L14 (C6) Flashcards
describe an astrocyte
“Star” shaped, long branched processes
Most numerous glia in grey matter
Non-excitable support cells, but able to
communicate
what is the most abundant cell type in the brain
astrocyte
astrocytes have many functions
what are these
modulation of communication
nutrient transport from blood to neuron
supporting myelin coverage of neurons
what allows astrocytes to communicate neurons, vasculature, intestinal volume and other cells
They have extensive processes
what can astrocytes be distinguished by
there cytoplasm as they have a well developed cytoskeleton which is dominated by intermediate filaments (glial fibrillary acidic
protein (GFAP)
or S100 = calcium binding protein ß (S100ß)
also microtubules and actin/mitochondria
they have many gap junctions
distal endfeet
Dilated on BVs
what is the most commonly used marker of astrocytes
GFAB is the most commonly used marker.
These are the major intermediate filaments proteins which compose within the cytoplasm
what is the role of GFAB
important for maintaining its structure, integrity and aiding its is movement and shape change
what is Heterogeneity
Heterogeneity = lots of different kinds
how many different subtypes of astrocytes are there in the brain
9
what are the 2 types of astrocytes
Fibrous -(white matter)
Protoplasmic – (grey matter)
describe fibrous astrocytes
Fibrous -(white matter)
radial glia - radially arranged in white matter and more specialized forms
they have very long processes
describe Protoplasmic astrocytes
Protoplasmic – (grey (gray) matter)
majority of astrocytes
envelops synapses
many short or long processes. Some branching distally, dilated endfeet
what is the form and shape of an astrocyte dependent on
the location and function of that astrocyte
where are astrocytes located
adjacent to blood vessels
astrocytes have exclusive territories. do these overlap
yes this is called discrete region of interaction of the fine
terminal processes
describe the arrangement of astrocytes
Astrocytes have ordered arrangements (scaffold like) with minimum overlap
they contain many gap junctions
astrocytes can pick up information and
pass it on – HOW?
through the astroglial network
they communicate via Ca2+ waves, Ca2+ binding protein, store and release Ca2+
they do this through hemichannels, intracellular gap junctions and reflexive gap junctions
what is a hemichannel
Gap junction to
release into ECS
what is a reflexive gap junction
a gap junction onto itself
(from one process onto another process of the same astrocyte)
intracellular is from one cell to another
Astrocytic processes show spontaneous morphological
changes in a matter of minutes.
what are the things that change
lamellipodia and filopodia
how do astrocytes modulate communication
synapses are enveloped by astrocytes
the synapps is build from 3 important parts. what are they
pre and postsynaptic membrane
and the astrocytes the surround the synapse
what happens at the synapps in terms of pre and postsynaptic membrane and the astrocytes the surround the synapse
Pre is where the neurotransmitter is released from which activates receptors in the postsynaptic terminal and in the presynaptic astroglial membrane
This results in a postsynaptic potential in the postsynaptic cell
And a Ca2+ signal in the astrocytes which can cause the release of glial transmitters which can affects the pre and postsynaptic membrane
what is meant by the astrocyte has a bidirectional effect on the synapse
they affect both the axon and the dendrites
Neurons are depend on astrocytes for glutamine, which causes synthesis of
Glutamate
GABA
Aspartate
what are some glutamate transporters found in astroglia
GLAST, (EAAT1) and Glt1 (EAAT2)
using the example of glutamate. explain how astrocytes regulate uptake and recycling of neurotransmitters
astrocytes uptake glutamate once it is released from the postsynaptic neuron (about 80%)
Astrocytes then convert glutamate to glutamine which then goes back into the presynaptic neuron to re make glutamate
This is important for clearing neurotransmitter from the synapse
explain astrocytes role in CNS ionic homeostasis
Astrocytes actively buffer potassium
ions
have all the proteins a neighbouring
neuron has. therefore they have voltage gated channels +
neurotransmitter receptors
how do astrocytes modulate neural activity
glutamate release presynaptically activates ionotropic glutamate receptors in postsynaptic neuron
glutamate also activates metabotropic receptors in the astrocyte which causes an increases in a and glial transmitters
Gliotransmitter release from astrocyte to post-synaptic neuron activates extrasynaptic NR2B-containing NMDA receptors to trigger slow inward currents (SICs) which changes membrane potential in the astrocyte
how do astrocytes lead neurotransmitter release at a distant synapps
glutamate that has been taken up from the synapse by a neighbouring astrocyte
from here it can diffuse and permeate through gap junction channels of astrocytic networks
This trafficking may result in subsequent release of gliotransmitter at a distant synapse or even extrasynaptic sites and hence affect
the activity of the underlying neuronal network.
what is a neuronal domain
Astrocyte contacts a number of neurons across 100µm
this results in neuronal synchronization of
these neurons which is known as a neuronal domain
how do astrocytes get energy
by controlling blood flow
The astrocytes have foot processes on the blood vessels
how do astrocytes control cerebral blood flow
At the end of the feet there are gap junctions which is critical to the vasodilation and constriction of the blood vessels
Increase in brain activity = increase in brain flow to that area
how does increased neural function lead to increased blood flow to that area
Neural activity leads to
vasodilation (oxygen delivery) which can be seen in PET scans and, fMRI
the above is coordinated by astrocytes
Glutamate receptors cause calcium transient in the end feet which release vasodilators
how do Astrocytes bring nutrients to the neurons
Astrocytes can convert glycogen into glucose and lactate
Glucoses can directly come from the capillaries to the neurons and be taken up by glucose transported in the neurons
Glucose can be imported into the astrocytes and converted into lactate which the neurons then use for energy
Distal astrocytes can also contribute lactate to the neurons via the gap junctions
what is the astrocytes contribution to energy dependent on
metabolic activity of the neurons because it is dependent on the glutamate activating the intracellular signaling
what part of astrocyte dysfunction leads to AD
Reactive astrocytes
become Aβ producers.
when dysfunctional astrocytes produce Aβ what does that cause
Aβ increases Ca2+ signaling in astrocytes and inhibits astrocyte
glutamate uptake
this causes glutamate excitotoxicity which increases Ca2+ signaling in neurons, leading to inhibition of LTP and memory loss
it also leads to impaired astrocytic glucose and reduced lactate release
Increased spontaneous Ca2+ signaling induces abnormal vascular responses in blood vessels
