L14 (C6)

Question 1

describe an astrocyte

Answer 1

“Star” shaped, long branched processes
Most numerous glia in grey matter
Non-excitable support cells, but able to
communicate

Question 2

what is the most abundant cell type in the brain

Answer 2

astrocyte

Question 3

astrocytes have many functions

what are these

Answer 3

modulation of communication

nutrient transport from blood to neuron

supporting myelin coverage of neurons

Question 4

what allows astrocytes to communicate neurons, vasculature, intestinal volume and other cells

Answer 4

They have extensive processes

Question 5

what can astrocytes be distinguished by

Answer 5

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

Question 6

what is the most commonly used marker of astrocytes

Answer 6

GFAB is the most commonly used marker.

These are the major intermediate filaments proteins which compose within the cytoplasm

Question 7

what is the role of GFAB

Answer 7

important for maintaining its structure, integrity and aiding its is movement and shape change

Question 8

what is Heterogeneity

Answer 8

Heterogeneity = lots of different kinds

Question 9

how many different subtypes of astrocytes are there in the brain

Answer 9

9

Question 10

what are the 2 types of astrocytes

Answer 10

Fibrous -(white matter)

Protoplasmic – (grey matter)

Question 11

describe fibrous astrocytes

Answer 11

Fibrous -(white matter)
radial glia - radially arranged in white matter and more specialized forms

they have very long processes

Question 12

describe Protoplasmic astrocytes

Answer 12

Protoplasmic – (grey (gray) matter)
majority of astrocytes
envelops synapses

many short or long processes. Some branching distally, dilated endfeet

Question 13

what is the form and shape of an astrocyte dependent on

Answer 13

the location and function of that astrocyte

Question 14

where are astrocytes located

Answer 14

adjacent to blood vessels

Question 15

astrocytes have exclusive territories. do these overlap

Answer 15

yes this is called discrete region of interaction of the fine
terminal processes

Question 16

describe the arrangement of astrocytes

Answer 16

Astrocytes have ordered arrangements (scaffold like) with minimum overlap

they contain many gap junctions

Question 17

astrocytes can pick up information and

pass it on – HOW?

Answer 17

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

Question 18

what is a hemichannel

Answer 18

Gap junction to

release into ECS

Question 19

what is a reflexive gap junction

Answer 19

a gap junction onto itself

(from one process onto another process of the same astrocyte)

intracellular is from one cell to another

Question 20

Astrocytic processes show spontaneous morphological
changes in a matter of minutes.

what are the things that change

Answer 20

lamellipodia and filopodia

Question 21

how do astrocytes modulate communication

Answer 21

synapses are enveloped by astrocytes

Question 22

the synapps is build from 3 important parts. what are they

Answer 22

pre and postsynaptic membrane

and the astrocytes the surround the synapse

Question 23

what happens at the synapps in terms of pre and postsynaptic membrane and the astrocytes the surround the synapse

Answer 23

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

Question 24

what is meant by the astrocyte has a bidirectional effect on the synapse

Answer 24

they affect both the axon and the dendrites

Question 25

Neurons are depend on astrocytes for glutamine, which causes synthesis of

Answer 25

Glutamate

GABA

Aspartate

Question 26

what are some glutamate transporters found in astroglia

Answer 26

GLAST, (EAAT1) and Glt1 (EAAT2)

Question 27

using the example of glutamate. explain how astrocytes regulate uptake and recycling of neurotransmitters

Answer 27

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

Question 28

explain astrocytes role in CNS ionic homeostasis

Answer 28

Astrocytes actively buffer potassium
ions

have all the proteins a neighbouring
neuron has. therefore they have voltage gated channels +
neurotransmitter receptors

Question 29

how do astrocytes modulate neural activity

Answer 29

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

Question 30

how do astrocytes lead neurotransmitter release at a distant synapps

Answer 30

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.

Question 31

what is a neuronal domain

Answer 31

Astrocyte contacts a number of neurons across 100µm

this results in neuronal synchronization of
these neurons which is known as a neuronal domain

Question 32

how do astrocytes get energy

Answer 32

by controlling blood flow

The astrocytes have foot processes on the blood vessels

Question 33

how do astrocytes control cerebral blood flow

Answer 33

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

Question 34

how does increased neural function lead to increased blood flow to that area

Answer 34

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

Question 35

how do Astrocytes bring nutrients to the neurons

Answer 35

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

Question 36

what is the astrocytes contribution to energy dependent on

Answer 36

metabolic activity of the neurons because it is dependent on the glutamate activating the intracellular signaling

Question 37

what part of astrocyte dysfunction leads to AD

Answer 37

Reactive astrocytes

become Aβ producers.

Question 38

when dysfunctional astrocytes produce Aβ what does that cause

Answer 38

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