11 - Fixing faulty neural circuits

Question 1

What is channelrhodopsin ChR?

Answer 1

A non-selective ion channel

Question 2

What happens when ChR opens?

Answer 2

The membrane depolarises.

Question 3

How is channelrhodopsin activated?

Answer 3

By light, specifically blue light.

Question 4

What did using channelrhodopsin in mouse brains tell us?

Answer 4

• That expressing ChR in certain neurons in vivo you can modify behaviour and the activity of different neurons.
• It can also be used to fix defected neurons.

Question 5

What is Halorhodopsin?

Answer 5

Another type of ion channel that is only selective to Chloride ions.

Question 6

How is Halorhodopsin activated?

Answer 6

By red light.

Question 7

What happens when halorhodopsin is stimulated?

Answer 7

The neuron hyperpolarises below the threshold.

Question 8

What do double bonds do in small organic compounds of ChR?

Answer 8

They create the possibility for the coumpound to have 2 compositions. Cis and Trans.

Question 9

What is transconformation?

Answer 9

When both parts of the molecule are on opposte sides of the double bond.

Question 10

What is cisconformation?

Answer 10

When both parts of the molecule are on the same side of the double bond.

Question 11

What happens of the compound/molecule when light is shined on it?

Answer 11

It turns from trans to cis conformation.

Question 12

What happens if another light with a different wavelength is shined on the molecule?

Answer 12

The proces reverses and it turns from cis conformation to trans confrmation.

Question 13

What does shining a light on a molecule help us do?

Answer 13

Regulate the distance fron the active part to the protein of interest.

Question 14

What can adding a GABA receptor ligand or glutamate receptor ligand help with?

Answer 14

Lets us activate the receptors using light rather than than GABA molecule itself.

Question 15

What is Retinitis Pigmentosa?

Answer 15

One of the most common caues of blindness, it decreases the field of view as it progresses.

Question 16

What causes retinitis pigmentosa?

Answer 16

• Mutations that cause a decrease in the number of photoreceptors.
• Bipolar cells don’t receive input from the photoreceptor so they start to degenerate.

Question 17

What are some ways to fix retinitis pigmentosa?

Answer 17

• Genetically modify photoreceptors to stop they from dying.
• Stimulate the visual neurons to help restore vision, done by electrodes or optogenetics. —> done by activating the retina/visual system through an electorde in the V1 cortex of the brain.

Question 18

What are the 2 major classes of ganglion cells?

Answer 18

Parvocellular cells and Magnocellular cells.

Question 19

What are some characteristics of parvocellular cells?

Answer 19

• They have centre surround organisation.
• They have a smaller receptive field.

Question 20

What are some characteristics of magnocellular cells?

Answer 20

• They also have centre surround
  organisation.
• They have a larger receptive field.
• They can respond to different colours of
  light.

Question 21

How is direction selectivity evident in the retina?

Answer 21

It responds to movements in some directions but not others.
To solve this light is used to stimulate deeper layers.

Question 22

What are brain circuits composed of?

Answer 22

Excitatory and inhibitory neurons.

Question 23

What do excitatory neurons release?

Answer 23

Glutamate.

Question 24

What do inhibitory neurons release?

Answer 24

GABA.

Question 25

How does epilepsy arise?

Answer 25

From an imbalance between excitation and inhibition

Question 26

What can be done to control seizures?

Answer 26

• Using halorhodpsin in excitatory cells
• Using channel rhodopsin in inhibitory cells.
• Inject a virus that expresses optogenetic tools.