Eva Braak

Staging of brain pathology related to sporadic Parkinson's disease.

Sporadic Parkinsons disease involves multiple neuronal systems and results from changes developing in a few susceptible types of nerve cells. Essential for neuropathological diagnosis are alpha-synuclein-immunopositive Lewy neurites and Lewy bodies. The pathological process targets specific induction sites: lesions initially occur in the dorsal motor nucleus of the glossopharyngeal and vagal nerves and anterior olfactory nucleus. Thereafter, less vulnerable nuclear grays and cortical areas gradually become affected. The disease process in the brain stem pursues an ascending course with little interindividual variation. The pathology in the anterior olfactory nucleus makes fewer incursions into related areas than that developing in the brain stem. Cortical involvement ensues, beginning with the anteromedial temporal mesocortex. From there, the neocortex succumbs, commencing with high order sensory association and prefrontal areas. First order sensory association/premotor areas and primary sensory/motor fields then follow suit. This study traces the course of the pathology in incidental and symptomatic Parkinson cases proposing a staging procedure based upon the readily recognizable topographical extent of the lesions.

Staging of alzheimer's disease-related neurofibrillary changes

Specific immunocytochemical methods (AT8) permit evaluation of neuronal changes well before the actual formation of neurofibrillary tangles and neuropil threads. Initial changes are found in the transentorhinal region (temporal lobe). From here the destructive process encroaches upon the entorhinal region, Ammons horn, and neocortex. Initial changes occur in comparatively young individuals and can also be observed at the same predilection sites in a few species of old aged domestic animals. In a later state of destruction, AT8 immunoreactive neurons develop typical argyrophilic neurofibrillary tangles and neuropil threads. Six stages of disease propagation can be distinguished with respect to the location of the tangle-bearing neurons and the severity of changes (transentorhinal stages I-II: clinically silent cases; limbic stages III-IV: incipient Alzheimers disease; neocortical stages V-VI: fully developed Alzheimers disease). Whole mount techniques reveal the lesional pattern of the particularly severely involved superficial entorhinal layer as seen from the free surface of the parahippocampal gyrus. This approach facilitates recognition of even subtle pathologic changes throughout the entire extent of cortical territories such as the transentorhinal and entorhinal regions.

Frequency of Stages of Alzheimer-Related Lesions in Different Age Categories

Alzheimers disease is a relentlessly progressing dementing disorder. Major pathological hallmarks include extracellular deposits of amyloid protein and intraneuronal neurofibrillary changes. No remissions occur in the course of the disease. Initial amyloid deposits develop in poorly myelinated areas of the basal neocortex. From there, they spread into adjoining areas and the hippocampus. Deposits eventually infiltrate all cortical areas, including densely myelinated primary fields of the neocortex (stages A-C). Intraneuronal lesions develop initially in the transentorhinal region, then spread in a predictable manner across other areas (stages I-VI). At stages I-II, neurofibrillary changes develop preferentially in the absence of amyloid deposits. A proportion of cases shows early development of amyloid deposits and/or intraneuronal changes. Advanced age is thus not a prerequisite for the evolution of the lesions. Alzheimers disease is an age-related, not an age-dependent disease. The degree of brain destruction at stages III-IV frequently leads to the appearance of initial clinical symptoms. The stages V-VI representing fully developed Alzheimers disease are increasingly prevalent with increasing age. The arithmetic means of the stages of both the amyloid-depositing and the neurofibrillary pathology increase with age. Age is a risk factor for Alzheimers disease.

Distribution of active glycogen synthase kinase 3β (GSK-3β) in brains staged for Alzheimer disease neurofibrillary changes

Accumulation of paired helical filaments (PHFs) in neurofibrillary tangles, neuropil threads, and dystrophic neurites is one of the major ncuropathological hallmarks of Alzheimer disease (AD). The principal protein subunit of PHFs is the abnormally hyperphosphorylated tau. Glycogen synthase kinase 3B (GSK-3B) is one of the candidate kinases involved in PHF-tau formation. To play a role in PHF-tau formation, it would be expected that GSK-3B is active in tangle bearing neurons. In the present study, we investigated the regional and intracellular distributions of active and inactive forms of GSK-3B in brains staged for neurofibrillary changes. We found that neurons with tangle-like inclusions positive for active, but not inactive, GSK-3β appear initially in the Pre-α layer of the entorhinal cortex and extend to other brain regions, coincident with the sequence of the development of neurofibrillary changes. Active, but not inactive, GSK-3β was found to initially accumulate in the cytoplasm of pretangle neurons. These data provide direct in situ evidence that is consistent with the involvement of GSK-3β in PHF-tau formation.

Demonstration of Amyloid Deposits and Neurofibrillary Changes in Whole Brain Sections

Selective and sensitive silver staining of extracellular amyloid deposits and intraneuronal neurofibrillary changes can be applied to 50–150 μ.m thick polyethylene glycol sections and/or 5–15 μ.m thick paraffin sections. The silver techniques take advantage of physical development of the nucleation sites thus permitting tight control of the entire procedure. Both techniques can be applied to routinely fixed autopsy material. They do not require particular skills and considerably facilitate processing of large numbers of sections through entire hemispheres of the human brain.

Evolution of neuronal changes in the course of Alzheimer's disease.

Alzheimers disease entails multiple neuronal systems and results from neuronal cytoskeletal degeneration of only a few types of nerve cells. Essential for neuropathological diagnosis is assessment of the presence of neurofibrillary tangles and neuropil threads. The destructive process begins in predisposed cortical induction sites, thereafter invading other portions of the cerebral cortex and specific sets of subcortical nuclei in a predictable sequence with little variation. The location of the tangle-bearing neurons and severity of the pathology allow the distinction of six stages in disease propagation (transentorhinal I-II: clinically silent cases; limbic III-IV: incipient Alzheimers disease; neocortical V-VI: fully-developed Alzheimers disease). The pattern of appearance of the neurofibrillary changes bears a striking resemblance to the inverse sequence of cortical myelination. The average myelin content is a negative image of the density of intraneuronal lipofuscin deposits. Pigment-laden neurons endowed with a long, thin, and sparsely myelinated axon are prone to develop AD-related changes. The emergence of the first neurofibrillary changes, at whatever age these occur, signals the onset of a degenerative process that persists until death. An extended period of time elapses between the beginning of histologically verifiable lesions and the appearance of initial clinical symptoms. Once initiated, however, cytoskeletal deterioration inexorably progresses, and neither remission nor recovery is observed.

Occurrence of neuropil threads in the senile human brain and in Alzheimer's disease: A third location of paired helical filaments outside of neurofibrillary tangles and neuritic plaques

Paired helical filaments, pathologically changed components of the cytoskeleton of human nerve cells, are demonstrated by a specific silver staining technique, immunostaining and electron microscopy. Accumulations of these filaments are found in the telencephalic cortex of old-aged individuals and patients suffering from Alzheimers disease. Apart from neurofibrillary tangles and neuritic plaques, paired helical filaments are encountered in neuropil threads. At this third location, pathological filaments occur in small and inconspicuous profiles scattered throughout both allocortical and isocortical areas. The pattern of distribution and packing density of neuropil threads varies between different cortical areas and layers.

Diagnostic Criteria for Neuropathologic Assessment of Alzheimer's Disease

Prior to any evaluation of morphologic brain changes, a decision must be made whether a given alteration is associated with aging or with disease. Patients with disease-related lesions may be in a clinically silent phase of a disease or show overt symptoms. Neurofibrillary tangles and neuropil threads are the hallmarks of Alzheimers disease. They should not be considered to be age-related changes, even when they are present only in small numbers. In general, the initial changes consist of neurofibrillary tangles and neuropil threads. Plaques (amyloid deposits and/or neuritic plaques) are consistently present in the end stage of the disease. Initial neurofibrillary tangles and neuropil threads develop at specific cortical predilection sites. The changes then spread in a predictable, nonrandom manner across other portions of the telencephalic cortex. The sequential changes in the distribution pattern of the lesions provide the basis for a staging procedure that takes the slow and gradual progression of the destructive process into consideration. The staging procedure provides accurate diagnoses in the initial stages and even reveals brain changes developing prior to the appearance of clinical symptoms. It is thus advantageous in characterizing nondemented controls. The staging procedure can be carried out easily and does not require knowledge of clinical data, quantitative assessments, or adjustments for the age of the patients. Application of advanced silver techniques (Gallyas, Campbell-Switzer) to demonstrate Alzheimers disease-related lesions also allows recognition of the hallmarks of other disorders, such as Lewy body disease (Parkinsons disease) and dementia with argyrophilic grains, which frequently co-occur with Alzheimers disease.

Distribution, levels, and activity of glycogen synthase kinase-3 in the Alzheimer disease brain

A number of studies have implicated a proline-directed protein kinase, glycogen synthase kinase-3 (GSK-3) in the hyperphosphorylation of tau in Alzheimers disease (AD). Toward understanding the role of GSK-3 in the abnormal hyperphosphorylation of tau in AD we have found that GSK-3 is prominently present in neuronal cell bodies and their processes and co-localizes with neurofibrillary changes in AD brain. Furthermore, the levels of GSK-3 as determined by indirect ELISA are ∼50% increased in the postsynaptosomal supernatant from AD brains as compared to the controls. However, no increase in GSK-3 enzyme activity was detected. In AD brain, with its reduced phosphatase activity, even normal levels of GSK-3 activity might be sufficient for the hyperphosphorylation of tau.

Pattern of brain destruction in Parkinson's and Alzheimer's diseases

SummaryAlzheimers disease (AD) and Parkinsons disease (PD) are the most common age-related degenerative disorders of the human brain. Both diseases involve multiple neuronal systems and are the consequences of cytoskeletal abnormalities which gradually develop in only a small number of neuronal types. In AD, susceptible neurons produce neurofibrillary tangles (NFTs) and neuropil threads (NTs), while in PD, they develop Lewy bodies (LBs) and Lewy neurites (LNs). The specific lesional pattern of both illnesses accrues slowly over time and remains remarkably consistent across cases.In AD, six developmental stages can be distinguished on account of the predictable manner in which the neurofibrillary changes spread across the cerebral cortex. The pathologic process commences in the transentorhinal region (clinically silent stages I and II), then proceeds into adjoining cortical and subcortical components of the limbic system (stages III and IV — incipient AD), and eventually extends into association areas of the neocortex (stages V and VI — fully developed AD).During the course of PD, important components of the limbic system undergo specific lesions as well. The predilection sites include the entorhinal region, the CA2-sector of the hippocampal formation, the limbic nuclei of the thalamus, anterior cingulate areas, agranular insular cortex (layer VI), and — within the amygdala — the accessory cortical nucleus, the ventromedial divisions both of the basal and accessory basal nuclei, and the central nucleus. The amygdala not only generates important projections to the prefrental association areas but also exerts influence upon all non-thalamic nuclei which in a non-specific manner project upon the cerebral cortex and upon the nuclei regulating endocrine and autonomie functions. All these amygdala-dependent structures themselves exhibit severe PD-specific lesions. In general, the extranigral destructions are in themselves not sufficient to produce overt intellectual deterioration. Similarly, AD-related pathology up to stage III may be asymptomatic as well. Fully developed PD with concurring incipient AD, however, is likely to cause impaired cognition. Presently available data support the view that the occurrence of additional lesions in the form of AD stage III (or more) destruction is the most common cause of intellectual decline in PD.