Topic 4 (Investigating the brain) Lecture 3 (Animal research techniques) Flashcards
What are 6 types of experimental lesions?
- electrical
- Excitotoxic lesions (Caused by overstimulation of neurons)
- Selective toxins
- Antagonism lesions
- Aspiration (Tissue removed by suction)
- Anaestesia
Which lesions are irreversible?
- electrical
- Excitotoxic
- Aspiration
Which lesions are reversible?
- Local anaestetics
How do electrical lesions work?
- All tissue around the tip of an electrode is removed
- This is often used to mark recording sites
Describe excitotoxic lesions
- This removes cell bodies but not the fibres passing through
- These can be induced with anything that acts as an antagonist to the main glutamate receptors (e.g NMDA, AMPA), meaning that levels of glutamate become toxically high leading to cell death
Describe Aspiration lesions
- All tissue from an area is effectively sucked away
Local Anaestetic
- Suppresses all activity of an area
- This includes the activity of the fibres passing through
- It can be hard to judge the extent of the suppression
What types of lesions are non selective lesions?
- Electrical
- Excitotoxic
- Aspiration
- Local anastetic
What is a selective lesion?
- Selective lesions can be used to inhibit specific cells or specific neurotransmitters
How do selective toxins work?
Selective toxins are toxins that target specific cells or neurotransmitters
They can be injected into the cell itself or into the pathway as it will travel back into the cell bodys
How does 6 Hydroxydopamine (6OHDA) work as an example of a selective toxin?
- It uses the model of parkinsons disease
- It selectively removes dopaminergic neurons in the Substantia Nigra Compact
- Because there is a dopamine pathway between SNc and the striatum, the removal of dopaminergic neurons reduces the amount of dopamine in the striatum
Describe intracellular electrophysiology
- Microelectrodes are placed inside individual neurons and the current is recorded
Describe extracellular electrophysiology
- Microelectrodes are placed in the extracellular space surrounding neurons and the current is recorded
- The downside of this is that it can be close to multiple neurons and can pick up electrical signals from the neighbouring neurons
What signals can electrophysiology pick up?
- Both action potentials and PSP’s
What is microdialysis?
- A probe is placed in the brain to continuously moniter the contents of the extracellular fluid
What are limitations of microdialysis?
- The temporal and spatial resolution is poor for this technique
- This is because it is not clear where the chemicals have come from (spatial)
- And you have to pump the fluid out of the brain very slowly to not damage it (temporal)
What is voltamettry
- Voltamettry measures the chemicals present in extracellular fluid by measuring electrical changes and inferring the chemicals present
Which way do anterograde tracers move?
They are injected into the cell body and move towards the axon terminal
Which way do retrograde tracers move?
They are injected into the axon terminal region and move towards the cell body
Describe immunohistochemistry
Antigens on cells of a tissue are selectively identified
These are then tagged with a stain which can be detected
These can be general markers e.g of cell activity (when neurons fire certain proteins are activated and these are the ones that are detected)
Or they can be specific say to an enzyme or reuptake channel protein, allowing the stain to identify specific types of neurons
Which techniques involve post-mortem examination?
Anything that involves cell staining
e.g golgi stains or immumohistochemistry
Why is the controlled environment an issue in animal research
Lab animals live in very controlled environments that is unrepresentative of the wild
