The acoustic cortex in Alzheimer's disease

Synaptopathy Mechanisms in ALS Caused by C9orf72 Repeat Expansion

Amyotrophic Lateral Sclerosis (ALS) is a complex neurodegenerative disease caused by degeneration of motor neurons (MNs). ALS pathogenic features include accumulation of misfolded proteins, glutamate excitotoxicity, mitochondrial dysfunction at distal axon terminals, and neuronal cytoskeleton changes. Synergies between loss of C9orf72 functions and gain of function by toxic effects of repeat expansions also contribute to C9orf72-mediated pathogenesis. However, the impact of haploinsufficiency of C9orf72 on neurons and in synaptic functions requires further examination. As the motor neurons degenerate, the disease symptoms will lead to neurotransmission deficiencies in the brain, spinal cord, and neuromuscular junction. Altered neuronal excitability, synaptic morphological changes, and C9orf72 protein and DPR localization at the synapses, suggest a potential involvement of C9orf72 at synapses. In this review article, we provide a conceptual framework for assessing the putative involvement of C9orf72 as a synaptopathy, and we explore the underlying and common disease mechanisms with other neurodegenerative diseases. Finally, we reflect on the major challenges of understanding C9orf72-ALS as a synaptopathy focusing on integrating mitochondrial and neuronal cytoskeleton degeneration as biomarkers and potential targets to treat ALS neurodegeneration.

What has electron microscopy contributed to Alzheimer's research?

Electron microscopy has enlarged the visual horizons of the morphological alterations in Alzheimer's disease (AD). Study of the mitochondria and Golgi apparatus in early cases of AD revealed the principal role that these important organelles play in the drama of pathogenic dialog of AD, substantially affecting energy production and supply, and protein trafficking in neurons and glia. In addition, study of the morphological alterations of the dendritic arbor, dendritic spines and neuronal synapses, which are associated with mitochondrial damage, may reasonably interpret the clinical phenomena of the irreversible decline of the mental faculties and an individual's personality changes. Electron microscopy also reveals the involvement of microvascular alterations in the etiopathogenic background of AD.

Staining of dead neurons by the Golgi method in autopsy material

Golgi silver impregnation techniques remain ideal methods for the visualization of the neurons as a whole in formalin fixed brains and paraffin sections, enabling to obtain insight into the morphological and morphometric characters of the dendritic arbor, and the estimation of the morphology of the spines and the spinal density, since they delineate the profile of nerve cells with unique clarity and precision. In addition, the Golgi technique enables the study of the topographic relationships between neurons and neuronal circuits in normal conditions, and the following of the spatiotemporal morphological alterations occurring during degenerative processes. The Golgi technique has undergone many modifications in order to be enhanced and to obtain the optimal and maximal visualization of neurons and neuronal processes, the minimal precipitations, the abbreviation of the time required for the procedure, enabling the accurate study and description of specific structures of the brain. In the visualization of the sequential stages of the neuronal degeneration and death, the Golgi method plays a prominent role in the visualization of degenerating axons and dendrites, synaptic “boutons,” and axonal terminals and organelles of the cell body. In addition, new versions of the techniques increases the capacity of precise observation of the neurofibrillary degeneration, the proliferation of astrocytes, the activation of the microglia, and the morphology of capillaries in autopsy material of debilitating diseases of the central nervous system.

Mitochondria are related to synaptic pathology in Alzheimer's disease

Morphological alterations of mitochondria may play an important role in the pathogenesis of Alzheimer's disease, been associated with oxidative stress and Aβ-peptide-induced toxicity. We proceeded to estimation of mitochondria on electron micrographs of autopsy specimens of Alzheimer's disease. We found substantial morphological and morphometric changes of the mitochondria in the neurons of the hippocampus, the neocortex, the cerebellar cortex, the thalamus, the globus pallidus, the red nucleus, the locus coeruleus, and the climbing fibers. The alterations consisted of considerable changes of the cristae, accumulation of osmiophilic material, and modification of the shape and size. Mitochondrial alterations were prominent in neurons, which showed a depletion of dendritic spines and loss of dendritic branches. Mitochondrial alterations are not related with the accumulation of amyloid deposits, but are prominent whenever fragmentation of the Golgi apparatus exists. Morphometric analysis showed also that mitochondria are significantly reduced in neurons, which demonstrated synaptic pathology.

Dendritic and spinal pathology in the acoustic cortex in Alzheimer's disease: morphological estimation in Golgi technique and electron microscopy

CONCLUSIONS

The morphological and morphometric estimation of the dendrites and the dendritic spines in the acoustic cortex in Alzheimer's disease revealed substantial alterations of the dendritic arborization and marked loss of the dendritic spines, which may be related to communication impairment even in early cases of Alzheimer's disease.

OBJECTIVES

Alzheimer's disease is characterized by progressive loss of memory, impairment of judgment, and decline in communication and speech eloquence. In the present study we attempted to describe the morphological and morphometric alterations of the dendrites and the dendritic spines in the acoustic cortex in early cases of Alzheimer's disease, in order to approach the communication impairment of patients suffering from Alzheimer's disease from a neuropathological point of view.

METHODS

We studied the acoustic cortex in 22 cases of Alzheimer's disease by Golgi technique and electron microscopy.

RESULTS

The morphological and morphometric estimation of the acoustic cortex revealed loss of Cajal-Retzius cells in layer I, as well as an impressive abbreviation of the dendritic fields associated with loss of dendritic spines in all the layers of the cortex. Numerous distorted, dystrophic, and degenerated dendritic spines were also seen, which were intermixed with a considerable number of giant spines. The dendritic and spinal alterations were closely associated with mitochondrial alterations.

The acoustic cortex in frontotemporal dementia: a Golgi and electron microscope study

CONCLUSION

The neuronal loss and the alteration of the synapses in the acoustic cortex in frontotemporal dementia (FTD) may be related to the impairment of communication and symbolic sound perception, which is noticed in the majority of the cases.

OBJECTIVES

FTD is a heterogeneous neurodegenerative disorder, causing progressive decline of intellectual faculties, impairment of behavior and social performance, and impairment of speech eloquence, associated with various neurological manifestations based on a variable neuropathological background. We attempted to determine the morphological alterations of the dendrites and the dendritic spines in the acoustic cortex of 10 cases who fulfilled the diagnostic criteria for FTD.

METHODS

For the histological study we applied (a) routine neuropathological techniques and (b) rapid Golgi method. We proceeded to electron microscopy for the ultrastructural study of the synapses and the morphological and morphometric study of the organelles, the dendrites, and the dendritic spines.

RESULTS

The morphological and morphometric analysis revealed substantial neuronal loss and synaptic alterations in the acoustic cortex in all the cases of FTD and particularly in Pick disease and in primary progressive aphasia. Mitochondria alterations and changes of the Golgi apparatus were seen mostly in Pick disease.

Dendritic spine dynamics

Dendritic spines are the postsynaptic components of most excitatory synapses in the mammalian brain. Spines accumulate rapidly during early postnatal development and undergo a substantial loss as animals mature into adulthood. In past decades, studies have revealed that the number and size of dendritic spines are regulated by a variety of gene products and environmental factors, underscoring the dynamic nature of spines and their importance to brain plasticity. Recently, in vivo time-lapse imaging of dendritic spines in the cerebral cortex suggests that, although spines are highly plastic during development, they are remarkably stable in adulthood, and most of them last throughout life. Therefore, dendritic spines may provide a structural basis for lifelong information storage, in addition to their well-established role in brain plasticity. Because dendritic spines are the key elements for information acquisition and retention, understanding how spines are formed and maintained, particularly in the intact brain, will likely provide fundamental insights into how the brain possesses the extraordinary capacity to learn and to remember.

Synaptic alterations in the medial geniculate bodies and the inferior colliculi in Alzheimer's disease: a Golgi and electron microscope study

CONCLUSION

The neuronal loss and the alteration of the synapses in the medial geniculate bodies and the inferior colliculi may be involved in the impairment of communication and symbolic sound perception, which is noticed even in the early stages of Alzheimer's disease.

OBJECTIVES

Alzheimer's disease (AD) is a neurodegenerative disorder, causing a progressive decline of intellectual faculties, gradual impairment of behavior and social performance, impairment of communication and speech eloquence, and various neurological manifestations. We attempted to figure out the synaptic alterations in the medial geniculate bodies and the inferior colliculi in 12 early cases of Alzheimer's disease, who fulfilled the clinical, and laboratory diagnostic criteria of Alzheimer's disease.

SUBJECTS AND METHODS

For the histological study we applied routine neuropathological techniques as well as Bodian staining and rapid Golgi method. We proceeded to electron microscopy for the ultrastructural study of synapses and dendritic spines.

RESULTS

The morphological and morphometric analysis revealed substantial neuronal loss and synaptic alterations in the medial geniculate bodies as well as in inferior colliculi. Dendritic spines of the polyhedral and elongated cells of the medial geniculate bodies were decreased in number. Mitochondrial alterations and fragmentation of Golgi apparatus were seen in 15% of the neurons of the medial geniculate bodies and in 5% of the neurons of the inferior colliculi. Senile plaques and neurofibrillary tangles were not seen in either the medial geniculate bodies or the inferior colliculi.

Dendritic and spinal pathology in the acoustic cortex in Alzheimer's disease: morphological and morphometric estimation by Golgi technique and electron microscopy

CONCLUSIONS

The morphological and morphometric estimation of the dendrites and the dendritic spines in the acoustic cortex in Alzheimer's disease revealed substantial alterations of the dendritic arborization and marked loss of the dendritic spines. This may be related to communication impairment even in early cases of Alzheimer's disease.

OBJECTIVES

Alzheimer's disease is characterized by progressive loss of memory, impairment of judgment, and decline in communication and speech eloquence. In the present study we attempted to describe the morphological and morphometric alterations of the dendrites and the dendritic spines in the acoustic cortex in early cases of Alzheimer's disease, in order to approach the communication impairment of patients suffering from Alzheimer's disease, from the neuropathological point of view.

MATERIALS AND METHODS

We studied the acoustic cortex in 22 cases of Alzheimer's disease by Golgi technique and electron microscopy.

RESULTS

The morphological and morphometric estimation of the acoustic cortex revealed loss of Cajal-Retzius cells in layer I, as well as an impressive abbreviation of the dendritic fields associated with loss of dendritic spines in all layers of the cortex. Numerous distorted, dystrophic and degenerated dendritic spines were also seen, which were intermixed with a considerable number of giant spines. The dendritic and spinal alterations were closely associated with mitochondrial alterations.

Rapid, concurrent alterations in pre- and postsynaptic structure induced by naturally-secreted amyloid-beta protein

In Alzheimer's disease increasing evidence attributes synaptic and cognitive deficits to soluble oligomers of amyloid beta protein (Abeta), even prior to the accumulation of amyloid plaques, neurofibrillary tangles, and neuronal cell death. Here we show that within 1-2 h picomolar concentrations of cell-derived, soluble Abeta induce specific alterations in pre- and postsynaptic morphology and connectivity in cultured hippocampal neurons. Clusters of presynaptic vesicle markers decreased in size and number at glutamatergic but not GABAergic terminals. Dendritic spines also decreased in number and became dysmorphic, as spine heads collapsed and/or extended long protrusions. Simultaneous time-lapse imaging of axon-dendrite pairs revealed that shrinking spines sometimes became disconnected from their presynaptic varicosity. Concomitantly, miniature synaptic potentials decreased in amplitude and frequency. Spine changes were prevented by blockers of nAChRs and NMDARs. Washout of Abeta within the first day reversed these spine changes. Further, spine changes reversed spontaneously by 2 days, because neurons acutely developed resistance to continuous Abeta exposure. Thus, rapid Abeta-induced synapse destabilization may underlie transient behavioral impairments in animal models, and early cognitive deficits in Alzheimer's patients.

The acoustic cortex in vascular dementia: a Golgi and electron microscope study

Morphological alterations in vascular dementia have been extensively described in the hippocampus, the cerebral cortex, the subcortical centers and the cerebellum. In the present study, we describe the morphological alterations of the acoustic cortex in five cases, which fulfilled the clinical, neuropsychological and laboratory diagnostic criteria of vascular dementia. The morphological alterations, seen in Golgi technique and electron microscopy concerned the capillaries, the dendritic arborization of the neurons, the astrocytes and the cytoarchitecture of the cortex. The neurons showed an impressive abbreviation of the dendritic fields and loss of spines. Astrocytic proliferation was seen in the cortex. The layer I showed marked decline of Cajal-Retzius cells. The majority of the synapses demonstrated changes in size and shape of the pre- and postsynaptic components and alterations of the organelles. The morphological alterations of the acoustic cortex in vascular dementia may be associated with the impairment of the verbal communication, which is not an uncommon phenomenon even in the early stages of the vascular dementia.

Mitochondrial alterations in Alzheimer's disease

Morphological alterations of mitochondria may be related to metabolic and energy deficiency in neurons in Alzheimer's disease (AD) and other neurodegenerative disorders. In previous studies on the morphological and morphometric estimation of mitochondria in AD electron microscopy revealed substantial morphological and morphometric changes in the hippocampus, the acoustic cortex, the frontal cortex, and the cerebellum. This study extends this observation to subcortical centers, namely the thalamus, the globus pallidus, the red nucleus, and the locus caeruleus in 10 brains of patients who suffered from AD. The morphological alterations consisted of very obvious changes of the mitochondrial cristae, accumulation of osmiophilic material and decrease of their size, in comparison with the normal controls. Mitochondrial alterations were particularly prominent in neurons, which showed loss of dendritic spines and abbreviation of the dendritic arborization. The ultrastructural study of a large number of neurons in the thalamus and the red nucleus revealed that the mitochondrial alterations did not coexist with cytoskeletal pathology and accumulation of amyloid deposits. However, they were prominent in neurons, which demonstrated fragmentation of the cisternae of the Golgi apparatus. The morphological alterations of the mitochondria presumably suggest oxidative damage in neurons in AD brains.

Dendritic spine loss in the hippocampus of young PDAPP and Tg2576 mice and its prevention by the ApoE2 genotype

Postmortem AD brains exhibit dendritic spine loss in the hippocampus. To determine whether this pathology may be associated with amyloid burden, the present study used the Golgi stain technique to assess age- and genotype-dependent changes in dendritic spine density in CA1 hippocampus of two transgenic mouse lines that produce high levels of Abeta. Tg2576 and PDAPP mice, as well as a group of Tg2576 mice crossed with human apoE2-expressing transgenic mice, were compared to respective transgene-negative controls. Since the time course of amyloid plaque deposition in the PDAPP and Tg2576 mice is well characterized, we examined changes in spine density at ages that corresponded to different levels of amyloid plaque load. The data show age- and genotype-dependent reductions in spine density in both Tg2576 and PDAPP mice, albeit at somewhat different time courses. The spine loss occurred prior to plaque deposition and was ameliorated by the overexpression of human apoE2. These results suggest that a soluble Abeta species may affect hippocampal synapses and thereby contribute to functional deficits evident in these animals.

Dendritic spine pathology: cause or consequence of neurological disorders?

Altered dendritic spines are characteristic of traumatized or diseased brain. Two general categories of spine pathology can be distinguished: pathologies of distribution and pathologies of ultrastructure. Pathologies of spine distribution affect many spines along the dendrites of a neuron and include altered spine numbers, distorted spine shapes, and abnormal loci of spine origin on the neuron. Pathologies of spine ultrastructure involve distortion of subcellular organelles within dendritic spines. Spine distributions are altered on mature neurons following traumatic lesions, and in progressive neurodegeneration involving substantial neuronal loss such as in Alzheimer's disease and in Creutzfeldt-Jakob disease. Similarly, spine distributions are altered in the developing brain following malnutrition, alcohol or toxin exposure, infection, and in a large number of genetic disorders that result in mental retardation, such as Down's and fragile-X syndromes. An important question is whether altered dendritic spines are the intrinsic cause of the accompanying neurological disturbances. The data suggest that many categories of spine pathology may result not from intrinsic pathologies of the spiny neurons, but from a compensatory response of these neurons to the loss of excitatory input to dendritic spines. More detailed studies are needed to determine the cause of spine pathology in most disorders and relationship between spine pathology and cognitive deficits.

Cortical distribution of neurofibrillary tangles in Alzheimer's disease matches the pattern of neurons that retain their capacity of plastic remodelling in the adult brain

The formation of neurofibrillary tangles in Alzheimer's disease shows a preferential involvement of certain cytoarchitecturally defined cortical areas suggesting systematic differences in regional neuronal vulnerability. The cellular and molecular nature of this selective neuronal vulnerability that follows a certain hierarchy of structural brain organization is largely unknown. In the present study, we compared the regional pattern of tangle density in Alzheimer's disease with systematic regional differences in neuronal plasticity that can be observed both during ageing and in Alzheimer's disease. Changes in dendritic length and arborization of Golgi-impregnated pyramidal neurons were analysed after three-dimensional reconstruction in 12 cortical areas. The intensity of dendritic remodelling that was observed during ageing as well as in Alzheimer's disease was regionally different and decreased in the following order: transentorhinal region > limbic areas (entorhinal region, hippocampus) > non-primary association areas (37, 40, 46) > primary sensory association areas (7, 18, 22) > primary sensory and motor cortex (17, 41, 4). These regional differences of neuronal plasticity follow the same pattern as the regional vulnerability to tangle formation in Alzheimer's disease. The results of the present study provide evidence that a high degree of structural neuronal plasticity might predispose neurons to tangle formation.

Age at onset of geriatric depression and sensorineural hearing deficits

Comorbidity of sensorineural hearing deficits and both depressive states and dementia in late life provided the rationale for this investigation. Cognitively intact geriatric major depressives (n = 43) were assessed for depressive symptoms, cognitive performance, and delusions while symptomatic, and following treatment, when audiometry was performed. Late-onset depressed patients (LOD) had more hearing deficits compared to early-onset depressives (EOD). Age at onset of depression was found to have a significant effect on Pure-Tone Thresholds for 0.5-4.0 kHz and on Word Recognition in Noise in the better ear (0.001 < p < 0.031; ANCOVA). Criteria for neural deficit were met more frequently in LODs compared to EODs, although this was attributable to the older age of LOD. Additional investigations can contribute to our understanding of the relationship between forms of hearing loss and both the course of geriatric depression and its relationship to dementia.

Studies on the 3-dimensional architecture of dendritic spines and varicosities in human cortex by confocal laser scanning microscopy and Lucifer yellow microinjections

A method for 3-dimensional (3-D) visualization of dendritic spines and varicosities in human cortical neurons is described. Intracellular microinjection of Lucifer Yellow was used to display the morphology of dendrites on pyramidal and non-pyramidal neurons. Confocal laser scanning microscopy was used for imaging, and 3-D reconstructions and analysis of spines and varicosities were performed. The frontal, temporal, parietal and occipital cortices, and hippocampus in normal and pathological human brains were studied. Using this technique spines can be visualized from both sides of dendrites, which are 'hidden' in 2-D representations, and therefore not usually included in the extimation of dendritic spine density/total spine numbers. In patients with Rett's syndrome and some epilepsy patients, a regional loss of dendritic spines ('naked' dendrites) was found. These results will be included in the Human Brain Mapping Project.

The structural organization of layer I of the adult human acoustic cortex. A Golgi and electron microscopy study

The cellular morphology and the three dimensional cytoarchitecture of layer I of the adult human acoustic cortex were studied by using sagittal, transverse and tangential Golgi preparations and electron microscopy. The prominent neuron of layer I of the acoustic cortex is the Retzius-Cajal cell which is a solitary neuron accompanied by satellite astrocytes located mostly below the pial surface in the upper third of the layer. This neuron demonstrates a marked polymorphism in the various regions of the acoustic cortex. The anterior part of the Hessl convolutions contains Retzius-Cajal cells which are horizontal, multipolar forming dense dendritic arborization by extending long horizontal dendrites to all directions within a tangential plane parallel to the surface of the convolutions. The axon of the Retzius-Cajal cell is a long myelinated nerve fibre which mostly run horizontally, parallel to the pial surface, descending finally to the deeper parts of the layer and projecting a large number of axonic collaterals which radiate in all directions forming dense axonic networks. The Retzius-Cajal cell in the posterior part of the Hessl convolutions is a large polyhedral or triangular cell which extends a large number of dendrites, forming two dendritic networks: one in the upper third of the layer and another in middle part of it. Both of the networks communicate with the axonic collaterals of the Retzius-Cajal cells, forming numerous axodendritic synapses as can be clearly seen in electron microscopy.(ABSTRACT TRUNCATED AT 250 WORDS)