic mutations that cause disease, and of environmental factors that affect disease risk are revealing cellular and molecular alterations that may cause excessive oxidative stress and trigger neuronal apoptosis. Accumulation of self-aggregating proteins such as amyloid beta-peptide, tau, alpha-synuclein, and huntingtin may be involved in apoptosis both upstream and downstream of oxidative stress. Membrane-associated oxidative stress resulting in perturbed lipid metabolism and disruption of cellular calcium homeostasis may trigger apoptosis in several different neurodegenerative disorders. Counteracting neurodegenerative processes are an array of mechanisms including neurotrophic factor signaling, antioxidant enzymes, protein chaperones, antiapoptotic proteins, and ionostatic systems. Emerging findings suggest that the resistance of neurons to death during aging can be enhanced by modifications of diet and lifestyle.

Caloric restriction and intermittent fasting: two potential diets for successful brain aging

The vulnerability of the nervous system to advancing age is all too often manifest in neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. In this review article we describe evidence suggesting that two dietary interventions, caloric restriction (CR) and intermittent fasting (IF), can prolong the health-span of the nervous system by impinging upon fundamental metabolic and cellular signaling pathways that regulate life-span. CR and IF affect energy and oxygen radical metabolism, and cellular stress response systems, in ways that protect neurons against genetic and environmental factors to which they would otherwise succumb during aging. There are multiple interactive pathways and molecular mechanisms by which CR and IF benefit neurons including those involving insulin-like signaling, FoxO transcription factors, sirtuins and peroxisome proliferator-activated receptors. These pathways stimulate the production of protein chaperones, neurotrophic factors and antioxidant enzymes, all of which help cells cope with stress and resist disease. A better understanding of the impact of CR and IF on the aging nervous system will likely lead to novel approaches for preventing and treating neurodegenerative disorders.

Proteomics analysis provides insight into caloric restriction mediated oxidation and expression of brain proteins associated with age-related impaired cellular processes: Mitochondrial dysfunction, glutamate dysregulation and impaired protein synthesis

Age-related impairment of functionality of the central nervous system (CNS) is associated with increased susceptibility to develop many neurodegenerative diseases. Increased oxidative stress in the CNS of aged animals is manifested by increased protein oxidation, which is believed to contribute to the age-related learning and memory deficits. Glutamate dysregulation, mitochondrial dysfunction and impaired protein synthesis are observed in aged brains, along with increased protein oxidation. Interestingly, all of these age-related cellular alterations can be improved by caloric restriction (CR), which can also improve the plasticity and recovery of the CNS. Although the beneficial effects of CR on brains are well established, the mechanism(s) of its action remains unclear. In order to gain insight into the mechanism of CR in the brain, we located the brain regions that are benefited the most from reduced oxidative stress by CR. Along with other brain regions, striatum (ST) showed significantly decreased bulk protein carbonyl levels and hippocampus (HP) showed decreased bulk protein 3-nitrotyrosine (3-NT) levels in CR aged rats when compared to those of age matched controls. To determine which proteins were oxidatively modified in these brain regions, we used parallel proteomics approach to identify the proteins that are altered in oxidation and expression. The specific carbonyl levels of pyruvate kinase M2 (PKM2), alpha-enolase (ENO1), inositol monophosphatase (INSP1), and F1-ATPase Chain B (ATP-F1B) were significantly decreased in ST of aged CR rats. In contrast, the expression levels of phosphoglycerate kinase 1 (PKG1), inosine monophosphate cyclohydrolase (IMPCH) and F1-ATPase Chain A (ATP-F1A) were significantly increased in the ST of CR rats. In the hippocampus of CR rats, the specific 3-NT levels of malate dehydrogenase (MDH), phosphoglycerate kinase 1 (PKG1) and 14-3-3 zeta protein were significantly decreased and expression levels of DLP1 splice variant 1 (DLP1), mitochondrial aconitase (ACO2), dihydrolipoamide dehydrogenase (DLDH), neuroprotective peptide H3 (NPH3), and eukaryotic translation initiation factor 5A (eIF-5A) are increased. Moreover, an unnamed protein product (UNP1) with similar sequence to initiation factor 2 (IF-2) was decreased in the HP of CR rats. Our data support the hypothesis that CR induces a mild metabolic stress response by increasing the production of neurotrophic proteins, therefore, priming neurons against apoptosis. Moreover, our study shows that the improvement of glutamate dysregulation, mitochondrial dysfunction and protein synthesis by CR is, at least partially, due to the CR-mediated alteration of the oxidation or the expression of PKM2, ENO1, INSP1, ATP-F1B, PKG1, IMPCH, ATP-F1A MDH, PKG1 and 14-3-3 zeta protein, DLP1, ACO2, DLDH, NPH3, eIF-5A and UNP1. This study provides valuable insights into the mechanisms of the beneficial factors on brain aging by CR.

Interferon-gamma is up-regulated in the hippocampus in response to intermittent fasting and protects hippocampal neurons against excitotoxicity

Dietary restriction (DR) increases the life span of many different organisms, and recent findings have demonstrated neuroprotective effects of DR in rodent and nonhuman primate models of neurodegenerative disorders. The neuroprotective mechanism of action of DR is unknown, but it may result from a mild cellular stress response involving increased production of neurotrophic factors. Because several different cytokines are known to be up-regulated in brain cells in response to stress, we determined whether DR affected cytokine expression in the rat brain. Levels of expression of interferon-gamma (IFN-gamma) and its receptor were significantly increased in the hippocampus of rats that had been maintained on an intermittent fasting DR regimen compared with rats on the ad libitum control diet. Pretreatment of embryonic rat hippocampal cell cultures with IFN-gamma protected neurons against glutamate-induced death. IFN-gamma-mediated neuroprotection was associated with an enhanced recovery of intracellular Ca(2+) concentrations following exposure to glutamate. Our data show that intermittent fasting DR stimulates IFN-gamma-mediated neuroprotective signaling in the hippocampus, suggesting a role for this cytokine in the previously reported ability of DR to protect neurons in animal models of severe epileptic seizures, stroke, and neurodegenerative disorders.

Stress resistance and aging: influence of genes and nutrition

Previous studies have shown that dermal fibroblast cell lines derived from young adult mice of the long-lived Snell dwarf (dw/dw), Ames dwarf (df/df) and growth hormone receptor knockout (GHR-KO) mouse stocks are resistant, in vitro, to the cytotoxic effects of hydrogen peroxide, cadmium, ultraviolet light, paraquat, and heat. Here we show that, in contrast, fibroblasts from mice on low-calorie (CR) or low methionine (Meth-R) diets are not stress resistant in culture, despite the longevity induced by both dietary regimes. A second approach, involving induction of liver cell death in live animals using acetaminophen (APAP), documented hepatotoxin resistance in the CR and Meth-R mice, but dw/dw and GHR-KO mutant mice were not resistant to this agent, and were in fact more susceptible than littermate controls to the toxic effects of APAP. These data thus suggest that while resistance to stress is a common characteristic of experimental life span extension in mice, the cell types showing resistance may differ among the various models of delayed or decelerated aging.

Hormesis/preconditioning mechanisms, the nervous system and aging

Throughout life, organisms and their cells are subjected to various stressors which they must respond to adaptively in order to avoid disease and death. Accordingly, cells possess a variety of stress-responsive signaling pathways that are coupled to kinase cascades and transcription factors that induce the expression of genes that encode cytoprotective proteins such as protein chaperones (PC), growth factors and antioxidant enzymes. Emerging findings suggest that many of the environmental factors that improve health and so prolong lifespan (for example, dietary restriction, exercise and cognitive stimulation) exert their beneficial effects through a hormesis-like mechanism. Here we describe data supporting the hormesis hypothesis of disease resistance and longevity, with a focus on findings from studies of the nervous system in this laboratory.

Ageing and neuronal vulnerability

Everyone ages, but only some will develop a neurodegenerative disorder in the process. Disease might occur when cells fail to respond adaptively to age-related increases in oxidative, metabolic and ionic stress, thereby resulting in the accumulation of damaged proteins, DNA and membranes. Determinants of neuronal vulnerability might include cell size and location, metabolism of disease-specific proteins and a repertoire of signal transduction pathways and stress resistance mechanisms. Emerging evidence on protein interaction networks that monitor and respond to the normal ageing process suggests that successful neural ageing is possible for most people, but also cautions that cures for neurodegenerative disorders are unlikely in the near future.

Calorie restriction mimetics: an emerging research field

When considering all possible aging interventions evaluated to date, it is clear that calorie restriction (CR) remains the most robust. Studies in numerous species have demonstrated that reduction of calories 30-50% below ad libitum levels of a nutritious diet can increase lifespan, reduce the incidence and delay the onset of age-related diseases, improve stress resistance, and decelerate functional decline. A current major focus of this research area is whether this nutritional intervention is relevant to human aging. Evidence emerging from studies in rhesus monkeys suggests that their response to CR parallels that observed in rodents. To assess CR effects in humans, clinical trials have been initiated. However, even if results from these studies could eventually substantiate CR as an effective pro-longevity strategy for humans, the utility of this intervention would be hampered because of the degree and length of restriction required. As an alternative strategy, new research has focused on the development of 'CR mimetics'. The objective of this strategy is to identify compounds that mimic CR effects by targeting metabolic and stress response pathways affected by CR, but without actually restricting caloric intake. For example, drugs that inhibit glycolysis (2-deoxyglucose), enhance insulin action (metformin), or affect stress signaling pathways (resveratrol), are being assessed as CR mimetics (CRM). Promising results have emerged from initial studies regarding physiological responses which resemble those observed in CR (e.g. reduced body temperature and plasma insulin) as well as protection against neurotoxicity (e.g. enhanced dopamine action and up-regulated neurotrophic factors). Ultimately, lifespan analyses in addition to expanded toxicity studies must be accomplished to fully assess the potential of any CRM. Nonetheless, this strategy clearly offers a very promising and expanding research endeavor.

Dietary restriction protects against chronic-ethanol-induced changes in exploratory behavior in Wistar rats

Chronic ethanol intake causes various types of neural damage and behavioral impairments, probably acting through oxidative stress and excitotoxicity, while dietary restriction is considered by some authors to protect the central nervous system from these kinds of damage. In the present study, a factorial experimental design was used to investigate the effects of chronic ethanol and dietary restriction treatments, associated or not, on Wistar rats' exploratory behavior, spatial memory aspects and cortical and hippocampal acetylcholinesterase (AChE) activity. Dietary restriction lasted for the whole experiment, while ethanol treatment lasted for only 3 weeks. Despite the short ethanol treatment duration, for two behavior categories assessed, moving and rearing, an interaction was observed between the effects of chronic ethanol and dietary restriction. There were no significant differences in AChE activities among the groups. Cerebellar neural nitric oxide synthase (nNOs) activity was measured as a first step to assess oxidative stress. Dietary restriction significantly reduced NO formation. The present results indicate that dietary restriction might exert a protective effect against chronic-ethanol-induced changes in exploratory behavior. It is hypothesized that the mechanisms underlying this protection can involve prevention of oxidative stress.

Revenge of the “Sit”: How lifestyle impacts neuronal and cognitive health through molecular systems that interface energy metabolism with neuronal plasticity

Exercise, a behavior that is inherently associated with energy metabolism, impacts the molecular systems important for synaptic plasticity and learning and memory. This implies that a close association must exist between these systems to ensure proper neuronal function. This review emphasizes the ability of exercise and other lifestyle implementations that modulate energy metabolism, such as diet, to impact brain function. Mechanisms believed to interface metabolism and cognition seem to play a critical role with the brain derived neurotrophic factor (BDNF) system. Behaviors concerned with activity and metabolism may have developed simultaneously and interdependently during evolution to determine the influence of exercise and diet on cognition. A look into our evolutionary past indicates that our genome remains unchanged from the times of our hunter-gatherer ancestors, whose active lifestyle predominated throughout almost 100% of humankind's existence. Consequently, the sedentary lifestyle and eating behaviors enabled by the comforts of technologic progress may be reaping "revenge" on the health of both our bodies and brains. In the 21st century we are confronted by the ever-increasing incidence of metabolic disorders in both the adult and child population. The ability of exercise and diet to impact systems that promote cell survival and plasticity may be applicable for combating the deleterious effects of disease and ageing on brain health and cognition.

Transient caloric restriction in early adulthood hastens disease endpoint in male, but not female, Cu/Zn-SOD mutant G93A mice

Long-term caloric restriction (CR) prolongs the lifespan in healthy insects, rodents, and nonhuman primates. We previously reported that long-term CR improves motor performance but hastens clinical onset of disease in an animal model of amyotrophic lateral sclerosis (G93A mice). G93A mice overexpress the mutant human Cu/Zn-SOD gene and show progressive lower motor neuron weakness and increased oxidative stress. To study short-term (15 days) CR in the same animal model, we investigated the effect of transient caloric restriction (TCR) on paw grip endurance, clinical onset, disease progression (time from clinical onset to endpoint), and lifespan. Starting at age 40 days, 32 separately caged G93A mice were randomly divided into two groups: ad libitum (AL, n = 17; 10 females, 7 males) and TCR (n = 15; 6 females, 9 males) with a diet equal to 60% of AL. When the TCR mice lost 30% of their weight they were offered food AL until endpoint, otherwise all TCR mice were provided food AL from age 55 days until endpoint (i.e., range of TCR = 13-15 days). Paw grip endurance started to decrease significantly at age 96 days compared with baseline values for all the groups. TCR males reached clinical onset 5 days sooner than TCR females. Disease progression was 8 days faster in TCR mice than AL mice and 6 days faster in male mice than female mice. The probability of survival was significantly different between the groups, with the TCR males having a faster rate of reaching endpoint than TCR females, AL males, and AL females. We conclude that TCR hastens clinical onset of disease and shortens the lifespan in male, but not female, G93A mice. Moreover, TCR hastens progress of disease but has no effect on paw grip endurance. The female sex is protective against the detrimental effects of short-term CR in G93A mice. Assuming we can extrapolate these results to humans, short-term CR should be avoided in patients with amyotrophic lateral sclerosis, especially men.

Dietary restriction increases hippocampal neurogenesis by molecular mechanisms independent of NMDA receptors

Neurogenesis occurs in the adult hippocampus and is promoted by various stimulatory factors, such as enriched environments, running exercises, learning and dietary restriction. We have previously shown that the promotion of adult neurogenesis in the hippocampus by running wheel exercise is mediated by NMDA receptors. In the present study, we report that dietary restriction enhanced the hippocampal neurogenesis in mice lacking NMDA receptor epsilon1 subunit as well as wild-type mice. This result suggests that the molecular mechanism by which dietary restriction promotes adult neurogenesis may be, in contrast to that of running exercise, independent on the NMDA receptor functions.

Neuroprotective potential of dietary restriction against kainate-induced excitotoxicity in adult male Wistar rats

The influence that dietary factors have on the nervous system and its susceptibility to disease, is an active area of biomedical research. Recent studies have shown that dietary restriction (DR) can have profound effect on brain function and vulnerability to injury and disease and can also enhance synaptic plasticity, which may increase the ability of brain to resist aging and restore function following injury. The dietary restriction may result in neuroprotection as suggested by marked reduction in neuronal cell death of the CA3 region of hippocampus after kainate administration in our study. We examined the effects of 3 months of DR (alternate day feeding regimen) on the antioxidants and antioxidant enzymes from different brain regions such as cerebral hemispheres, diencephalon, cerebellum and brain stem after kainate-induced excitotoxicity in adult male Wistar rats. The present study reports the beneficial effects of dietary restriction on different antioxidants and antioxidant enzymes against kainate-induced excitotoxicity in different brain regions of young adult male Wistar rats. The expression of stress response protein heat shock protein 70 (HSP 70) was also studied from discrete regions of rat brain under the same set of experimental conditions. DR significantly enhanced the expression of HSP 70 in kainic acid (KA)-treated rats, whereas KA treatment of ad libitum fed rats resulted in decreased HSP 70 expression. The DR was observed to exert neuroprotection by enhancing the expression of HSP 70 in kainic acid treated rats.

Energy intake, meal frequency, and health: a neurobiological perspective

The size and frequency of meals are fundamental aspects of nutrition that can have profound effects on the health and longevity of laboratory animals. In humans, excessive energy intake is associated with increased incidence of cardiovascular disease, diabetes, and certain cancers and is a major cause of disability and death in industrialized countries. On the other hand, the influence of meal frequency on human health and longevity is unclear. Both caloric (energy) restriction (CR) and reduced meal frequency/intermittent fasting can suppress the development of various diseases and can increase life span in rodents by mechanisms involving reduced oxidative damage and increased stress resistance. Many of the beneficial effects of CR and fasting appear to be mediated by the nervous system. For example, intermittent fasting results in increased production of brain-derived neurotrophic factor (BDNF), which increases the resistance of neurons in the brain to dysfunction and degeneration in animal models of neurodegenerative disorders; BDNF signaling may also mediate beneficial effects of intermittent fasting on glucose regulation and cardiovascular function. A better understanding of the neurobiological mechanisms by which meal size and frequency affect human health may lead to novel approaches for disease prevention and treatment.

Prophylactic activation of neuroprotective stress response pathways by dietary and behavioral manipulations

It is well established that when most types of cells, including neurons, are exposed to a mild stress they increase their ability to resist more severe stress. This "preconditioning" phenomenon involves up-regulation of genes that encode cytoprotective proteins such as heat-shock proteins and growth factors. We found that a similar beneficial cellular stress response can be induced in neurons throughout the brain by a "meal-skipping" dietary restriction (DR) regimen in rats and mice. DR is effective in protecting neurons and improving functional outcome in models of stroke, Alzheimer's, Parkinson's and Huntington's diseases. DR induces an increase in the levels of brain-derived neurotrophic factor (BDNF) and heat-shock proteins in neurons. DR also stimulates neurogenesis in the hippocampus, and BDNF plays a role in this effect of DR. Physical exercise and environmental enrichment are two other manipulations that have been shown to induce BDNF expression in the brain, presumably because it is a mild cellular stress. When taken together with epidemiological and clinical studies in humans, the data from animal studies suggest that it may be possible to reduce the risk for age-related neurodegenerative disorders through dietary and behavioral modifications that act by promoting neuronal plasticity and survival.

Caloric restriction attenuates Aβ-deposition in Alzheimer transgenic models

Dietary influences on Alzheimer disease (AD) are gaining recognition. Because many aging processes are attenuated in laboratory mammals by caloric restriction (CR), we examined the effects of short-term CR in two AD-transgenic mice, APP(swe/ind) (J20) and APP(swe) + PS1(M146L) (APP + PS1). CR substantially decreased the accumulation of Abeta-plaques in both lines: by 40% in APP(swe/ind) (CR, 6 weeks), and by 55% in APP + PS1 (CR, 14 weeks). CR also decreased astrocytic activation (GFAP immunoreactivity). These influences of CR on AD-transgenic mice are consistent with epidemiological reports that show that high caloric diets associate with the risk of AD, and suggest that dietary interventions in adult life might slow disease progression.

Dietary restriction counteracts age-related changes in cholesterol metabolism in the rat

The effects of ageing on the metabolism of cholesterol were examined in three different organs (liver, aorta and brain) of 6-, 12- and 24-month-old male Sprague-Dawley rats. Ageing was associated with a significant increase in intracellular cholesterol esters in all three organs. Steady state mRNA levels of multidrug resistance protein (MDR) and acylCoA:cholesterol acyl transferase (ACAT), enzymes involved in cholesterol import and esterification, were also increased. By contrast, expression of mRNA for neutral cholesterol ester hydrolase (nCEH) and caveolin-1, proteins involved in cholesterol ester hydrolysis and export, were significantly reduced. Dietary restriction is the only intervention shown to extend lifespan and retard age-related declines in function in mammals. To further explore the possible correlation between changes in cholesterol esterification and ageing, we analysed cholesterol metabolism in liver, aorta, and brain of aged rats exposed to two dietary restriction regimens: intermittent (alternate-day) fasting (IF) and food intake restriction (60% of ad libitum feeding). Both dietary regimens attenuated the age-related changes in cholesterol esters and in the expression of genes involved in cholesterol metabolism. These results provide evidence that distinctive age-associated changes in intracellular cholesterol metabolism occur in rats. Furthermore, these modifications can be partially reversed by dietary restriction, a condition known to affect the ageing process. Age-related changes in cholesterol metabolism may play a role in triggering and/or aggravating senescence-related disorders characterized by altered cholesterol homeostasis.

Glucose metabolism and Alzheimer's disease

The brain is the organ with the highest basal rate of glucose consumption. Most of the energy generated by the oxidation of glucose is used for the work necessary to maintain the ionic balances associated with synaptic transmission. When the nervous system is subjected to the oxidative stress of age-associated disease, there is a redistribution of glucose breakdown to pathways that more efficiently produce molecules involved in antioxidant metabolism. This shift is at least in part mediated by the transcription factor HIF-1. The clinical implications of this change in glucose metabolism are discussed in the context of aging and Alzheimer's disease.

Brain aging: reorganizing discoveries about the aging mind

New discoveries challenge the long-held view that aging is characterized by progressive loss and decline. Evidence for functional reorganization, compensation and effective interventions holds promise for a more optimistic view of neurocognitive status in later life. Complexities associated with assigning function to age-specific activation patterns must be considered relative to performance and in light of pathological aging. New biological and genetic markers, coupled with advances in imaging technologies, are enabling more precise characterization of healthy aging. This interdisciplinary, cognitive neuroscience approach reveals dynamic and optimizing processes in aging that might be harnessed to foster the successful aging of the mind.

Ketogenic diet prevents clusterin accumulation induced by kainic acid in the hippocampus of male ICR mice

We investigated the effect of ketogenic diet (KD) on clusterin accumulation in the kainic acid (KA)-induced seizure model. Two days after KA administration, strong clusterin-like immunoreactivity (IR) was detected in the hippocampus in the normal diet (ND)-fed mice. But in the KD-fed mice, few clusterin-like IR was detected. These results indicate that KD has neuroprotective effects throughout diminishing nuclear clusterin accumulation that is involved in caspase-3 independent cell death mechanism.

Calorie restriction to retard aging and increase longevity

Calorie restriction increases longevity in rodents, delays the onset of certain diseases and has positive effects on ageing. Studies are ongoing in non-human primates. Eight persons following such a diet for 2 years reacted as anticipated (loss of body weight and fat, decrease in glycaemia and body temperature, etc.). Calorie restriction perhaps teaches us more on the means of resisting malnutrition than on ageing in normal dietary conditions. Calorie restriction is a tool for research, but it should not be recommended by practitioners, notably in elderly patients.

Caloric restriction transiently improves motor performance but hastens clinical onset of disease in the Cu/Zn-superoxide dismutase mutant G93A mouse

Caloric restriction (CR) prolongs lifespan in insects, rodents, and nonhuman primates, a process attributed to a reduction in oxidative stress. Transgenic mice that overexpress the mutant human Cu/Zn-superoxide dismutase (SOD1) gene (G93A mice) are an animal model of amyotrophic lateral sclerosis showing progressively lower motor neuron weakness and increased oxidative stress. We investigated the effect of CR on motor performance, clinical onset, disease progression, and lifespan in G93A mice. Starting at 40 days of age, 14 separately caged G93A mice were randomly divided into two groups: ad libitum (AL; n = 6) and calorie-restricted (CR; n = 8) with a diet equal to 60% of AL. The CR mice (mean +/- SEM: 14.0 +/- 0.7 g) weighed 31% less than the AL mice (20.3 +/- 1.0 g) (P = 0.0002). From 74 to 93 days of age, the CR mice performed better on the rotarod than the AL mice: fall time, P = 0.039; fall speed, P = 0.009. The CR mice had a faster rate of reaching clinical onset than the AL mice (hazard ratio = 4.3, P = 0.0006). The CR and AL mice reached clinical onset of disease at age 99 +/- 1 and 110 +/- 2 days, respectively (P = 0.0003), with no significant difference in disease progression. The CR mice tended to reach endpoint sooner than the AL mice (age-specific death: 125 +/- 3 vs. 133 +/- 3 days, respectively, P = 0.09). We conclude that CR diet transiently improves motor performance but hastens clinical onset of disease in G93A mice. These results suggest that CR diet is not a protective strategy for patients with amyotrophic lateral sclerosis (ALS) and hence is contraindicated.

Dietary restriction affects striatal glutamate in the MPTP-induced mouse model of nigrostriatal degeneration

One month following subchronic treatment with the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (30 mg/kg/d x 7 days), there is a decrease in the extracellular level of striatal glutamate. It has been reported that following dietary restriction (DR) (fed on alternate days) of C57BL/6 mice, MPTP administration resulted in a reduction in the loss of tyrosine hydroxylase-positive neurons within the substantia nigra pars compacta (SN-PC) compared to the ad libitum (AL)-fed MPTP-treated mice. However, there have been no reports of whether the MPTP-induced alterations in brain neurochemistry or morphology can be similarly attenuated by DR if initiated after administration of the toxin. In the MPTP/AL group there is a decrease in the extracellular level of striatal glutamate compared to the Vehicle/AL group. However, 21 days of DR starting 1 day after the last subchronic dose of MPTP results in a reversal in the extracellular level of striatal glutamate compared to the MPTP/AL group. DR alone resulted in a decrease in extracellular striatal glutamate. There was no change in the relative density of the glutamate transporter, GLT-1, within the striatum or SN-PC between any of the groups, suggesting that the alterations in striatal extracellular glutamate were not due to a change in this specific transporter. There was an increase in the density of nerve terminal glutamate immunolabeling in the MPTP/AL and MPTP/DR groups compared to the Vehicle/AL group. There was a similar decrease in the relative density of tyrosine hydroxylase immunolabeling within the striatum and the SN-PC in both the MPTP/AL and MPTP/DR groups compared to the Vehicle/AL group. Since a decrease in the activity of the corticostriatal glutamate pathway has been reported in both Parkinson's disease and in animal models of nigrostriatal loss, these data suggest that DR initiated after the partial loss of striatal dopamine appears to reverse the decrease in striatal glutamate.

Caloric restriction increases neurotrophic factor levels and attenuates neurochemical and behavioral deficits in a primate model of Parkinson's disease

We report that a low-calorie diet can lessen the severity of neurochemical deficits and motor dysfunction in a primate model of Parkinson's disease. Adult male rhesus monkeys were maintained for 6 months on a reduced-calorie diet [30% caloric restriction (CR)] or an ad libitum control diet after which they were subjected to treatment with a neurotoxin to produce a hemiparkinson condition. After neurotoxin treatment, CR monkeys exhibited significantly higher levels of locomotor activity compared with control monkeys as well as higher levels of dopamine (DA) and DA metabolites in the striatal region. Increased survival of DA neurons in the substantia nigra and improved manual dexterity were noted but did not reach statistical significance. Levels of glial cell line-derived neurotrophic factor, which is known to promote the survival of DA neurons, were increased significantly in the caudate nucleus of CR monkeys, suggesting a role for glial cell line-derived neurotrophic factor in the anti-Parkinson's disease effect of the low-calorie diet.

Proactive transplantation of human neural stem cells prevents degeneration of striatal neurons in a rat model of Huntington disease

We have investigated the effectiveness of transplantation of human neural stem cells into adult rat striatum prior to induction of striatal damage with the mitochondrial toxin 3-nitropropionic acid (3-NP). Systemic 3-NP administration caused widespread neuropathological deficits similar to ones found in Huntington disease (HD) including impairment in motor function (rotarod balance test) and extensive degeneration of neuron-specific nuclear antigen (NeuN)(+) neurons, calbindin(+) neurons and glutamic acid decarboxylase (GAD)(+) striatal neurons. Animals receiving intrastriatal implantation of human neural stem cells (hNSCs) 1 week before 3-NP treatments exhibited significantly improved motor performance and reduced damage to striatal neurons compared with control sham injections. In contrast, transplantation of hNSCs at 12 h after the initial 3-NP administration did not lead to any improvement in motor performance or protect striatal neurons from the 3-NP-induced toxicity. These results indicate that the presence of grafted hNSCs before 3-NP treatment is required for host striatal neuronal protection and enhanced motor function. Immunoreactivity of brain-derived neurotrophic factor (BDNF) was found in vitro in cultured hNSCs and in vivo in grafted NSCs with expression and secretion of BDNF demonstrated by RT-PCR, immunocytochemistry, dot-blot, and ELISA analyses. Thus, protective effects of proactive transplantation of hNSCs may be due, in part, to effects mediated by BDNF. The findings in this work have particular relevance to a rat model of HD in that proactive transplanted hNSCs protect host striatal neurons against neuronal injury and improve motor impairment induced by 3-NP toxicity.

Effect of food deprivation during early development on cognition and neurogenesis in the rat

Food deprivation has been recognized as having pronounced beneficial effects in adult animals, increasing longevity, reducing seizure susceptibility, and enhancing resistance to neurotoxins. It is not known whether food deprivation in developing animals is neuroprotective or harmful. To evaluate the effects of food deprivation on brain development, we evaluated visual-spatial learning and memory and neurogenesis in the dentate gyrus of the hippocampus in food-deprived (FD) and well-fed (WF) rats. To induce food deprivation, pups were removed from their dams for 12 hours per day from Postnatal Day (P) 2 to P19. FD and WF rat pups were then subjected to status epilepticus (SE) induced by lithium-pilocarpine at P20. After SE, neurogenesis was measured, while in another group of P38 rats, learning and memory were evaluated using the Morris water maze. Food deprivation was found to reduce neurogenesis when assessed after the period of food deprivation. Although SE reduced neurogenesis in the WF animals, it had little effect additional to food deprivation on neurogenesis in the FD rats. Compared with the WF group, FD rats had a mild impairment in memory in the water maze testing after SE. Our study demonstrates that food deprivation during the neonatal period in rats is associated with a decrease in neurogenesis and mild impairment of visual-spatial memory. Although SE decreased neurogenesis in the WF group, in FD animals, SE did not reduce neurogenesis more than what was seen with food deprivation alone. Our results suggest that although food deprivation during early development reduces dentate gyrus neurogenesis, the reduced neurogenesis is not a major factor in cognitive impairment after SE in FD rats.

Development of Calorie Restriction Mimetics as a Prolongevity Strategy

By applying calorie restriction (CR) at 30-50% below ad libitum levels, studies in numerous species have reported increased life span, reduced incidence and delayed onset of age-related diseases, improved stress resistance, and decelerated functional decline. Whether this nutritional intervention is relevant to human aging remains to be determined; however, evidence emerging from CR studies in nonhuman primates suggests that response to CR in primates parallels that observed in rodents. To evaluate CR effects in humans, clinical trials have been initiated. Even if evidence could substantiate CR as an effective antiaging strategy for humans, application of this intervention would be problematic due to the degree and length of restriction required. To meet this challenge for potential application of CR, new research to create "caloric restriction mimetics" has emerged. This strategy focuses on identifying compounds that mimic CR effects by targeting metabolic and stress response pathways affected by CR, but without actually restricting caloric intake. Microarray studies show that gene expression profiles of key enzymes in glucose (energy) handling pathways are modified by CR. Drugs that inhibit glycolysis (2-deoxyglucose) or enhance insulin action (metformin) are being assessed as CR mimetics. Promising results have emerged from initial studies regarding physiological responses indicative of CR (reduced body temperature and plasma insulin) as well as protection against neurotoxicity, enhanced dopamine action, and upregulated brain-derived neurotrophic factor. Further life span analyses in addition to expanded toxicity studies must be completed to assess the potential of any CR mimetic, but this strategy now appears to offer a very promising and expanding research field.

Metal-catalyzed disruption of membrane protein and lipid signaling in the pathogenesis of neurodegenerative disorders

Membrane lipid peroxidation and oxidative modification of various membrane and associated proteins (e.g., receptors, ion transporters and channels, and signal transduction and cytoskeletal proteins) occur in a range of neurodegenerative disorders. This membrane-associated oxidative stress (MAOS) is promoted by redox-active metals, most notably iron and copper. The mechanisms whereby different genetic and environmental factors initiate MAOS in specific neurological disorders are being elucidated. In Alzheimer's disease (AD), the amyloid beta-peptide generates reactive oxygen species and induces MAOS, resulting in disruption of cellular calcium homeostasis. In Parkinson's disease (PD), mitochondrial toxins and perturbed ubiquitin-dependent proteolysis may impair ATP production and increase oxyradical production and MAOS. The inheritance of polyglutamine-expanded huntingtin may promote neuronal degeneration in Huntington's disease (HD), in part, by increasing MAOS. Increased MAOS occurs in amyotrophic lateral sclerosis (ALS) as the result of genetic abnormalities (e.g., Cu/Zn-superoxide dismutase mutations) or exposure to environmental toxins. Levels of iron are increased in vulnerable neuronal populations in AD and PD, and dietary and pharmacological manipulations of iron and copper modify the course of the disease in mouse models of AD and PD in ways that suggest a role for these metals in disease pathogenesis. An increasing number of pharmacological and dietary interventions are being identified that can suppress MAOS and neuronal damage and improve functional outcome in animal models of AD, PD, HD, and ALS. Novel preventative and therapeutic approaches for neurodegenerative disorders are emerging from basic research on the molecular and cellular actions of metals and MAOS in neural cells.

Neuronal susceptibility to damage: comparison of the retinas of young, old and old/caloric restricted rats before and after transient ischemia

Compared to young rats, old age increases susceptibility and caloric restriction decreases susceptibility for the loss of retinal ganglion cells and displaced amacrine cells following retinal ischemia/reperfusion. In retinas of old animals before ischemia, reactive gliosis, including activation of Muller cells, microglia and astrocytes, is increased compared to retinas from young and old/caloric restricted animals. Post-ischemia, the existing reactive gliosis in retinas of old animals is not neuroprotective and the reactive gliosis is even further increased in old animals compared to young or old/caloric restricted animals. In retinas from old/caloric restricted animals, inducible heat shock protein-70 and brain-derived neurotrophic factor increased more markedly after ischemia/reperfusion compared to retinas from young and old animals. Thus, compared to retinas in young animals, neurons of old animals may be more susceptible to cell death by secondary glial mechanisms after retinal ischemia/reperfusion. Caloric restriction in old animals is neuroprotective against damage in the retina following ischemia, perhaps by suppressing glial activity and by the neuroprotective effects of inducible heat shock protein-70 and brain-derived neurotrophic factor.

Dietary restriction differentially protects from neurodegeneration in animal models of excitotoxicity

Reduced caloric intake obtained through long-term dietary restriction has been found beneficial in some animal models of neurodegeneration. We report here that rats maintained under dietary restriction from the second to the eighth month of age are fully protected towards degeneration of GABAergic neurons in the hippocampus and the olfactory-entorhinal cortex caused by systemic administration of the convulsant toxin, kainic acid. However, in a different model of excitotoxic neurodegeneration, injection of ibotenic acid in the forebrain magnocellular basal nucleus, the decrease of a cholinergic marker in the target areas of the cortex was only partially protected by dietary restriction. Thus, in different experimental models neurodegeneration can be differentially rescued by dietary restriction. Analysis of alterations in the expression of relevant genes in different experimental conditions, could help in better understanding these differences.

Neuronal and glial calcium signaling in Alzheimer's disease

Cognitive impairment and emotional disturbances in Alzheimer's disease (AD) result from the degeneration of synapses and death of neurons in the limbic system and associated regions of the cerebral cortex. An alteration in the proteolytic processing of the amyloid precursor protein (APP) results in increased production and accumulation of amyloid beta-peptide (Abeta) in the brain. Abeta has been shown to cause synaptic dysfunction and can render neurons vulnerable to excitotoxicity and apoptosis by a mechanism involving disruption of cellular calcium homeostasis. By inducing membrane lipid peroxidation and generation of the aldehyde 4-hydroxynonenal, Abeta impairs the function of membrane ion-motive ATPases and glucose and glutamate transporters, and can enhance calcium influx through voltage-dependent and ligand-gated calcium channels. Reduced levels of a secreted form of APP which normally regulates synaptic plasticity and cell survival may also promote disruption of synaptic calcium homeostasis in AD. Some cases of inherited AD are caused by mutations in presenilins 1 and 2 which perturb endoplasmic reticulum (ER) calcium homeostasis such that greater amounts of calcium are released upon stimulation, possibly as the result of alterations in IP(3) and ryanodine receptor channels, Ca(2+)-ATPases and the ER stress protein Herp. Abnormalities in calcium regulation in astrocytes, oligodendrocytes, and microglia have also been documented in studies of experimental models of AD, suggesting contributions of these alterations to neuronal dysfunction and cell death in AD. Collectively, the available data show that perturbed cellular calcium homeostasis plays a prominent role in the pathogenesis of AD, suggesting potential benefits of preventative and therapeutic strategies that stabilize cellular calcium homeostasis.

Calorie restriction and ketogenic diet diminish neuronal excitability in rat dentate gyrus in vivo

PURPOSE

The ketogenic diet (KD) is an effective treatment for intractable epilepsy. However, little is known about its underlying mechanisms.

METHODS

In this study, in vivo extracellular field responses to angular bundle stimulation were recorded in the dentate gyrus of Sprague-Dawley rats fed one of three diets: ketogenic calorie-restricted (KCR), normal calorie-restricted (NCR), or normal ad libitum (NAL). Input/output curves and paired-pulse relations were used to assess network excitability. A maximal dentate activation (MDA) protocol was used to measure electrographic seizure threshold and duration.

RESULTS

Animals fed calorie-restricted (CR) diets exhibited greater paired-pulse inhibition, an elevated MDA threshold, and an absence of spreading depression-like events compared with ad libitum-fed controls. In the MDA model of epileptogenesis, the rate of increase in electrographic seizure duration after repeated stimuli was markedly reduced in KCR-fed animals compared with NCR- and NAL-fed controls.

CONCLUSIONS

These data suggest that CR, by itself, can be anticonvulsant, and treatment with a KCR diet may be both anticonvulsant and antiepileptogenic.

Reversal of behavioral and metabolic abnormalities, and insulin resistance syndrome, by dietary restriction in mice deficient in brain-derived neurotrophic factor

Dietary restriction (DR) extends life span and improves glucose metabolism in mammals. Recent studies have shown that DR stimulates the production of brain-derived neurotrophic factor (BDNF) in brain cells, which may mediate neuroprotective and neurogenic actions of DR. Other studies have suggested a role for central BDNF signaling in the regulation of glucose metabolism and body weight. BDNF heterozygous knockout (BDNF+/-) mice are obese and exhibit features of insulin resistance. We now report that an intermittent fasting DR regimen reverses several abnormal phenotypes of BDNF(+/-) mice including obesity, hyperphagia, and increased locomotor activity. DR increases BDNF levels in the brains of BDNF(+/-) mice to the level of wild-type mice fed ad libitum. BDNF(+/-) mice exhibit an insulin-resistance syndrome phenotype characterized by elevated levels of circulating glucose, insulin, and leptin; DR reduces levels of each of these three factors. DR normalizes blood glucose responses in glucose tolerance and insulin tolerance tests in the BDNF(+/-) mice. These findings suggest that BDNF is a major regulator of energy metabolism and that beneficial effects of DR on glucose metabolism are mediated, in part, by BDNF signaling. Dietary and pharmacological manipulations of BDNF signaling may prove useful in the prevention and treatment of obesity and insulin resistance syndrome-related diseases.

Intermittent food deprivation improves cardiovascular and neuroendocrine responses to stress in rats

Stressful events may trigger disease processes in many different organ systems, with the cardiovascular system being particularly vulnerable. Five-mo-old male rats had ad libitum (AL) access to food or were deprived of food every other day [intermittent food deprivation (IF)] for 6 mo, during which time their heart rate (HR), blood pressure (BP), physical activity and body temperature were measured by radiotelemetry under nonstress and stress (immobilization or cold-water swim) conditions. IF rats had significantly lower basal HR and BP, and significantly lower increases in HR and BP after exposures to the immobilization and swim stressors. Basal levels of adrenocorticotropic hormone (ACTH) and corticosterone were greater in the IF rats. However, in contrast to large stress-induced increases in ACTH, corticosterone and epinephrine levels in AL rats, increases in these hormones in response to repeated immobilization stress sessions were reduced or absent in IF rats. Nevertheless, the IF rats exhibited robust hypothalamic/pituitary and sympathetic neuroendocrine responses to a different stress (swim). The IF treatment improved glucose metabolism, as indicated by lower basal levels of circulating glucose and insulin, but with maintenance of glucose and insulin responses to stress. We concluded that improvements in cardiovascular risk factors and cardiovascular and neuroendocrine stress adaptation occur in response to IF.