Subcellular pathways through VGluT3-expressing mouse amacrine cells provide locally tuned object-motion-selective signals in the retina.

VGluT3-expressing mouse retinal amacrine cells (VG3s) respond to small-object motion and connect to multiple types of bipolar cells (inputs) and retinal ganglion cells (RGCs, outputs). Because these input and output connections are intermixed on the same dendrites, making sense of VG3 circuitry requires comparing the distribution of synapses across their arbors to the subcellular flow of signals. Here, we combine subcellular calcium imaging and electron microscopic connectomic reconstruction to analyze how VG3s integrate and transmit visual information. VG3s receive inputs from all nearby bipolar cell types but exhibit a strong preference for the fast type 3a bipolar cells. By comparing input distributions to VG3 dendrite responses, we show that VG3 dendrites have a short functional length constant that likely depends on inhibitory shunting. This model predicts that RGCs that extend dendrites into the middle layers of the inner plexiform encounter VG3 dendrites whose responses vary according to the local bipolar cell response type.

Presenilin-1 mutation position influences amyloidosis, small vessel disease, and dementia with disease stage.

INTRODUCTION: Amyloidosis, including cerebral amyloid angiopathy, and markers of small vessel disease (SVD) vary across dominantly inherited Alzheimer's disease (DIAD) presenilin-1 (PSEN1) mutation carriers. We investigated how mutation position relative to codon 200 (pre-/postcodon 200) influences these pathologic features and dementia at different stages. METHODS: Individuals from families with known PSEN1 mutations (n = 393) underwent neuroimaging and clinical assessments. We cross-sectionally evaluated regional Pittsburgh compound B-positron emission tomography uptake, magnetic resonance imaging markers of SVD (diffusion tensor imaging-based white matter injury, white matter hyperintensity volumes, and microhemorrhages), and cognition. RESULTS: Postcodon 200 carriers had lower amyloid burden in all regions but worse markers of SVD and worse Clinical Dementia Rating® scores compared to precodon 200 carriers as a function of estimated years to symptom onset. Markers of SVD partially mediated the mutation position effects on clinical measures. DISCUSSION: We demonstrated the genotypic variability behind spatiotemporal amyloidosis, SVD, and clinical presentation in DIAD, which may inform patient prognosis and clinical trials. HIGHLIGHTS: Mutation position influences Aß burden, SVD, and dementia. PSEN1 pre-200 group had stronger associations between Aß burden and disease stage. PSEN1 post-200 group had stronger associations between SVD markers and disease stage. PSEN1 post-200 group had worse dementia score than pre-200 in late disease stage. Diffusion tensor imaging-based SVD markers mediated mutation position effects on dementia in the late stage.

Reconstructing neural circuits using multiresolution correlated light and electron microscopy.

Correlated light and electron microscopy (CLEM) can be used to combine functional and molecular characterizations of neurons with detailed anatomical maps of their synaptic organization. Here we describe a multiresolution approach to CLEM (mrCLEM) that efficiently targets electron microscopy (EM) imaging to optically characterized cells while maintaining optimal tissue preparation for high-throughput EM reconstruction. This approach hinges on the ease with which arrays of sections collected on a solid substrate can be repeatedly imaged at different scales using scanning electron microscopy. We match this multiresolution EM imaging with multiresolution confocal mapping of the aldehyde-fixed tissue. Features visible in lower resolution EM correspond well to features visible in densely labeled optical maps of fixed tissue. Iterative feature matching, starting with gross anatomical correspondences and ending with subcellular structure, can then be used to target high-resolution EM image acquisition and annotation to cells of interest. To demonstrate this technique and range of images used to link live optical imaging to EM reconstructions, we provide a walkthrough of a mouse retinal light to EM experiment as well as some examples from mouse brain slices.

Comparing amyloid-ß plaque burden with antemortem PiB PET in autosomal dominant and late-onset Alzheimer disease.

Pittsburgh compound B (PiB) radiotracer for positron emission tomography (PET) imaging can bind to different types of amyloid-ß plaques and blood vessels (cerebral amyloid angiopathy). However, the relative contributions of different plaque subtypes (diffuse versus cored/compact) to in vivo PiB PET signal on a region-by-region basis are incompletely understood. Of particular interest is whether the same staging schemes for summarizing amyloid-ß burden are appropriate for both late-onset and autosomal dominant forms of Alzheimer disease (LOAD and ADAD). Here, we compared antemortem PiB PET with follow-up postmortem estimation of amyloid-ß burden using stereologic methods to estimate the relative area fraction of diffuse and cored/compact amyloid-ß plaques across 16 brain regions in 15 individuals with ADAD and 14 individuals with LOAD. In ADAD, we found that PiB PET correlated with diffuse plaques in the frontal, parietal, temporal, and striatal regions commonly used to summarize amyloid-ß burden in PiB PET, and correlated with both diffuse and cored/compact plaques in the occipital lobe and parahippocampal gyrus. In LOAD, we found that PiB PET correlated with both diffuse and cored/compact plaques in the anterior cingulate, frontal lobe (middle frontal gyrus), and parietal lobe, and showed additional correlations with diffuse plaque in the amygdala and occipital lobe, and with cored/compact plaque in the temporal lobe. Thus, commonly used PiB PET summary regions predominantly reflect diffuse plaque burden in ADAD and a mixture of diffuse and cored/compact plaque burden in LOAD. In direct comparisons of ADAD and LOAD, postmortem stereology identified much greater mean amyloid-ß plaque burdens in ADAD versus LOAD across almost all brain regions studied. However, standard PiB PET did not recapitulate these stereologic findings, likely due to non-trivial amyloid-ß plaque burdens in ADAD within the cerebellum and brainstem-commonly used reference regions in PiB PET. Our findings suggest that PiB PET summary regions correlate with amyloid-ß plaque burden in both ADAD and LOAD; however, they might not be reliable in direct comparisons of regional amyloid-ß plaque burden between the two forms of AD.

Utility of perfusion PET measures to assess neuronal injury in Alzheimer's disease.

INTRODUCTION: 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) is commonly used to estimate neuronal injury in Alzheimer's disease (AD). Here, we evaluate the utility of dynamic PET measures of perfusion using 11C-Pittsburgh compound B (PiB) to estimate neuronal injury in comparison to FDG PET. METHODS: FDG, early frames of PiB images, and relative PiB delivery rate constants (PiB-R1) were obtained from 110 participants from the Dominantly Inherited Alzheimer Network. Voxelwise, regional cross-sectional, and longitudinal analyses were done to evaluate the correlation between images and estimate the relationship of the imaging biomarkers with estimated time to disease progression based on family history. RESULTS: Metabolism and perfusion images were spatially correlated. Regional PiB-R1 values and FDG, but not early frames of PiB images, significantly decreased in the mutation carriers with estimated year to onset and with increasing dementia severity. DISCUSSION: Hypometabolism estimated by PiB-R1 may provide a measure of brain perfusion without increasing radiation exposure.

AV-1451 PET imaging of tau pathology in preclinical Alzheimer disease: Defining a summary measure.

Utilizing [18F]-AV-1451 tau positron emission tomography (PET) as an Alzheimer disease (AD) biomarker will require identification of brain regions that are most important in detecting elevated tau pathology in preclinical AD. Here, we utilized an unsupervised learning, data-driven approach to identify brain regions whose tau PET is most informative in discriminating low and high levels of [18F]-AV-1451 binding. 84 cognitively normal participants who had undergone AV-1451 PET imaging were used in a sparse k-means clustering with resampling analysis to identify the regions most informative in dividing a cognitively normal population into high tau and low tau groups. The highest-weighted FreeSurfer regions of interest (ROIs) separating these groups were the entorhinal cortex, amygdala, lateral occipital cortex, and inferior temporal cortex, and an average SUVR in these four ROIs was used as a summary metric for AV-1451 uptake. We propose an AV-1451 SUVR cut-off of 1.25 to define high tau as described by imaging. This spatial distribution of tau PET is a more widespread pattern than that predicted by pathological staging schemes. Our data-derived metric was validated first in this cognitively normal cohort by correlating with early measures of cognitive dysfunction, and with disease progression as measured by ß-amyloid PET imaging. We additionally validated this summary metric in a cohort of 13 Alzheimer disease patients, and showed that this measure correlates with cognitive dysfunction and ß-amyloid PET imaging in a diseased population.

Correction: Quantitative Amyloid Imaging in Autosomal Dominant Alzheimer's Disease: Results from the DIAN Study Group.

[This corrects the article DOI: 10.1371/journal.pone.0152082.].

Evaluation of Tau Imaging in Staging Alzheimer Disease and Revealing Interactions Between ß-Amyloid and Tauopathy.

IMPORTANCE: In vivo tau imaging may become a diagnostic marker for Alzheimer disease (AD) and provides insights into the pathophysiology of AD. OBJECTIVE: To evaluate the usefulness of [18F]-AV-1451 positron emission tomography (PET) imaging to stage AD and assess the associations among ß-amyloid (Aß), tau, and volume loss. DESIGN, SETTING, AND PARTICIPANTS: An imaging study conducted at Knight Alzheimer Disease Research Center at Washington University in St Louis, Missouri. A total of 59 participants who were cognitively normal (CN) (Clinical Dementia Rating [CDR] score, 0) or had AD dementia (CDR score, >0) were included. MAIN OUTCOMES AND MEASURES: Standardized uptake value ratio (SUVR) of [18F]-AV-1451 in the hippocampus and a priori-defined AD cortical signature regions, cerebrospinal fluid Aß42, hippocampal volume, and AD signature cortical thickness. RESULTS: Of the 59 participants, 38 (64%) were male; mean (SD) age was 74 (6) years. The [18F]-AV-1451 SUVR in the hippocampus and AD cortical signature regions distinguished AD from CN participants (area under the receiver operating characteristic curve range [95% CI], 0.89 [0.73-1.00] to 0.98 [0.92-1.00]). An [18F]-AV-1451 SUVR cutoff value of 1.19 (sensitivity, 100%; specificity, 86%) from AD cortical signature regions best separated cerebrospinal fluid Aß42-positive (Aß+) AD from cerebrospinal fluid Aß42-negative (Aß-) CN participants. This same cutoff also divided Aß+ CN participants into low vs high tau groups. Moreover, the presence of Aß+ was associated with an elevated [18F]-AV-1451 SUVR in AD cortical signature regions (Aß+ participants: mean [SD], 1.3 [0.3]; Aß- participants: 1.1 [0.1]; F = 4.3, P = .04) but not in the hippocampus. The presence of Aß+ alone was not related to hippocampal volume or AD signature cortical thickness. An elevated [18F]-AV-1451 SUVR was associated with volumetric loss in both the hippocampus and AD cortical signature regions. The observed [18F]-AV-1451 SUVR volumetric association was modified by Aß status in the hippocampus but not in AD cortical signature regions. An inverse association between hippocampal [18F]-AV-1451 SUVR and volume was seen in Aß+ participants (R2 = 0.55; P < .001) but not Aß- (R2 = 0; P = .97) participants. CONCLUSIONS AND RELEVANCE: Use of [18F]-AV-1451 has a potential for staging of the preclinical and clinical phases of AD. ß-Amyloid interacts with hippocampal and cortical tauopathy to affect neurodegeneration. In the absence of Aß, hippocampal tau deposition may be insufficient for the neurodegenerative process that leads to AD.

The relationship between cerebrospinal fluid markers of Alzheimer pathology and positron emission tomography tau imaging.

The two primary molecular pathologies in Alzheimer's disease are amyloid-ß plaques and tau-immunoreactive neurofibrillary tangles. Investigations into these pathologies have been restricted to cerebrospinal fluid assays, and positron emission tomography tracers that can image amyloid-ß plaques. Tau tracers have recently been introduced into the field, although the utility of the tracer and its relationship to other Alzheimer biomarkers are still unknown. Here we examined tau deposition in 41 cognitively normal and 11 cognitively impaired older adults using the radioactive tau ligand (18)F-AV-1451 (previously known as T807) who also underwent a lumbar puncture to assess cerebrospinal fluid levels of total tau (t-tau), phosphorylated tau181 (p-tau181) and amyloid-ß42 Voxel-wise statistical analyses examined spatial patterns of tau deposition associated with cognitive impairment. We then related the amount of tau tracer uptake to levels of cerebrospinal fluid biomarkers. All analyses controlled for age and gender and, when appropriate, the time between imaging and lumbar puncture assessments. Symptomatic individuals (Clinical Dementia Rating > 0) demonstrated markedly increased levels of tau tracer uptake. This elevation was most prominent in the temporal lobe and temporoparietal junction, but extended more broadly into parietal and frontal cortices. In the entire cohort, there were significant relationships among all cerebrospinal fluid biomarkers and tracer uptake, notably for tau-related cerebrospinal fluid markers. After controlling for levels of amyloid-ß42, the correlations with tau uptake were r = 0.490 (P < 0.001) for t-tau and r = 0.492 (P < 0.001) for p-tau181 Within the cognitively normal cohort, levels of amyloid-ß42, but not t-tau or p-tau181, were associated with elevated tracer binding that was confined primarily to the medial temporal lobe and adjacent neocortical regions. AV-1451 tau binding in the medial temporal, parietal, and frontal cortices is correlated with tau-related cerebrospinal fluid measures. In preclinical Alzheimer's disease, there is focal tauopathy in the medial temporal lobes and adjacent cortices.

Tau and Aß imaging, CSF measures, and cognition in Alzheimer's disease.

Alzheimer's disease (AD) is characterized by two molecular pathologies: cerebral ß-amyloidosis in the form of ß-amyloid (Aß) plaques and tauopathy in the form of neurofibrillary tangles, neuritic plaques, and neuropil threads. Until recently, only Aß could be studied in humans using positron emission tomography (PET) imaging owing to a lack of tau PET imaging agents. Clinical pathological studies have linked tau pathology closely to the onset and progression of cognitive symptoms in patients with AD. We report PET imaging of tau and Aß in a cohort of cognitively normal older adults and those with mild AD. Multivariate analyses identified unique disease-related stereotypical spatial patterns (topographies) for deposition of tau and Aß. These PET imaging tau and Aß topographies were spatially distinct but correlated with disease progression. Cerebrospinal fluid measures of tau, often used to stage preclinical AD, correlated with tau deposition in the temporal lobe. Tau deposition in the temporal lobe more closely tracked dementia status and was a better predictor of cognitive performance than Aß deposition in any region of the brain. These data support models of AD where tau pathology closely tracks changes in brain function that are responsible for the onset of early symptoms in AD.

Quantitative Amyloid Imaging in Autosomal Dominant Alzheimer's Disease: Results from the DIAN Study Group.

Amyloid imaging plays an important role in the research and diagnosis of dementing disorders. Substantial variation in quantitative methods to measure brain amyloid burden exists in the field. The aim of this work is to investigate the impact of methodological variations to the quantification of amyloid burden using data from the Dominantly Inherited Alzheimer's Network (DIAN), an autosomal dominant Alzheimer's disease population. Cross-sectional and longitudinal [11C]-Pittsburgh Compound B (PiB) PET imaging data from the DIAN study were analyzed. Four candidate reference regions were investigated for estimation of brain amyloid burden. A regional spread function based technique was also investigated for the correction of partial volume effects. Cerebellar cortex, brain-stem, and white matter regions all had stable tracer retention during the course of disease. Partial volume correction consistently improves sensitivity to group differences and longitudinal changes over time. White matter referencing improved statistical power in the detecting longitudinal changes in relative tracer retention; however, the reason for this improvement is unclear and requires further investigation. Full dynamic acquisition and kinetic modeling improved statistical power although it may add cost and time. Several technical variations to amyloid burden quantification were examined in this study. Partial volume correction emerged as the strategy that most consistently improved statistical power for the detection of both longitudinal changes and across-group differences. For the autosomal dominant Alzheimer's disease population with PiB imaging, utilizing brainstem as a reference region with partial volume correction may be optimal for current interventional trials. Further investigation of technical issues in quantitative amyloid imaging in different study populations using different amyloid imaging tracers is warranted.

Local and distributed PiB accumulation associated with development of preclinical Alzheimer's disease.

Amyloid-beta plaques are a hallmark of Alzheimer's disease (AD) that can be assessed by amyloid imaging (e.g., Pittsburgh B compound [PiB]) and summarized as a scalar value. Summary values may have clinical utility but are an average over many regions of interest, potentially obscuring important topography. This study investigates the longitudinal evolution of amyloid topographies in cognitively normal older adults who had normal (N = 131) or abnormal (N = 26) PiB scans at baseline. At 3 years follow-up, 16 participants with a previously normal PiB scan had conversion to PiB scans consistent with preclinical AD. We investigated the multivariate relationship (canonical correlation) between baseline and follow-up PiB topographies. Furthermore, we used penalized regression to investigate the added information derived from PiB topography compared to summary measures. PiB accumulation can be local, that is, a topography predicting the same topography in the future, and/or distributed, that is, one topography predicting another. Both local and distributed PiB accumulation was associated with conversion of PiB status. Additionally, elements of the multivariate topography, and not the commonly used summary scalar, correlated with future PiB changes. Consideration of the entire multivariate PiB topography provides additional information regarding the development of amyloid-beta pathology in very early preclinical AD.

Neuropathologic assessment of participants in two multi-center longitudinal observational studies: the Alzheimer Disease Neuroimaging Initiative (ADNI) and the Dominantly Inherited Alzheimer Network (DIAN).

It has been hypothesized that the relatively rare autosomal dominant Alzheimer disease (ADAD) may be a useful model of the more frequent, sporadic, late-onset AD (LOAD). Individuals with ADAD have a predictable age at onset and the biomarker profile of ADAD participants in the preclinical stage may be used to predict disease progression and clinical onset. However, the extent to which the pathogenesis and neuropathology of ADAD overlaps with that of LOAD is equivocal. To address this uncertainty, two multicenter longitudinal observational studies, the Alzheimer Disease Neuroimaging Initiative (ADNI) and the Dominantly Inherited Alzheimer Network (DIAN), leveraged the expertise and resources of the existing Knight Alzheimer Disease Research Center (ADRC) at Washington University School of Medicine, St. Louis, Missouri, USA, to establish a Neuropathology Core (NPC). The ADNI/DIAN-NPC is systematically examining the brains of all participants who come to autopsy at the 59 ADNI sites in the USA and Canada and the 14 DIAN sites in the USA (eight), Australia (three), UK (one) and Germany (two). By 2014, 41 ADNI and 24 DIAN autopsies (involving nine participants and 15 family members) had been performed. The autopsy rate in the ADNI cohort in the most recent year was 93% (total since NPC inception: 70%). In summary, the ADNI/DIAN NPC has implemented a standard protocol for all sites to solicit permission for brain autopsy and to send brain tissue to the NPC for a standardized, uniform and state-of-the-art neuropathologic assessment. The benefit to ADNI and DIAN of the implementation of the NPC is very clear. The NPC provides final "gold standard" neuropathological diagnoses and data against which the antecedent observations and measurements of ADNI and DIAN can be compared.

Partial volume correction in quantitative amyloid imaging.

Amyloid imaging is a valuable tool for research and diagnosis in dementing disorders. As positron emission tomography (PET) scanners have limited spatial resolution, measured signals are distorted by partial volume effects. Various techniques have been proposed for correcting partial volume effects, but there is no consensus as to whether these techniques are necessary in amyloid imaging, and, if so, how they should be implemented. We evaluated a two-component partial volume correction technique and a regional spread function technique using both simulated and human Pittsburgh compound B (PiB) PET imaging data. Both correction techniques compensated for partial volume effects and yielded improved detection of subtle changes in PiB retention. However, the regional spread function technique was more accurate in application to simulated data. Because PiB retention estimates depend on the correction technique, standardization is necessary to compare results across groups. Partial volume correction has sometimes been avoided because it increases the sensitivity to inaccuracy in image registration and segmentation. However, our results indicate that appropriate PVC may enhance our ability to detect changes in amyloid deposition.