Lecture 1: Neuroinflammation, Excitoxicity, Oxidative Damage

Question 1

Glial Cells in the CNS

Answer 1

Oligodendrocytes
Ependymal cells
Astrocytes
Microglia

Question 2

Oligodendrocytes

Answer 2

Wrap axons in myelin

Question 3

Ependymal cells

Answer 3

Line ventricles

Produce cerebrospinal fluid

Question 4

Microglia

Answer 4

Similar to Monocytes/macrophages

Differentiate upon activation

Long survival (over 6 months)

Friend of neurons

• Phagocytose apoptotic neurons
• Secrete neuroprotective factors: BDNF, Neurotrophin 3
• Resting microglia secrete IL10

Foe of neurons

• Secrete neurotoxic molecules: TNF and IL1, glutamate, free radical species
• Can induce apoptosis

Interact with astrocytes

Question 5

Microglial Activation

Answer 5

How do microglia become activated? Microglia constantly monitor the environment.

Change in pH, osmolarity, extracellular ATP, heat
shock proteins, cytokines, chemokines, bacterial
components, viral components, cellular debris can activate microglia.

Question 6

Resting&raquo_space;> Activation

slide 8

Answer 6

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Resting&raquo_space; Stretches out&raquo_space; Stretches are thins out more&raquo_space; Shrinks up until neurites are pulled in&raquo_space; Activated

Question 7

Astrocytes

Answer 7

Star shaped

Structural frame work

Participate in blood brain barrier

Regulate what substances from the blood reach neurons

Survey neurons

Recent evidence that astrocytes also regulate synaptic communication among neurons

Also have both protective and damaging effects in injury and disease.

Question 8

Astrocytes and microglia form “glial scar”

slide 11

Answer 8

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Glial scars block axon growth through the site of injury.

Question 9

Ablation

Answer 9

Can’t win for losing…

Ablation of glial scar formation allows axons to grow through site of injury.
Unfortunately it also causes massive loss of neurons.

Question 10

Inflammation is both damaging and necessary.

Answer 10

§ In some cases anti-inflammatory treatments are
effective, in many cases not.

§ Inflammation has been implicated in depression,
Alzheimer’s, stroke, TBI, spinal cord injury, Parkinson’s, retinal degeneration, ALS, etc. etc.

Question 11

Glutamate Excitoxicity

Answer 11

Glutamate is the most common amino acid in the brain. Also potentially toxic.

MSG (monosodium glutamate), may cause dizziness and numbness

Electrophysiological response: application of glutamate → nerve cell depolarized

Question 12

MSG

Answer 12

monosodium glutamate

May cause dizziness and numbness

*Remember the story of the monkey who was given too much glutamate and died.

Question 13

Glutamate

Answer 13

Neurotransmitter that is….

1. Concentrated in vesicles
2. Released by exocytosis
3. Uptaken across the cellular membrane
4. Binds to receptors
5. Functional effects

Glutamate is generally acknowledged to be the most important transmitter for normal brain function. Nearly all excitatory neurons in the CNS are glutamatergic, and it is estimated that over half of all brain synapses release this agent. Glutamate plays an especially important role in clinical neurology because elevated concentrations of extracellular glutamate, released as a result of neural injury, are toxic to neurons.

Question 14

Ionotropic Glutamate Receptors

Answer 14

NMDA
AMPA
KAINATE

Question 15

AMPA and Kainate receptors

Answer 15

Ligand-gated ion channels

AMPA and Kainate receptors generally allow the passage of
Sodium (Na+) and K+

Question 16

NMDA receptors

Answer 16

NMDA receptors allows the passage of both Na+ and Ca++ ions. More permeable to Ca++

mediate most fast EPSPs in the CNS

Anaesthesia
Learning and memory 
Developmental plasticity 
Epilepsy 
Excitotoxicity (e.g., stroke) 
Schizophrenia

Question 17

AMPA receptors

Answer 17

mediate most fast EPSPs in the CNS

Question 18

Kainate receptors

Answer 18

Regulation of neuronal excitability, epilepsy, excitotoxicity, and pain

Question 19

Glutamate and Excitotoxicity

Answer 19

Glutamate activates 2 types of ion channels: AMPA & NMDA

Cell Death is associated with excessive calcium entry through NMDA receptors

Glutamate can activate multiple receptor systems. A crucial component of excitotoxicity is mediated through the NMDA receptor, which allows high levels of calcium entry. Such calcium selectively activates a variety of downstream events, many of which are toxic to the cell when excessive levels of activation are reached.

Question 20

Glutamate in Human Brain Following Stroke

Answer 20

Glutamate levels remain high after stroke.

Threonine, a structural amino acid, is measured as a control.

Question 21

Calcium and Neurotoxicity

Answer 21

Localized increases in [Ca2+]i trigger physiological events

Excessive Ca2+ loading activates processes that lead to cell death

Neurotoxicity mediated by glutamate receptors is largely calcium dependent

Question 22

Oxidative Stress (RNS, ROS):
Free Radicals

Answer 22

Free Radicals:
An atom or group of atoms
that has at least one unpaired electron and is therefore unstable and highly reactive. In animal tissues, free radicals can damage cells and are believed to accelerate the progression of
cancer, cardiovascular disease, and age-related diseases.

Question 23

The Chemistry of Oxygen

Answer 23

Oxygen produces numerous free-radicals—some more reactive than others:

§ Superoxide free radical (•O2-) 
§ Hydrogen peroxide (H2O2) 
§ Hydroxyl free radical (•OH) 
§ Nitric oxide (•NO) 
§ Singlet oxygen (1O2) 
§ Ozone (O3)

The amount of free-radicals is dynamic. It reflects a balance between the # of free-radicals present and the # of anti-oxidants present.

Question 24

The body has enzyme systems that can process low levels of free radicals.

Answer 24

Oxygen&raquo_space;» Supperoxide&raquo_space;[Superoxide Dismutase]» Hydrogen Peroxide&raquo_space; [Perixadases Catalase]&raquo_space; Water

Question 25

Oxidative Stress

Answer 25

An excess of free-radicals damages cells and is called oxidative stress.

This can occur when there is excess oxidants (ROS) or depleted Antioxidants (AOX)

Question 26

Stroke

Answer 26

The brain is vulnerable to oxidative stress because:
It contains more fatty acids.
It has few antioxidants.
It has high oxygen consumption.
It has high levels of iron and ascorbate (worse oxidative stress).
Dopamine and glutamine oxidation.

Question 27

Oxidative Stress & Cell Damage

Answer 27

•High doses:
directly damages/kills cells

• Low doses/chronic overproduction of oxidants:

• activation of cellular pathways
• stimulation of cell proliferation
• damage to cellular proteins, DNA, and lipids

Question 28

STUDY LIST

Answer 28

Ependymal cells

Microglia Secrete
§ BDNF, Neurotrophin 3
§ Resting microglia secrete IL10
§ TNF and IL1, glutamate, free radical species

resting/activated microglia

glial scar, ablation

Glutamate, MSG, Excitoxicity

Ionotropic

RNS, ROS, AOX

Calcium and neurotoxicity

Question 29

Ionotropic

Answer 29

Ionotropic receptors are transmembrane molecules that can “open” or “close” a channel that would allow smaller particles to travel in and out of the cell. IONotropic receptors allow different kinds of ions to travel in and out of the cell.

Ionotropic receptors are not opened or closed all the time. They are generally closed until another small molecule (called a ligand, In many cases, a neurotransmitter) binds to the receptor.

As soon as the ligand binds to the receptor, the receptor changes conformation (the protein that makes up the channel changes shape), and as they do so they create a small opening that is big enough for ions to travel through.

Therefore, ionotropic receptors are “ligand-gated transmembrane ion channels”.
The ions that can travel through ionotropic receptors are generally limited to K+, Na+, Cl-, and Ca2+.

Question 30

RNS

Answer 30

Reactive nitrogen species (RNS) are a family of antimicrobial molecules derived from nitric oxide (·NO) and superoxide (O2·−) produced via the enzymatic activity of inducible nitric oxide synthase 2 (NOS2) and NADPH oxidase respectively. NOS2 is expressed primarily in macrophages after induction by cytokines and microbial products, notably interferon-gamma (IFN-γ) and lipopolysaccharide (LPS).

Reactive nitrogen species act together with reactive oxygen species (ROS) to damage cells, causing nitrosative stress. Therefore, these 2 species are often collectively referred to as ROS/RNS.