Download Introduction to Neuroglia

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Definition of neuroglia
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There is no clear definition for neuroglia: most of the existing ones
depict neuroglia as a supportive element of the nervous system
For example:
“The supportive tissue of the nervous system”
http://www.thefreedictionary.com/
“sustentacular tissue that surrounds and supports neurons in the
central nervous system”
Web definitions from google.com
“supporting structure of nervous tissue”
www.aimsusa.org/UsefulDefinitions.htm
Introduction to Neuroglia:
Definition, Classification, Evolution
Neuroglia (always plural) represent all cells in the brain which
are not neurones and which are electrically non-excitable
We may define neuroglia as a heterogeneous population of
cells of neural and non-neural origin responsible for brain
homeostasis (all neuroglia), myelination (oligodendrocytes)
and defence (astrocytes and microglia).
Diversity of Neuroglia
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Neuronal-glial network
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etc.
Verkhratsky & Butt (2013): Physiology and Pathophysiology
of Neuroglia, Wiley, 560 pp.
Kettenmann, Kirchhoff & Verkhratsky A. (2013). Neuron 77, 10-18.
Glia to neurone ratio
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Glia to neurone ratio
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Glia-neuronal ratio in various structures of the human brain:
Cortical grey matter 1.65 : 1
White mater: ~ infinity: 0
Thalamus 17 : 1
Brainstem ~ 10 : 1
Cerebellum 0.1 – 0.25 : 1
Neurones/Non-neuronal cells numbers were determined by isotopic fractionation,
which calculates total number of nuclei and total number of NeuN-positive cells
that are considered to be neurones.
Azevedo, Carvalho, Grinberg, Farfel, Ferretti, Leite, Jacob Filho, Lent & Herculano-Houzel (2009):
J Comp Neurol 513, 532-541.
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Evolution of glia
Evolution of neuroglia
Verkhratsky & Butt (2013): Physiology and Pathophysiology
of Neuroglia, Wiley
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Phylogenetic advance of glia
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Primate-specific glial cells
Oberheim, Wang, Goldman, Nedergaard (2006):
Trends Neurosci 29, 547-553.
Oberheim, Wang, Goldman, Nedergaard (2006): Trends Neurosci 29, 547-553
Verkhratsky & Butt (2007): Glial Neurobiology, A Textbook; Wiley & Sons
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Functions of invertebrate glia: Ancestral astrocytes
Metabolic support of neurones (Nematodes)
Regulation of development (Nematodes)
Evolution of glial function
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Control of extracellular ion homeostasis
(Nematodes)
Isolation/separation of nervous circuits
Compartmentalisation of the nervous
system (Annelida)
Increase of axonal conduction velocity
through formation of multilayered glial
sheath around axons (Annelida and some
Arthropoda – prawns)
Formation of blood-brain barrier (Arthropoda)
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Neuroglia in Caenorhabditis elegans
Neuroglia in Caenorhabditis elegans
C. elegans has 302 neurons and 56 glial cells.
Glial cell types:
50 cells cover dendrites of sensory neurons; 4 of
these 50 (CEP sheath glia) envelop the nerve
ring and send processes to some synaptic sites
in the brain.
6 cells (GLR glia) form gap junctions to both
muscle cells and motor neurons.
C. elegans has 302 neurons and 56 glial cells.
Glial cell types:
50 cells cover dendrites of sensory neurons; 4 of
these 50 (CEP sheath glia) envelop the nerve
ring and send processes to some synaptic sites
in the brain.
6 cells (GLR glia) form gap junctions to both
muscle cells and motor neurons.
Artificial ablation of glia in C. elegans does
not kill neurones but greatly affects their
development (neuronal assembly and neurite
morphogenesis) and function
Artificial ablation of glia in C. elegans does
not kill neurones but greatly affects their
development (neuronal assembly and neurite
morphogenesis) and function
Bacaj, T, Tevlin, M, Lu, Y & Shaham, S, (2008): Science 322, 744-747.
Bacaj, T, Tevlin, M, Lu, Y & Shaham, S, (2008): Science 322, 744-747.
C. elegans glia may also have sensory functions
(from Shai Shaham laboratory webpage
http://shahamlab.rockefeller.edu/research.php)
C. elegans glia may also have sensory functions
(from Shai Shaham laboratory webpage
http://shahamlab.rockefeller.edu/research.php)
Calcium signalling in C.elegans glia is controlled mainly by voltage-gated Ca channels
(Vlad Parpura, personal communication.
Calcium signalling in C.elegans glia is controlled mainly by voltage-gated Ca channels
(Vlad Parpura, personal communication.
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The ancestral glia retains some neuronal features
The ancestral glia retains some neuronal features
Verkhratsky & Butt (2013): Physiology and Pathophysiology
of Neuroglia, Wiley, pp.560
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Neuroglia in leech (Annelida)
Neuropil
Glial cell types:
Packet glial cells
(ensheath neuronal
somatas)
Connective glial cells
(ensheath axons)
Giant glial cells
(form neuropil and provide
for ion and neurotransmitter
homeostasis)
All glial cells are coupled
through gap junctions and
form a panglial syncytium
Inner capsule
Glial cell types:
Surface glia
Cortex glia
Neuropile glia
Tract glia
Packet glial cell
Outer capsule
Side nerve
Giant glial cell
Functions:
Metabolic support
Control over ion and
neurotransmitter homeostasis
Deitmer, Rose, Munsch, Schmidt, Nett, Schneider & Lohr (1999): Glia, 28, 175 - 182
Neuronal cell bodies
Neuroglia in insects (Arthropoda)
Further diversity:
Optic lobe glia
Fenestrated glia
Pseudocartridge glia
Satellite glia
Epithelial glia
Marginal glia
Glia of the deeper optic lobe regions
Glia of the olfactory system
Glia of the antenna
Mushroom body glia
Main functions:
Formation of blood-brain barrier
Transport of substances from haemolymph to
neurones
Compartmentalisation of the nervous system
Neurotransmitter homeostasis (histamine and
glutamate)
Ion homeostasis
Trophic support
Neuroprotection (especially of dopaminergic
neurones)
Circadian rhythms
Development of the CNS
Reactive gliosis
Phagocytosis
Evolutionary advances:
1) Great increase in morphological/functional diversity
2) New function (BBB; compartmentalisation)
3) Removal of glia kills neurones
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Neuroglia in vertebrates
Main Glial cell types:
Astrocytes
Oligodendrocytes
Radial glia
NG2 cells
Microlgia
Peripheral glia
(Schwann cells)
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Main functions:
Development of CNS/PNS
Control over blood-brain barrier
Main homeostatic elements of the brain
(metabolic, transport, control over ions and
neurotrasnmitters etc.)
Myelination
Brain defence
Higher brain functions
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Evolution of myelination
Great morphological
and functional diversity
Profound morpho-functional heterogeneity
of neuroglia between various brain regions
and within regions
Evolutionary advances:
Neuroglia becomes main homeostatic/defensive system
of the brain
Early evolutionary roots of myelin sheath and
fast action potential propagation
Action potential propagation velocity is the highest in prawns and shrimps
where it reaches 180 – 210 m/s; in humans the fastest fibres conduct with a
speed of ~100 – 120 m/s
Xu &Terakawa (1999): J Exp Biol 202,:1979-1989
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Early evolutionary roots of myelin sheath and
fast action potential propagation
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The giant prawns, the Anomalocaris, where the largest and the most ferocious
predators of the Cambrian period (500 - 540 millions years ago) oceans; they were
> 1 meter long and had exceedingly complex composite external eyes with
composed from tens of thousands of hexagonal ommatidial lenses.
Paterson, Garcia-Bellido, Lee, Brock, Jago, Edgecombe (2011): Nature, 480, 237-240
Myelin sheath increases the speed of action potential propagation
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Oligodendroglia – myelinating cells of the CNS
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Without myelination each human optic nerve would have a diameter of 0.75 m
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The NG2 Glia – the cells of oligodendroglial
lineage with an unknown function
Kettenmann & Verkhratsky, 2011
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NG2 glia – enigmatic “fifth” glial element
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NG2 glia are present throughout the brain
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NG2 glial cells receive proper glutamatergic synapses
Peripheral glia
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Types of Schwann cells
Satellite glia: homeostatic cells of sensory and sympathetic ganglia
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Morphology of Schwann cell
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Enteric nervous system
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Enteric glia integrates cellular elements of the gut
Olfactory encheathing glial cells
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Olfactory system
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