25 Non-neuronal glial cells Flashcards
Why are glial cells called this?
“Glia” is Greek for “glue”
What percentage of brain cells do they make up?
90%
What is the most common type of cell in the brain?
The astrocytes
What do astrocytes do?
Provide neurons with structural, tropic (nutritional) support
How do you see astrocytes in the brain?
Stain with GFAP
What’s strange about microglia?
They don’t come from the brain. They’re immune cells made in bone marrow.
What are microglia?
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.
What are oligodendrocytes?
Neuroglial cells that wrap themselves around the axon of the neuron - make myelin sheath
What are Schwann cells?
They are the same as oligodendrocytes, but sheath axons in the peripheral nervous system.
What are the classic functions of glial cells?
- Structural. They hold in shape the rest of the neurons, separate them from blood vessels.
- 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.
- 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.
- Insulate axons to speed up action potentials.
- 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.
When you see a bold signal (increased blood flow) in an fMRI, what does that signal represent?
Astrocyte activity, as they take up glucose and oxygen from the blood.
What was the finding that changed view of glial cells?
They respond to electrical stimulation
What happens when glial cells are stimulated?
They release calcium from internal stores in response to stimulation
What chemical has been implicated in triggering astrocyte stimulation?
ATP - Adenosine triphosphate, coenzyme used as an energy carrier in the cells of all known organisms.
How do calcium waves propagate?
Via inositol triphosphate (IP3) diffusing through the gap junctions connecting the glia
How do astrocytes communicate?
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.
How do neurons stimulate glial cells?
Glial cells have glutamate receptors. When neuron fires, they stimulate astrocyte cells as well.
What effect does glutamate stimulation have on astrocyte?
IP3 is made and calcium and IP3 are released from stores within the cell. ATP also released. These stimulate next glial cell.
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.
- You’re never alone
- You’re never disconnected
- You’re home with your own
- When company’s expected, you’re well protected.
How do astrocytes stimulate neurons?
When a glial cell is active, glutamate pumps slow down; glutamate accumulates in the synapse. This increases stimulation of post-synaptic neuron.
How can astrocytes help form memories?
When more glutamate is present in synapse of hippocampus, this can cause LTP. Presence of astrocytes makes bonding between neurons stronger.
Do glial cells modulate activity at just one neuron at a time?
No, by communicating with each other, they modulate activity at related neurons throughout the brain.
What are the components of the “tripartite synapse”?
Presynaptic neuron
Postsynaptic neuron
Glial cells
What evidence is there that glia help synaptic development?
Neurons cultured without glia produce fewer synapses
What do glial cells do to inactive (dead) neurons?
They EAT them! Mwa-ha-ha!!! Either phagocytose them or release chemicals that cause the cells to kill themselves, called apoptosis
What happens when microglia detect infection, cancer, viruses…?
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.
How can glial response be dangerous?
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.
How do glial cells help fight neuropathologies? Two ways
- Remove dying or diseased neurons, through phagocytosis or triggering apoptosis
- Guide new axonal growth into damaged area through release of neurotrophic hormones
How can glia CAUSE neuropathologies?
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
What can treatments, such as minocycline, that reduce microglial activity do?
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
Why are peripheral benzodiazepine receptors (also known as translocator proteins) important in studying microglial cells?
Only microglia express this receptor in the brain - and ONLY when they become active
How can microglial cells be used to diagnose disease?
Given they are activated in presence of neuropathology, their activation can be measured through chemical that binds to peripheral benzodiazepine receptors.
What does minocycline do?
It’s a drug that inhibits microglia
What weird side effect does minocycline have?
Inhibits honeypot effect
