Physical activity and risk of cognitive impairment and dementia in elderly persons

Exercise induces BDNF and synapsin I to specific hippocampal subfields

To assess the relationship between brain-derived neurotrophic factor (BDNF) and synapsin I in the hippocampus during exercise, we employed a novel microsphere injection method to block the action of BDNF through its tyrosine kinase (Trk) receptor and subsequently measure the mRNA levels of synapsin I, using real-time TaqMan RT-PCR for RNA quantification. After establishing a causal link between BDNF and exercise-induced synapsin I mRNA levels, we studied the exercise-induced distribution of BDNF and synapsin I in the rodent hippocampus. Quantitative immunohistochemical analysis revealed increases of BDNF and synapsin I in CA3 stratum lucidum and dentate gyrus, and synapsin I alone in CA1 stratum radiatum and stratum laconosum moleculare. These results indicate that exercise induces plasticity of select hippocampal transsynaptic circuitry, possibly comprising a spatial restriction on synapsin I regulation by BDNF.

More than the epidemiology of Alzheimer's disease: contributions of the Canadian Study of Health and Aging

OBJECTIVE

To highlight contributions to knowledge made by the Canadian Study of Health and Aging (CSHA).

METHOD

The CSHA began in 1991, with follow-ups in 1996 and 2001. It was national in scope, with 18 study centres and a coordinating centre. It included 10 263 participants; of these, 9008 were in the community, and 1255 were in institutions. In each phase, community participants were screened for cognitive impairment, and where appropriate, cognitive status was determined by a detailed clinical examination. Data on possible risk factors for dementia were collected at baseline. Data on caring for people with dementia were collected in each phase.

RESULTS

The prevalence of dementia was established at 8% of those aged 65 years and over; incidence (new cases each year) was about 2%. Cognitive impairment not dementia (CIND) was more than twice as common as dementia. Factors affecting the risk of institutionalization, mortality, and the health of caregivers were examined. The costs of dementia were conservatively estimated at dollar 3.9 billion in 1991. Risk factors for Alzheimer's disease (AD) and vascular dementia are presented; it is noteworthy that physical activity appeared to protect against all forms of cognitive decline, particularly for women. Clinical contributions include the development of norms for several neuropsychological tests. Other topics include the health of those with CIND, predicting dementia, medication use, frailty and healthy aging, and urinary incontinence.

CONCLUSION

The CSHA has contributed substantially to knowledge of the epidemiology of dementia, including AD, and to many other topics relevant to seniors' health.

Voluntary exercise following traumatic brain injury: brain-derived neurotrophic factor upregulation and recovery of function

Voluntary exercise leads to an upregulation of brain-derived neurotrophic factor (BDNF) and associated proteins involved in synaptic function. Activity-induced enhancement of neuroplasticity may be considered for the treatment of traumatic brain injury (TBI). Given that during the first postinjury week the brain is undergoing dynamic restorative processes and energetic changes that may influence the outcome of exercise, we evaluated the effects of acute and delayed exercise following experimental TBI. Male Sprague-Dawley rats underwent either sham or lateral fluid-percussion injury (FPI) and were housed with or without access to a running wheel (RW) from postinjury days 0-6 (acute) or 14-20 (delayed). FPI alone resulted in significantly elevated levels of hippocampal phosphorylated synapsin I and phosphorylated cyclic AMP response element-binding-protein (CREB) at postinjury day 7, of which phosphorylated CREB remained elevated at postinjury day 21. Sham and delayed FPI-RW rats showed increased levels of BDNF, following exercise. Exercise also increased phosphorylated synapsin I and CREB in sham rats. In contrast to shams, the acutely exercised FPI rats failed to show activity-dependent BDNF upregulation and had significant decreases of phosphorylated synapsin I and total CREB. Additional rats were cognitively assessed (learning acquisition and memory) by utilizing the Morris water maze after acute or delayed RW exposure. Shams and delayed FPI-RW animals benefited from exercise, as indicated by a significant decrease in the number of trials to criterion (ability to locate the platform in 7 s or less for four consecutive trials), compared with the delayed FPI-sedentary rats. In contrast, cognitive performance in the acute FPI-RW rats was significantly impaired compared with all the other groups. These results suggest that voluntary exercise can endogenously upregulate BDNF and enhance recovery when it is delayed after TBI. However, when exercise is administered to soon after TBI, the molecular response to exercise is disrupted and recovery may be delayed.

Kognitive und körperliche Aktivität

Zusammenfassung: Eine Analyse des aktuellen Forschungsstandes zeigt, dass lebenslang erhöhte kognitive Anforderungen einher gehen mit einem selteneren und auch späteren Auftreten von Demenzerkrankungen. In Bezug auf die Auswirkungen regelmäßiger körperlicher Aktivitäten auf das Auftreten demenzieller Erkrankungen zeigen sich die in der Literatur berichteten Befunde zwar teilweise widersprüchlich, scheinen jedoch auf einen positiven Einfluss hinsichtlich spezifischer kognitiver Funktionen sowie exekutiver Gedächtnisleistungen hinzuweisen. Die Ergebnisse der Literaturrecherche werden anschließend mit denjenigen der SimA-Studie verglichen, in der gezeigt werden konnte, dass die Kombination aus Psychomotorik- und Gedächtnistraining auch langfristig einerseits einen positiven Einfluss auf den kognitiven Status ausübt und andererseits das Risiko einer Demenzerkrankung deutlich vermindert. Schließlich wird die protektive Wirkung kombinierter Interventionsmaßnahmen vor dem Hintergrund neuerer neurophysiologischer Beobachtungen diskutiert.

The role of cardiovascular risk factors in Alzheimer's disease

The distinction between Alzheimer's disease and vascular dementia, the two most common types of dementia, has been undermined by recent advances in epidemiologic, clinical, imaging, and neuropathological studies. Cardiovascular risk factors, traditionally regarded as distinguishing criteria between the two entities, have been shown to be associated with both AD and vascular dementia. In this article, we propose mechanisms of action of cardiovascular risk factors in AD, suggest possible explanations for the overlap with vascular dementia and discuss the implications this might have on future differential diagnosis, research, and treatment strategies.

Age, Vascular Risk, and Cognitive Decline in an Older, British, African-Caribbean Population

OBJECTIVES

To investigate associations between baseline factors and subsequent cognitive decline in an older African-Caribbean population.

DESIGN

Three-year follow-up of a community sample.

SETTING

Registration lists for seven primary care services in south London, United Kingdom.

PARTICIPANTS

Of 290 Caribbean-born people aged 55 to 75 recruited at baseline, 216 (75%) were reinterviewed after a 3-year period. Sufficient data for analysis were present for 207.

MEASUREMENTS

Tests of verbal memory (immediate and delayed), orientation, and attention were administered at baseline and at 3 years. A composite measure of cognitive change was derived through factor analysis. Participants in the lowest quintile were defined as having cognitive decline and were compared with the rest of the sample with respect to baseline characteristics.

RESULTS

Cognitive decline was strongly associated with increased age, but not with sex, education, or occupation. It was also not directly associated with hypertension, diabetes mellitus, or exercise, but the age-decline association was significantly stronger in people with diabetes mellitus and was lower in those reporting vigorous physical exercise at baseline. When cognitive decline was investigated separately for individual tests, both these patterns of association were particularly strong for decline in delayed verbal recall.

CONCLUSION

The association between increased age and cognitive decline, particularly decline in verbal recall, was stronger in people with diabetes mellitus (but not hypertension) and weaker in people who were more physically active.

Increase in Serum S100B Protein Level After a Swimming Race

Physical activity has been shown to be a beneficial stimulus to the central and peripheral nervous systems. The S100B is a cytokine physiologically produced and released predominantly by astrocytes on the central nervous system (CNS). In order to study the possible influence of a nonimpact exercise on S100B serum levels, we measured this protein serum level after a 7,600-meter swimming race. We observed an increase in S100B levels in athletes post-race compared with their baseline values, pointing to a potential acute influence of physical exercise on serum S100B levels not related with CNS injury. We discuss this result and emphasize the possible central and peripheral origins of S100B serum levels. Key words: exercise, serotonin, astrocytes

Dietary lipids in the aetiology of Alzheimer's disease: implications for therapy

Amyloid plaques and neurofibrillary tangles are the neuropathological hallmarks of Alzheimer's disease (AD), but no conclusive evidence has emerged showing that these hallmarks are the cause and not a product of the disease. Many studies have implicated oxidation and inflammation in the AD process, and there is growing evidence that abnormalities of lipid metabolism also play a role. Using epidemiology to elucidate risk factors and histological changes to suggest possible mechanisms, the hypothesis is advanced that dietary lipids are the principal risk factor for the development of late-onset sporadic AD. The degree of saturation of fatty acids and the position of the first double bond in essential fatty acids are the most critical factors determining the effect of dietary fats on the risk of AD, with unsaturated fats and n-3 double bonds conferring protection and an overabundance of saturated fats or n-6 double bonds increasing the risk. The interaction of dietary lipids and apolipoprotein E isoforms may determine the risk and rate of sustained autoperoxidation within cellular membranes and the efficacy of membrane repair. Interventions involving dietary lipids and lipid metabolism show great promise in slowing or possibly averting the development of AD, including dietary changes, cholesterol-modifying agents and antioxidants.

Enhancement of neurogenesis by running wheel exercises is suppressed in mice lacking NMDA receptor epsilon 1 subunit

Neurogenesis continues throughout adulthood in the dentate gyrus in mice, and is regulated by environmental, endocrine, and pharmacological stimuli. Although running wheel exercises have been reported to enhance neurogenesis, details of molecule mechanisms of the enhancement are not well understood. We report here that the hippocampal neurogenesis is enhanced when wild-type mice are raised in cages with running wheels for 3 weeks, but the wheel exercise does not enhance the neurogenesis in mice lacking the NMDA receptor epsilon1 subunit. Brain-derived neurotrophic factor (BDNF) has been reported to affect neuronal cell proliferation and survival. We examined the BDNF levels in the hippocampi of wild-type and epsilon1 knockout mice, and found that the BDNF level was increased through wheel exercises in the wild-type but not in the knockout mice. The enhancement of neurogenesis by the wheel exercise was also found to be reversible: when the exercise-stimulated wild-type mice were returned to the environment without running wheels for 3 weeks, the neurogenesis was the same as that in the mice which had never experienced the exercise. These results suggest that the wheel exercise may activate NMDA receptors in the hippocampus, which in turn may enhance BDNF production and neurogenesis.

Cognitive reserve and lifestyle

The concept of cognitive reserve (CR) suggests that innate intelligence or aspects of life experience like educational or occupational attainments may supply reserve, in the form of a set of skills or repertoires that allows some people to cope with progressing Alzheimer's disease (AD) pathology better than others. There is epidemiological evidence that lifestyle characterized by engagement in leisure activities of intellectual and social nature is associated with slower cognitive decline in healthy elderly and may reduce the risk of incident dementia. There is also evidence from functional imaging studies that subjects engaging in such leisure activities can clinically tolerate more AD pathology. It is possible that aspects of life experience like engagement in leisure activities may result in functionally more efficient cognitive networks and therefore provide a CR that delays the onset of clinical manifestations of dementia.

The effect of a multisensory exercise program on engagement, behavior, and selected physiological indexes in persons with dementia

A multisensory exercise approach that evokes the stimulation and use of various senses, such as combining physical and cognitive stimuli, can assist in the management of persons with Alzheimer's disease (AD). The objective of this study was to evaluate the outcomes of a multisensory exercise program on cognitive function (engagement), behavior (mood), and physiological indices (blood pressure, resting heart rate, and weight) in 13 nursing home residents diagnosed with moderate to severe AD. A one-group pretest/post-test, quasi-experimental design was used. The program combined a variety of sensory stimulations, integrating storytelling and imaging strategies. Results showed an improvement in resting heart rate, overall mood, and in engagement of physical activity. The findings suggest that a multisensory exercise approach can be beneficial for individuals with AD.

Leisure activities and the risk of dementia in the elderly

BACKGROUND

Participation in leisure activities has been associated with a lower risk of dementia. It is unclear whether increased participation in leisure activities lowers the risk of dementia or participation in leisure activities declines during the preclinical phase of dementia.

METHODS

We examined the relation between leisure activities and the risk of dementia in a prospective cohort of 469 subjects older than 75 years of age who resided in the community and did not have dementia at base line. We examined the frequency of participation in leisure activities at enrollment and derived cognitive-activity and physical-activity scales in which the units of measure were activity-days per week. Cox proportional-hazards analysis was used to evaluate the risk of dementia according to the base-line level of participation in leisure activities, with adjustment for age, sex, educational level, presence or absence of chronic medical illnesses, and base-line cognitive status.

RESULTS

Over a median follow-up period of 5.1 years, dementia developed in 124 subjects (Alzheimer's disease in 61 subjects, vascular dementia in 30, mixed dementia in 25, and other types of dementia in 8). Among leisure activities, reading, playing board games, playing musical instruments, and dancing were associated with a reduced risk of dementia. A one-point increment in the cognitive-activity score was significantly associated with a reduced risk of dementia (hazard ratio, 0.93 [95 percent confidence interval, 0.90 to 0.97]), but a one-point increment in the physical-activity score was not (hazard ratio, 1.00). The association with the cognitive-activity score persisted after the exclusion of the subjects with possible preclinical dementia at base line. Results were similar for Alzheimer's disease and vascular dementia. In linear mixed models, increased participation in cognitive activities at base line was associated with reduced rates of decline in memory.

CONCLUSIONS

Participation in leisure activities is associated with a reduced risk of dementia, even after adjustment for base-line cognitive status and after the exclusion of subjects with possible preclinical dementia. Controlled trials are needed to assess the protective effect of cognitive leisure activities on the risk of dementia.

Regulation of brain function by exercise

The effect of excercise on brain function was investigated through animal experiments. Exercise leads to increased serum calcium levels, and the calcium is transported to the brain. This in turn enhances brain dopamine synthesis through a calmodulin-dependent system, and increased dopamine levels regulate various brain functions. There are abnormally low levels of dopamine in the neostriatum and nucleus accumbens of epileptic mice (El mice strain) and spontaneously hypertensive rats (SHR). The low dopamine levels in those animals were improved following intracerebroventricular administration of calcium chloride. Dopamine levels and blood pressure in SHR were also normalized by exercise. In epileptic El mice, convulsions normalized dopamine levels and physiologic function. These findings suggest that exercise or convulsions affect brain function through calcium/calmodulin-dependent dopamine synthesis. This leads to the possibility that some symptoms of Parkinson's disease or senile dementia might be improved by exercise.

Exercise increases the vulnerability of rat hippocampal neurons to kainate lesion

Available evidence suggests that regular, moderate-intensity exercise has beneficial effects on neural health, perhaps including neuroprotection. To evaluate this idea further, we compared the severity of kainate-induced neuronal loss in exercised versus sedentary female rats. Stereological estimations of neuron number revealed that rats in the exercise condition exhibited significantly greater neuron loss in hippocampal region CA2/3, suggesting that high levels of physical activity may increase neuronal vulnerability to excitotoxicity.

Student-led exercise sessions yield significant fitness gains for Alzheimer's patients

At a time when they are losing skills in virtually all arenas of life, persons with Alzheimer's disease can experience significant, esteem-building achievements in physical fitness and mood through supervised participation in an exercise program. The effects of physical exercise plus cognitive and social stimulation on persons with early stage Alzheimer's disease were assessed in a longitudinal study. Twenty-four such individuals, aged 54 to 88 at program entry, participated in 16 to 20 exercise sessions and 10 community activity sessions per semester for two to eight semesters. Half of the weekly exercise sessions included memory and language stimulation activities. Students, supplemented by family caregivers, supervised the sessions. Exercise sessions consisted of flexibility, balance, aerobic, and weight resistance activities. Preparticipation and semiannual post-testing of aerobic fitness and duration and upper and lower body strength was done. Highly significant fitness gains (p < .001) were achieved in the six-minute walk test, upper and lower body strength, and duration of aerobic exercise. Five participants, aged 86 to 91, completed six to eight semesters and were doing 27 to 45 minutes of aerobics per session at program's end. Five participants scored within the normal range for age-matched healthy active adults on the six-minute walk test at baseline. Nine others achieved and three exceeded the normal range during treatment. Cognitive decline was slowed and mood improved. First-year cognitive outcomes have been published elsewhere. An article reporting final cognitive outcomes is in preparation; Outcome data is summarized on the project website: www.u.arizona.edu/ ~sarkin/elderrehab.html. The benefits of physical exercise can be made available at nominal cost to Alzheimer's patients and other elderly persons by using students to provide transportation, supervision, and the motivational support that is key to exercise adherence. Further research is needed to determine the relative contributions of each program component to the positive outcomes.

A longitudinal study of cardiorespiratory fitness and cognitive function in healthy older adults

OBJECTIVES

To determine whether cardiorespiratory fitness at baseline is associated with maintenance of cognitive function over 6 years or with level of cognitive function on tests performed 6 years later in a longitudinal study of healthy older people.

DESIGN

Prospective cohort.

SETTING

Community-based study of noninstitutionalized adults aged 55 and older living in Sonoma, California.

PARTICIPANTS

Three hundred forty-nine cohort members without evidence of cardiovascular disease, musculoskeletal disability, or cognitive impairment at baseline.

MEASUREMENTS

Cardiorespiratory fitness measures were based on a standard treadmill exercise test protocol and included peak oxygen consumption (peak VO2), treadmill exercise duration, and oxygen uptake efficiency slope (OUES). Cognitive function was evaluated at baseline with a modified Mini-Mental State Examination (mMMSE) and after 6 years of follow-up with a detailed cognitive test battery that included the full MMSE, three tests of attention/executive function, two measures of verbal memory, and two tests of verbal fluency.

RESULTS

Participants with worse cardiorespiratory fitness at baseline experienced greater decline on the mMMSE over 6 years (mean mMMSE decline (95% confidence interval) by baseline peak VO2 tertile: lowest = -0.5 (-0.8 to -0.3), middle = -0.2 (-0.5-0.0), highest = 0.0 (-0.3-0.2), P =.002 for trend over tertiles). Participants with worse baseline cardiorespiratory fitness also performed worse on all cognitive tests conducted 6 years later. Results were similar for analyses based on peak VO2, treadmill exercise duration, and OUES. After adjustment for demographic and health-related covariates, measures of cardiorespiratory fitness were associated most strongly with measures of global cognitive function and attention/executive function.

CONCLUSION

Baseline measures of cardiorespiratory fitness are positively associated with preservation of cognitive function over a 6-year period and with levels of performance on cognitive tests conducted 6 years later in healthy older adults. High cardiorespiratory fitness may protect against cognitive dysfunction in older people.

Is the distinction between Alzheimer's disease and vascular dementia possible and relevant?

Advances in epidemiological, clinical, imaging, and neuropathological studies have undermined the clear distinction between vascular and Alzheimer-type dementia, which has characterized the last two decades of research in dementia. A significant degree of overlap between the two entities was demonstrated in terms of clinical expression, risk factors, and postmortem brain autopsy. In this article, we propose mechanisms by which cardiovascular risk factors might affect the manifestation of Alzheimer's disease, suggest possible explanations for the overlap with vascular dementia, and discuss the implications this might have on future differential diagnosis and treatment strategies.

The role of insulin resistance in the pathogenesis of Alzheimer's disease: implications for treatment

An emerging body of evidence suggests that an increased prevalence of insulin abnormalities and insulin resistance in Alzheimer's disease may contribute to the disease pathophysiology and clinical symptoms. It has long been known that insulin is essential for energy metabolism in the periphery. In the past 2 decades, convergent findings have begun to demonstrate that insulin also plays a role in energy metabolism and other aspects of CNS function. Investigators reported 20 years ago that insulin and insulin receptors were densely but selectively expressed in the brain, including the medial temporal regions that support the formation of memory. It has recently been demonstrated that insulin-sensitive glucose transporters are localised to the same regions supporting memory and that insulin plays a role in memory functions. Collectively, these findings suggest that insulin may contribute to normal cognitive functioning and that insulin abnormalities may exacerbate cognitive impairments, such as those associated with Alzheimer's disease. Insulin may also play a role in regulating the amyloid precursor protein and its derivative beta-amyloid (Abeta), which is associated with senile plaques, a neuropathological hallmark of Alzheimer's disease. It has been proposed that insulin can accelerate the intracellular trafficking of Abeta and interfere with its degradation. These findings are consistent with the notion that insulin abnormalities may potentially influence levels of Abeta in the brains of patients with Alzheimer's disease. The increased occurrence of insulin resistance in Alzheimer's disease and the numerous mechanisms through which insulin may affect clinical and pathological aspects of the disease suggest that improving insulin effectiveness may have therapeutic benefit for patients with Alzheimer's disease. The thiazolidinedione rosiglitazone has been shown to have a potent insulin-sensitising action that appears to be mediated through the peroxisome proliferator-activated receptor-gamma (PPAR-gamma). PPAR-gamma agonists, such as rosiglitazone, also have anti-inflammatory effects that may be of therapeutic benefit in patients with Alzheimer's disease. This review presents evidence suggesting that insulin resistance plays a role in the pathophysiology and clinical symptoms of Alzheimer's disease. Based on this evidence, we propose that treatment of insulin resistance may reduce the risk or retard the development of Alzheimer's disease.

Association of life activities with cerebral blood flow in Alzheimer disease: implications for the cognitive reserve hypothesis

BACKGROUND

Regional cerebral blood flow (CBF), a good indirect index of cerebral pathologic changes in Alzheimer disease (AD), is more severely reduced in patients with higher educational attainment and IQ when controlling for clinical severity. This has been interpreted as suggesting that cognitive reserve allows these patients to cope better with the pathologic changes in AD.

OBJECTIVE

To evaluate whether premorbid engagement in various activities may also provide cognitive reserve.

DESIGN

We evaluated intellectual, social, and physical activities in 9 patients with early AD and 16 healthy elderly controls who underwent brain H(2)(15)O positron emission tomography. In voxelwise multiple regression analyses that controlled for age and clinical severity, we investigated the association between education, estimated premorbid IQ, and activities, and CBF.

RESULTS

In accordance with previous findings, we replicated an inverse association between education and CBF and IQ and CBF in patients with AD. In addition, there was a negative correlation between previous reported activity score and CBF in patients with AD. When both education and IQ were added as covariates in the same model, a higher activity score was still associated with more prominent CBF deficits. No significant associations were detected in the controls.

CONCLUSIONS

At any given level of clinical disease severity, there is a greater degree of brain pathologic involvement in patients with AD who have more engagement in activities, even when education and IQ are taken into account. This may suggest that interindividual differences in lifestyle may affect cognitive reserve by partially mediating the relationship between brain damage and the clinical manifestation of AD.

Association between the psychosocial network and dementia--a case-control study

In a case-control study, we investigated the possible etiological relevance to dementia of psychosocial network factors, such as marital status, confidants and close relatives, sports activities, cultural activities, club membership; and education. In 23 general practices we recruited 195 patients with dementia. Of these, 108 were suffering from possible Alzheimer's disease, 59 from possible vascular dementia and 28 from secondary or unclassified dementia. A total of 229 control subjects was recruited: 122 population controls and 107 dementia-free ambulatory patients. Data were gathered in a structured personal interview and analyzed using logistic regression, to control for age, region, sex, dementia in parents, education and smoking. There were significantly decreased odds ratios for the number of confidants, sports activities, and cultural activities at age 30, at age 50 and at 10 years before data collection. When all psychosocial network factors were included simultaneously in the logistic regression model, these factors remained statistically significant, indicating independent effects. Restriction of the analysis to cases with possible Alzheimer's disease or to cases with possible vascular dementia led to similar results. Adjustment for the psychosocial network neutralized the otherwise protective effect of education for dementia of any type and for possible vascular dementia. In keeping with the results from recently published studies, these results support a protective role for the psychosocial network-especially for the number of confidants and for sports and cultural activities-in the etiology of dementia.

Dependence of rat hippocampal c-Fos expression on intensity and duration of exercise

The expression of c-Fos, an immediately early gene, is a marker of neural activity. In the present study, the effect of treadmill exercise on c-Fos expression was investigated in various regions of the rat hippocampus via immunohistochemistry. The first part of the experiment was aimed at determining the dependence of c-Fos expression on the intensity of treadmill exercise. In most of the hippocampal regions studied, increasing c-Fos expression was observed with increasing exercise intensity. In the second part of the experiment, the dependence of c-Fos expression on the duration of treadmill exercise was investigated. The c-Fos expression induced by mild-intensity exercise increased until the 7th day of exercise and subsequently decreased. Results of the present study suggest that the effect of treadmill exercise on neuronal activity in the hippocampus is intensity-and duration-dependent.

Interplay between brain-derived neurotrophic factor and signal transduction modulators in the regulation of the effects of exercise on synaptic-plasticity

This study was designed to identify molecular mechanisms by which exercise affects synaptic-plasticity in the hippocampus, a brain area whose function, learning and memory, depends on this capability. We have focused on the central role that brain-derived neurotrophic factor (BDNF) may play in mediating the effects of exercise on synaptic-plasticity. In fact, this impact of exercise is exemplified by our finding that BDNF regulates the mRNA levels of two end products important for neural function, i.e. cAMP-response-element binding (CREB) protein and synapsin I. CREB and synapsin I have the ability to modify neuronal function by regulating gene-transcription and affecting synaptic transmission, respectively. Furthermore, we show that BDNF is capable of concurrently increasing the mRNA levels of both itself and its tyrosine kinaseB (TrkB) receptor, suggesting that exercise may employ a feedback loop to augment the effects of BDNF on synaptic-plasticity. The use of a novel microbead injection method in our blocking experiments and Taqman reverse transcription polymerase reaction (RT-PCR) for RNA quantification, have enabled us to evaluate the contribution of different pathways to the exercise-induced increases in the mRNA levels of BDNF, TrkB, CREB, and synapsin I. We found that although BDNF mediates exercise-induced hippocampal plasticity, additional molecules, i.e. the N-methyl-D-aspartate receptor, calcium/calmodulin protein kinase II and the mitogen-activated protein kinase cascade, modulate its effects. Since these molecules have a well-described association to BDNF action, our results illustrate a basic mechanism through which exercise may promote synaptic-plasticity in the adult brain.

Implications of amyloid precursor protein and subsequent beta-amyloid production to the pharmacotherapy of Alzheimer's disease

Alzheimer's disease is the most common type of dementia in older people. It is highly prevalent, affecting 35-45% of those aged 85 years or older. This disease has devastating consequences to patients, their families, caregivers, and the health care system. Much has been learned about its pathobiology, which has led to the beta-amyloid (Abeta) hypothesis. This hypothesis continues to be the predominant postulate of the pathobiology of Alzheimer's disease. Under this hypothesis, abnormal accumulation of Abeta is followed by a cascade of neurotoxic effects, which eventually result in neurodegeneration and development of Alzheimer's disease. This is thought to be the result of altered processing of the amyloid precursor protein (APP), preferentially by beta- and gamma-secretase enzymes rather than nonamyloidogenic processing by alpha-secretase. The growing body of knowledge regarding the processing of APP to various forms of Abeta has resulted in new approaches to the investigation of putative anti-Alzheimer's disease compounds, including immune-based therapies and various agents that can positively affect APP processing.

Differential effects of acute and chronic exercise on plasticity-related genes in the rat hippocampus revealed by microarray

Studies were performed to determine the effects of acute and chronic voluntary periods of exercise on the expression of hippocampal genes. RNAs from rodents exposed to a running wheel for 3, 7 and 28 days were examined using a microarray with 1176 cDNAs expressed primarily in the brain. The expression of selected genes was quantified by Taqman RT-PCR or RNase protection assay. The largest up-regulation was observed in genes involved with synaptic trafficking (synapsin I, synaptotagmin and syntaxin); signal transduction pathways (Ca2+/calmodulin-dependent protein kinase II, CaM-KII; mitogen-activated/extracellular signal-regulated protein kinase, MAP-K/ERK I and II; protein kinase C, PKC-delta) or transcription regulators (cyclic AMP response element binding protein, CREB). Genes associated with the glutamatergic system were up-regulated (N-methyl-d-aspartate receptor, NMDAR-2A and NMDAR-2B and excitatory amino acid carrier 1, EAAC1), while genes related to the gamma-aminobutyric acid (GABA) system were down-regulated (GABAA receptor, glutamate decarboxylase GAD65). Brain-derived neurotrophic factor (BDNF) was the only trophic factor whose gene was consistently up-regulated at all timepoints. These results, together with the fact that most of the genes up-regulated have a recognized interaction with BDNF, suggest a central role for BDNF on the effects of exercise on brain plasticity. The temporal profile of gene expression seems to delineate a mechanism by which specific molecular pathways are activated after exercise performance. For example, the CaM-K signal system seems to be active during acute and chronic periods of exercise, while the MAP-K/ERK system seems more important during long-term exercise.

Neuroplasticity in old age: sustained fivefold induction of hippocampal neurogenesis by long-term environmental enrichment

Neurons are continually born from endogenous stem cells and added to the dentate gyrus throughout life, but adult hippocampal neurogenesis declines precipitously with age. Short-term exposure to an enriched environment leads to a striking increase in new neurons, along with a substantial improvement in behavioral performance. Could this plastic response be relevant for explaining the beneficial effects of leading "an active life" on brain function and pathology? Adult hippocampal neurogenesis in mice living in an enriched environment from the age of 10 to 20 months was fivefold higher than in controls. Relatively, the increase in neuronal phenotypes was entirely at the expense of newly generated astrocytes. This cellular plasticity occurred in the context of significant improvements of learning parameters, exploratory behavior, and locomotor activity. Enriched living mice also had a reduced lipofuscin load in the dentate gyrus, indicating decreased nonspecific age-dependent degeneration. Therefore, in mice signs of neuronal aging can be diminished by a sustained active and challenging life, even if this stimulation started only at medium age. Activity exerts not only an acute but also a sustained effect on brain plasticity.

Waging war on physical inactivity: using modern molecular ammunition against an ancient enemy

A hypothesis is presented based on a coalescence of anthropological estimations of Homo sapiens' phenotypes in the Late Paleolithic era 10,000 years ago, with Darwinian natural selection synergized with Neel's idea of the so-called thrifty gene. It is proposed that humans inherited genes that were evolved to support a physically active lifestyle. It is further postulated that physical inactivity in sedentary societies directly contributes to multiple chronic health disorders. Therefore, it is imperative to identify the underlying genetic and cellular/biochemical bases of why sedentary living produces chronic health conditions. This will allow society to improve its ability to effect beneficial lifestyle changes and hence improve the overall quality of living. To win the war against physical inactivity and the myriad of chronic health conditions produced because of physical inactivity, a multifactorial approach is needed, which includes successful preventive medicine, drug development, optimal target selection, and efficacious clinical therapy. All of these approaches require a thorough understanding of fundamental biology and how the dysregulated molecular circuitry caused by physical inactivity produces clinically overt disease. The purpose of this review is to summarize the vast armamentarium at our disposal in the form of the extensive scientific basis underlying how physical inactivity affects at least 20 of the most deadly chronic disorders. We hope that this information will provide readers with a starting point for developing additional strategies of their own in the ongoing war against inactivity-induced chronic health conditions.

Exercise enhances and protects brain function

Physical activity, in the form of voluntary wheel running, induces gene expression changes in the brain. Animals that exercise show an increase in brain-derived neurotrophic factor, a molecule that increases neuronal survival, enhances learning, and protects against cognitive decline. Microarray analysis of gene expression provides further support that exercise enhances and supports brain function.

Environmental enrichment slows disease progression in R6/2 Huntington's disease mice

Huntington's disease is a genetic disorder that causes motor dysfunction, personality changes, dementia, and premature death. There is currently no effective therapy. Several transgenic models of Huntington's disease are available, the most widely used of which is the R6/2 mouse, because of its rapid disease progression. Environmental enrichment alters gene expression in the normal mouse brain, and modulates the course of several neurological disorders. Environmentally enriched mice may actually mimic human disease more accurately. We found that even limited environmental enrichment slows decline in RotaRod performance in R6/2 mice, despite rapid disease progression, whereas in normal littermates, maximal enrichment was required to induce a marked improvement in behavioral tests. Enrichment also delayed the loss of peristriatal cerebral volume in R6/2 brains. These results could provide the basis for a rational approach to ameliorate the effects of Huntington's disease.

Effects of exercise on gene-expression profile in the rat hippocampus

Exercise has beneficial effects on brain function, including the promotion of plasticity and the enhancement of learning and memory performance. Previously we found that exercise increases the expression of certain neurotrophic factors including brain derived neurotrophic factor in the rat hippocampus. To further explore the molecular mechanisms underlying these changes, we used high-density oligonucleotide microarrays containing probe sets representing approximately 5000 genes to analyze the level of gene transcripts in the hippocampus of rats voluntary running for 3 weeks in comparison with sedentary animals. An improved statistical approach for the analysis of DNA microarray data, Cyber-T, was utilized in data analysis. Here we show that exercise leads to changes in the level of a large number of gene transcripts, many of which are known to be associated with neuronal activity, synaptic structure, and neuronal plasticity. Our data indicate that exercise elicits a differential gene expression pattern with significant changes in genes of relevance for brain function.

Estrogen and exercise interact to regulate brain-derived neurotrophic factor mRNA and protein expression in the hippocampus

We investigated the possibility that estrogen and exercise interact in the hippocampus and regulate brain-derived neurotrophic factor (BDNF), a molecule increasingly recognized for its role in plasticity and neuron function. An important aspect of this study is to examine the effect of different time intervals between estrogen loss and estrogen replacement intervention. We demonstrate that in the intact female rat, physical activity increases hippocampal BDNF mRNA and protein levels. However, the exercise effect on BDNF up-regulation is reduced in the absence of estrogen, in a time-dependent manner. In addition, voluntary activity itself is stimulated by the presence of estrogen. In exercising animals, estrogen deprivation reduced voluntary activity levels, while estrogen replacement restored activity to normal levels. In sedentary animals, estrogen deprivation (ovariectomy) decreased baseline BDNF mRNA and protein, which were restored by estrogen replacement. Despite reduced activity levels in the ovariectomized condition, exercise increased BDNF mRNA levels in the hippocampus after short-term (3 weeks) estrogen deprivation. However, long-term estrogen-deprivation blunted the exercise effect. After 7 weeks of estrogen deprivation, exercise alone no longer affected either BDNF mRNA or protein levels. However, exercise in combination with long-term estrogen replacement increased BDNF protein above the effects of estrogen replacement alone. Interestingly, protein levels across all conditions correlated most closely with mRNA levels in the dentate gyrus, suggesting that expression of mRNA in this hippocampal region may be the major contributor to the hippocampal BDNF protein pool. The interaction of estrogen, physical activity and hippocampal BDNF is likely to be an important issue for maintenance of brain health, plasticity and general well-being, particularly in women.

Demographic and psychosocial correlates of physical activity in late life

INTRODUCTION

According to the Centers for Disease Control and Prevention and the World Health Organization, increasing physical activity may help prolong health and preserve the quality of life in late adulthood. Physical activity has taken center stage as the behavior most likely to alter health. However, there is little recent population-wide information about the demographic and psychosocial correlates of physical activity in the elderly population. The purpose of the study was to identify the factors associated with older adults' frequency of physical activity. The study may have implications for preventive interventions.

METHODS

Data for 12,611 community-dwelling people aged > or = 65 from the 1996-1997 Canadian National Population Health Survey were examined. Predictors of frequent versus infrequent self-reported physical activity lasting > 15 minutes were examined using logistic regression analyses. The predictor variables included geographic location, psychological distress (Generalized Distress Scale), demographic factors (age, gender, educational level, and marital status), perceived social support, chronic medical conditions, physical limitations due to injury, functional limitations, smoking behavior, and body mass index (BMI).

RESULTS

Gender (male); younger age; higher levels of education; being unmarried; absence of chronic conditions, injuries, and functional limitations; lower BMI; social support (females); nonsmoking; region; and lower levels of psychological distress were associated with frequent physical activity in late life. Older adults in western Canadian provinces were more active than those in eastern provinces.

CONCLUSIONS

The results will be useful for the design of interventions aimed at improving older adults' health behavior and other health and functional outcomes, especially for subgroups in particular need. Recommendations for further longitudinal research are presented.

Clinical Research on Older Adults in Canada: Summary of Recent Progress

Geriatric Medicine is a young specialty in Canada, having been formally recognized in 1981. The early years of research chiefly involved designing and describing programs of care. As the specialty matured, so too did the nature of research into the clinical problems of older adults. This article discusses research published by Canadian geriatricians since 1998, the date of a previous review. Two prominent areas of research are frailty and dementia. Several groups have studied the natural history of frailty, and designed techniques to better measure outcomes. Interventional trials are also gaining prominence, with the Systeme de services intégrés pour personnes agees en perte d'automonie (SIPA) and Mobile Geriatric Assessment Team (MGAT) being good examples. The Canadian Study of Health and Aging (CSHA) is one of the largest studies of dementia epidemiology ever conducted, and the upcoming third wave will provide new data on the outcomes of cognitive impairment not meeting criteria for dementia. Other areas of interest include pharmacoepidemiology, difficult clinical problems, advanced directives and bioethics. Canadian research in geriatrics will continue to develop, with the establishment of the Canadian Institutes of Health Research providing exciting new opportunities.