Walking stabilizes cognitive functioning in Alzheimer's disease (AD) across one year.

AD is a public health epidemic, which seriously impacts cognition, mood and daily activities; however, one type of activity, exercise, has been shown to alter these states. Accordingly, we sought to investigate the relationship between exercise and mood, in early-stage AD patients (N=104) from California, over a 1-year period. Patients completed the Mini-Mental State Examination (MMSE), Geriatric Depression Scale (GDS), and Blessed-Roth Dementia Rating Scale (BRDRS), while their caregivers completed the Yale Physical Activity Survey (YALE), Profile of Mood States (POMS), the Neuropsychiatric Inventory (NPI) and Functional Abilities Questionnaire (FAQ). Approximately half of the participants were female, from a variety of ethnic groups (Caucasian=69.8%; Latino/Hispanic Americans=20.1%). Our results demonstrated that the patients spent little time engaged in physical activity in general, their overall activity levels decreased over time, and this was paired with a change in global cognition (e.g., MMSE total score) and affect/mood (e.g., POMS score). Patients were parsed into Active and Sedentary groups based on their Yale profiles, with Active participants engaged in walking activities, weekly, over 1 year. Here, Sedentary patients had a significant decline in MMSE scores, while the Active patients had an attenuation in global cognitive decline. Importantly, among the Active AD patients, those individuals who engaged in walking for more than 2 h/week had a significant improvement in MMSE scores. Structured clinical trials which seek to increase the amount of time AD patients were engaged in walking activities and evaluate the nature and scope of beneficial effects in the brain are warranted.

Effects of diet and behavioral enrichment on free fatty acids in the aged canine brain.

Despite several recent studies suggesting that dysregulation of brain lipid metabolism might contribute to the mechanisms of aging and Alzheimer's disease (AD), lipid metabolism has not been evaluated extensively in the aging brain. Here, we use a lipidomic approach to demonstrate that antioxidants plus mitochondrial cofactors treatment, either alone or in combination with behavioral enrichment, attenuates lipid abnormalities in the frontal cortices of aged canine in a manner correlated with cognitive scores. Our analyses revealed that the levels of free palmitoleic acid and nervonic acid were decreased in frontal cortices of aged dogs (n=5-6/group) treated with antioxidant compared with the control group. The monounsaturated/saturated fatty acid ratio, also known as "desaturation index"-an ex-vivo indicator of stearoyl-CoA desaturase activity, was also reduced in the frontal cortex of dogs treated with antioxidants compared with control groups. Increased palmitoleic acid levels and desaturation index were positively correlated with increased reversal learning errors and decreased cognitive performance. In conclusion, our study indicates that the addition of antioxidants and mitochondrial cofactors to the regular diet alters the composition of free fatty acids in the aged brain. Together with data showing increased palmitoleic acid levels in AD patients, our data suggest that reducing palmitoleic acid levels and desaturation index in the brain may be associated with improved cognitive performance.

Exercise and time-dependent benefits to learning and memory.

While it is well established that exercise can improve cognitive performance, it is unclear how long these benefits endure after exercise has ended. Accordingly, the effects of voluntary exercise on cognitive function and brain-derived neurotrophic factor (BDNF) protein levels, a major player in the mechanisms governing the dynamics of memory formation and storage, were assessed immediately after a 3-week running period, or after a 1-week or 2-week delay following the exercise period. All exercised mice showed improved performance on the radial arm water maze relative to sedentary animals. Unexpectedly, fastest acquisition (fewest errors and shortest latency) occurred in animals trained following a 1-week delay, while best memory performance in the probe trial was observed in those trained immediately after the exercise period. Assessment of the time course of hippocampal BDNF availability following exercise revealed significant elevations of BDNF immediately after the exercise period (186% of sedentary levels) and at 1 and 2 weeks after exercise ended, with levels returning to baseline by 3-4 weeks. BDNF protein levels showed a positive correlation with cognitive improvement in radial water maze training and with memory performance on day 4, supporting the idea that BDNF availability contributes to the time-dependent cognitive benefits of exercise revealed in this study. Overall, this novel approach assessing the temporal endurance of cognitive and biochemical effects of exercise unveils new concepts in the exercise-learning field, and reveals that beneficial effects of exercise on brain plasticity continue to evolve even after exercise has ended.

Effects of age, dietary, and behavioral enrichment on brain mitochondria in a canine model of human aging.

Dogs develop cognitive decline and a progressive accumulation of oxidative damage. In a previous longitudinal study, we demonstrated that aged dogs treated with either an antioxidant diet or with behavioral enrichment show cognitive improvement. The antioxidant diet included cellular antioxidants (vitamins E and C, fruits and vegetables) and mitochondrial cofactors (lipoic acid and carnitine). Behavioral enrichment consisted of physical exercise, social enrichment, and cognitive training. We hypothesized that the antioxidant treatment improved neuronal function through increased mitochondrial function. Thus, we measured reactive oxygen species (ROS) production and bioenergetics in mitochondria isolated from young, aged, and treated aged animals. Aged canine brain mitochondria show significant increases in ROS production and a reduction in NADH-linked respiration. Mitochondrial function (ROS and NADH-linked respiration) was improved selectively in aged dogs treated with an antioxidant diet. In contrast, behavioral enrichment had no effect on any mitochondrial parameters. These results suggest that an antioxidant diet improves cognition by maintaining mitochondrial homeostasis, which may be an independent molecular pathway not engaged by behavioral enrichment.

Short-term exercise in aged Tg2576 mice alters neuroinflammation and improves cognition.

Exercise is a treatment paradigm that can ameliorate cognitive dysfunction in Alzheimer disease (AD) and AD mouse models. Since exercise is also known to alter the peripheral immune response, one potential mechanism for the cognitive improvement following exercise may be by modulating the inflammatory repertoire in the central nervous system. We investigated the effects of voluntary exercise in the Tg2576 mouse model of AD at a time-point at which pathology has already developed. Inflammatory mRNA markers are increased in sedentary Tg2576 mice versus non-transgenic controls. We demonstrate that short-term voluntary wheel running improved spatial learning in aged transgenic mice as compared to sedentary Tg2576 controls. Inflammatory profiles of the Tg2576 and non-transgenic mice were different following exercise with the non-transgenic mice showing a broader response as compared to the Tg2576. Notably, exercising Tg2576 exhibited increases in a few markers including CXCL1 and CXCL12, two chemokines that may affect cognition.

R-alpha-lipoic acid and acetyl-L-carnitine complementarily promote mitochondrial biogenesis in murine 3T3-L1 adipocytes.

AIMS/HYPOTHESIS: The aim of the study was to address the importance of mitochondrial function in insulin resistance and type 2 diabetes, and also to identify effective agents for ameliorating insulin resistance in type 2 diabetes. We examined the effect of two mitochondrial nutrients, R-alpha-lipoic acid (LA) and acetyl-L-carnitine (ALC), as well as their combined effect, on mitochondrial biogenesis in 3T3-L1 adipocytes. METHODS: Mitochondrial mass and oxygen consumption were determined in 3T3-L1 adipocytes cultured in the presence of LA and/or ALC for 24 h. Mitochondrial DNA and mRNA from peroxisome proliferator-activated receptor gamma and alpha (Pparg and Ppara) and carnitine palmitoyl transferase 1a (Cpt1a), as well as several transcription factors involved in mitochondrial biogenesis, were evaluated by real-time PCR or electrophoretic mobility shift (EMSA) assay. Mitochondrial complexes proteins were measured by western blot and fatty acid oxidation was measured by quantifying CO2 production from [1-14C]palmitate. RESULTS: Treatments with the combination of LA and ALC at concentrations of 0.1, 1 and 10 micromol/l for 24 h significantly increased mitochondrial mass, expression of mitochondrial DNA, mitochondrial complexes, oxygen consumption and fatty acid oxidation in 3T3L1 adipocytes. These changes were accompanied by an increase in expression of Pparg, Ppara and Cpt1a mRNA, as well as increased expression of peroxisome proliferator-activated receptor (PPAR) gamma coactivator 1 alpha (Ppargc1a), mitochondrial transcription factor A (Tfam) and nuclear respiratory factors 1 and 2 (Nrf1 and Nrf2). However, the treatments with LA or ALC alone at the same concentrations showed little effect on mitochondrial function and biogenesis. CONCLUSIONS/INTERPRETATION: We conclude that the combination of LA and ALC may act as PPARG/A dual ligands to complementarily promote mitochondrial synthesis and adipocyte metabolism.

Reduced CXCL12/CXCR4 results in impaired learning and is downregulated in a mouse model of Alzheimer disease.

Alzheimer disease (AD) is characterized by the presence of plaques and tangles in parallel with progressive cognitive decline. The underlying cause of the cognitive decline is unknown. The purpose of this study was to identify factors that could affect learning and memory using the Tg2576 mouse model of AD. Un-biased GeneChip analysis at the time-point coinciding with the onset of behavioral deficits but prior to plaque deposition revealed that Tg2576 show altered gene expression for a number of molecules including the chemokine CXCL12. We show that this chemokine's mRNA, protein and receptor are downregulated in this mouse model coinciding with cognitive deficits. Furthermore, we demonstrate that CXCL12 levels are decreased in AD patients as compared to controls. To determine if CXCL12 might be related to impaired learning and memory, we chronically treated young non-transgenic mice with an antagonist to the CXCL12 receptor to simulate the reduction seen in transgenic animals. Treated animals showed selectively impaired learning and memory suggesting a potential role for this chemokine in cognitive functioning.

Beta-amyloid causes downregulation of calcineurin in neurons through induction of oxidative stress.

Calcineurin is an abundant cytosolic protein that is implicated in the modulation of glutamate release. Here we show that the expression level of this enzyme is reduced in primary neuronal cultures treated with beta-amyloid. Parallel experiments in ETNA cell lines expressing SOD1 suggested that the effect of beta-amyloid on calcineurin expression is mediated by oxidative stress. The relevance of the in vitro experiments was assessed by analysis of tissue from patients with Alzheimer's disease (AD) and tissue from two strains of transgenic mice that mimic aspects of AD. The tissue from the AD brains displayed a pronounced downregulation of calcineurin immunoreactivity in profiles that were negative for glial fibrillary acidic protein (GFAP). In the hippocampus of the transgenic animals (which were analyzed in an early stage of the disease) the downregulation of calcineurin was restricted to mossy fiber terminals. A downregulation of the presynaptic pool of calcineurin may contribute to the dysregulation of glutamate release that is considered a hallmark of AD.

Inflammatory changes parallel the early stages of Alzheimer disease.

Alzheimer disease (AD) is the most prominent cause of dementia in the elderly. To determine changes in the AD brain that may mediate the transition into dementia, the gene expression of approximately 10,000 full-length genes was compared in mild/moderate dementia cases to non-demented controls that exhibited high AD pathology. Including this latter group distinguishes this work from previous studies in that it allows analysis of early cognitive loss. Compared to non-demented high-pathology controls, the hippocampus of AD cases with mild/moderate dementia had increased gene expression of the inflammatory molecule major histocompatibility complex (MHC) II, as assessed with microarray analysis. MHC II protein levels were also increased and inversely correlated with cognitive ability. Interestingly, the mild/moderate AD dementia cases also exhibited decreased number of T cells in the hippocampus and the cortex compared to controls. In conclusion, transition into AD dementia correlates with increased MHC II(+) microglia-mediated immunity and is paradoxically paralleled by a decrease in T cell number, suggesting immune dysfunction.

Melatonin treatment in old mice enables a more youthful response to LPS in the brain.

Melatonin modulates the expression of a number of genes related to inflammation and immunity. Declining levels of melatonin with age may thus relate to some of the changes in immune function that occur with age. mRNA expression levels in murine CNS were measured using oligonucleotide microarrays in order to determine whether a dietary melatonin supplement may modify age-related changes in the response to an inflammatory challenge. CB6F1 male mice were fed 40-ppm melatonin for 9 weeks prior to sacrifice at 26.5 months of age, and compared with age-matched untreated controls and 4.5-month-old controls. A subset of both young and old animals was injected i.p. with lipopolysaccharide (LPS). After 3 h, total RNA was extracted from whole brain (excluding brain stem and cerebellum), and individual samples were hybridized to Affymetrix Mouse 430-2.0 arrays. Data were analyzed in Dchip and GeneSpring. Melatonin treatment markedly altered the response in gene expression of older animals subjected to an LPS challenge. These changes in general, caused the response to more closely resemble that of young animals subjected to the same LPS challenge. Thus melatonin treatment effects a major shift in the response of the CNS to an inflammatory challenge, causing a transition to a more youthful mRNA expression profile.

Wheel running and fluoxetine antidepressant treatment have differential effects in the hippocampus and the spinal cord.

Exercise and antidepressants used independently have been shown to increase hippocampal brain-derived neurotrophic factor (BDNF) and neurogenesis. Despite the fact that patients with depression are often prescribed both, the effects of the exercise and fluoxetine antidepressant treatment used in combination are unknown. Using C57Bl/10 female mice, BDNF protein, insulin-like growth factor 1 (IGF-1) protein and neurogenesis were measured in the hippocampus after 21 days of wheel running, 21 days of fluoxetine antidepressant therapy (daily i.p. injections of 5 mg/kg, 10 mg/kg or 25 mg/kg) and the combination of the two. BDNF protein and cytogenesis/neurogenesis increased in the hippocampus with fluoxetine (high dose), but not wheel running. Hippocampal IGF-1 protein did not change with either treatment. There were no synergistic effects of combining exercise and fluoxetine treatment. Recent reports have also shown that exercise induces molecular mechanisms that benefit the spinal cord and can improve recovery after spinal cord injury (SCI); therefore, we repeated the assays in the spinal cord. Results showed that BDNF, IGF-1 and neurogenesis behave independently in the hippocampus and spinal cord. BDNF protein did not change in the spinal cord with either wheel running or fluoxetine treatment. Spinal cord IGF-1 protein did not change with wheel running, but it decreased with fluoxetine (high dose). Furthermore, spinal cord cytogenesis decreased with fluoxetine treatment. The combined wheel running and fluoxetine groups did not show synergistic results. Thus, the hippocampus and the spinal cord respond in distinct ways to wheel running and fluoxetine, and a prior induction of BDNF, IGF-1 or cytogenesis is unlikely to be the mechanism for wheel running providing a margin of protection against SCI.

Exercise primes a molecular memory for brain-derived neurotrophic factor protein induction in the rat hippocampus.

Exercise is an important facet of behavior that enhances brain health and function. Increased expression of the plasticity molecule brain-derived neurotrophic factor (BDNF) as a response to exercise may be a central factor in exercise-derived benefits to brain function. In rodents, daily wheel-running exercise increases BDNF gene and protein levels in the hippocampus. However, in humans, exercise patterns are generally less rigorous, and rarely follow a daily consistency. The benefit to the brain of intermittent exercise is unknown, and the duration that exercise benefits endure after exercise has ended is unexplored. In this study, BDNF protein expression was used as an index of the hippocampal response to exercise. Both daily exercise and alternating days of exercise increased BDNF protein, and levels progressively increased with longer running duration, even after 3 months of daily exercise. Exercise on alternating days was as effective as daily exercise, even though exercise took place only on half as many days as in the daily regimen. In addition, BDNF protein remained elevated for several days after exercise ceased. Further, after prior exercise experience, a brief second exercise re-exposure insufficient to cause a BDNF change in naïve animals, rapidly reinduced BDNF protein to levels normally requiring several weeks of exercise for induction. The protein reinduction occurred with an intervening "rest" period as long as 2 weeks. The rapid reinduction of BDNF by an exercise stimulation protocol that is normally subthreshold in naïve animals suggests that exercise primes a molecular memory for BDNF induction. These findings are clinically important because they provide guidelines for optimizing the design of exercise and rehabilitation programs, in order to promote hippocampal function.

Learning ability in aged beagle dogs is preserved by behavioral enrichment and dietary fortification: a two-year longitudinal study.

The effectiveness of two interventions, dietary fortification with antioxidants and a program of behavioral enrichment, was assessed in a longitudinal study of cognitive aging in beagle dogs. A baseline protocol of cognitive testing was used to select four cognitively equivalent groups: control food-control experience (C-C), control food-enriched experience (C-E), antioxidant fortified food-control experience (A-C), and antioxidant fortified food-enriched experience(A-E). We also included two groups of young behaviorally enriched dogs, one receiving the control food and the other the fortified food. Discrimination learning and reversal was assessed after one year of treatment with a size discrimination task, and again after two years with a black/white discrimination task. The four aged groups were comparable at baseline. At one and two years, the aged combined treatment group showed more accurate learning than the other aged groups. Discrimination learning was significantly improved by behavioral enrichment. Reversal learning was improved by both behavioral enrichment and dietary fortification. By contrast, the fortified food had no effect on the young dogs. These results suggest that behavioral enrichment or dietary fortification with antioxidants over a long-duration can slow age-dependent cognitive decline, and that the two treatments together are more effective than either alone in older dogs.

Voluntary exercise protects against stress-induced decreases in brain-derived neurotrophic factor protein expression.

Exercise is increasingly recognized as an intervention that can reduce CNS dysfunctions such as cognitive decline, depression and stress. Previously we have demonstrated that brain-derived neurotrophic factor (BDNF) is increased in the hippocampus following exercise. In this study we tested the hypothesis that exercise can counteract a reduction in hippocampal BDNF protein caused by acute immobilization stress. Since BDNF expression is suppressed by corticosterone (CORT), circulating CORT levels were also monitored. In animals subjected to 2 h immobilization stress, CORT was elevated immediately following, and at 1 h after the cessation of stress, but remained unchanged from baseline up to 24 h post-stress. The stress protocol resulted in a reduction in BDNF protein at 5 and 10 h post-stress that returned to baseline at 24 h. To determine if exercise could prevent this stress-induced reduction in BDNF protein, animals were given voluntary access to running wheels for 3 weeks prior to the stress. Stressed animals, in the absence of exercise, again demonstrated an initial elevation in CORT (at 0 h) and a subsequent decrease in hippocampal BDNF at the 10 h time point. Exercising animals, both non-stressed and stressed, demonstrated circulating CORT and hippocampal BDNF protein levels that were significantly elevated above control values at both time points examined (0 and 10 h post-stress). Thus, the persistently high CORT levels in exercised animals did not affect the induction of BDNF with exercise, and the effect of immobilization stress on BDNF protein was overcome. To examine the role of CORT in the stress-related regulation of BDNF protein, experiments were carried out in adrenalectomized (ADX) animals. BDNF protein was not downregulated as a result of immobilization stress in ADX animals, while there continued to be an exercise-induced upregulation of BDNF. This study demonstrates that CORT modulates stress-related alterations in BDNF protein. Further, exercise can override the negative effects of stress and high levels of CORT on BDNF protein. Voluntary physical activity may, therefore, represent a simple non-pharmacological tool for the maintenance of neurotrophin levels in the brain.

Temporal cortex hypermetabolism in Down syndrome prior to the onset of dementia.

BACKGROUND: Adults with Down syndrome (DS) are at increased risk for dementia and provide an opportunity to identify patterns of brain activity that may precede dementia. Studies of early Alzheimer's disease (AD) and risk of AD show decreased function in posterior cingulate and temporal cortex as initial indicators of the disease process, but whether the origin and sequence of predementia brain changes are the same in DS is unknown. METHODS: The regional cerebral glucose metabolic rates (GMR) among middle-aged nondemented people with DS (n = 17), people with moderate AD (n = 10), and age-matched control subjects (n = 24) were compared using PET during a cognitive task. RESULTS: Statistical parametric mapping conjunction analyses showed that 1) both DS and AD groups had lower GMR than their respective controls primarily in posterior cingulate and 2) compared with respective controls, the subjects with DS had higher GMR in the same areas of inferior temporal/entorhinal cortex where the AD subjects had lower GMR. The same results were replicated after 1 year of follow-up. CONCLUSIONS: As the DS subjects were not clinically demented, inferior temporal/entorhinal cortex hypermetabolism may reflect a compensatory response early in disease progression. Compensatory responses may subsequently fail, leading to neurodegenerative processes that the authors anticipate will be detectable in vivo as future GMR decreases in inferior temporal/entorhinal cortex are accompanied by clinical signs of dementia.

Parallel compensatory and pathological events associated with tau pathology in middle aged individuals with Down syndrome.

Aged individuals with Down syndrome (DS) develop senile plaques and neurofibrillary tangles consistent with Alzheimer disease (AD). Prior to or in parallel with AD pathology, compensatory growth responses may occur. Immunohistochemistry and confocal microscopy studies in the hippocampus from 15 individuals ranging in age from 5 months to 67 years compared markers of normal and abnormal tau accumulation (phosphorylated tau [AT8, MC-1], tau-1, N-terminal tau) with the extent and location of neuronal growth marker immunoreactivity (BDNF, GAP-43, MAP-2). In middle age (30-40 years), prior to entorhinal neuron loss, the earliest tau accumulation occurred in the outer molecular layer (OML), which was consistent with both pathological and compensatory fetal tau expression. These events were followed at a later age, associated with entorhinal neuron loss, by an increase in GAP-43. Hilar neurons exhibiting a sprouting morphology were also noted. Age-dependent observations in the DS brain in the current study parallel hippocampal compensatory responses described in entorhinal cortex lesion studies in rodents. Thus, compensatory growth responses may occur in DS prior to extensive AD pathology and may be one mechanism underlying observations in PET studies of hypermetabolism in the entorhinal cortex of individuals with DS.

Identification of neuronal plasma membrane microdomains that colocalize beta-amyloid and presenilin: implications for beta-amyloid precursor protein processing.

Alzheimer's disease (AD) is associated with the accumulation of extracellular deposits of the beta-amyloid protein (Abeta). Abeta is a result of misprocessing of the beta-amyloid precursor protein (APP). Gamma-secretase is involved in APP misprocessing and one hypothesis holds that this secretase is identical to PS1. We tested this hypothesis by determining whether PS is co-localised with Abeta in situ. Using confocal analyses and a sensitive immunogold procedure we show that PS and Abeta are co-localised within discrete microdomains of neuronal plasma membranes in AD patients and in aged dogs, an established model of human brain aging. Our data indicate that APP misprocessing occurs in discrete plasma membrane domains of neurons and provide evidence that PS1 is critically involved in Abeta formation.

The influence of specific noradrenergic and serotonergic lesions on the expression of hippocampal brain-derived neurotrophic factor transcripts following voluntary physical activity.

Previous studies have shown that hippocampal brain-derived neurotrophic factor (BDNF) mRNA levels are significantly increased in rats allowed free access to exercise wheels and/or administered antidepressant medications. Enhancement of BDNF may be crucial for the clinical effect of antidepressant interventions. Since increased function of the noradrenergic and/or serotonergic systems is thought to be an important initial mechanism of antidepressant medications, we sought to test the hypothesis that noradrenergic or serotonergic function is essential for the increased BDNF transcription occurring with exercise. In addition, individual transcript variants of BDNF were examined, as evidence exists they are differentially regulated by discrete interventions, and are expressed in distinct sub-regions of the hippocampus. The neurotransmitter system-specific neurotoxins p-chloroamphetamine (serotonergic) and N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (noradrenergic) were administered to rats prior to commencing voluntary wheel-running activity. In situ hybridization experiments revealed an absence of exercise-induced full-length BDNF mRNA elevations in the hippocampi of noradrenergic-lesioned rats. In addition, the striking elevation of the exon I transcript in the dentate gyrus was removed with this noradrenergic lesion. In contrast, other transcript variants (exons II and III) were elevated in several hippocampal regions as a result of this lesion. In serotonin-lesioned rats, the significant increases in full-length BDNF, exon I and exon II mRNA levels were sustained without alteration (with the exception of exon IV in the cornus ammonis subregion 4, CA4). Overall, these results indicate that an intact noradrenergic system may be crucial for the observed ability of exercise to enhance full-length and exon I hippocampal BDNF mRNA expression. In addition, these results suggest that the promoter linked to exon I may provide a major regulatory point for BDNF mRNA expression in the dentate gyrus. Elevations of other exons, such as II and III, may require the activation of separate neurotransmitter systems and intracellular pathways.

Landmark discrimination learning in the dog: effects of age, an antioxidant fortified food, and cognitive strategy.

The landmark discrimination learning test can be used to assess the ability to utilize allocentric spatial information to locate targets. The present experiments examined the role of various factors on performance of a landmark discrimination learning task in beagle dogs. Experiments 1 and 2 looked at the effects of age and food composition. Experiments 3 and 4 were aimed at characterizing the cognitive strategies used in performance on this task and in long-term retention. Cognitively equivalent groups of old and young dogs were placed into either a test group maintained on food enriched with a broad-spectrum of antioxidants and mitochondrial cofactors, or a control group maintained on a complete and balanced food formulated for adult dogs. Following a wash-in period, the dogs were tested on a series of problems, in which reward was obtained when the animal responded selectively to the object closest to a thin wooden block, which served as a landmark. In Experiment 1, dogs were first trained to respond to a landmark placed directly on top of coaster, landmark 0 (L0). In the next phase of testing, the landmark was moved at successively greater distances (1, 4 or 10 cm) away from the reward object. Learning varied as a function of age group, food group, and task. The young dogs learned all of the tasks more quickly than the old dogs. The aged dogs on the enriched food learned L0 significantly more rapidly than aged dogs on control food. A higher proportion of dogs on the enriched food learned the task, when the distance was increased to 1cm. Experiment 2 showed that accuracy decreased with increased distance between the reward object and landmark, and this effect was greater in old animals. Experiment 3 showed stability of performance, despite using a novel landmark, and new locations, indicating that dogs learned the landmark concept. Experiment 4 found age impaired long-term retention of the landmark task. These results indicate that allocentric spatial learning is impaired in an age-dependent manner in dogs, and that age also affects performance when the distance between the landmark and target is increased. In addition, these results both support a role of oxidative damage in the development of age-associated cognitive dysfunction and indicate that short-term administration of a food enriched with supplemental antioxidants and mitochondrial cofactors can partially reverse the deleterious effects of aging on cognition.