Locus coeruleus volume and cell population changes during Alzheimer's disease progression: A stereological study in human postmortem brains with potential implication for early-stage biomarker discovery.

INTRODUCTION: Alzheimer's disease (AD) progression follows a specific spreading pattern, emphasizing the need to characterize those brain areas that degenerate first. The brainstem's locus coeruleus (LC) is the first area to develop neurofibrillary changes (neurofibrillary tangles [NFTs]). METHODS: The methods include unbiased stereological analyses in human brainstems to estimate LC volume and neuronal population in controls and individuals across all AD stages. RESULTS: As the Braak stage increases by 1 unit, the LC volume decreases by 8.4%. Neuronal loss started only midway through AD progression. Age-related changes spare the LC. DISCUSSION: The long gap between NFT accumulation and neuronal loss suggests that a second trigger may be necessary to induce neuronal death in AD. Imaging studies should determine whether LC volumetry can replicate the stage-wise atrophy observed here and how these changes are specific to AD. LC volumetry may develop into a screening biomarker for selecting high-yield candidates to undergo expensive and less accessible positron emission tomography scans and to monitor AD progression from presymptomatic stages.

Three-dimensional and stereological characterization of the human substantia nigra during aging.

The human brain undergoes non-uniform changes during aging. The substantia nigra (SN), the source of major dopaminergic pathways in the brain, is particularly vulnerable to changes in the progression of several age-related neurodegenerative diseases. To establish normative data for high-resolution imaging, and to further clinical and anatomical studies we analyzed SNs from 15 subjects aged 50-91 cognitively normal human subjects without signs of parkinsonism. Complete brains or brainstems with substantia nigra were formalin-fixed, celloidin-mounted, serially cut and Nissl-stained. The shapes of all SNs investigated were reconstructed using fast, high-resolution computer-assisted 3D reconstruction software. We found a negative correlation between age and SN volume (p = 0.04, rho = -0.53), with great variability in neuronal numbers and density across participants. The 3D reconstructions revealed SN inter- and intra-individual variability. Furthermore, we observed that human SN is a neuronal reticulum, rather than a group of isolated neuronal islands. Caution is required when using SN volume as a surrogate for SN status in individual subjects. The use of multimodal sequences including those for fiber tracts may enhance the value of imaging as a diagnostic tool to assess SN in vivo. Further studies with a larger sample size are needed for understanding the structure-function interaction of human SN.

A novel approach for integrative studies on neurodegenerative diseases in human brains.

Despite a massive research effort to elucidate Alzheimer's disease (AD) in recent decades, effective treatment remains elusive. This failure may relate to an oversimplification of the pathogenic processes underlying AD and also lack of understanding of AD progression during its long latent stages. Although evidence shows that the two specific neuropathological hallmarks in AD (neuronal loss and protein accumulation), which are opposite in nature, do not progress in parallel, the great majority of studies have focused on only one of these aspects. Furthermore, research focusing on single structures is likely to render an incomplete picture of AD pathogenesis because as AD involves complete brain networks, potential compensatory mechanisms within the network may ameliorate impairment of the system to a certain extent. Here, we describe an approach for enabling integrative analysis of the dual-nature lesions, simultaneously, in all components of one of the brain networks most vulnerable to AD. This approach is based on significant development of methods previously described mainly by our group that were optimized and complemented for this study. It combines unbiased stereology with immunohistochemistry and immunofluorescence, making use of advanced graphics computing for three-dimensional (3D) volume reconstructions. Although this study was performed in human brainstem and focused in AD, it may be applied to the study of any neurological disease characterized by dual-nature lesions, in humans and animal models. This approach does not require a high level of investment in new equipment and a significant number of specimens can be processed and analyzed within a funding cycle.

Cell number changes in Alzheimer's disease relate to dementia, not to plaques and tangles.

Alzheimer's disease is the commonest cause of dementia in the elderly, but its pathological determinants are still debated. Amyloid-ß plaques and neurofibrillary tangles have been implicated either directly as disruptors of neural function, or indirectly by precipitating neuronal death and thus causing a reduction in neuronal number. Alternatively, the initial cognitive decline has been attributed to subtle intracellular events caused by amyloid-ß oligomers, resulting in dementia after massive synaptic dysfunction followed by neuronal degeneration and death. To investigate whether Alzheimer's disease is associated with changes in the absolute cell numbers of ageing brains, we used the isotropic fractionator, a novel technique designed to determine the absolute cellular composition of brain regions. We investigated whether plaques and tangles are associated with neuronal loss, or whether it is dementia that relates to changes of absolute cell composition, by comparing cell numbers in brains of patients severely demented with those of asymptomatic individuals-both groups histopathologically diagnosed as Alzheimer's-and normal subjects with no pathological signs of the disease. We found a great reduction of neuronal numbers in the hippocampus and cerebral cortex of demented patients with Alzheimer's disease, but not in asymptomatic subjects with Alzheimer's disease. We concluded that neuronal loss is associated with dementia and not the presence of plaques and tangles, which may explain why subjects with histopathological features of Alzheimer's disease can be asymptomatic; and exclude amyloid-ß deposits as causes for the reduction of neuronal numbers in the brain. We found an increase of non-neuronal cell numbers in the cerebral cortex and subcortical white matter of demented patients with Alzheimer's disease when compared with asymptomatic subjects with Alzheimer's disease and control subjects, suggesting a reactive glial cell response in the former that may be related to the symptoms they present.

Prevalence of dementia subtypes in a developing country: a clinicopathological study.

OBJECTIVES: To assess the distribution of dementia subtypes in Brazil using a population-based clinicopathological study. METHOD: Brains from deceased individuals aged ≥50 years old were collected after the next of kin signed an informed consent form and provided information through standardized questionnaires. Post-mortem clinical diagnoses were established in consensus meetings, and only cases with moderate or severe dementia or without cognitive impairment were included in the analysis. Immunohistochemical neuropathological examinations were performed following the universally accepted guidelines. A diagnosis of Alzheimer's disease was made when there were at least both a moderate density of neuritic plaques (Consortium to Establish a Register for Alzheimer's disease B or C) and Braak stage III for neurofibrillary tangle distribution. For the diagnosis of vascular dementia, at least three zones or strategic areas had to be affected by infarcts, lacunae, or microinfarcts. RESULTS: From 1,291 subjects, 113 cases were classified as having moderate or severe dementia, and 972 cases were free of cognitive impairment. The neuropathological diagnoses of the dementia sub-group were Alzheimer's disease (35.4%), vascular dementia (21.2%), Alzheimer's disease plus vascular dementia (13.3%), and other causes of dementia (30.1%). Small-vessel disease, which alone was not considered sufficient for a vascular dementia diagnosis, was present in 38.9% of all of the dementia cases and in 16.8% of the group without cognitive impairment (odds ratio = 2.91; 95% confidence interval, 1.53-5.51), adjusted for age, sex, and education. CONCLUSIONS: The relatively high frequencies of vascular dementia and small-vessel disease in the dementia sub-group constitute relevant findings for public health initiatives because control of vascular risk factors could decrease the prevalence of dementia in developing countries.

Automatic isotropic fractionation for large-scale quantitative cell analysis of nervous tissue.

Isotropic fractionation is a quantitative technique that allows reliable estimates of absolute numbers of neuronal and non-neuronal brain cells. However, being fast for single small brains, it requires a long time for processing large brains or many small ones, if done manually. To solve this problem, we developed a machine to automate the method, and tested its efficiency, consistency, and reliability as compared with manual processing. The machine consists of a set of electronically controlled rotation and translation motors coupled to tissue grinders, which automatically transform fixed tissue into homogeneous nuclei suspensions. Speed and torque of the motors can be independently regulated by electronic circuits, according to the volume of tissue being processed and its mechanical resistance to fractionation. To test the machine, twelve paraformaldehyde-fixed rat brains and eight human cerebella were separated into two groups, respectively: one processed automatically and the other, manually. Both pairs of groups (rat and human tissue) followed the same, published protocol of the method. We compared the groups according to nuclei morphology, degree of clustering and number of cells. The machine proved superior for yielding faster results due to simultaneous processing in multiple grinders. Quantitative analysis of machine-processed tissue resulted in similar average numbers of total brain cells, neurons, and non-neuronal cells, statistically similar to the manually processed tissue and equivalent to previously published data. We concluded that the machine is more efficient because it utilizes many homogenizers simultaneously, equally consistent in producing high quality material for counting, and quantitatively reliable as compared to manual processing.

Prevalence of dementia subtypes in a developing country: a clinicopathological study

OBJECTIVES: To assess the distribution of dementia subtypes in Brazil using a population-based clinicopathological study. METHOD: Brains from deceased individuals aged ≥50 years old were collected after the next of kin signed an informed consent form and provided information through standardized questionnaires. Post-mortem clinical diagnoses were established in consensus meetings, and only cases with moderate or severe dementia or without cognitive impairment were included in the analysis. Immunohistochemical neuropathological examinations were performed following the universally accepted guidelines. A diagnosis of Alzheimer's disease was made when there were at least both a moderate density of neuritic plaques (Consortium to Establish a Register for Alzheimer's disease B or C) and Braak stage III for neurofibrillary tangle distribution. For the diagnosis of vascular dementia, at least three zones or strategic areas had to be affected by infarcts, lacunae, or microinfarcts. RESULTS: From 1,291 subjects, 113 cases were classified as having moderate or severe dementia, and 972 cases were free of cognitive impairment. The neuropathological diagnoses of the dementia sub-group were Alzheimer's disease (35.4%), vascular dementia (21.2%), Alzheimer's disease plus vascular dementia (13.3%), and other causes of dementia (30.1%). Small-vessel disease, which alone was not considered sufficient for a vascular dementia diagnosis, was present in 38.9% of all of the dementia cases and in 16.8% of the group without cognitive impairment (odds ratio = 2.91; 95% confidence interval, 1.53-5.51), adjusted for age, sex, and education. CONCLUSIONS: The relatively high frequencies of vascular dementia and small-vessel disease in the dementia sub-group constitute relevant findings for public health initiatives because control of vascular risk factors could decrease the prevalence of dementia in developing countries. .