Topic 4 (Investigating the brain) Lecture 3 (Animal research techniques)

Question 1

What are 6 types of experimental lesions?

Answer 1

• electrical
• Excitotoxic lesions (Caused by overstimulation of neurons)
• Selective toxins
• Antagonism lesions
• Aspiration (Tissue removed by suction)
• Anaestesia

Question 2

Which lesions are irreversible?

Answer 2

• electrical
• Excitotoxic
• Aspiration

Question 3

Which lesions are reversible?

Answer 3

• Local anaestetics

Question 4

How do electrical lesions work?

Answer 4

• All tissue around the tip of an electrode is removed

- This is often used to mark recording sites

Question 5

Describe excitotoxic lesions

Answer 5

• 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

Question 6

Describe Aspiration lesions

Answer 6

• All tissue from an area is effectively sucked away

Question 7

Local Anaestetic

Answer 7

• 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

Question 8

What types of lesions are non selective lesions?

Answer 8

• Electrical
• Excitotoxic
• Aspiration
• Local anastetic

Question 9

What is a selective lesion?

Answer 9

• Selective lesions can be used to inhibit specific cells or specific neurotransmitters

Question 10

How do selective toxins work?

Answer 10

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

Question 11

How does 6 Hydroxydopamine (6OHDA) work as an example of a selective toxin?

Answer 11

• 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

Question 12

Describe intracellular electrophysiology

Answer 12

• Microelectrodes are placed inside individual neurons and the current is recorded

Question 13

Describe extracellular electrophysiology

Answer 13

• 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

Question 14

What signals can electrophysiology pick up?

Answer 14

• Both action potentials and PSP’s

Question 15

What is microdialysis?

Answer 15

• A probe is placed in the brain to continuously moniter the contents of the extracellular fluid

Question 16

What are limitations of microdialysis?

Answer 16

• 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)

Question 17

What is voltamettry

Answer 17

• Voltamettry measures the chemicals present in extracellular fluid by measuring electrical changes and inferring the chemicals present

Question 18

Which way do anterograde tracers move?

Answer 18

They are injected into the cell body and move towards the axon terminal

Question 19

Which way do retrograde tracers move?

Answer 19

They are injected into the axon terminal region and move towards the cell body

Question 20

Describe immunohistochemistry

Answer 20

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

Question 21

Which techniques involve post-mortem examination?

Answer 21

Anything that involves cell staining

e.g golgi stains or immumohistochemistry

Question 22

Why is the controlled environment an issue in animal research

Answer 22

Lab animals live in very controlled environments that is unrepresentative of the wild