The medial temporal lobe (MTL) cortex, located adjacent to the hippocampus, is crucial for memory and prone to the accumulation of certain neuropathologies such as Alzheimer's disease neurofibrillary ...tau tangles. The MTL cortex is composed of several subregions which differ in their functional and cytoarchitectonic features. As neuroanatomical schools rely on different cytoarchitectonic definitions of these subregions, it is unclear to what extent their delineations of MTL cortex subregions overlap. Here, we provide an overview of cytoarchitectonic definitions of the entorhinal and parahippocampal cortices as well as Brodmann areas (BA) 35 and 36, as provided by four neuroanatomists from different laboratories, aiming to identify the rationale for overlapping and diverging delineations. Nissl‐stained series were acquired from the temporal lobes of three human specimens (two right and one left hemisphere). Slices (50 μm thick) were prepared perpendicular to the long axis of the hippocampus spanning the entire longitudinal extent of the MTL cortex. Four neuroanatomists annotated MTL cortex subregions on digitized slices spaced 5 mm apart (pixel size 0.4 μm at 20× magnification). Parcellations, terminology, and border placement were compared among neuroanatomists. Cytoarchitectonic features of each subregion are described in detail. Qualitative analysis of the annotations showed higher agreement in the definitions of the entorhinal cortex and BA35, while the definitions of BA36 and the parahippocampal cortex exhibited less overlap among neuroanatomists. The degree of overlap of cytoarchitectonic definitions was partially reflected in the neuroanatomists' agreement on the respective delineations. Lower agreement in annotations was observed in transitional zones between structures where seminal cytoarchitectonic features are expressed less saliently. The results highlight that definitions and parcellations of the MTL cortex differ among neuroanatomical schools and thereby increase understanding of why these differences may arise. This work sets a crucial foundation to further advance anatomically‐informed neuroimaging research on the human MTL cortex.
The perinatal period, sensitive for newborn survival, is also one of the most critical moments in human brain development. Perinatal hypoxia due to reduced blood supply to the brain (ischemia) is one ...of the main causes of neonatal mortality. Brain damage caused by perinatal hypoxia–ischemia (HI) can lead to neuro‐ and psychological disorders. However, its impact seems to be region‐dependent, with the hippocampus being one of the most affected areas. Among the neuronal populations of the hippocampus, some interneuron groups – such as somatostatin‐ or neuropeptide Y‐expressing neurons – seem to be particularly vulnerable. The limited information available about the effects of HI in the hippocampus comes mainly from animal models and adult human studies. This article presents an immunohistochemical analysis of somatostatin (SOM) and neuropeptide Y (NPY) expression in the developing human hippocampus after perinatal HI. Two rostrocaudal sections of the body of the hippocampus were analysed, and the number of immunostained cells in the polymorphic layer of the dentate gyrus (DG) and the pyramidal cell layer and stratum oriens of the CA3, CA2 and CA1 fields of the hippocampus proper were quantified. The results showed a lower density of both neuropeptides in hypoxic compared to control cases. In the HI group, the number of SOM‐immunoreactive cell bodies was statistically significantly lower in the pyramidal cell layer and stratum oriens of CA1, while the number of NPY‐expressing neurons was statistically lower in the pyramidal cell layer of CA2. Besides, the number of SOM‐expressing neurons was significantly higher in the stratum oriens of CA1 compared to that in CA2. In sum, we observed a different vulnerability of SOM‐ and NPY‐containing neurons in the developing human hippocampus following perinatal HI damage. Our results could contribute to a better understanding of the behaviour of these neuronal populations under stressful conditions during the perinatal period.
Hypoxia‐ischemia during the perinatal period could damage the hippocampal interneuron populations which might lead to the appearance of different problems during subsequent development. Interneurons containing Somatostatin and Neuropeptide Y located in the hippocampal ammonic fields are affected differently, although there is a global reduction after suffering perinatal hypoxia‐ischemia. This work is the first study that describes this issue in depth in the developmental human hippocampus.
Abstract Our current understanding of the spread and neurodegenerative effects of tau neurofibrillary tangles (NFTs) within the medial temporal lobe (MTL) during the early stages of Alzheimer’s ...Disease (AD) is limited by the presence of confounding non-AD pathologies and the two-dimensional (2-D) nature of conventional histology studies. Here, we combine ex vivo MRI and serial histological imaging from 25 human MTL specimens to present a detailed, 3-D characterization of quantitative NFT burden measures in the space of a high-resolution, ex vivo atlas with cytoarchitecturally-defined subregion labels, that can be used to inform future in vivo neuroimaging studies. Average maps show a clear anterior to poster gradient in NFT distribution and a precise, spatial pattern with highest levels of NFTs found not just within the transentorhinal region but also the cornu ammonis (CA1) subfield. Additionally, we identify granular MTL regions where measures of neurodegeneration are likely to be linked to NFTs specifically, and thus potentially more sensitive as early AD biomarkers.
We present a method for human brain fixation based on simultaneous perfusion of 4% paraformaldehyde through carotids after a flush with saline. The left carotid cannula is used to perfuse the body ...with 10% formalin, to allow further use of the body for anatomical research or teaching. The aim of our method is to develop a vascular fixation protocol for the human brain, by adapting protocols that are commonly used in experimental animal studies. We show that a variety of histological procedures can be carried out (cyto- and myeloarchitectonics, histochemistry, immunohistochemistry, intracellular cell injection, and electron microscopy). In addition,
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high-resolution MRI (9.4T) can be obtained in the same specimens. This procedure resulted in similar morphological features to those obtained by intravascular perfusion in experimental animals, provided that the postmortem interval was under 10 h for several of the techniques used and under 4 h in the case of intracellular injections and electron microscopy. The use of intravascular fixation of the brain inside the skull provides a fixed whole human brain, perfectly fitted to the skull, with negligible deformation compared to conventional techniques. Given this characteristic of
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fixation, this procedure can probably be considered the most suitable one available for
MRI scans of the brain. We describe the compatibility of the method proposed for intravascular fixation of the human brain and fixation of the donor's body for anatomical purposes. Thus, body donor programs can provide human brain tissue, while the remainder of the body can also be fixed for anatomical studies. Therefore, this method of human brain fixation through the carotid system optimizes the procurement of human brain tissue, allowing a greater understanding of human neurological diseases, while benefiting anatomy departments by making the remainder of the body available for teaching purposes.
Tau protein neurofibrillary tangles (NFT) are linked to neuronal and synaptic loss and cognitive decline in Alzheimer's disease (AD) and related dementias. In AD, NFT pathology is known to spread ...through the cortex in a characteristic pattern, starting in the medial temporal lobe. However, the exact 3D pattern of NFT progression has not been described, and capturing this pattern quantitatively can help inform in vivo AD imaging biomarkers. We present a computational framework for generating 3D maps of NFT load from ex vivo MRI and serial histology. Weakly supervised deep learning is used to detect NFTs on histology slides prepared with an anti-tau immunohistochemistry stain, and a multi-stage registration pipeline that leverages 3D printing is used for histology-MRI alignment. Derived maps of NFT density are strongly concordant with manual NFT counting, as well as categorical NFT severity ratings used for clinical diagnosis.
Earliest neuropathological changes in Alzheimer's Disease (AD) emerge in the medial temporal lobe (MTL). In order for MRI biomarkers to detect changes linked specifically to AD pathology (as opposed ...to aging or other pathological factors) macroscopic patterns of structural change in the MTL must be linked to the underlying neuropathology. To provide such a linkage, we are conducting an autopsy imaging study combining ex vivo MRI and serial histopathology. Information from multiple subjects can be studied by creating a "population average" atlas of the MTL. We present a groupwise registration approach for constructing the atlas that is able to successfully capture the complex structure of the MTL, and anatomical variability across subjects. This atlas allows us to generate maps of cortical thickness measurements and identify regions in the MTL where structural changes correlate most strongly with AD progression. We show that using this atlas, we are able to find a significant correlation between atrophy and AD pathology in the MTL sub-regions associated with the earliest stages of AD pathology as described by Braak and Braak 1.
Background
The anterior portion of the medial temporal lobe (MTL) is one of the earliest regions showing tau deposition in Alzheimer’s disease (AD) and hence a key focus area for AD imaging ...biomarkers. However, the anatomical variability of the anterior MTL presents a challenge for segmentation protocols. Leveraging a novel postmortem dataset with histology and MRI, we aimed to develop a histologically‐informed segmentation protocol for the anterior entorhinal cortex (ERC), Brodmann Area (BA) 35 (approximates transentorhinal cortex), and BA36 for in vivo 3 tesla (T) MRI.
Method
Digitized 50‐µm thick MTL Nissl‐stained coronal histology sections from 20 cases (Table 1) were annotated by expert neuroanatomists. Cases with and without neurodegenerative diseases were included to ensure broad generalizability of the protocol. The histology sections were registered to same‐subject 0.2×0.2×0.2‐mm3 9.4 T postmortem MRI and were analyzed together to determine the location of the histological borders of the MTL cortices in relation to anatomical landmarks observable on MRI.
Result
The distance between the anterior histological border of ERC, BA35 and BA36 was assessed in relation to different anatomical landmarks observable on MRI. The distance relative to the hippocampus was chosen, as there was relatively low between‐subject variability in distance (low SD in Table 2) and this region is easily identifiable on MRI. The ERC starts 4.75 mm (median) anterior to the hippocampus, BA35 9.25 mm and BA36 10.25 mm. There was no significant difference in distances between patients with and without neurodegenerative disease. Next, we analyzed the location of the ERC on histology sections. We determined that regardless of the depth of the collateral sulcus (CS) (contrary to more posterior regions), the inferior border of the ERC is on average at the edge of the CS and the superior border at the superior edge of the parahippocampal gyrus (Figure 1a), but at the halfway point for the first section with ERC. These segmentation rules for ERC can be applied to T1‐MRI (Figure 1b).
Conclusion
Segmentation rules for anterior BA35 and BA36 are under development. This histologically‐informed segmentation protocol is expected to improve the efficacy of imaging biomarkers for tau deposition in AD.
Background
Accumulation of tau neurofibrillary tangles (NFT) in the medial temporal lobe (MTL) is an early pathological change associated with neurodegeneration in Alzheimer’s Disease (AD). Current ...understanding of the spread of NFTs within the MTL is based on 2‐D histological sections sampled at sparse locations. Here, using human MTL specimens from donors with diagnoses spanning the AD continuum, we examine 3‐D quantitative maps of NFT burden derived from serial histology leveraging a high‐resolution, ex vivo MRI atlas, thus enabling more granular analyses.
Method
We combined ex vivo MRI scans (0.2×0.2×0.2mm3, 9.4T) of 55 MTL specimens using a customized registration approach to construct a 3‐D atlas (Ravikumar et al., Acta Neuropathol Comm, 2021). MTL subregions in the atlas were labelled based on cytoarchitecture using serial Nissl histology (n = 17) (Fig.1). For 25 specimens with a primary diagnosis of AD or primary age‐related tauopathy (78.6±10.9 years; 16M/9F), quantitative NFT burden maps were derived from serial anti‐tau immunohistochemistry histology and registered to the atlas for group‐level analysis (Yushkevich et al., Brain, 2021). For quantitative comparisons, we computed the mean NFT burden and cortical thickness within each subregion.
Result
Fig.2A shows average and summary frequency maps of NFT burden, computed separately for specimens with a low Braak stage (Braak0‐II; n = 11) and high Braak stage (BraakIV‐VI), that reveal a clear anterior‐to‐posterior gradient in NFT burden. At low Braak stages, we observe high levels of NFT burden in cornu ammonis (CA)1, entorhinal cortex (EC), and Brodmann area 35 (BA35;≈transentorhinal region), particularly in the outer cortical layers. CA1 and EC also show higher NFT burden relative to BA35 (Fig.2C). At high Braak stages, overall NFT burden is visibly higher and more widespread, with significant increases found across almost all subregions (Fig.2B). Moreover, significant correlations between NFT burden and cortical thinning were found in the perforant pathway (PP; molecular layer of the subiculum), dentate gyrus, EC and Areas TE, TF and TH (Fig.3).
Conclusion
Building on earlier work, we provide a detailed characterization of the distribution of NFT burden in the MTL. Our findings of specific subregional involvement of early NFT pathology can help inform the development of improved in vivo neuroimaging biomarkers
Introduction
Neurodegenerative disorders are associated with different pathologies that often co‐occur but cannot be measured specifically with in vivo methods.
Methods
Thirty‐three brain hemispheres ...from donors with an Alzheimer's disease (AD) spectrum diagnosis underwent T2‐weighted magnetic resonance imaging (MRI). Gray matter thickness was paired with histopathology from the closest anatomic region in the contralateral hemisphere.
Results
Partial Spearman correlation of phosphorylated tau and cortical thickness with TAR DNA‐binding protein 43 (TDP‐43) and α‐synuclein scores, age, sex, and postmortem interval as covariates showed significant relationships in entorhinal and primary visual cortices, temporal pole, and insular and posterior cingulate gyri. Linear models including Braak stages, TDP‐43 and α‐synuclein scores, age, sex, and postmortem interval showed significant correlation between Braak stage and thickness in the parahippocampal gyrus, entorhinal cortex, and Broadman area 35.
Conclusion
We demonstrated an association of measures of AD pathology with tissue loss in several AD regions despite a limited range of pathology in these cases.
Highlights
Neurodegenerative disorders are associated with co‐occurring pathologies that cannot be measured specifically with in vivo methods.
Identification of the topographic patterns of these pathologies in structural magnetic resonance imaging (MRI) may provide probabilistic biomarkers.
We demonstrated the correlation of the specific patterns of tissue loss from ex vivo brain MRI with underlying pathologies detected in postmortem brain hemispheres in patients with Alzheimer's disease (AD) spectrum disorders.
The results provide insight into the interpretation of in vivo structural MRI studies in patients with AD spectrum disorders.
Background
Measurements of medial temporal lobe (MTL) neurodegeneration derived using MRI have been shown to be sensitive to changes during the early stages of AD. The specificity of these ...measurements to tau neurofibrillary tangle (NFT) pathology is limited by other frequently comorbid non‐AD factors which also cause structural changes in the MTL. Here, we directly link changes in MTL structure to underlying NFT pathology by combining ex vivo MRI with ratings of NFT severity derived from serial histology using a dataset of 18 human MTL specimens. We hypothesize that such an analysis can be used to define MTL “hotspots” where in vivo measures will be more sensitive to disease progression in preclinical AD than current state of the art biomarkers.
Method
Ex vivo specimens from 18 donors were scanned at 0.2x0.2x0.2mm3 on 9.4T MRI. Following MRI scanning, the specimens underwent histological processing with staining for cytoarchitecture and in 15 specimens, immunohistochemistry (IHC) with the anti‐tau AT8 antibody. Using a topological unfolding method (DeKraker et al. 2018), we created 2D representations of the extra‐hippocampal cortex which implicitly align cortical folding patterns across specimens (Fig. 1). An average MTL subregion segmentation was generated in unfolded space using manual segmentations completed in 11 specimens on the basis of cytoarchitecture. Additionally, heat maps quantifying NFT burden in each of the specimens with anti‐tau IHC sections were generated using a deep learning algorithm (Yushkevich et al. 2021). Using the heatmaps and the average subregion segmentation, we investigated the relationship between NFT severity and cortical thickness.
Result
Correlation analysis between NFT measures and thickness (correcting for age) reveals strong associations in the entorhinal cortex and the border of Brodmann Area 35, consistent with the early Braak regions, and parts of Brodmann Area 36 (Fig. 2).
Conclusion
We present an unfolding framework applied to the MTL cortex, which allows us to visualize, for the first time, the distribution of MTL subregions and NFT pathology in an unfolded space. This framework provides a promising tool for detailed investigation of structural changes due to NFT pathology while explicitly accounting for the complex topology of the MTL, thereby enhancing our understanding of early AD.
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