Documented head injury in early adulthood and risk of Alzheimer's disease and other dementias

Brain function decline in healthy retired athletes who sustained their last sports concussion in early adulthood

Recent studies have shown that the detrimental effects of sports concussions on cognitive and motor function may persist up to a few years post-injury. The present study sought to investigate the effects of having sustained a sports concussion more than 30 years prior to testing on cognitive and motor functions. Nineteen healthy former athletes, in late adulthood (mean age = 60.79; SD = 5.16), who sustained their last sport-related concussion in early adulthood (mean age = 26.05; SD = 9.21) were compared with 21 healthy former athletes with no history of concussion (mean age = 58.89; SD = 9.07). Neuropsychological tests sensitive to age-related changes in cognition were administered. An auditory oddball paradigm was used to evoke P3a and P3b brain responses. Four TMS paradigms were employed to assess motor cortex excitability: (i) resting motor threshold; (ii) paired-pulse intracortical inhibition and intracortical facilitation; (iii) input/output curve and (iv) cortical silent period (CSP). A rapid alternating movement task was also used to characterize motor system dysfunctions. Relative to controls, former athletes with a history of concussion had: (i) lower performance on neuropsychological tests of episodic memory and response inhibition; (ii) significantly delayed and attenuated P3a/P3b components; (iii) significantly prolonged CSP and (iv) significantly reduced movement velocity (bradykinesia). The finding that the P3, the CSP as well as neuropsychological and motor indices were altered more than three decades post-concussion provides evidence for the chronicity of cognitive and motor system changes consecutive to sports concussion.

Cortical injury increases cholesterol 24S hydroxylase (Cyp46) levels in the rat brain

In traumatic brain injury (TBI), cellular loss from initial impact as well as secondary neurodegeneration leads to increased cholesterol and lipid debris at the site of injury. Cholesterol accumulation in the periphery can trigger inflammatory mechanisms while cholesterol clearance may be anti-inflammatory. Here we investigated whether TBI altered the regulation of cholesterol 24S-hydroxylase (Cyp46), an enzyme that converts cholesterol to the more hydrophilic 24S-hydroxycholesterol. We examined by Western blot and immunohistochemistry changes in Cyp46 expression following fluid percussion injury. Under normal conditions, most Cyp46 was present in neurons, with very little measurable in glia. Cyp46 levels were significantly increased at 7 days post-injury, and cell type specific analysis at 3 days post-injury showed a significant increase in levels of Cyp46 (84%) in microglia. Since 24-hydroxycholesterol induces activation of genes through the liver X receptor (LXR), we examined protein levels of ATP-binding cassette transporter A1 and apolipoprotein E, two LXR regulated cholesterol homeostasis proteins. Apolipoprotein E and ATP-binding cassette transporter A1 were increased at 7 days post-injury, indicating that increased LXR activity coincided with increased Cyp46 levels. We found that activation of primary rat microglia by LPS in vitro caused increased Cyp46 levels. These data suggest that increased microglial Cyp46 activity is part of a system for removal of damaged cell membranes post-injury, by conversion of cholesterol to 24-hydroxycholesterol and by activation of LXR-regulated gene transcription.

Systemic lipopolysaccharide plus MPTP as a model of dopamine loss and gait instability in C57Bl/6J mice

In most environmental models of Parkinson's disease (PD), a single neurodegenerative agent is introduced to cause nigrostriatal dopamine depletion. However, cell loss in human PD often might derive, at least in part, from multiple toxins or vulnerabilities, any one of which alone does not inevitably lead to chronic dopamine depletion. In the present research, male C57BL/6J mice were systemically administered the inflammatory bacterial endotoxin, lipopolysaccharide (LPS) and the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) alone or in combination and the behavior as well as striatal dopamine levels were compared to saline-treated mice. Mice in the combination (LPS+MPTP) group, but not in the single-factor groups, showed both dopamine depletion and parkinsonian symptoms, i.e., reduced stride length, at 4 months post-injection. MPTP alone acutely reduced striatal dopamine levels but this effect was transient as striatal dopamine recovered to normal levels after time (4 months). The LPS-only group showed no dopamine depletion or reduced stride length. These data are consistent with the view that nigrostriatal dopamine neurons might succumb after time to multiple toxic agents that independently may have only a transient, adverse effect.

Long-term outcome of serious traumatic brain injury

Follow-up studies on individuals who suffer severe head injury give a picture of poor cognitive and psychosocial outcome. However, recent evidence suggests that with the passage of time, many individuals make adjustments that compensate for early disability, leading to a reduction in social handicap with a corresponding improvement in life quality and personal satisfaction. This article will attempt to briefly review the main sources of evidence contributing to long-term outcome following serious head trauma.

Consortium to Establish a Registry for Alzheimer's Disease (CERAD): the first twenty years

The Consortium to Establish a Registry for Alzheimer's Disease (CERAD) was funded by the National Institute on Aging in 1986 to develop standardized, validated measures for the assessment of Alzheimer's disease (AD). The present report describes the measures that CERAD developed during its first decade and their continued use in their original and translated forms. These measures include clinical, neuropsychological, neuropathologic, and behavioral assessments of AD and also assessment of family history and parkinsonism in AD. An approach to evaluating neuroimages did not meet the standards desired. Further evaluations that could not be completed because of lack of funding (but where some materials are available) include evaluation of very severe AD and of service use and need by patient and caregiver. The information that was developed in the U.S. and abroad permits standardized assessment of AD in clinical practice, facilitates epidemiologic studies, and provides information valuable for individual and public health planning. CERAD materials and data remain available for those wishing to use them.

Risk of dementia associated with the ApoE epsilon4 allele and falls causing head injury without explicit traumatic brain injury

OBJECTIVES

Severe head injury (HI) and the apolipoprotein E (ApoE) epsilon4 allele are risk factors for dementia. The corresponding effect of falls causing HI without explicit traumatic brain injury (TBI) in association with the ApoE epsilon4 is not known.

MATERIALS AND METHODS

Altogether 134 persons aged 70 years or older constituted a retrospective population sample, who scored > or =26 in the MiniMental State Examination (MMSE) test at baseline and were clinically examined for dementia 9 years afterward. Fall-related HI causing superficial laceration or bruises or wounds that require suturing were prospectively recorded during the 9-year follow-up. We used Cox regression with age at the diagnosis of dementia as a dependent variable.

RESULTS

Twenty-eight (21%) subjects had falls causing HI without explicit TBI, the ApoE epsilon4 allele was seen in 44 (33%), and clinical dementia was diagnosed in 25 (19%). Adjusted for the baseline MMSE score, sex and educational status, the hazard ratio for subsequent dementia in subjects having falls with HI without explicit TBI and the ApoE epsilon4 allele as compared with those who do not possess these characteristics was 2.70 (95% confidence interval, 1.02-7.16).

CONCLUSIONS

According to the results of this small retrospective study, falls with HI without explicit TBI in connection with the ApoE epsilon4 allele is associated with subsequent dementia among older adults.

Increased expression of the gamma-secretase components presenilin-1 and nicastrin in activated astrocytes and microglia following traumatic brain injury

Gamma-secretase is an aspartyl protease composed of four proteins: presenilin (PS), nicastrin (Nct), APH1, and PEN2. These proteins assemble into a membrane complex that cleaves a variety of substrates within the transmembrane domain. The gamma-secretase cleavage products play an important role in various biological processes such as embryonic development and Alzheimer's disease (AD). The major role of gamma-secretase in brain pathology has been linked to AD and to the production of the amyloid beta-peptide. However, little is known about the possible role of gamma-secretase following acute brain insult. Here we examined by immunostaining the expression patterns of two gamma-secretase components, PS1 and Nct, in three paradigms of brain insult in mice: closed head injury, intracerebroventricular injection of LPS, and brain stabbing. Our results show that in naïve and sham-injured brains expression of PS1 and Nct is restricted mainly to neurons. However, following insult, the expression of both proteins is also observed in nonneuronal cells, consisting of activated astrocytes and microglia. Furthermore, the proteins are coexpressed within the same astrocytes and microglia, implying that these cells exhibit an enhanced gamma-secretase activity following brain damage. In view of the important role played by astrocytes and microglia in brain disorders, our findings suggest that gamma-secretase may participate in brain damage and repair processes by regulating astrocyte and microglia activation and/or function.

A lack of amyloid beta plaques despite persistent accumulation of amyloid beta in axons of long-term survivors of traumatic brain injury

Traumatic brain injury (TBI) is a risk factor for developing Alzheimer's disease (AD). Additionally, TBI induces AD-like amyloid beta (Abeta) plaque pathology within days of injury potentially resulting from massive accumulation of amyloid precursor protein (APP) in damaged axons. Here, progression of Abeta accumulation was examined using brain tissue from 23 cases with post-TBI survival of up to 3 years. Even years after injury, widespread axonal pathology was consistently observed and was accompanied by intra-axonal co-accumulations of APP with its cleavage enzymes, beta-site APP cleaving enzyme and presenilin-1 and their product, Abeta. However, in marked contrast to the plaque pathology noted in short-term cases post TBI, virtually no Abeta plaques were found in long-term survivors. A potential mechanism for Abeta plaque regression was suggested by the post-injury accumulation of an Abeta degrading enzyme, neprilysin. These findings fail to support the premise that progressive plaque pathology after TBI ultimately results in AD.

Prevalence of cognitive impairment without dementia in the United States

BACKGROUND

Cognitive impairment without dementia is associated with increased risk for disability, increased health care costs, and progression to dementia. There are no population-based prevalence estimates of this condition in the United States.

OBJECTIVE

To estimate the prevalence of cognitive impairment without dementia in the United States and determine longitudinal cognitive and mortality outcomes.

DESIGN

Longitudinal study from July 2001 to March 2005.

SETTING

In-home assessment for cognitive impairment.

PARTICIPANTS

Participants in ADAMS (Aging, Demographics, and Memory Study) who were age 71 years or older drawn from the nationally representative HRS (Health and Retirement Study). Of 1770 selected individuals, 856 completed initial assessment, and of 241 selected individuals, 180 completed 16- to 18-month follow-up assessment.

MEASUREMENTS

Assessments, including neuropsychological testing, neurologic examination, and clinical and medical history, were used to assign a diagnosis of normal cognition, cognitive impairment without dementia, or dementia. National prevalence rates were estimated by using a population-weighted sample.

RESULTS

In 2002, an estimated 5.4 million people (22.2%) in the United States age 71 years or older had cognitive impairment without dementia. Prominent subtypes included prodromal Alzheimer disease (8.2%) and cerebrovascular disease (5.7%). Among participants who completed follow-up assessments, 11.7% with cognitive impairment without dementia progressed to dementia annually, whereas those with subtypes of prodromal Alzheimer disease and stroke progressed at annual rates of 17% to 20%. The annual death rate was 8% among those with cognitive impairment without dementia and almost 15% among those with cognitive impairment due to medical conditions.

LIMITATIONS

Only 56% of the nondeceased target sample completed the initial assessment. Population sampling weights were derived to adjust for at least some of the potential bias due to nonresponse and attrition.

CONCLUSION

Cognitive impairment without dementia is more prevalent in the United States than dementia, and its subtypes vary in prevalence and outcomes.

Diagnosis and treatment of dementia: 1. Risk assessment and primary prevention of Alzheimer disease

BACKGROUND

In addition to nonmodifiable genetic risk factors, potentially modifiable factors such as hypertension, hyperlipidemia and environmental exposures have been identified as risk factors for Alzheimer disease. In this article, we provide physicians with practical guidance on risk assessment and primary prevention of Alzheimer disease based on recommendations from the Third Canadian Consensus Conference on the Diagnosis and Treatment of Dementia, held in March 2006.

METHODS

We developed evidence-based guidelines using systematic literature searches, with specific criteria for study selection and quality assessment, and a clear and transparent decision-making process. We selected studies published from January 1996 to December 2005 that met the following criteria: dementia (all-cause, Alzheimer disease or vascular dementia) as the outcome; longitudinal cohort study; study population broadly reflective of Canadian demographics; and genetic risk factors and general risk factors (e.g., hypertension, education, occupation and chemical exposure) identified. We graded the strength of evidence using the criteria of the Canadian Task Force on Preventive Health Care.

RESULTS

Of 3424 articles on potentially modifiable risk factors for dementia, 1719 met our inclusion criteria; 60 were deemed to be of good or fair quality. Of 1721 articles on genetic risk factors, 62 that met our inclusion criteria were deemed to be of good or fair quality. On the basis of evidence from these articles, we made recommendations for the risk assessment and primary prevention of Alzheimer disease. For the primary prevention of Alzheimer's disease, there is good evidence for controlling vascular risk factors, especially hypertension (grade A), and weak or insufficient evidence for manipulation of lifestyle factors and prescribing of medications (grade C). There is good evidence to avoid estrogens and high-dose (> 400 IU/d) of vitamin E for this purpose (grade E). Genetic counselling and testing may be offered to at-risk individuals with an apparent autosomal dominant inheritance (grade B). Screening for the apolipoprotein E genotype in asymptomatic individuals in the general population is not recommended (grade E).

INTERPRETATION

Despite the personal and societal burden of dementia, our understanding of genetic predisposition to dementias and the contribution of other risk factors remains limited. More importantly, there are few data to explain the overall risks and benefits of prevention strategies or their impact of risk modification.

Alzheimer's disease-related changes in diseases characterized by elevation of intracranial or intraocular pressure

In this review, we focus on the coexistence of Alzheimer's disease-related changes in brain diseases, such as normal pressure hydrocephalus and traumatic brain injury, and in glaucoma at the level of the retinal ganglion cells. This is a group of diseases that affect central nervous system tissue and are characterized by elevation of intracranial or intraocular pressure and/or local shear stress and strain. In considering possible mechanisms underlying Alzheimer-type changes in these diseases, we briefly summarize recent evidence indicating that caspase activation and abnormal processing of beta-amyloid precursor protein, which are important events in Alzheimer's disease, may play a role both in glaucoma and following traumatic brain injury. With regard to normal pressure hydrocephalus, evidence suggests that changes in cerebrospinal fluid circulatory dynamics ultimately may result in reduced clearance of neurotoxins, such as beta-amyloid peptides and tau protein, that play a role in the pathogenesis of Alzheimer's disease. Data presented in this review could be interpreted to suggest that Alzheimer-type changes in these diseases may result at least in part from exposure of central nervous system tissue to increased levels of mechanical stress. Evidence for such a relationship is of major importance because it may support an association between elevated mechanical load and the development of Alzheimer-type lesions. Further studies are warranted, however, especially to elucidate the role of elevated mechanical forces in Alzheimer's disease neuropathogenesis.

[Risk factors and protective factors of the insanities]

The Alzheimer's disease (AD) is multifactorial. How to explain this group of very heterogeneous factors? Many of them can be considered as biopsychosocial risk factors. In other words, the risk factors, in link with the physiological functioning and a physiopathology, are difficultly dissociable of contingencies of psychological and/or social nature. The vital lead could be the stress bound to these variables, be it biological or psychosocial. It remains to ask the question of the preventive efficiency of treatments to relieve the impact of the traumatizing events of life that entail a depressive state or a state of posttraumatic stress. The hippocamp has to be the object of a quite particular attention. AD is a disease of the adaptation. This integrative model combines three vulnerabilities: a genetic vulnerability which would be there to dictate the type of lesions, their localization and the age of occurence; a psychobiographic vulnerability corresponding to a personality with inadequate mechanisms of defence, precarious adaptability in front of the adversity, weak impact strength and biography built on events of life during childhood, then during the grown-up life of traumatic nature, with a psychosocial environment insufficiently auxiliary; a neuroendocrinologic vulnerability which would base on a deregulation of the corticotrope axis, acquired during its infantile maturation, hampered by too premature stress. It would lead to a bad biological adaptability in stress later, at the origin of the observable lesions in the insanities.

Apolipoprotein E and traumatic brain injury in a military population: evidence of a neuropsychological compensatory mechanism?

OBJECTIVE

Although research has implicated the apolipoprotein E (APOE) epsilon-4 genotype as having a negative effect on neuropsychological outcomes following traumatic brain injury (TBI), the potentially negative role of the epsilon4 allele on TBI outcomes has recently been challenged. In light of this debate, the present study served to examine the role of APOE genotype on neuropsychological outcomes approximately 1 month following mild to moderate TBI in a military population. Because of the well documented role of the APOE-epsilon4 allele in increasing the risk of Alzheimer's disease, we predicted that persons with the APOE-epsilon4 genotype would display relatively greater deficits in cognition than their non-epsilon4 counterparts.

METHODS

78 participants were consecutively recruited following a mild to moderate TBI and were divided into two groups based on the presence or absence of an APOE epsilon4 allele. Groups were comparable on demographic characteristics and psychosocial outcomes. Participants were administered a comprehensive neuropsychological battery.

RESULTS

Analyses revealed comparable performances on most neuropsychological measures and better performances by epsilon4 carriers on select measures of attention, executive functioning and episodic memory encoding. Furthermore, differences remained after accounting for the effects of TBI severity.

CONCLUSIONS

Evidence from these analyses supports current literature refuting the notion of relatively poorer neuropsychological functioning associated with the APOE-epsilon4 genotype among young adult participants shortly following mild or moderate brain injury. Neuropsychological performance differences by APOE genotype following TBI are discussed in terms of the importance of considering severity of injury, timing of postinjury assessment and possible neurocognitive compensatory mechanisms.

Multiple proteins implicated in neurodegenerative diseases accumulate in axons after brain trauma in humans

Studies in animal models have shown that traumatic brain injury (TBI) induces the rapid accumulation of many of the same key proteins that form pathologic aggregates in neurodegenerative diseases. Here, we examined whether this rapid process also occurs in humans after TBI. Brain tissue from 18 cases who died after TBI and from 6 control cases was examined using immunohistochemistry. Following TBI, widespread axonal injury was persistently identified by the accumulation of neurofilament protein and amyloid precursor protein (APP) in axonal bulbs and varicosities. Axonal APP was found to co-accumulate with its cleavage enzymes, beta-site APP cleaving enzyme (BACE), presenilin-1 (PS1) and their product, amyloid-beta (Abeta). In addition, extensive accumulation of alpha-synuclein (alpha-syn) was found in swollen axons and tau protein was found to accumulate in both axons and neuronal cell bodies. These data show rapid axonal accumulation of proteins implicated in neurodegenerative diseases including Alzheimer's disease and the synucleinopathies. The cause of axonal pathology can be attributed to disruption of axons due to trauma, or as a secondary effect of raised intracranial pressure or hypoxia. Such axonal pathology in humans may provide a unique environment whereby co-accumulation of APP, BACE, and PS1 leads to intra-axonal production of Abeta as well as accumulation of alpha-syn and tau. This process may have important implications for survivors of TBI who have been shown to be at greater risk of developing neurodegenerative diseases.

Acute stress increases interstitial fluid amyloid-beta via corticotropin-releasing factor and neuronal activity

Aggregation of the amyloid-beta (Abeta) peptide in the extracellular space of the brain is critical in the pathogenesis of Alzheimer's disease. Abeta is produced by neurons and released into the brain interstitial fluid (ISF), a process regulated by synaptic activity. To determine whether behavioral stressors can regulate ISF Abeta levels, we assessed the effects of chronic and acute stress paradigms in amyloid precursor protein transgenic mice. Isolation stress over 3 months increased Abeta levels by 84%. Similarly, acute restraint stress increased Abeta levels over hours. Exogenous corticotropin-releasing factor (CRF) but not corticosterone mimicked the effects of acute restraint stress. Inhibition of endogenous CRF receptors or neuronal activity blocked the effects of acute stress on Abeta. Thus, behavioral stressors can rapidly increase ISF Abeta through neuronal activity in a CRF-dependent manner, and the results suggest a mechanism by which behavioral stress may affect Alzheimer's disease pathogenesis.

Genetic influences on outcome following traumatic brain injury

Several genes have been implicated as influencing the outcome following traumatic brain injury (TBI). Currently the most extensively studied gene has been APOE. APOE can influence overall and rehabilitation outcome, coma recovery, risk of posttraumatic seizures, as well as cognitive and behavioral functions following TBI. Pathologically, APOE is associated with increased amyloid deposition, amyloid angiopathy, larger intracranial hematomas and more severe contusional injury. The proposed mechanism by which APOE affects the clinicopathological consequences of TBI is multifactorial and includes amyloid deposition, disruption of cytoskeletal stability, cholinergic dysfunction, oxidative stress, neuroprotection and central nervous system plasticity in response to injury. Other putative genes have been less extensively studied and require replication of the clinical findings. The COMT and DRD2 genes may influence dopamine dependent cognitive processes such as executive/frontal lobe functions. Inflammation which is a prominent component in the pathophysiological cascade initiated by TBI, is in part is mediated by the interleukin genes, while apoptosis that occurs as a consequence of TBI may be modulated by polymorphisms of the p53 gene. The ACE gene may affect TBI outcome via mechanisms of cerebral blood flow and/or autoregulation and the CACNA1A gene may exert an influence via the calcium channel and its effect on delayed cerebral edema. Although several potential genes that may influence outcome following TBI have been identified, future investigations are needed to validate these genetic studies and identify new genes that might influence outcome following TBI.

The epidemiology and impact of traumatic brain injury: a brief overview

Traumatic brain injury (TBI) is an important public health problem in the United States and worldwide. The estimated 5.3 million Americans living with TBI-related disability face numerous challenges in their efforts to return to a full and productive life. This article presents an overview of the epidemiology and impact of TBI.

Traumatic brain injury and Alzheimer's disease: a review

In an effort to identify the factors that are involved in the pathogenesis of Alzheimer's disease (AD), epidemiological studies have featured prominently in contemporary research. Of those epidemiological factors, accumulating evidence implicates traumatic brain injury (TBI) as a possible predisposing factor in AD development. Exactly how TBI triggers the neurodegenerative cascade of events in AD remains controversial. There has been extensive research directed towards understanding the potential relationship between TBI and AD and the putative influence that apolipoprotein E (APOE) genotype has on this relationship. The aim of the current paper is to provide a critical summary of the experimental and human studies regarding the association between TBI, AD and APOE genotype. It will be shown that despite significant discrepancies in the literature, there still appears to be an increasing trend to support the hypothesis that TBI is a potential risk factor for AD. Furthermore, although it is known that APOE genotype plays an important role in AD, its link to a deleterious outcome following TBI remains inconclusive and ambiguous.

Outcome of Traumatic Brain Injury after Three Decades— Relationship to ApoE Genotype

Significant traumatic brain injury (TBI) is nearly always associated with cognitive deficits, but in a highly variable manner. Apolipoprotein E (ApoE) plays a pivotal role in CNS response to injury. To examine the association of ApoE genotype with long-term outcome in TBI patients, we determined the ApoE genotype from 61 TBI patients who had been injured over three decades earlier. All patients had been studied neuropsychologically after their injuries. The long-term outcome was evaluated with repeated neuropsychological testing and by applying various measures of everyday functioning and quality of life. After three decades, TBI patients with the ApoE epsilon4 allele showed significantly poorer general cognitive level than those without this allele. This decline was wholly accounted for by a subgroup of these patients who had developed incident or clinical dementia, while the majority of the ApoE epsilon4 positive patients showed no decline at all. The other outcome measures describing vocational, physical, or subjective symptom outcome did not show significant relationships to the ApoE genotype. A portion of the TBI patients with the ApoE epsilon4 allele seem to be at risk of long-term cognitive decline.

Traumatic brain injury in older adults: epidemiology, outcomes, and future implications

Traumatic brain injury (TBI) is a significant problem in older adults. In persons aged 65 and older, TBI is responsible for more than 80,000 emergency department visits each year; three-quarters of these visits result in hospitalization as a result of the injury. Adults aged 75 and older have the highest rates of TBI-related hospitalization and death. Falls are the leading cause of TBI for older adults (51%), and motor vehicle traffic crashes are second (9%). Older age is known to negatively influence outcome after TBI. Although geriatric and neurotrauma investigators have identified the prognostic significance of preadmission functional ability, comorbidities, sex, and other factors such as cerebral perfusion pressure on recovery after illness or injury, these variables remain understudied in older adults with TBI. In the absence of good clinical data, predicting outcomes and providing care in the older adult population with TBI remains problematic. To address this significant public health issue, a refocusing of research efforts on this population is justified to prevent TBI in the older adult and to discern unique care requirements to facilitate best patient outcomes.

Long-term effect of head trauma on intellectual abilities: a 16-year outcome study

BACKGROUND

Intelligence was assessed in a group of 74 people with head injury, 16 years after injury (mean 16.77 years; range 10-32 years), and compared with their performance when assessed at an early stage in recovery (mean 1.05 years).

AIMS

To confirm the presence of long-term impairment relative to estimates of pre-accident ability, to confirm signs of deterioration between early (T1) and late (T2) measures, and to examine relationships between severity of injury, time since injury, length of education, sex and age, and performance on intelligence tests at T2.

EXPECTED OUTCOMES

On the basis of evidence from other studies, a significant difference was expected between estimates of pre-accident intelligence and abilities measured at T1 and T2. Deterioration in performance between T1 and T2, and relationships between demographic variables, severity of injury and intellectual performance were also expected.

RESULTS AND CONCLUSION

The data supported long-term intellectual impairment, but there was no deterioration in abilities between T1 and T2. Performance on intelligence tests was associated with years of education but not with other factors.

Apolipoprotein E, cholesterol metabolism, diabetes, and the convergence of risk factors for Alzheimer's disease and cardiovascular disease

High fat diets and sedentary lifestyles are becoming major concerns for Western countries. They have led to a growing incidence of obesity, dyslipidemia, high blood pressure, and a condition known as the insulin-resistance syndrome or metabolic syndrome. These health conditions are well known to develop along with, or be precursors to atherosclerosis, cardiovascular disease, and diabetes. Recent studies have found that most of these disorders can also be linked to an increased risk of Alzheimer's disease (AD). To complicate matters, possession of one or more apolipoprotein E epsilon4 (APOE epsilon4) alleles further increases the risk or severity of many of these conditions, including AD. ApoE has roles in cholesterol metabolism and Abeta clearance, both of which are thought to be significant in AD pathogenesis. The apparent inadequacies of ApoE epsilon4 in these roles may explain the increased risk of AD in subjects carrying one or more APOE epsilon4 alleles. This review describes some of the physiological and biochemical changes that the above conditions cause, and how they are related to the risk of AD. A diversity of topics is covered, including cholesterol metabolism, glucose regulation, diabetes, insulin, ApoE function, amyloid precursor protein metabolism, and in particular their relevance to AD. It can be seen that abnormal lipid, cholesterol and glucose metabolism are consistently indicated as central in the pathophysiology, and possibly the pathogenesis of AD. As diagnosis of mild cognitive impairment and early AD are becoming more reliable, and as evidence is accumulating that health conditions such as diabetes, obesity, and coronary artery disease are risk factors for AD, appropriate changes to diets and lifestyles will likely reduce AD risk, and also improve the prognosis for people already suffering from such conditions.

RCAN1 (DSCR1 or Adapt78) stimulates expression of GSK-3beta

The RCAN1 protein (previously called calcipressin 1 or MCIP1) binds to calcineurin, a serine/threonine phosphatase (PP2B), and inhibits its activity. Here we demonstrate that regulated overexpression of an RCAN1 transgene (this gene was previously called DSCR1 or Adapt78) also stimulates expression of the GSK-3beta kinase, which can antagonize the action of calcineurin. We also show that GSK-3beta is regulated by RCAN1 at a post-transcriptional level. In humans, high RCAN1 expression is found in the brain, where at least two mRNA isoforms have been reported. Therefore, we further investigated expression of the various RCAN1 isoforms, resulting from differential splicing and alternative promotors in human brain. We detected at least three distinct RCAN1s: RCAN1-1 Short at 31 kDa (RCAN1-1S), RCAN1-1 Long at 38 kDa (RCAN1-1 L), and RCAN1-4. Furthermore, the levels of RCAN1-1S, but not RCAN1-1 L or RCAN1-4 correlated with the levels of GSK-3beta. This suggests that RCAN1-1S might induce production of GSK-3beta in vivo. While RCAN1s can regulate calcineurin and GSK-3beta, it has also been shown that calcineurin and GSK-3beta can regulate RCAN1s. Here we propose a new model (incorporating all these findings) in which cells maintain an equilibrium between RCAN1s, calcineurin, and GSK-3beta.

Traumatic brain injury in the elderly: diagnostic and treatment challenges

The purpose of this review is to introduce geriatric practitioners to issues and challenges presented in the elderly after onset of traumatic brain injury (TBI). Issues discussed include the magnitude of TBI in the elderly, mechanisms of onset, issues specific to both acute and rehabilitation care for the elderly with TBI, and specific physical and behavioral manifestations of TBI that may need to be addressed on an inpatient or outpatient basis. General guidelines are provided for the diagnosis and treatment of older individuals who have TBI, with specific clinical scenarios illustrating key points.

NMDA receptor activation inhibits alpha-secretase and promotes neuronal amyloid-beta production

Acute brain injuries have been identified as a risk factor for developing Alzheimer's disease (AD). Because glutamate plays a pivotal role in these pathologies, we studied the influence of glutamate receptor activation on amyloid-beta (Abeta) production in primary cultures of cortical neurons. We found that sublethal NMDA receptor activation increased the production and secretion of Abeta. This effect was preceded by an increased expression of neuronal Kunitz protease inhibitory domain (KPI) containing amyloid-beta precursor protein (KPI-APP) followed by a shift from alpha-secretase to beta-secretase-mediated APP processing. This shift is a result of the inhibition of the alpha-secretase candidate tumor necrosis factor-alpha converting enzyme (TACE) when associated with neuronal KPI-APPs. This KPI-APP/TACE interaction was also present in AD brains. Thus, our findings reveal a cellular mechanism linking NMDA receptor activation to neuronal Abeta secretion. These results suggest that even mild deregulation of the glutamatergic neurotransmission may increase Abeta production and represent a causal risk factor for developing AD.

Binge drinking in midlife and dementia risk

BACKGROUND

Studies examining the long-term effects of alcohol consumption on cognitive functioning have produced conflicting results. Our goal was to determine whether a long follow-up period combined with information about drinking patterns, in addition to total alcohol consumption, would provide new insights about the relationship of alcohol use with dementia risk.

METHODS

A population-based cohort of 554 Finnish twins, who had provided data on alcohol consumption in questionnaires in 1975 and 1981, was followed for 25 years. Subjects were age 65 years or older at the time of dementia assessment in 1999-2001. Dementia risk was analyzed with respect to varying patterns of alcohol use by log-linear modeling, adjusted for age, sex, and education.

RESULTS

By the end of follow-up, 103 participants had developed dementia. Binge drinking (ie, alcohol exceeding the amount of 5 bottles of beer or a bottle of wine on 1 occasion at least monthly), as reported in 1975, was associated with a relative risk of 3.2 (95% confidence interval=1.2-8.6) for dementia. Passing out at least twice as a result of excessive alcohol use during the previous year, as reported in 1981, was associated with a relative risk of 10.5 (2.4-46) for dementia in drinkers.

CONCLUSIONS

Binge drinking in midlife is associated with an increased risk of dementia.

Morris water maze search strategy analysis in PDAPP mice before and after experimental traumatic brain injury

Traumatic brain injury (TBI) is a common cause of cognitive dysfunction and a major risk factor for Alzheimer's disease (AD). PDAPP mice, a transgenic line overexpressing a mutant human amyloid precursor protein (APP) implicated in familial AD, have markedly impaired behavioral performance in the Morris water maze relative to wild-type (WT) littermates. Performance further deteriorates following experimental TBI in both PDAPP and WT mice. However, the aspects of cognitive function involved are not well understood. Here, we have analyzed search strategies used in the water maze by 3-4 month old PDAPP and WT C57Bl6 littermates both before and after moderate controlled cortical impact TBI. Prior to TBI, PDAPP mice used less spatial strategies and more nonspatial systematic strategies and strategies involving repetitive looping than WT mice. With training, PDAPP mice used more spatial strategies and less repetitive looping. After TBI, PDAPP mice lost use of spatial strategies and relied more on repetitive looping. TBI in WT mice also reduced their use of spatial strategies but instead caused a switch to nonspatial systematic strategies. We also analyzed changes in the efficiency with which mice used each individual strategy, but found that differences in which strategies were used quantitatively accounted for most of the differences in performance between groups. These results demonstrate that suboptimal search strategy use in addition to effects on spatial learning and memory underlies the impaired performance of PDAPP mice and further deterioration following TBI. Human TBI patients may have analogous poor use of problem solving strategies.

Caspase inhibition therapy abolishes brain trauma-induced increases in Abeta peptide: implications for clinical outcome

The detrimental effects of traumatic brain injury (TBI) on brain tissue integrity involve progressive axonal damage, necrotic cell loss, and both acute and delayed apoptotic neuronal death due to activation of caspases. Post-injury accumulation of amyloid precursor protein (APP) and its toxic metabolite amyloid-beta peptide (Abeta) has been implicated in apoptosis as well as in increasing the risk for developing Alzheimer's disease (AD) after TBI. Activated caspases proteolyze APP and are associated with increased Abeta production after neuronal injury. Conversely, Abeta and related APP/Abeta fragments stimulate caspase activation, creating a potential vicious cycle of secondary injury after TBI. Blockade of caspase activation after brain injury suppresses apoptosis and improves neurological outcome, but it is not known whether such intervention also prevents increases in Abeta levels in vivo. The present study examined the effect of caspase inhibition on post-injury levels of soluble Abeta, APP, activated caspase-3, and caspase-cleaved APP in the hippocampus of nontransgenic mice expressing human Abeta, subjected to controlled cortical injury (CCI). CCI produced brain tissue damage with cell loss and elevated levels of activated caspase-3, Abeta(1-42) and Abeta(1-40), APP, and caspase-cleaved APP fragments in hippocampal neurons and axons. Post-CCI intervention with intracerebroventricular injection of 100 nM Boc-Asp(OMe)-CH(2)F (BAF, a pan-caspase inhibitor) significantly reduced caspase-3 activation and improved histological outcome, suppressed increases in Abeta and caspase-cleaved APP, but showed no significant effect on overall APP levels in the hippocampus after CCI. These data demonstrate that after TBI, caspase inhibition can suppress elevations in Abeta. The extent to which Abeta suppression contributes to improved outcome following inhibition of caspases after TBI is unclear, but such intervention may be a valuable therapeutic strategy for preventing the long-term evolution of Abeta-mediated pathology in TBI patients who are at risk for developing AD later in life.

Cognitive impairment in preclinical Alzheimer's disease: a meta-analysis

To determine the size of the impairment across different cognitive domains in preclinical Alzheimer's disease (AD), a meta-analysis based on 47 studies involving 9,097 controls and 1,207 preclinical AD cases was conducted. There were marked preclinical deficits in global cognitive ability, episodic memory, perceptual speed, and executive functioning; somewhat smaller deficits in verbal ability, visuospatial skill, and attention; and no preclinical impairment in primary memory. Younger age (< 75 years) and shorter follow-up intervals (< 3 years) were associated with larger effect sizes for both global cognitive ability and episodic memory. For global cognitive ability, studies that used population-based sampling yielded larger effect sizes; for episodic memory, larger differences were seen in studies that preidentified groups in terms of baseline cognitive impairment. Within episodic memory, delayed testing and recall-based assessment resulted in the largest effect sizes. The authors conclude that deficits in multiple cognitive domains are characteristic of AD several years before clinical diagnosis. The generalized nature of the deficit is consistent with recent observations that multiple brain structures and functions are affected long before the AD diagnosis.

The Aging, Demographics, and Memory Study: Study Design and Methods

OBJECTIVE

We describe the design and methods of the Aging, Demographics, and Memory Study (ADAMS), a new national study that will provide data on the antecedents, prevalence, outcomes, and costs of dementia and "cognitive impairment, not demented" (CIND) using a unique study design based on the nationally representative Health and Retirement Study (HRS). We also illustrate potential uses of the ADAMS data and provide information to interested researchers on obtaining ADAMS and HRS data.

METHODS

The ADAMS is the first population-based study of dementia in the United States to include subjects from all regions of the country, while at the same time using a single standardized diagnostic protocol in a community-based sample. A sample of 856 individuals age 70 or older who were participants in the ongoing HRS received an extensive in-home clinical and neuropsychological assessment to determine a diagnosis of normal, CIND, or dementia. Within the CIND and dementia categories, subcategories (e.g. Alzheimer's disease, vascular dementia) were assigned to denote the etiology of cognitive impairment.

CONCLUSION

Linking the ADAMS dementia clinical assessment data to the wealth of available longitudinal HRS data on health, health care utilization, informal care, and economic resources and behavior, will provide a unique opportunity to study the onset of CIND and dementia in a nationally representative population-based sample, as well as the risk factors, prevalence, outcomes, and costs of CIND and dementia.

Associations Between Dementia/Mild Cognitive Impairment and Cognitive Performance and Activity Levels in Youth

OBJECTIVES

To study the associations between dementia/mild cognitive impairment (MCI) and cognitive performance and activity levels in youth.

DESIGN

Retrospective cohort study.

SETTING

Research volunteers living throughout the United States.

PARTICIPANTS

A total of 396 persons (mean age 75) who were graduates of the same high school in the mid-1940s.

MEASUREMENTS

Adolescent intelligence quotient (IQ) scores were gathered from archived student records, and activity levels were determined from yearbooks. A two-stage telephone screening procedure (Modified Telephone Interview for Cognitive Status or Informant Questionnaire on Cognitive Decline in the Elderly followed by Dementia Questionnaire) was used to determine adult cognitive status. Data were analyzed using logistic regression to model the risk of cognitive impairment (dementia/MCI) versus no cognitive impairment as a function of IQ and activity level, adjusting for sex and education.

RESULTS

High adolescent IQ and greater activity level were each independently associated with a lower risk for dementia/MCI (odds ratio (OR) for a 1-standard deviation increase in IQ=0.51, 95% confidence interval (CI)=0.32-0.79; OR for a unit increase in activity=0.32, 95% CI=0.12-0.84). No association was found between sex or education and adult cognitive status in this model.

CONCLUSION

High IQ and greater activity levels in youth reduce the risk for cognitive impairments in aging. The mechanism(s) underlying these associations are unknown, but intelligence may be a marker for cognitive/neurological "reserve," and involvement in activities may contribute to "reserve." Early neuropathology and ascertainment bias are also possible explanations for the observed associations.

Traumatic brain injury: cause or risk of Alzheimer's disease? A review of experimental studies

Traumatic Brain Injury is the leading cause of death and disability among young individuals in our society. Moreover, according to some epidemiological studies, head trauma is one of the most potent environmental risk factors for subsequent development of Alzheimer's disease. Interestingly, pathological features that are present also in Alzheimer's disease (in particular deposition of beta-amyloid protein) were observed in traumatised brains already a few hours after the initial insult. The primary objective of this review is to present methodology and results of numerous recent human and animal studies dealing with this issue. Special emphasis was placed on head trauma experiments in transgenic mouse models of Alzheimer's disease. We further evaluate the connection between traumatic brain insults and subsequent development of dementia and try to differentiate between primary and secondary pathological mechanisms.

Head injury and dementia

PURPOSE OF REVIEW

The link between head injury and dementia/Alzheimer's disease is controversial. This review discusses some recent epidemiological, human autopsy and experimental studies on the relationship between traumatic head injury and dementia.

RECENT FINDINGS

Recent epidemiological studies have shown that head injury is a risk factor for the development of dementia/Alzheimer's disease, whereas others have not. After experimental brain trauma the long-term accumulation of amyloid beta peptide suggests that neurodegeneration is influenced by apolipoprotein E epsilon 4, and after human brain injury both amyloid beta peptide deposition and tau pathology are seen, even in younger patients. Amyloid beta peptide levels in the cerebrospinal fluid and the overproduction of beta amyloid precursor protein in humans and animals after traumatic brain injury are increased. Repeated mild head trauma in both animals and humans accelerates amyloid beta peptide accumulation and cognitive impairment. Retrospective autopsy data support clinical studies suggesting that severe traumatic brain injury with long-lasting morphological residuals are a risk factor for the development of dementia/Alzheimer's disease. The influence of the apolipoprotein E genotype on the prognosis of traumatic brain injury is under discussion.

SUMMARY

Although epidemiological studies and retrospective autopsy data provide evidence that a later cognitive decline may occur after severe traumatic brain injury, the relationship between dementia after head/brain trauma and apolipoprotein E status is still ambiguous. Both human postmortem and experimental studies showing apolipoprotein beta deposition and tau pathology after head injury support the link between traumatic brain injury and dementia, and further studies are warranted to clarify this relationship.

Fall-related brain injuries and the risk of dementia in elderly people: a population-based study

Severe head injury in early adulthood may increase the risk of dementia in older age, but it is not known whether head injury in later life also increases the risk of dementia. A representative sample (82%) of persons aged 70 years or older with a Mini-Mental State Examination (MMSE) test score of > or =26 (n = 325) were followed-up for 9 years to record all their fall-related head injuries resulting in traumatic brain injury (TBI). At the end of the follow-up period, 152 persons (81% of the surviving population) were examined for clinical dementia, according to DSM-IV criteria. Eight persons sustained a TBI and 34 developed dementia. Brain injury was associated with younger age at detection of dementia even when adjusted for sex and educational status (low educational status significantly associated with dementia); age-specific hazard ratio (95% confidence interval) 2.80 (1.35-5.81). In a population scoring > or =28 points in the baseline MMSE an apolipoprotein E (ApoE) epsilon4 phenotype was also associated with younger age at the time of detecting dementia; 3.56 (1.35-9.34), and the effect of brain injury and ApoE epsilon4 phenotype was synergistic; 7.68 (2.32-25.3). We conclude that fall-related TBI predicts earlier onset of dementia and the effect is especially high amongst subjects who carry the ApoE epsilon4 allele.

The impact of age on traumatic brain injury

Older individuals with TBI differ from younger adults with TBI in several ways, including their incidence rates, etiology of injury, nature of complications, lengths of hospitalization, functional outcomes, and mortality. Despite the greater likelihood of poorer functional outcomes, older adults with TBI often achieve good functional outcomes and can live in community settings after receiving appropriate rehabilitation services, although at higher costs and longer hospitalizations than younger individuals. The future of rehabilitation care for elderly patients after TBI is uncertain due to financial limitations associated with the implementation of the PPS payment system by CMS. Little is known regarding the long-term impact of TBI on individuals as they age, but this is an important issue as the population ages.

Alzheimer's pathology in human temporal cortex surgically excised after severe brain injury

Traumatic brain injury (TBI) is a risk factor for the development of Alzheimer's disease (AD). This immunohistochemical study determined the extent of AD-related changes in temporal cortex resected from individuals treated surgically for severe TBI. Antisera generated against Abeta species (total Abeta, Abeta(1-42), and Abeta(1-40)), the C-terminal of the Abeta precursor protein (APP), apolipoprotein E (apoE), and markers of neuron structure and degeneration (tau, ubiquitin, alpha-, beta-, and gamma-synuclein) were used to examine the extent of Abeta plaque deposition and neurodegenerative changes in 18 TBI subjects (ages 18-64 years). Diffuse cortical Abeta deposits were observed in one third of subjects (aged 35-62 years) as early as 2 h after injury, with only one (35-year old) individual exhibiting "mature", dense-cored plaques. Plaque-like deposits, neurons, glia, and axonal changes were also immunostained with APP and apoE antibodies. In plaque-positive cases, the only statistically significant change in cellular immunostaining was increased neuronal APP (P = 0.013). There was no significant correlation between the distribution of Abeta plaques and markers of neuronal degeneration. Diffuse tau immunostaining was localized to neuronal cell soma, axons or glial cells in a larger subset of individuals. Tau-positive, neurofibrillary tangle (NFT)-like changes were detected in only two subjects, both of more advanced age and who were without Abeta deposits. Other neurodegenerative changes, evidenced by ubiquitin- and synuclein-immunoreactive neurons, were abundant in the majority of cases. Our results demonstrate a differential distribution and course of intra- and extra-cellular AD-like changes during the acute phase following severe TBI in humans. Abeta plaques and early evidence of neuronal degenerative changes can develop rapidly after TBI, while fully developed NFTs most likely result from more chronic disease- or injury-related processes. These observations lend further support to the hypothesis that head trauma significantly increases the risk of developing pathological and clinical symptoms of AD, and provide insight into the molecular mechanisms that initiate these pathological cascades very early during severe brain injury.

A community survey demonstrated cohort differences in the lifetime prevalence of self-reported head injury

OBJECTIVE

The objective of the study was to assess the lifetime prevalence and validity of self-reported head injury.

STUDY DESIGN AND SETTING

Analysis of a cross-sectional community survey, stratified by birth cohort. Seven thousand four hundred eighty-eight residents of Canberra and Queanbeyan, 3,678 males and 3,810 females, representing three cohorts aged in their 20s, 40s and 60s at the time of the survey, were randomly selected from the Australian Electoral Roll.

RESULTS

The lifetime prevalence of head injury with at least 15 min loss of consciousness ranged from 5.6 to 6.0% across the three cohorts. Self-reported head injury was associated with symptoms of traumatic brain injury or postconcussion syndrome. Reported head injury did not differ across the birth cohorts, contrary to expectations that prevalence rates would increase with age. Analysis of age at first head injury showed significant differences between cohorts in the reported prevalence at age 20, with estimates considerably higher for the youngest cohort.

CONCLUSION

Although the data may reflect real increases in the risk of head injury, it may be that self-reported measures of lifetime prevalence of head injury underestimate prevalence in older cohorts.

Methodology and preliminary results from the neurocognitive outcomes of depression in the elderly study

A methodology is presented for following a cohort of older depressed patients to examine neurocognitive outcomes of depression. A total of 265 depressed individuals and 138 healthy, nondepressed controls age 60 and older who completed at least 1 year of follow-up data underwent periodic clinical evaluation by a geriatric psychiatrist. A subset of 141 patients and 137 controls had neuropsychological testing. A consensus panel of experts reviewed 63 depressed subjects with suspected cognitive impairment. Twenty-seven individuals in the depressed group were assigned diagnoses of dementia, including 11 with Alzheimer's disease, 8 with vascular dementia, and 8 with dementia of undetermined etiology. In addition, 25 individuals had other forms of cognitive impairment, and 11 were considered cognitively normal. Among elderly controls, 2 developed substantial cognitive impairment with clinical diagnoses of dementia. Among the depressed group, the incidence rates for dementia for this age are much higher than would be expected. These results are consistent with prior evidence linking depression and later dementia. Future studies are needed to examine neuroimaging and genetic, clinical, and social predictors of neurocognitive decline in depression.

Neuropsychological results and neuropathological findings at autopsy in a case of mild traumatic brain injury

Autopsy studies were undertaken in a 47-year-old college-educated male patient who, 7 months prior to an unexpected death, had sustained a mild traumatic brain injury (TBI) as manifested by brief loss of consciousness and an initial Glasgow Coma Scale score of 14. The patient died from cardiac arrest secondary to an undiagnosed and unknown arteriosclerotic cardiovascular disease as assessed by the coroners office at the time of autopsy. Gross inspection of the brain at autopsy was normal; however, microscopic analysis demonstrated what were considered trauma findings of hemosiderin-laden macrophages in the perivascular space and macrophages in the white matter, particularly the section taken from the frontal lobe. The patient had partially returned to work at the time of death, but had encountered problems with diminished cognitive performance in his work as an appraiser. Neuropsychological studies were generally within normal limits although several tests of either speed of processing or short-term memory showed lower than expected performance. This case demonstrates the presence of subtle neuropathological changes in the brain of a patient who sustained a mild TBI and was still symptomatic for the residual effects of the injury 7 months post injury when he unexpectedly died.

Multiple cognitive deficits during the transition to Alzheimer's disease

The literature on cognitive markers in preclinical AD is reviewed. The findings demonstrate that impairment in multiple cognitive domains is typically observed several years before clinical diagnosis. Measures of executive functioning, episodic memory and perceptual speed appear to be most effective at identifying at-risk individuals. The fact that these cognitive domains are most implicated in normal cognitive aging suggests that the cognitive deficit observed preclinically is not qualitatively different from that observed in normal aging. The degree of cognitive impairment prior to the diagnosis of Alzheimer's disease (AD) appears to generalize relatively well across major study characteristics, including sample ascertainment procedures, age and cognitive status of participants, as well as time to diagnosis of dementia. In episodic memory, there is evidence that the size of the preclinical deficit increases with increasing cognitive demands. The global cognitive impairment observed is highly consistent with observations that multiple brain structures and functions are affected long before the diagnosis of AD. However, there is substantial overlap in the distribution of cognitive scores between those who will and those who will not be diagnosed with AD, hence limiting the clinical utility of cognitive markers for early identification of cases. Future research should consider combining cognitive indicators with other types of markers (i.e. social, somatic, genetic, brain-based) in order to increase prediction accuracy.

Long-term accumulation of amyloid-beta, beta-secretase, presenilin-1, and caspase-3 in damaged axons following brain trauma

Plaques composed of amyloid beta (Abeta) have been found within days following brain trauma in humans, similar to the hallmark plaque pathology of Alzheimer's disease (AD). Here, we evaluated the potential source of this Abeta and long-term mechanisms that could lead to its production. Inertial brain injury was induced in pigs via head rotational acceleration of 110 degrees over 20 ms in the coronal plane. Animals were euthanized at 3 hours, 3 days, 7 days, and 6 months post-injury. Immunohistochemistry and Western blot analyses of the brains were performed using antibodies specific for amyloid precursor protein (APP), Abeta peptides, beta-site APP-cleaving enzyme (BACE), presenilin-1 (PS-1), caspase-3, and caspase-mediated cleavage of APP (CCA). Substantial co-accumulation for all of these factors was found in swollen axons at all time points up to 6 months following injury. Western blot analysis of injured brains confirmed a substantial increase in the protein levels of these factors, particularly in the white matter. These data suggest that impaired axonal transport due to trauma induces long-term pathological co-accumulation of APP with BACE, PS-1, and activated caspase. The abnormal concentration of these factors may lead to APP proteolysis and Abeta formation within the axonal membrane compartment.

Genetic aspects of Alzheimer's disease, Pick's disease, and other dementias

Although genetic testing is available for some degenerative diseases, in most types of dementia, both genetic and environmental factors are involved. Overall, dementing diseases can be either sporadic or inherited, and in general, the earlier the onset, the more likely a disease is to be inherited. Before genetic testing is performed, the ethical issues, such as the effect the tests might have on asymptomatic children, should be considered. The ethical use of DNA samples in research is another genetic testing issue to be considered.

Can dementia be prevented? Brain aging in a population-based context

As a consequence of global aging of the human population, the occurrence of cognitive impairment and dementia is rapidly becoming a significant burden for medical care and public health systems. By the year 2020, the WHO predicts there will be nearly 29 million demented people in both developed and developing countries. Primary and secondary prevention of dementia through individual and population-level interventions could reduce this imminent risk. Vascular risk factors such as type 2 diabetes, hypertension, dietary fat intake, high cholesterol, and obesity have emerged as important influences on the risk of both vascular and Alzheimer's dementia. Understanding the reasons for differences between populations in genetic vulnerability and environmental exposures may help to identify modifiable risk factors that may lead to effective prevention of vascular and Alzheimer's dementia.

Bicycle helmets — does the dental profession have a role in promoting their use?

OBJECTIVES

To review the available literature regarding the: epidemiology of bicycle related head injuries; consequences of head injuries; rates of cycle helmet use; impact of educational campaigns and legislation on usage rates; effectiveness of cycle helmets in protecting against head and facial injuries; arguments against the compulsory use of bicycle helmets.

DATA SOURCES

A computerised Medline search was conducted using the keywords: head injury, facial injury, bicycle helmets, accidents.

DATA SELECTION

All available information was considered.

DATA SYNTHESIS

Data was collated manually.

CONCLUSIONS

The wearing of bicycle helmets contributes significantly to the prevention of head injuries (HI) and traumatic brain injury (TBI), particularly in children and adolescents. There is evidence to support the role of cycle helmets in the prevention of injuries to the middle third of the face and some dental injuries. There is a case for the implementation of legislation accompanied by educational campaigns to increase significantly the use of cycle helmets. The dental profession could: play an active role in promoting cycle helmet use; support calls for the compulsory wearing of cycling helmets, particularly for children; press for modification of helmet design and standards to increase protection of the face.