Constructional apraxia in Alzheimer's disease correlates with neuritic neuropathology in occipital cortex

A variety of measures of neuropathology in Alzheimer's disease (AD) correlate with dementia severity. However, the role of beta-amyloid protein and abnormally phosphorylated tau protein in the decline of specific cognitive abilities is unknown. "Constructional praxis' (e.g., copying, constructing) is believed to require integrity of the parietal-occipital lobes. Unlike most other cognitive tasks, some AD patients are able to perform some constructional tasks even late in the disease course. Thus, it may be an ideal task to evaluate the relationship between various measures of AD neuropathology and cognitive performance. Fixed brain tissue was obtained from 16 AD patients who were cognitively assessed shortly before death. Parietal, frontal, entorhinal, and occipital cortices were examined by immunocytochemistry for beta-amyloid protein and abnormally phosphorylated tau protein at both early and later stages of neuropil thread and tangle formation. Constructional praxis in AD was strongly related to early-stage tau hyperphosphorylation in occipital cortex. Praxis ability was specific in that it was not significantly related to pathology in other areas and non-constructive tasks were not associated with occipital cortex pathology. In contrast, global dementia severity was related to beta-amyloid deposition in entorhinal, parietal, and frontal regions. These findings suggest that occipital cortex is critical for some constructional praxis tasks and that some regionally localizable tasks may be good indices of underlying pathology in corresponding brain regions.

Alzheimer-associated presenilin-2 confers increased sensitivity to apoptosis in PC12 cells

Presenilin-2 is a gene of unknown function recently identified based upon linkage with some forms of familial Alzheimer's disease. To investigate potential effects of PS-2 on cell viability, rat pheochromocytoma (PC12) cells were stably transfected with cDNA constructs encoding either full-length human PS-2 or, for comparison, mouse Bcl-X(L). Overexpression of PS-2 conferred increased sensitivity to the apoptotic stimuli staurosporine and hydrogen peroxide. In contrast, Bcl-X(L) overexpression significantly reduced cell death induced by these stimuli. These results suggest that one function of PS-2 may involve modulation of cell viability.

Plaque biogenesis in brain aging and Alzheimer's disease. I. Progressive changes in phosphorylation states of paired helical filaments and neurofilaments

Paired helical filament (PHF)/tau immunoreactive dystrophic neurites are a common pathological feature in the brain of patients with Alzheimer's disease. Recent studies suggest that swollen neurofilament-immunoreactive neurites are also present in senile plaques. In the present study, we investigated whether PHF/tau-positive dystrophic neurites are located in all subtypes of plaques and whether swollen neurofilament-immunoreactive neurites are hyper-phosphorylated, using a battery of antibodies to PHF/tau, neurofilament, and beta-amyloid protein. PHF/tau-positive dystrophic neurites were present in and around nearly all subtypes of plaques, including small amyloid deposits, diffuse plaques, and perivascular plaques in the hippocampal formation of Alzheimer brain. The earlier changes were detectable with AT8 antibody and later changes with PHF-1 antibody. Plaque-associated PHF/tau-positive dystrophic neurites were rare or absent in the hippocampal formation of normal aged brain. Swollen neurofilament-positive neurites appeared to be hyper-phosphorylated in Alzheimer's disease and to a lesser degree in aged control brains. Neurites that contained hyper-phosphorylated tau as well as neurofilament were strongly argentophilic because both populations of dystrophic neurites stained with silver stains. Swollen neurofilament-positive plaque-associated neurites were often present in the absence of PHF/tau-positive plaque-associated dystrophic neurites. These data suggest that PHF/tau-positive dystrophic neurites are a common component of all subtypes of plaques in Alzheimer brain and neurofilament protein in swollen neurites, like tau protein, is hyper-phosphorylated. Hyper-phosphorylated neurofilaments in plaque-associated neurites may represent one of the earliest cytoskeletal changes in vulnerable neurons in Alzheimer's disease and aged control brains.

Beta-amyloid deposition and other measures of neuropathology predict cognitive status in Alzheimer's disease

The relationship between progressive cognitive decline and underlying neuropathology associated with Alzheimer s disease (AD) is a key issue in defining the mechanisms responsible for functional loss. This has been a subject of much controversy, with separate studies comparing various clinical and neuropathological indices in AD. Further, it is difficult to compare studies with differences in histochemical staining protocols, brain regions examined, and data quantification criteria. There are many difficulties in designing a clinical-pathological correlative study involving AD patients. It is necessary to control for several key parameters. For example, a broad range of cognitively impaired subjects is needed, as well as short postmortem delays, brief intervals between cognitive testing and death, and the most sensitive detection and quantification techniques. In this study, we carefully controlled for each of these parameters to determine if there is a relationship between global cognitive dysfunction and multiple neuropathological indices. We selected 20 individuals representing a broad range of cognitive ability from normal to severely impaired based on the MMSE, Blessed IMC, and CDR. We counted plaque number, NFT number, dystrophic neurite number, and the relative extent of thioflavine positive plaques and neuritic involvement within plaques. We also quantified cortical area occupied by beta-amyloid immunoreactivity (A beta Load) and PHF-1 positive neuropil threads and tangles (PHF Load) using computer-based image analysis. Interestingly, we found that most pathologic measures correlated highly with the severity of dementia. However, the strongest predictor of premortem cognitive dysfunction on all three cognitive measures was the relative area of entorhinal cortex occupied by beta-amyloid deposition. In conclusion, our data show that in a carefully controlled correlative study, a variety of neuropathological variables are strongly correlated with cognitive impairment. Plaque related variables may be as strongly related to cognitive dysfunction as other established measures, including synapse loss, cell death and tau hyperphosphorylation, although no correlative study can demonstrate causality.

Cross-linking of concanavalin A receptors on cortical neurons induces programmed cell death

The loss of neurons by programmed cell death is a normal feature of the nervous system during development and has recently been implicated as a major mechanism of cell death in neurodegenerative diseases. In some cases, programmed cell death is induced by the activation of membrane receptors and is referred to as activation-induced programmed cell death. Activation-induced programmed cell death has been previously described in cells from the immune system, in which the activation of receptors by receptor clustering leads to programmed cell death. To determine whether activation-induced programmed cell death occurs in neurons, Concanavalin A was used to cross-link membrane receptors on cortical neurons. Concanavalin A-induced neuronal death was dose dependent and effective at concentrations previously shown to induce activation-induced programmed cell death in lymphocytes. Programmed cell death was attenuated when Concanavalin A-specific binding to neurons was blocked with methyl alpha-D-mannopyranoside. Succinyl Concanavalin A, which bound to Concanavalin A receptors but was ineffective at cross-linking them, did not induce programmed cell death. Concanavalin A-induced neuronal death exhibited many of the hallmarks associated with programmed cell death, such as membrane blebbing, nuclear condensation and margination, and internucleosomal DNA cleavage. In addition, neurons exposed to Concanavalin A displayed a rapid, robust, and persistent increase in the immediate early gene protein c-Jun. A similar increase in c-Jun precedes programmed cell death induced by beta-amyloid in neurons, and under some conditions an increase in c-Jun has been shown to be required for programmed cell death to occur in neurons. Increased expression of c-jun and other immediate early genes has also been correlated with activation-induced programmed cell death in lymphocytes. These observations suggest that Concanavalin A induces activation-induced programmed cell death in neurons via signals produced from the cross-linking of receptors on neuronal membranes. These results also raise the possibility that beta-amyloid induces programmed cell death in a similar manner, by causing the cross-linking of receptors on neuronal membranes. This mechanism may be relevant to neuronal programmed cell death that occurs during development and neurodegeneration.

Mechanisms of neuronal death in Alzheimer's disease

Recent data in cell culture has shown that brain neurons are particularly vulnerable to degeneration by apoptosis. Further the inducers that activate the program (e.g. beta-amyloid, oxidatative damage, low energy metabolism) correspond to conditions present in the Alzheimer's disease (AD) brain. This suggests the possibility that apoptosis may be one of the mechanisms contributing to neuronal loss in this disease. Indeed, some neurons in vulnerable regions of the AD brain show evidence of DNA damage, nuclear apoptotic bodies, chromatin condensation, and the induction of select genes characteristic of apoptosis in cell culture and animal models. This suggests the existence of apoptosis in the AD brain, a hypothesis also consistent with evolving research in one of the regulatory functions of the presenilin genes. On the other hand, DNA damage is present in the majority of neurons in vulnerable regions in early and mild cases. In most tissues, cells in fully activated apoptosis degenerate and are removed within hours to days and thus it seems all DNA damage is unlikely to signify terminal apoptosis. The presence of extensive DNA damage suggests an acceleration of damage, faulty repair process, loss of protective mechanisms, or an activation and arrest of aspects of the apoptotic program. DNA damage is unlikely to be an artifact of postmortem delay or agonal state. The existence of protective mechanisms for neurons may exist as these cells are nondividing and essential. In this context it is interesting that Bcl-2 is upregulated in most neurons with DNA damage. Further, at least one DNA repair enzyme is also upregulated. Thus it appears as if neurons are in a struggle between degeneration and repair. As research advances it is critical to reduce the stimuli that cause the neuronal damage and discover the key intervention points to assist neurons in the repair processes.

Attenuation of beta-amyloid neurotoxicity in vitro by potassium-induced depolarization

The cell death of cultured neurons triggered by beta-amyloid peptides has been theorized to model, at least in part, the neurodegeneration associated with Alzheimer's disease. To investigate potential strategies to interrupt beta-amyloid neurotoxicity in vitro, we examined the effects of potassium-induced membrane depolarization, a treatment previously demonstrated to reduce development-related apoptosis in cultured neurons. We report here that cultured rat hippocampal neurons pretreated for several hours with 30 mM KCl exhibit significantly reduced vulnerability to aggregated beta-amyloid peptides. The potassium-mediated neuroprotection was mimicked by activation of voltage-sensitive calcium channels using S(-)-Bay K8644 and was attenuated by R(+)-Bay K 8644, a blocker of voltage-dependent calcium channels, and KN-82, an inhibitor of calcium/calmodulin-dependent protein kinase II. The protein synthesis inhibitor cycloheximide also attenuated beta-amyloid neurotoxicity. Addition of cycloheximide following 30 mM KCl significantly increased protection offered by membrane depolarization, whereas cycloheximide addition during membrane depolarization blocked the protective effect. These data suggest that one cellular pathway that can inhibit neuronal death induced by beta-amyloid involves calcium influx through voltage-sensitive channels followed by stimulation of calcium/calmodulin-dependent protein kinase activity and synthesis of new protein(s).

Exposure of astrocytes to thrombin reduces levels of the metabotropic glutamate receptor mGluR5

Thrombin is one of the first regulatory molecules present at sites of CNS trauma or injury. Exposure of neuronal and glial cells to thrombin produces potent morphological as well as cytoprotective and cytotoxic effects, but little is known about how this important modulator affects neurotransmitter signaling. In astrocyte cultures that have been morphologically differentiated by exposure to transforming growth factor-alpha, addition of thrombin induced a retraction of astrocytic processes and suppressed the stimulation of phosphoinositide hydrolysis by the selective metabotropic glutamate receptor (mGluR) agonist 1-aminocyclopentane-1S,3R-dicarboxylic acid. In addition to the suppression of phosphoinositide hydrolysis, thrombin treatment produced a corresponding reduction in level of mGluR5 mRNA as demonstrated with ribonuclease protection assay and reduced content of mGluR5 receptor protein as seen with western blotting. In contrast, thrombin exposure up-regulated astrocyte beta-actin mRNA levels. A synthetic hexapeptide with a sequence corresponding to the amino-terminus of the thrombin receptor's tethered ligand also mimicked the ability of thrombin to suppress mGluR5 levels and to increase beta-actin mRNA content, suggesting that these effects of thrombin are mediated by proteolytically activated cell surface thrombin receptors. Thrombin's suppressive effect on mGluR5 was resistant to pretreatment with pertussis toxin or various protein kinase and protein phosphatase inhibitors. However, the serine/threonine protein kinase inhibitor H-7 did prevent thrombin-induced reversal of astrocyte stellation and induction of beta-actin mRNA levels, indicating that these effects of thrombin involve a signaling pathway distinct from the one that mediates the suppressive effects of thrombin on mGluR5.

Gene expression of Alzheimer-associated presenilin-2 in the frontal cortex of Alzheimer and aged control brain

The presenilin-2 (PS2) gene expression pattern in Alzheimer's disease (AD) and control brains was examined using nonradioactive in situ hybridization. Message for PS2 was primarily detectable in neurons, particularly in somal cytoplasm. Intense staining signal was most commonly found in large pyramidal neurons, whereas moderate or faint staining was usually present in smaller neurons. The pattern of PS2 gene expression exhibited a laminar distribution profile in the frontal cortex. A small subset of tangle-bearing neurons exhibited PS2 hybridization signal in AD. PS2 mRNA expression appeared correlated to a high degree with lipofuscin autofluorescence in a large subset of neurons.

beta-Amyloid converts an acute phase injury response to chronic injury responses

As the brain ages, amyloid deposits accumulate and, as these deposits condense into a beta-sheet conformation, they contribute to the organization of cellular responses and maintain a chronic level of stimulation and injury. Furthermore, accompanying reactions can lead to the production of additional beta-amyloid, the build up of additional fibrillar beta-amyloid, and prolongation of the response. As it accumulates, beta-amyloid appears to develop properties that drive many signal transduction processes in the classic injury cascade and also activate complement, which results in an amplified beta-amyloid AD cascade. In this way several mechanisms, although apparently independent, proceed in parallel, reinforce each other, and perpetuate pathology and structural damage to the brain. Specifically, we suggest that via the activation of complement, initiation, and perpetuation of other cascades, and its own direct toxic actions, beta-amyloid converts an acute response to injury into a chronic damaging inflammatory reaction thereby contributing to neuronal dysfunction and degeneration.

Apolipoprotein-E genotyping of diabetic dementia patients: is diabetes rare in Alzheimer's disease?

OBJECTIVES

To determine whether diabetes is rare in Alzheimer disease (AD) relative to other types of dementia and whether diabetics with dementia have a low frequency of the Apolipoprotein-E E4 genotype.

DESIGN

Observational survey study.

SETTING

An Irvine, California, outpatient dementia assessment center.

PARTICIPANTS

A total of 123 patients with AD, 51 with vascular dementia, 57 with "mixed" vascular dementia and AD, and 34 with "other" dementias (non-vascular non-AD).

MEASUREMENTS

Demographic data; histories and evidence of diabetes, hypertension, heart disease, stroke; and Apolipoprotein-E genotype for 95 cases distributed across the groups.

RESULTS

There were 15 diabetics in the sample (5.7%), all of whom had extensive vascular disease. Diabetes was rare in AD patients (0.8%) relative to vascular dementia (11.8%), mixed vascular/AD dementia (8.8%), and "other" dementia patients (8.8%). In addition, the E4 allele of apolipoprotein-E, associated with high risk for AD, was frequent in the AD group (71.4%), but in the diabetic group it was only as frequent as in the general population (38.5%). In the diabetics with E4, 60% (3/5) had mixed dementia.

CONCLUSIONS

Diabetics with dementia rarely have AD except as a component of mixed dementia. Apo-E genotyping showed only average E4 allele frequency in diabetics compared with the high E4 frequency found in AD patients. However, mixed dementia in diabetics may be associated with the E4 allele, suggesting that close control of diabetes may be particularly important for those with E4 since they may be more likely than others to develop both diseases.

Dopaminergic denervation of striatum results in elevated expression of NR2A subunit

An imbalance between glutamate and dopamine in the striatum may contribute to the pathophysiology of Parkinson's disease. We therefore studied the effect of dopaminergic denervation of the rat striatum (unilateral 6-OHDA lesions of the medial forebrain bundle) on NMDA receptors. The expression of NMDA receptor genes (NR1, NR2A-B) was examined by in situ hybridization using oligonucleotide probes, and binding to NMDA receptors assessed using L-[3H]glutamate. Three weeks after lesioning, denervated striatum exhibited a selective increase (+13%) in the level of NR2A mRNA, NMDA receptor binding was unchanged. These results demonstrate that dopaminergic denervation exerts differential effects on NMDA receptor gene expression. Because the properties of NMDA receptors depend on the subunit composition, selective changes in the expression of mRNAs encoding the subunits may lead to modified NMDA receptor function.

Injury induces presenilin-1 gene expression in mouse brain

Information regarding the genetic factors and environmental conditions that influence presenilin-1 (PS-1) gene expression is essential for the elucidation of its pathophysiological role in Alzheimer's disease (AD). Previous in situ hybridization studies have demonstrated that neurons are the predominant cell type expressing PS-1 in the mammalian central nervous system (CNS) under physiological conditions. In this study, we examined the consequences of an experimentally induced focal injury on PS-1 gene expression in the mouse CNS. Physical lesions to white matter regions produced a robust increase in PS-1 gene expression in non-neuronal cells immediately surrounding the site of injury. These findings underscore the epidemiological evidence that implicate head injury as a risk factor for AD and suggest a possible role for PS-1 in this capacity.

Physical activity increases mRNA for brain-derived neurotrophic factor and nerve growth factor in rat brain

Brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) support the viability and function of many types of neurons, and are likely mediators of activity-dependent changes in the CNS. We examined BDNF and NGF mRNA levels in several brain areas of adult male rats following 0, 2, 4, or 7 nights with ad libitum access to running wheels. BDNF mRNA was significantly increased in several brain areas, most notably in the hippocampus and caudal 1/3 of cerebral cortex following 2, 4, and 7 nights with exercise. Significant elevations in BDNF mRNA were localized in Ammon's horn areas 1 (CA1) and 4 (CA4) of the hippocampus, and layers II-III of the caudal neocortex and retrosplenial cortex. NGF mRNA was also significantly elevated in the hippocampus and caudal 1/3 of the cortex, affecting primarily the dentate gyrus granular layer (DG) and CA4 of the hippocampus and layers II-III in caudal neocortex.

Beta-amyloid accumulation correlates with cognitive dysfunction in the aged canine

It is well known that beta-amyloid accumulates abnormally in Alzheimer's disease; however, beta-amyloid's relationship to cognitive dysfunction has not been clearly established and is often confounded by the presence of neurofibrillary tangles. We used canines to investigate the relationship between beta-amyloid accumulation and cognitive function in an animal model of aging lacking neurofibrillary tangles. The performance of 20 canines (11 purebred beagles and 9 mongrels) on a battery of six cognitive tasks was measured. These tasks included Reward Approach and Object Approach learning, as well as Discrimination, Reversal, Object Recognition, and Spatial learning and memory. Aged canines were impaired on some tasks but not others. beta-Amyloid-immunopositive plaques were found in many of the older animals. Plaques were all of the diffuse subtype and many contained intact neurons detected with double-labeling for neurofilaments. No neurofibrillary tangles were detected. beta-Amyloid was also associated with the processes of many neurons and with blood vessels. Using computerized image analysis, we quantified the area occupied by beta-amyloid in entorhinal cortex, frontal cortex, and cerebellum. Controlling for age-related increases in beta-amyloid, we observed that increased beta-amyloid deposition is strongly associated with deficits on Discrimination learning (r = .80), Reversal learning (r = .65), and Spatial learning (r = .54) but not the other tasks. There were a few differences between breeds which are discussed in the text. Overall, these data suggest that beta-amyloid deposition may be a contributing factor to age-related cognitive dysfunction prior to the onset of neurofibrillary tangle formation.

Diffuse plaques contain C-terminal A beta 42 and not A beta 40: evidence from cats and dogs

Recent reports have suggested that beta-amyloid (A beta) species of variable length C-termini are differentially deposited within early and late-stage plaques and the cerebrovasculature. Specifically, longer C-terminal length A beta 42/3 fragments (i.e., A beta forms extending to residues 42 and/or 43) are thought to be predominant within diffuse plaques while both A beta 42/3 and A beta 40 (A beta forms terminating at residue 40) are present within a subset of neuritic plaques and cerebrovascular deposits. We sought to clarify the issue of differential A beta deposition using aged canines, a partial animal model of Alzheimer's disease that exhibits extensive diffuse plaques and frequent vascular amyloid, but does not contain neuritic plaques or neurofibrillary tangles. We examined the brains of 20 aged canines, 3 aged felines, and 17 humans for the presence of A beta immunoreactive plaques, using antibodies to A beta 1(-17), A beta 17(-24), A beta 1(-28), A beta 40, and A beta 42. We report that plaques within the canine and feline brain are immunopositive for A beta 42 but not A beta 40. This is the first observation of nascent AD pathology in the aged feline brain. Canine plaques also contained epitopes within A beta 1(-17), A beta 17(-24), and A beta 1(-28). In all species examined, vascular deposits were immunopositive for both A beta 40 and A beta 42. In the human brain, diffuse plaques were preferentially A beta 42 immunopositive, while neuritic plaques and vascular deposits were both A beta 40 and A beta 42 immunopositive. However, not all neuritic plaques contain A beta 40 epitopes.

beta-Amyloid increases enzyme activity and protein levels of glutamine synthetase in cultured astrocytes

Previous studies have reported that beta-amyloid peptides induce properties of reactivity in cultured astrocytes. We report here that aggregated A beta peptides increase expression of the enzyme glutamine synthetase in cultured astrocytes, as assessed by enzyme assay, Western blot analysis, and immunocytochemistry. The enhanced enzyme levels occur gradually over a period of 4 days after A beta exposure and maintain peak values for at least several days thereafter. These data suggest that A beta-related reactive astrocytosis in Alzheimer's disease brain may benefit local neurons by enhancing glial capacity to regulate levels of the excitotoxin glutamate.

Thrombin attenuates neuronal cell death and modulates astrocyte reactivity induced by beta-amyloid in vitro

beta-Amyloid protein has been implicated as a potential causative agent in the neuropathology associated with Alzheimer's disease. This possibility is supported by observations that beta-amyloid induces neuronal degeneration and astrocyte reactivity in vitro by as yet undefined mechanism(s). In this report, we present data demonstrating that the pathological effects of beta-amyloid on cultured cells are modulated by activation of the thrombin receptor. At concentrations between 50 and 500 nM, thrombin pretreatment significantly attenuates neurotoxicity mediated by fibrillar aggregates of beta 1-42 and beta 25-35 peptides. In cultured astrocytes, the stellate morphology induced by beta 1-42 and beta 25-35 aggregates can be prevented and reversed by thrombin exposures between 10 pM and 1 microM. In contrast, thrombin potentiates rather than attenuates the beta-amyloid-induced increased expression of basic fibroblast growth factor, suggesting that thrombin differentially modulates the effects of beta-amyloid on astrocytes. Thrombin's effects on both neurons and astrocytes are mimicked by thrombin receptor-activating peptide and inhibited by two potent thrombin inhibitors, hirudin and protease nexin-1. These data provide both new insight into the signaling pathways underlying the cellular effects of beta-amyloid and additional support for the role of thrombin as an important mediator of neuropathological events.

The canine as an animal model of human aging and dementia

The aged canine displays many features that make it an excellent model for studying the progression of pathology in brain aging and linking these findings to learning, memory and other cognitive functions. Canines develop extensive beta-amyloid deposition within neurons and their synaptic fields, which appears to give rise to senile plaques. These plaques are primarily of the early diffuse subtype. Aged canines also exhibit accumulations of lipofuscin, cerebral vascular changes, dilation of the ventricles, and cytoskeletal changes. Neurofibrillary tangles (NFTs) are not present in the aged canine. Thus, the aged canine brain provides a suitable model for studying early degeneration normally considered to be pre-Alzheimer's. This supposition is also supported by behavioral data. We have found that the extent of beta-amyloid deposition correlates with a decline in select measures of cognitive function. These data provide the first evidence of a correlation between beta-amyloid accumulation and cognitive decline in the absence of NFTs. We summarize four lines of evidence that support using the aged canine as a model of human aging: (a) Aged canines develop aspects of neuropathology similar to that observed in aged humans; (b) Veterinarians have observed that many canines exhibit a clinical syndrome of age-related cognitive dysfunction; (c) Aged canines are deficient on a variety of neuropsychological tests of cognitive function; (d) The level of beta-amyloid accumulation correlates with cognitive dysfunction in the canine. These data indicate that the aged canine is a particularly useful model for studying age-related cognitive dysfunction (ARCD), early neuronal changes associated with aging, and the initial stages of senile plaque formation.

Localization and cell association of C1q in Alzheimer's disease brain

The complement protein, C1q, has been shown to bind to fibrillar beta-amyloid, resulting in the activation of the classical complement pathway. C1q has also been found associated with most but not all amyloid deposits in brain. To determine whether C1q is exclusively associated with plaques containing the fibrillar form of beta-amyloid, normal and Alzheimer brain were immunohistochemically double labeled using thioflavine, which specifically stains beta-amyloid in a beta-sheet conformation, and an affinity- purified antibody to human C1q. C1q immunostaining was colocalized with nearly all thioflavine-positive plaques, while C1q was not detected in beta-amyloid immunopositive plaques which were thioflavine-negative. Beta-amyloid plaques in nondemented controls (which are typically thioflavine-negative) were also negative for C1q. Microglia and astrocytes of reactive morphology were also associated with C1q-positive plaques and neurons. Interestingly, many neuronal cells in the AD brain, but not microglia or astrocytes, stained prominently with anti-C1q. Neurons in control brain were not C1q positive. Our data suggest that some of these C1q-positive structures were neurofibrillary tangles immunoreactive for hyperphosphorylated tau, which may be binding extracellular C1q. However, a large number of the C1q-positive neurons had intact cell morphology; suggesting that these cells may be synthesizing this critical complement component. Since the presence of C1q suggests the activation of complement and/or the activation of proinflammatory events, and the specific class of plaques that contain C1q are the type that corresponds to observed clinical dementia, these findings further support the hypothesis that complement plays a role in the pathogenesis of AD.

DNA damage and apoptosis in Alzheimer's disease: colocalization with c-Jun immunoreactivity, relationship to brain area, and effect of postmortem delay

Many neurons in Alzheimer's disease (AD) exhibit terminal deoxynucleotidyl transferase (TdT) labeling for DNA strand breaks with a distribution suggestive of apoptosis. We have shown previously that immunoreactivity for c-Jun is elevated in AD and found in association with neuronal pathology. In addition, cultured neurons undergoing beta-amyloid-mediated apoptosis exhibit a selective and prolonged induction of c-Jun. Consequently, we conducted double-labeling experiments to examine whether c-Jun is associated with DNA strand breaks in AD tissue; we observed a strong colocalization between these markers. As would be predicted based on the distribution of AD pathology, we also found that TdT labeling was prominent in the entorhinal cortex, but absent or at very low levels in cerebellum. Furthermore, we confirmed that postmortem delay (PMD) does not affect TdT labeling within the limits used for tissue used in this study. However, in contrast to previous studies, we report an increase in TdT labeling with more extended PMDs. Finally, gel electrophoresis of genomic DNA isolated from AD and control cases failed to reveal evidence for either an apoptotic or a necrotic mechanism of cell death in AD, possibly because of a low number of cells actually undergoing cell death at any given time. Our findings support the hypothesis that DNA damage labeled using TdT reflects neuronal vulnerability and cell loss associated with AD pathology, and that at least a portion of the cells labeled with this technique is undergoing apoptosis. Furthermore, in agreement with in vitro findings, these results suggest a relationship between the expression of c-Jun and neuronal risk and/or cell death in AD.

Acquisition and long-term retention of a gross motor skill in Alzheimer's disease patients under constant and varied practice conditions

This study examined the acquisition and long-term retention of a gross motor skill, namely, tossing, in 23 moderately to severely demented Alzheimer's disease (AD) patients and 22 health older adults. To identify optimal learning strategies, subjects received 10 weeks of training under either constant or variable practice conditions. Accuracy at the tossing task was assessed immediately, one week, and one month following training. AD patients given constant practice were able to learn and retain the tossing task as well as healthy adults. Although controls performed equally well in both conditions, AD patients showed significantly less improvement when practiced at various distances from the target. By the one-month post-test, these patients had lost any minimal gains achieved through practice. In comparison, AD patients receiving constant practice showed essentially no forgetting across post-tests. The inability to benefit from varied practice suggests that AD patients may have difficulty accessing and/or forming motor schemas.

Spatial learning and memory as a function of age in the dog

Spatial learning and memory were studied in dogs of varying ages and sources. Compared to young dogs, a significantly higher proportion of aged dogs could not acquire a spatial delayed nonmatching-to-sample task. A regression analysis revealed a significant age effect during acquisition. Spatial memory was studied by comparing performance at delay interval of 20, 70, and 110 s. At short delays aged and young dogs were similar; at longer delays, errors increased to a greater extent in old than in young dogs; however this was not statistically significant. It was possible to identify 2 groups of aged animals, age-impaired and age-unimpaired. Several of the dogs were also tested on an object recognition memory task, which was more difficult to learn than the spatial task. The possibility that these findings are confounded by breed differences is considered. Overall, the present results provide further evidence of the value of a canine model of aging.

Up-regulation of Bcl-2 is associated with neuronal DNA damage in Alzheimer's disease

Cell death and neurofibrillary tangle formation are prominent features of Alzheimer's disease (AD). It has been suggested that DNA damage may reflect neuronal vulnerability. In this context, the Ced homologue Bcl-2 is able to repress a number of cell death programs. Recently we found both numerous nuclei exhibiting DNA damage within neurons in the AD brain and increases in Bcl-2 immunoreactivity. In this study, we examined the relationship between Bcl-2 expression and nuclear DNA damage or tangle formation. Nuclei exhibiting DNA damage were associated with an up-regulation of Bcl-2 expression, whereas tangle-bearing neurons were associated with a down-regulation of Bcl-2 expression.

Image analysis of beta-amyloid load in Alzheimer's disease and relation to dementia severity

The protein beta-amyloid is said to be central to the disease process of Alzheimer's disease (AD). Several groups have developed transgenic models that overexpress the amyloid precursor protein or beta-amyloid and then develop AD-like neuropathology. Another report suggests that beta-amyloid accumulation in old dogs correlates with cognitive impairment. However, many other researchers argue that beta-amyloid deposition in senile plaques is a secondary event because plaque numbers in man do not correlate well with cognition. We set out to analyse this conumdrum in man. We selected 16 mild to severely demented AD cases on the basis of mini-mental state exam scores (MMSE; n = 16). We also included 4 controls who represented the upper range of cognitive ability. We used a computer-based image analysis of cross-sectional area of the brain occupied by beta-amyloid immunopositive deposition. We used this technique in preference to conventional methods of manual plaque counts and found a strong relation between beta-amyloid load in entorhinal cortex and cognition measured on various scales (r = -0.93 versus the Blessed IMC). Our study suggests that the size of cortical area affected by beta-amyloid deposition is an important factor in the clinical manifestation of dementia, and lends support to the possibility that beta-amyloid is central to the aetiology of AD.