Faulty Circuits

Question 1

What is the difference between channelrhodopsin and halorhodopsin?

Answer 1

Channel rhodopsin = depolarises neurons and is stimulating by blue light
Halo rhodopsin = allows entry of Cl- ions and is stimulated by yellow light (stops neurons from spiking)
has been used with epilepsy to ‘calm down’ neurons

Question 2

What can be used instead of ChR?

Answer 2

Small organic molecules
Double bond in the molecule can rotate
Light can induce cis-trans isomerisation
e.g. in one configuration it blocks a channel and then if you shine a brighter light it will remove the block

Question 3

What are the benefits of using small molecules to stimulate/inhibit channels and neurons?

Answer 3

Can be used to activate single synapses or single parts of the membrane (v. specific)
Can work on a vast range of channels e.g. GABA and K+

Question 4

How is stimulation of visual neurons being used to cure blindness?

Answer 4

Retinal degeneration = mixing up of retinal layers meaning visual field gets smaller

Can stimulate the retina and the visual cortex

Can use electrode stimulation or ChR or HaR

Question 5

Why do you need halo rhodopsin to activate photoreceptor cells

Answer 5

Because human photoreceptor cell hyperpolarise in response to light

Question 6

What does epilepsy arise from?

Answer 6

An imbalance between excitatory and inhibitory input (tilting towards excitatory)

Question 7

How can you reduce epilepsy in mice?

Answer 7

Expressing ChR in GABAergic neurons
Expresing HoR in Glutamatergic neurons

Question 8

What are the problems with using ChR and HoR in the brain?

Answer 8

Eventually the neurons around the implant will start dying
How do you know when the onset of a seizure will be?
Where does the seizure originate from?
etc etc