Cholinergic neuronal loss in the globus pallidus of Alzheimer disease patients

Relationship between Alzheimer dementia and QT interval: A meta-analysis

While the link between aging and mortality from dementia is widely appreciated, the mechanism is not clear. The objective of this study was to determine whether there is a direct relationship between Alzheimer dementia (AD) and the QT interval, because the latter has been related to cardiac mortality. A systematic review and meta-analysis were conducted after a Medline and EMBASE search using terms "Alzheimer disease or Dementia AND QT interval, QT dispersion or cardiac repolarization." Four studies with control groups were identified. There were significant differences in QT interval between individuals with AD vs individuals without dementia (controls) (odds ratio (OR)1.665 [random effects model] and 1.879 [fixed effect model]) (p < 0.001). There were significant differences in QT interval between individuals with AD vs individuals with mild cognitive impairment (MCI) (OR 1.760 [random effects] and 1.810 [fixed effect]) (p < 0.001). A significant (p <0.001) correlation exists between the QTc and the Mini-Mental State Exam (MMSE), a test of cognitive function. Two studies examined QT variability (the difference between the longest and shortest QT interval on a 12 lead ECG); the OR for QT variability AD vs MCI was 3.858 [random effects model] and 3.712 [fixed effects model] (p < 0.001). When compared to the control group, the OR for QT dispersion in AD was 6.358 [random effects model] or 5.143 ( P< 0.001) [fixed effects model]. A qualitative analysis of the data raised questions about paucity of data defining the nature of the control groups, the pathophysiologic mechanism, and the uniform use of a poor QT heart rate correction factor. The longer QT in AD, greater QT variability in AD, and the direct relationship between QT interval and AD severity supports a brain-heart connection in AD that might be fundamental to aging-induced AD and mortality. Issues with defining the control group, limited number of studies, conflicting data in population studies, and the lack of a strong electrophysiological basis underscore the need for additional research in this field.

Systematic comparison of 3D Deep learning and classical machine learning explanations for Alzheimer's Disease detection

Black-box deep learning (DL) models trained for the early detection of Alzheimer's Disease (AD) often lack systematic model interpretation. This work computes the activated brain regions during DL and compares those with classical Machine Learning (ML) explanations. The architectures used for DL were 3D DenseNets, EfficientNets, and Squeeze-and-Excitation (SE) networks. The classical models include Random Forests (RFs), Support Vector Machines (SVMs), eXtreme Gradient Boosting (XGBoost), Light Gradient Boosting (LightGBM), Decision Trees (DTs), and Logistic Regression (LR). For explanations, SHapley Additive exPlanations (SHAP) values, Local Interpretable Model-agnostic Explanations (LIME), Gradient-weighted Class Activation Mapping (GradCAM), GradCAM++ and permutation-based feature importance were implemented. During interpretation, correlated features were consolidated into aspects. All models were trained on the Alzheimer's Disease Neuroimaging Initiative (ADNI) dataset. The validation includes internal and external validation on the Australian Imaging and Lifestyle flagship study of Ageing (AIBL) and the Open Access Series of Imaging Studies (OASIS). DL and ML models reached similar classification performances. Regarding the brain regions, both types focus on different regions. The ML models focus on the inferior and middle temporal gyri, and the hippocampus, and amygdala regions previously associated with AD. The DL models focus on a wider range of regions including the optical chiasm, the entorhinal cortices, the left and right vessels, and the 4th ventricle which were partially associated with AD. One explanation for the differences is the input features (textures vs. volumes). Both types show reasonable similarity to a ground truth Voxel-Based Morphometry (VBM) analysis. Slightly higher similarities were measured for ML models.

Inclusion of African American/Black adults in a pilot brain proteomics study of Alzheimer's disease

Alzheimer's disease (AD) disproportionately affects certain racial and ethnic subgroups, such as African American/Black and Hispanic adults. Genetic, comorbid, and socioeconomic risk factors contribute to this disparity; however, the molecular contributions have been largely unexplored. Herein, we conducted a pilot proteomics study of postmortem brains from African American/Black and non-Hispanic White adults neuropathologically diagnosed with AD compared to closely-matched cognitively normal individuals. Examination of hippocampus, inferior parietal lobule, and globus pallidus regions using quantitative proteomics resulted in 568 differentially-expressed proteins in AD. These proteins were consistent with the literature and included glial fibrillary acidic protein, peroxiredoxin-1, and annexin A5. In addition, 351 novel proteins in AD were identified, which could partially be due to cohort diversity. From linear regression analyses, we identified 185 proteins with significant race x diagnosis interactions across various brain regions. These differences generally were reflective of differential expression of proteins in AD that occurred in only a single racial/ethnic group. Overall, this pilot study suggests that disease understanding can be furthered by including diversity in racial/ethnic groups; however, this must be done on a larger scale.

Discriminative analysis of early-stage Alzheimer's disease and normal aging with automatic segmentation technique in subcortical gray matter structures: a multicenter in vivo MRI volumetric and DTI study

BACKGROUND

Previous studies have revealed that amyloid depositions exist in not only the hippocampus but in other subcortical gray matter structures as well. Diffusion-tensor imaging (DTI) parameters might be more sensitive measures of early degeneration in Alzheimer's disease (AD) than conventional magnetic resonance imaging (MRI) techniques.

PURPOSE

To evaluate the significance of the volumes and the mean diffusivity (MD) values of subcortical gray matter structures in discrimination between early-stage AD and normal subjects using the Integrated Registration and Segmentation Tool in FMRIB's Software Library.

MATERIAL AND METHODS

Fifty-three cases of early-stage AD and 30 normal aging volunteers from two hospitals were scanned with 3D-FSPGRIR and SSSE-EPI sequences using two similar 1.5T MR systems. The mean relative volumes and mean MD values of subcortical gray matter structures were compared between early-stage AD and control groups. Binary logistic regression analysis and receiver-operating characteristic (ROC) curves were applied to assess the diagnostic significance of every structure's relative volume, MD value, and combination of both.

RESULTS

The relative volumes of the left hippocampus, right amygdala, bilateral thalamus, right caudate, left putamen, and bilateral pallidum were significantly lower in the early-stage AD group than in the control group (P < 0.05). The MD values of the bilateral hippocampus and pallidum, and of the right thalamus and caudate were significantly elevated in the early-stage AD group (P < 0.05). In binary logistic regression analysis, the relative volume of left hippocampus and age entered the final model of volumetric analysis. The MD values of bilateral hippocampi and pallidums entered the final model of MD analysis. The MD values of bilateral hippocampi and pallidums, and the relative volume of left pallidum, entered the final model of combination analysis. The accuracy of three models was 84.7%, 88.9%, and 93.1%, respectively.

CONCLUSION

Pathological changes takes place in the hippocampus and other subcortical gray matter structures in early-stage AD. Diffusive imaging has great diagnostic significance in early-stage AD. The combination of both imaging modalities can lead to better discrimination between early-stage AD and normal aging.

QT dispersion in mild cognitive impairment: a possible tool for predicting the risk of progression to dementia?

OBJECTIVE

The aim of this research was to investigate relationships between cognitive function and non-invasive, repeatable cardiac parameters in elderly subjects suffering from mild cognitive impairment (MCI) or Alzheimer's disease (AD).

METHODS

Two hundred and twenty-four community-living elderly subjects, 31 AD patients, 77 MCI patients, and 116 cognitively normal subjects (CNS), were evaluated for cognitive abilities (Mini Mental State Examination score (MMSE)) and for electrocardiographic [corrected heart rate QT interval dispersion (QTcD)] and echocardiographic [Left ventricular ejection fraction (LVEF)] parameters.

RESULTS

Mean values of LVEF were not significantly different between the three groups; QTcD mean values were significantly lower in CNS group than in subjects with MCI and AD. The Pearson Product Moment Correlation test, carried out in the three study groups, showed a significant inverse correlation between QTcD and MMSE score (r = -0.357; p < 0.01) in the group of MCI patients, only. In multivariable-adjusted linear regression tests, QTcD (p = 0.030) and education (p = 0.021) are associated with MMSE score in MCI group. Only the parameter of education appears to predict MMSE in CNS group; none of these parameters appear to predict MMSE in the group of patients with AD.

CONCLUSION

The association between QTcD and MMSE requires cautious interpretation and further extensive investigation. However, if confirmed by longitudinal studies, the finding could play a role in the management of the subjects with MCI.

Subcortical morphological correlates of impaired clock drawing performance

The objective of this study was to investigate the associations between clock drawing test (CDT) performance and subcortical brain morphology. Fifty-four participants (21 patients with Alzheimer's disease, 23 with mild cognitive impairment and 10 healthy controls) underwent neuropsychological assessment and high-resolution magnetic resonance imaging at 3T. CDT performance was related to volume and shape measurements of amygdala, caudate nucleus, hippocampus, nucleus accumbens, pallidum, putamen, and thalamus, respectively. Impaired CDT performance was correlated with alterations predominantly in the hippocampus bilaterally and in the right globus pallidus. These associations referred to regionally specific morphometric alterations rather than to global atrophy of the respective structures. Our findings support an involvement of subcortical brain regions in CDT performance.

Three-dimensional cartography of functional territories in the human striatopallidal complex by using calbindin immunoreactivity

This anatomic study presents an analysis of the distribution of calbindin immunohistochemistry in the human striatopallidal complex. Entire brains were sectioned perpendicularly to the mid-commissural line into 70-microm-thick sections. Every tenth section was immunostained for calbindin. Calbindin labeling exhibited a gradient on the basis of which three different regions were defined: poorly labeled, strongly labeled, and intermediate. Corresponding contours were traced in individual sections and reformatted as three-dimensional structures. The poorly labeled region corresponded to the dorsal part of the striatum and to the central part of the pallidum. The strongly labeled region included the ventral part of the striatum, the subcommissural part of the external pallidum but also the adjacent portion of its suscommissural part, and the anterior pole of the internal pallidum. The intermediate region was located between the poorly and strongly labeled regions. As axonal tracing and immunohistochemical studies in monkeys show a similar pattern, poorly, intermediate, and strongly labeled regions were considered as the sensorimotor, associative, and limbic territories of the human striatopallidal complex, respectively. However, the boundaries between these territories were not sharp but formed gradients of labeling, which suggests overlapping between adjacent territories. Similarly, the ventral boundary of the striatopallidal complex was blurred, suggesting a structural intermingling with the substantia innominata. This three-dimensional partitioning of the human striatopallidal complex could help to define functional targets for high-frequency stimulation with greater accuracy and help to identify new stimulation sites.

Cholinergic septal afferent terminals preferentially contact neuropeptide Y-containing interneurons compared to parvalbumin-containing interneurons in the rat dentate gyrus

Septal cholinergic neurons may affect hippocampal memory encoding and retrieval by differentially targeting parvalbumin (PARV)-containing basket cells and neuropeptide Y (NPY) interneurons. Thus, the cellular associations of cholinergic efferents, identified by the low-affinity, p75 neurotrophin receptor (p75(NTR)), with interneurons containing either PARV or NPY in the hilus of the rat dentate gyrus were examined in single sections using dual labeling immunoelectron microscopy. Most profiles immunoreactive (IR) for PARV and NPY were perikaryal and dendritic and found within the infragranular and central hilar regions, respectively, whereas most profiles with p75(NTR)-labeling were unmyelinated axons and axon terminals. Although PARV-labeled profiles were more numerous, p75(NTR)-labeled axons and terminals contacted few PARV-IR profiles compared to NPY-labeled profiles (2% of 561 for PARV vs 12% of 433 for NPY). Moreover, structures targeted by p75(NTR)-IR axon terminals varied depending on the presence of PARV or NPY immunoreactivity. p75(NTR)-IR terminals primarily contacted PARV-IR dendrites (87%) compared to somata (13%); however, they contacted more NPY-IR somata (57%) than dendrites (43%). p75(NTR)-labeled terminals formed exclusively symmetric (inhibitory-type) synapses with PARV-IR somata and dendrites; however, they formed mostly symmetric but also asymmetric (excitatory-type) synapses with NPY-IR somata and dendrites. These results suggest that septal cholinergic efferents in the dentate gyrus: (1) preferentially innervate NPY-containing interneurons compared to PARV-containing basket cells; and (2) may provide a more powerful (i.e., somatic contacts), yet functionally diverse (i.e., asymmetric and symmetric synapses), modulation of NPY-containing interneurons. Moreover, they provide evidence that neurochemical subsets of hippocampal interneurons can be distinguished by afferent input.

Neurofibrillary tangles without cell loss in the lateral vestibular nucleus of patients with Alzheimer's disease

The lateral vestibular nucleus (LVN, nucleus of Deiters) was examined in the brains of four control subjects and four patients with dementia of the Alzheimer type (DAT). Neuronal counts on sections stained with silver and a polyclonal antibody to human choline acetyltransferase (ChAT) revealed an undiminished number of LVN neurons in patients with DAT. Numerous silver-stained neurofibrillary tangles (NFTs) were found in the DAT group, some also in the LVN of controls. These findings suggest that DAT affects LVN neurons, however without causing neuronal loss.

Alteration of pallidal cholinergic activity in MPTP-treated monkeys: effect of dihydro-alpha-ergocryptine (DEK)

Monkeys, intravenously administered with MPTP at the dose of 0.3 mg/kg for 5 consecutive days, develop a severe Parkinson-like syndrome. Cholinergic enzyme activities are increased in the internal segment of the globus pallidus (GPi) and into a lesser extent in the external globus pallidus (GPe). Cholinergic activities are not significantly affected in the caudate and putamen nor in the frontal, parietotemporal, occipital cortices and in the cerebellum. The treatment of the animals twice daily for 2 weeks with dihydro-alpha-ergocryptine (DEK) starting 5 days before the first MPTP administration counteracts the neurotoxin-induced alteration in the internal pallidum and ameliorates some motor related parkinsonian symptoms.

Interactions between the effects of basal forebrain lesions and chronic treatment with MDL 26,479 on learning and markers of cholinergic transmission

The effects of ibotenic acid-induced basal forebrain lesions and treatment with the triazole MDL 26,479 on the acquisition of an operant visual conditional discrimination task and on [3H]hemicholinium-3 and [3H]vesamicol binding were examined. Lesioned animals required more training sessions to acquire the stimulus-response rules of this task. They also showed longer response latencies throughout the experiment. The effects of the treatment with MDL 26,479 (5 mg/kg; i.p. 60 min before each training session) interacted with the effects of the lesion, producing a decrease in the number of sessions required to perform above chance-level in lesioned but not in control animals. MDL 26,479 did not seem to produce immediate performance effects but interacted with the learning process. The lesions destroyed the cell bodies in the area of the substantia innominata, basal nucleus of Meynert, and the globus pallidus. The number of frontocortical cholinergic terminals as primarily indicated by hemicholinium-3 binding was reduced in lesioned animals; however, another measure of cholinergic terminals, vesamicol binding, was unchanged. Behavioral performance of animals correlated significantly with hemicholinium binding in the frontal cortex of the right hemisphere. The fact that the lesion delayed but did not block the acquisition of the task may have been a result of compensatory mechanisms in remaining cholinergic terminals as indicated by stable vesamicol binding. These data allow assumptions about the conditions for the demonstration of beneficial behavioral effects of MDL 26,479. They also suggest that the long-term effects of basal forebrain lesions on cortical cholinergic transmission remain unsettled.

Heterogeneity and selectivity of the degeneration of cholinergic neurons in the basal forebrain of patients with Alzheimer's disease

Cholinergic neurons were studied by immunohistochemistry, with an antiserum against choline acetyltransferase (ChAT), in the basal forebrain (Ch1 to Ch4) of four patients with Alzheimer's disease (AD) and four control subjects. ChAT-positive cell bodies were mapped and counted in Ch1 (medial septal nucleus), Ch2 (vertical nucleus of the diagonal band), Ch3 (horizontal nucleus of the diagonal band) and Ch4 (nucleus basalis of Meynert). Compared to controls, the number of cholinergic neurons in AD patients was reduced by 50% on average. The interindividual variations in cholinergic cell loss were high, neuronal loss ranging from moderate (27%) to severe (63%). Despite the small number of brains studied, a significant correlation was found between the cholinergic cell loss and the degree of intellectual impairment. To determine the selectivity of cholinergic neuronal loss in the basal forebrain of AD patients, NPY-immunoreactive neurons were also investigated. The number of NPY-positive cell bodies was the same in controls and AD patients. The results (1) confirm cholinergic neuron degeneration in the basal forebrain in AD and the relative sparing of these neurons in some patients, (2) indicate that degeneration of cholinergic neurons in the basal forebrain contributes to intellectual decline, and (3) show that, in AD, such cholinergic cell loss is selective, since NPY-positive neurons are preserved in the basal forebrain.

Decreased choline acetyltransferase mRNA expression in the nucleus basalis of Meynert in Alzheimer disease: an in situ hybridization study

The subnormal choline acetyltransferase (ChoAcTase) activity in the cerebral cortex of patients with Alzheimer disease (AD) is thought to originate from the loss of cholinergic neurons in the nucleus basalis of Meynert (nbM). To examine possible changes in the functional activity of the remaining cholinergic neurons in the nbM of patients with AD, the level of expression of ChoAcTase mRNA was evaluated. A procedure for double-labeling cholinergic neurons to detect ChoAcTase mRNA and the corresponding protein in the same cell was developed, taking advantage of an anti-ChoAcTase antibody and the recently isolated cDNA complementary to a sequence of the human ChoAcTase mRNA. In the study of three controls and four patients with AD, the presence of both ChoAcTase mRNA and protein was observed in the same large neurons in both nbM and putamen. Specificity of in situ hybridization was further supported by the absence of neuronal staining with a sense probe. In AD patients a subnormal level of expression of ChoAcTase mRNA per cholinergic cell was detected in the nbM but not in the putamen. Our data support the hypothesis that expression of ChoAcTase mRNA might be down-regulated in the surviving cholinergic neurons in the nbM of patients with AD, raising the possibility of functional restoration by stimulating ChoAcTase synthesis.