25 Non-neuronal glial cells

Question 1

Why are glial cells called this?

Answer 1

“Glia” is Greek for “glue”

Question 2

What percentage of brain cells do they make up?

Answer 2

90%

Question 3

What is the most common type of cell in the brain?

Answer 3

The astrocytes

Question 4

What do astrocytes do?

Answer 4

Provide neurons with structural, tropic (nutritional) support

Question 5

How do you see astrocytes in the brain?

Answer 5

Stain with GFAP

Question 6

What’s strange about microglia?

Answer 6

They don’t come from the brain. They’re immune cells made in bone marrow.

Question 7

What are microglia?

Answer 7

Small glial cells which migrate through nerve tissue and remove waste products by phagocytosis. They act like immune cells - crawl through the brain and look for signs of inflammation, injury or bacteria.

Question 8

What are oligodendrocytes?

Answer 8

Neuroglial cells that wrap themselves around the axon of the neuron - make myelin sheath

Question 9

What are Schwann cells?

Answer 9

They are the same as oligodendrocytes, but sheath axons in the peripheral nervous system.

Question 10

What are the classic functions of glial cells?

Answer 10

1. Structural. They hold in shape the rest of the neurons, separate them from blood vessels.
2. Transporting nutrients from the blood to the neurons. Take up glucose from the blood, convert into glycogen or lactate and transport from the capillary to neurons themselves.
3. Neural development. They release trophic factors which encourage axons to grow from one part of the cell body to another. Axons sniff out trophic factors and follow them.
4. Insulate axons to speed up action potentials.
5. Regulating integrity and efficiency of synapses.
   - Insulate synapses so NT doesn’t spill out.
   - Regulate synaptic transmission by removing excess NT from the synapse, and by helping to maintain ionic balance.

Question 11

When you see a bold signal (increased blood flow) in an fMRI, what does that signal represent?

Answer 11

Astrocyte activity, as they take up glucose and oxygen from the blood.

Question 12

What was the finding that changed view of glial cells?

Answer 12

They respond to electrical stimulation

Question 13

What happens when glial cells are stimulated?

Answer 13

They release calcium from internal stores in response to stimulation

Question 14

What chemical has been implicated in triggering astrocyte stimulation?

Answer 14

ATP - Adenosine triphosphate, coenzyme used as an energy carrier in the cells of all known organisms.

Question 15

How do calcium waves propagate?

Answer 15

Via inositol triphosphate (IP3) diffusing through the gap junctions connecting the glia

Question 16

How do astrocytes communicate?

Answer 16

Astrocytes signal each other using calcium. The gap junctions (also known as electrical synapses) between astrocytes allow the messenger molecule IP3 to diffuse from one astrocyte to another. IP3 activates calcium channels on cellular organelles, releasing calcium into the cytoplasm. This calcium may stimulate the production of more IP3. The net effect is a calcium wave that propagates from cell to cell. Extracellular release of ATP, and consequent activation of purinergic receptors on other astrocytes, may also mediate calcium waves in some cases.

Question 17

How do neurons stimulate glial cells?

Answer 17

Glial cells have glutamate receptors. When neuron fires, they stimulate astrocyte cells as well.

Question 18

What effect does glutamate stimulation have on astrocyte?

Answer 18

IP3 is made and calcium and IP3 are released from stores within the cell. ATP also released. These stimulate next glial cell.

Question 19

According to Bernstein et al. (1962), when you’re a Jet you’re a Jet all the way. List 4 advantages of being a Jet.

Answer 19

1. You’re never alone
2. You’re never disconnected
3. You’re home with your own
4. When company’s expected, you’re well protected.

Question 20

How do astrocytes stimulate neurons?

Answer 20

When a glial cell is active, glutamate pumps slow down; glutamate accumulates in the synapse. This increases stimulation of post-synaptic neuron.

Question 21

How can astrocytes help form memories?

Answer 21

When more glutamate is present in synapse of hippocampus, this can cause LTP. Presence of astrocytes makes bonding between neurons stronger.

Question 22

Do glial cells modulate activity at just one neuron at a time?

Answer 22

No, by communicating with each other, they modulate activity at related neurons throughout the brain.

Question 23

What are the components of the “tripartite synapse”?

Answer 23

Presynaptic neuron
Postsynaptic neuron
Glial cells

Question 24

What evidence is there that glia help synaptic development?

Answer 24

Neurons cultured without glia produce fewer synapses

Question 25

What do glial cells do to inactive (dead) neurons?

Answer 25

They EAT them! Mwa-ha-ha!!! Either phagocytose them or release chemicals that cause the cells to kill themselves, called apoptosis

Question 26

What happens when microglia detect infection, cancer, viruses…?

Answer 26

They flip into active mode and start destroying neurons around them, through release of cytokines. Can attract other immune cells into brain and affect function of astrocytes and neurons.

Question 27

How can glial response be dangerous?

Answer 27

In stroke, for instance, especially ischemic stroke, or head injury, glial cell response can be worse than damage itself. They detect abnormalities and start to kill everything.

Question 28

How do glial cells help fight neuropathologies? Two ways

Answer 28

1. Remove dying or diseased neurons, through phagocytosis or triggering apoptosis
2. Guide new axonal growth into damaged area through release of neurotrophic hormones

Question 29

How can glia CAUSE neuropathologies?

Answer 29

Most neurodegenerative disorders are associated with abnormal glial activity

• brains of Alzheimer’s and Parkinson’s patients show increased glial activation
• increased cytokine activity in neuropathologies

Question 30

What can treatments, such as minocycline, that reduce microglial activity do?

Answer 30

Reduce onset of neurodegenerative diseases

May reduce negative symptoms of SZ - flat affect, aversive emotional states

May stop spreading activation in epilepsy

Has been shown to slow heroine addiction in rats

Question 31

Why are peripheral benzodiazepine receptors (also known as translocator proteins) important in studying microglial cells?

Answer 31

Only microglia express this receptor in the brain - and ONLY when they become active

Question 32

How can microglial cells be used to diagnose disease?

Answer 32

Given they are activated in presence of neuropathology, their activation can be measured through chemical that binds to peripheral benzodiazepine receptors.

Question 33

What does minocycline do?

Answer 33

It’s a drug that inhibits microglia

Question 34

What weird side effect does minocycline have?

Answer 34

Inhibits honeypot effect