Neuroglia: Definition, Classification, Evolution, Numbers, Development

Verkhratsky, Alexei; Butt, Arthur M.

doi:10.1002/9781118402061.ch3

Cited by 16 publications

(1 citation statement)

References 79 publications

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“…They are mainly divided in astrocytes, microglia and oligodendrocytes. Glial cells are essentially involved in all brain functions and are approximately as numerous as neurons in the human CNS (Allen and Barres, 2009;von Bartheld et al, 2016) with recent estimates suggesting that in human neocortex approximately 75% of glial cells are oligodendrocytes, 5% microglia and 20% are astrocytes (Pelvig et al, 2008;Butt and Verkhratsky, 2013) Astrocytes enclose endothelial cells, provide trophic support for other cell types, maintaining the homeostasis of water and ions in the brain (Kandel et al, 2012), contact and enclose synapses with their fine perisynaptic processes (Allen and Eroglu, 2017) and are involved in synaptic recycling (Allen and Barres, 2009). Microglia are the resident immune and inflammatory cells of the CNS and its primary defense against pathogens.…”

Section: Chapter 1 Introduction 11 Glia Cells In the Central Nervous ...mentioning

confidence: 99%

Investigation of myelin maintenance and turnover by inducible MBP knock-out in adult mice

Meschkat¹

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The turnover and maintenance of myelin in the adult CNSMyelin is a multilayered membrane structure generated by oligodendrocytes in the CNS that insulates and supports axons. While most of the oligodendrocyte population differentiates early in life and persist for most of the lifetime, myelin proteins are slowly turned over and replaced within weeks to months. However, the mechanisms of this turnover and replacement processes within the myelin sheath are largely unknown. One reason is the absence of a suitable model system. To study myelin turnover in the adult animal a model system is required that allows to investigate myelin maintenance under conditions of ongoing turnover, survival of oligodendrocytes and the avoidance of acute inflammation. In this thesis a new model system was established that meets these requirements and was used to study turnover within the individual myelin sheath. This model system is based on a strategy for the visualization of myelin renewal by the application of an inducible deletion of myelin basic protein (Mbp) expression in the adult. For this purpose, ablation of MBP was induced in young adult mice after completion of developmental myelination at the age of 8 weeks. After the knock-out was induced, any newly synthetized myelin membrane lacked MBP and therefore the essential component for myelin compaction. The absence of compaction served as a marker for newly made myelin and was studied by electron microscopy. Using volume imaging by focused ion beam scanning electron microscopy (FIB-SEM) we observed the emergence of non-compact myelin membranes at the inner tongue of the juxta-paranodal region. The localized emergence of these membranes suggests the juxta-paranode as a site of MBP integration within the myelin sheath. Furthermore, the progressive loss of compact myelin after ablation of MBP synthesis was quantified and a shortening of internodes in the optic nerve by 50% within 19-21 weeks was observed. This shows that under these conditions half of the internode is turned over within 4-5 months. We performed proteome analysis of the optic nerve eight, 16 and 40 weeks after Mbp knockout induction to investigate systemic responses after loss of de novo MBP synthesis and found reduced abundance for proteins associated to the myelin sheath and cell adhesion molecules while many cytoskeleton-associated proteins were increased in abundance. These results are in accordance with the detected loss of the compact myelin compartment. To identify potential mechanisms for oligodendrocyte intrinsic or extrinsic recycling of myelin we analyzed individual axons in 3D FIB-SEM volumes and detected an increased number of myelin spheres at the inner tongue of the oligodendrocytes. We suggest that these myelin spheres are very likely involved in disposal of aged myelin. Visualization of the observed processes of membrane integration and removal were made possible by combination of high-quality structural preservation, 3D FIB-SEM microscopy and the novel mouse model system. In conclusion, this stud...

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Section: Chapter 1 Introduction 11 Glia Cells In the Central Nervous ...mentioning

confidence: 99%

Investigation of myelin maintenance and turnover by inducible MBP knock-out in adult mice

Meschkat¹

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The Cellular Composition and Glia–Neuron Ratio in the Spinal Cord of a Human and a Nonhuman Primate: Comparison With Other Species and Brain Regions

Bahney

Bartheld

2017

The Anatomical Record

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The cellular composition of brains shows largely conserved, gradual evolutionary trends between species. In the primate spinal cord, however, the glia-neuron ratio was reported to be greatly increased over that in the rodent spinal cord. Here, we re-examined the cellular composition of the spinal cord of one human and one nonhuman primate species by employing two different counting methods, the isotropic fractionator and stereology. We also determined whether segmental differences in cellular composition, possibly reflecting increased fine motor control of the upper extremities, may explain a sharply increased glia-neuron ratio in primates. In the cynomolgus monkey spinal cord, the isotropic fractionator and stereology yielded 206-275 million cells, of which 13.3-25.1% were neurons (28-69 million). Stereological estimates yielded 21.1% endothelial cells and 65.5% glial cells (glia-neuron ratio of 4.9-5.6). In human spinal cords, the isotropic fractionator and stereology generated estimates of 1.5-1.7 billion cells and 197-222 million neurons (13.4% neurons, 12.2% endothelial cells, 74.8% glial cells), and a glia-neuron ratio of 5.6-7.1, with estimates of neuron numbers in the human spinal cord based on morphological criteria. The non-neuronal to neuron ratios in human and cynomolgus monkey spinal cords were 6.5 and 3.2, respectively, suggesting that previous reports overestimated this ratio. We did not find significant segmental differences in the cellular composition between cervical, thoracic and lumbar levels. When compared with brain regions, the spinal cord showed gradual increases of the glia-neuron ratio with increasing brain mass, similar to the cerebral cortex and the brainstem. Anat Rec, 301:697-710, 2018. © 2017 Wiley Periodicals, Inc.

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Neurons and Plasticity: What Do Glial Cells Have to Do with This?

Iannella

Condemine²

2020

Brain Informatics and Health

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Neuroglia: Definition, Classification, Evolution, Numbers, Development

Cited by 16 publications

References 79 publications

Investigation of myelin maintenance and turnover by inducible MBP knock-out in adult mice

Investigation of myelin maintenance and turnover by inducible MBP knock-out in adult mice

The Cellular Composition and Glia–Neuron Ratio in the Spinal Cord of a Human and a Nonhuman Primate: Comparison With Other Species and Brain Regions

Neurons and Plasticity: What Do Glial Cells Have to Do with This?

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