Barbara J. Crain

The Consortium to Establish a Registry for Alzheimer's Disease (CERAD). Part II. Standardization of the neuropathologic assessment of Alzheimer's disease

The Neuropathology Task Force of the Consortium to Establish a Registry for Alzheimers Disease (CERAD) has developed a practical and standardized neuropathology protocol for the postmortem assessment of dementia and control subjects. The protocol provides neuropathologic definitions of such terms as “definite Alzheimers disease” (AD), “probable AD,” “possible AD,” and “normal brain” to indicate levels of diagnostic certainty, reduce subjective interpretation, and assure common language. To pretest the protocol, neuropathologists from 15 participating centers entered information on autopsy brains from 142 demented patients clinically diagnosed as probable AD and on eight nondemented patients. Eighty-four percent of the dementia cases fulfilled CERAD neuropathologic criteria for definite AD. As increasingly large numbers of prospectively studied dementia and control subjects are autopsied, the CERAD neuropathology protocol will help to refine diagnostic criteria, assess overlapping pathology, and lead to a better understanding of early subclinical changes of AD and normal aging.

Three-dimensional tracking of axonal projections in the brain by magnetic resonance imaging.

The relationship between brain structure and complex behavior is governed by large‐scale neurocognitive networks. The availability of a noninvasive technique that can visualize the neuronal projections connecting the functional centers should therefore provide new keys to the understanding of brain function. By using high‐resolution three‐dimensional diffusion magnetic resonance imaging and a newly designed tracking approach, we show that neuronal pathways in the rat brain can be probed in situ. The results are validated through comparison with known anatomical locations of such fibers. Ann Neurol 1999;45:265–269

Correlation of Alzheimer Disease Neuropathologic Changes With Cognitive Status: A Review of the Literature

Abstract Clinicopathologic correlation studies are critically important for the field of Alzheimer disease (AD) research. Studies on human subjects with autopsy confirmation entail numerous potential biases that affect both their general applicability and the validity of the correlations. Many sources of data variability can weaken the apparent correlation between cognitive status and AD neuropathologic changes. Indeed, most persons in advanced old age have significant non-AD brain lesions that may alter cognition independently of AD. Worldwide research efforts have evaluated thousands of human subjects to assess the causes of cognitive impairment in the elderly, and these studies have been interpreted in different ways. We review the literature focusing on the correlation of AD neuropathologic changes (i.e. &bgr;-amyloid plaques and neurofibrillary tangles) with cognitive impairment. We discuss the various patterns of brain changes that have been observed in elderly individuals to provide a perspective forunderstanding AD clinicopathologic correlation and conclude that evidence from many independent research centers strongly supports the existence of a specific disease, as defined by the presence of A&bgr; plaques and neurofibrillary tangles. Although A&bgr; plaques may play a key role in AD pathogenesis, the severity of cognitive impairment correlates best with the burden of neocortical neurofibrillary tangles.

Transplanted bone marrow generates new neurons in human brains.

Adult bone marrow stem cells seem to differentiate into muscle, skin, liver, lung, and neuronal cells in rodents and have been shown to regenerate myocardium, hepatocytes, and skin and gastrointestinal epithelium in humans. Because we have demonstrated previously that transplanted bone marrow cells can enter the brain of mice and differentiate into neurons there, we decided to examine postmortem brain samples from females who had received bone marrow transplants from male donors. The underlying diseases of the patients were lymphocytic leukemia and genetic deficiency of the immune system, and they survived between 1 and 9 months after transplant. We used a combination of immunocytochemistry (utilizing neuron-specific antibodies) and fluorescent in situ hybridization histochemistry to search for Y chromosome-positive cells. In all four patients studied we found cells containing Y chromosomes in several brain regions. Most of them were nonneuronal (endothelial cells and cells in the white matter), but neurons were certainly labeled, especially in the hippocampus and cerebral cortex. The youngest patient (2 years old), who also lived the longest time after transplantation, had the greatest number of donor-derived neurons (7 in 10,000). The distribution of the labeled cells was not homogeneous. There were clusters of Y-positive cells, suggesting that single progenitor cells underwent clonal expansion and differentiation. We conclude that adult human bone marrow cells can enter the brain and generate neurons just as rodent cells do. Perhaps this phenomenon could be exploited to prevent the development or progression of neurodegenerative diseases or to repair tissue damaged by infarction or trauma.

Utility of the Apolipoprotein E Genotype in the Diagnosis of Alzheimer's Disease

BACKGROUND The epsilon4 allele of the gene encoding apolipoprotein E (APOE) is strongly associated with Alzheimers disease, but its value in the diagnosis remains uncertain. METHODS We reviewed clinical diagnoses and diagnoses obtained at autopsy in 2188 patients referred to 1 of 26 Alzheimers disease centers for evaluation of dementia. The sensitivity and specificity of the clinical diagnosis or the presence of an APOE epsilon4 allele were calculated, with pathologically confirmed Alzheimers disease used as the standard. The added value of the APOE genotype was estimated with pretest and post-test probabilities from multivariate analyses to generate receiver-operating-characteristic curves plotting sensitivity against the false positive rate. RESULTS Of the 2188 patients, 1833 were given a clinical diagnosis of Alzheimers disease, and the diagnosis was confirmed pathologically in 1770 patients at autopsy. Sixty-two percent of patients with clinically diagnosed Alzheimers disease, as compared with 65 percent of those with pathologically confirmed Alzheimers disease, had at least one APOE epsilon4 allele. The sensitivity of the clinical diagnosis was 93 percent, and the specificity was 55 percent, whereas the sensitivity and specificity of the APOE epsilon4 allele were 65 and 68 percent, respectively. The addition of information about the APOE genotype increased the overall specificity to 84 percent in patients who met the clinical criteria for Alzheimers disease, although the sensitivity decreased. The improvement in specificity remained statistically significant in the multivariate analysis after adjustment for differences in age, clinical diagnosis, sex, and center. CONCLUSIONS APOE genotyping does not provide sufficient sensitivity or specificity to be used alone as a diagnostic test for Alzheimers disease, but when used in combination with clinical criteria, it improves the specificity of the diagnosis.

In vivo three-dimensional reconstruction of rat brain axonal projections by diffusion tensor imaging.

The in situ assessment of axonal projections of the brain has been severely limited by the lack of noninvasive techniques to study this type of anatomy. We show here that in vivo three‐dimensional (3D) reconstruction of axonal projections can be achieved using a rapid 3D high‐resolution diffusion‐weighted imaging technique combined with a recently designed fiber reconstruction algorithm. As a first example, neuronal pathways in the rat brain were probed. Eight well‐known fiber projections; genu and splenium of corpus callosum, internal and external capsule, fimbria, anterior commissure, optic tract, and stria terminalis were tracked and shown to be in agreement with the location of these known axonal projections. The experiment took 2 hr and shorter times should be possible in the clinical situation. By combining anisotropy information with fiber tracking, the anisotropy of individual projections was also documented. Magn Reson Med 42:1123–1127, 1999.

17β-Estradiol Reduces Stroke Injury in Estrogen-Deficient Female Animals

BACKGROUND AND PURPOSE The importance of postmenopausal estrogen replacement therapy for stroke in females remains controversial. We previously showed that female rats sustain less infarction in reversible middle cerebral artery occlusion (MCAO) than their ovariectomized counterparts and that vascular mechanisms are partly responsible for improved tissue outcomes. Furthermore, exogenous estrogen strongly protects the male brain, even when administered in a single injection before MCAO injection. The present study examined the hypothesis that replacement of 17beta-estradiol to physiological levels improves stroke outcome in ovariectomized, estrogen-deficient female rats, acting through blood flow-mediated mechanisms. METHODS Age-matched, adult female Wistar rats were ovariectomized and treated with 0, 25, or 100 microgram of 17beta-estradiol administered through a subcutaneous implant or with a single Premarin (USP) injection (1 mg/kg) given immediately before ischemia was induced (n=10 per group). Each animal subsequently underwent 2 hours of MCAO by the intraluminal filament technique, followed by 22 hours of reperfusion. Ipsilateral parietal cortex perfusion was monitored by laser-Doppler flowmetry throughout ischemia. Cortical and caudate-putamen infarction volumes were determined by 2,3, 5-triphenyltetrazolium chloride staining and digital image analysis. End-ischemic regional cerebral blood flow was measured in ovariectomized females with 0- or 25-microgram implants (n=4 per group) by (14)C-iodoantipyrine quantitative autoradiography. RESULTS Plasma estradiol levels were 3.0+/-0.6, 20+/-8, and 46+/-10 pg/mL in the 0-, 25-, and 100-microgram groups, respectively. Caudate-putamen infarction (% of ipsilateral caudate-putamen) was reduced by long-term, 25-microgram estrogen treatment (13+/-4% versus 31+/-6% in the 0-microgram group, P<0.05, and 22+/-3% in the 100-microgram group). Similarly, cortical infarction (% of ipsilateral cortex) was reduced only in the 25-microgram group (3+/-2% versus 12+/-3% in the 0-microgram group, P<0.05, and 6+/-3% in the 100-microgram group. End-ischemic striatal or cortical blood flow was not altered by estrogen treatment at the neuroprotective dose. Infarction volume was unchanged by acute treatment before MCAO when estrogen-treated animals were compared with saline vehicle-treated animals. CONCLUSIONS Long-term estradiol replacement within a low physiological range ameliorates ischemic brain injury in previously ovariectomized female rats. The neuroprotective mechanism is flow-independent, not through preservation of residual ischemic regional cerebral blood flow. Furthermore, the therapeutic range is narrow, because the benefit of estrogen in transient vascular occlusion is diminished at larger doses, which yield high, but still physiologically relevant, plasma 17beta-estradiol levels. Lastly, unlike in the male brain, single-injection estrogen exposure does not salvage ischemic tissue in the female brain. Therefore, although exogenous steroid therapy protects both male and female estrogen-deficient brain, the mechanism may not be identical and depends on long-term hormone augmentation in the female.

Specificity, sensitivity, and predictive value of apolipoprotein-E genotyping for sporadic Alzheimer's disease

BACKGROUND We aimed to determine the specificity, sensitivity, and predictive value of apolipoprotein E (APOE) genotyping in 67 consecutive patients with clinical diagnoses of sporadic Alzheimers disease (AD) who underwent necropsy. METHODS We studied patients who attended the Duke Memory Disorders Clinic and were diagnosed as having probable AD. These patients were followed up until they died. APOE genotyping was done during life in most cases, but in some brain tissue obtained at necropsy was used. Members of known AD families were excluded. FINDINGS After neuropathological examination 57 (85%) of 67 of our patients were confirmed as having AD including all 43 who had at least one APOE-epsilon 4 allele. None of the patients found not to have AD carried an epsilon 4 allele. In this series, the specificity of the epsilon 4 allele was 100%, the sensitivity 75%, the positive predictive value 100%, and the negative predictive value 42%. In this necropsy-confirmed series, the epsilon 4/epsilon 4 genotype predicted AD with 100% accuracy. The epsilon 3/epsilon 4 and epsilon 2/epsilon 4 genotypes were also unexpectedly highly specific for AD. INTERPRETATION Data from hundreds of necropsy-confirmed non-AD patients in other longitudinal necropsy series will allow the predictive value of APOE genotypes to be assessed with useful confidence limits.

Effect of Infarcts on Dementia in the Baltimore Longitudinal Study of Aging

To define the magnitude and mechanism of the effect of brain infarcts on the odds of dementia in a prospective study.

A Mouse Model of Blast Injury to Brain: Initial Pathological, Neuropathological, and Behavioral Characterization

The increased use of explosives in recent wars has increased the number of veterans with blast injuries. Of particular interest is blast injury to the brain, and a key question is whether the primary overpressure wave of the blast is injurious or whether brain injury from blast is mostly due to secondary and tertiary effects. Using a shock tube generating shock waves comparable to open-field blast waves, we explored the effects of blast on parenchymatous organs of mice with emphasis on the brain. The main injuries in nonbrain organs were hemorrhages in the lung interstitium and alveolar spaces and hemorrhagic infarcts in liver, spleen, and kidney. Neuropathological and behavioral outcomes of blast were studied at mild blast intensity, that is, 68 ± 8 kPag (9.9 ±1.2 psig) static pressure, 103 kPag (14.9 psig) total pressure and 183 ± 14 kPag (26.5 ± 2.1 psig) membrane rupturepressure. Under these conditions, weobserved multifocal axonal injury, primarily in the cerebellum/brainstem, the corticospinal system, and the optic tract. We also found prolonged behavioral and motor abnormalities, including deficits in social recognition and spatial memory and in motor coordination. Shielding of the torso ameliorated axonal injury and behavioral deficits. These findings indicate that long CNS axon tracts are particularly vulnerable to the effects of blast, even at mild intensities that match the exposure of most veterans in recent wars. Prevention of some of these neurological effects by torso shielding may generate new ideas as to how to protect military and civilian populations in blast scenarios.