L13 - Retina 5 GC

Question 1

T/F: Different GC conveying different streams of info regarding vision to the brain

Answer 1

T

Question 2

GC tiling - every part of an image is passed onto the brain at least once where different GCs converge the different info they receive

1) X-type?
2) Y-type?
3) DS?
4) Blue-on GCs?

Answer 2

1) X type: Brightness
2) Y type: Sensitivity to movement
3) DS: movement in one direction
4) Blue-on GCs: blue-green info

Question 3

Describe intrinsically photosensitive GCs

Answer 3

Bistratified (can see blue light), small, sparse (5000 in retina)

Depol to light

Able to pick up a light source and communicate it to the brain (doesn’t need photoreceptors)

Question 4

When comparing wavelengths of light, red and ___, blue and ___

Answer 4

Red and green

Blue and yellow

Question 5

Midget/P GC exhibit a colour opponent centre-surround

• (Colour) ON centre excites
• (Colour) OFF surround inhibits

Answer 5

Red ON
Green OFF
*Others are excited by blue or yellow lights following on their receptive field centres

Question 6

Red ON centre hyperpolarizes photoR which leads to?

Answer 6

Depol BP, depol GC

Question 7

Green OFF centre hyperpolarizes __ which leads to?

Answer 7

HC, less GABA release, excitation of photoR (mGluR6) -> inhibits NT release -> doesn’t activate BP or GC anymore

Question 8

What if you shined red light on BOTH Red ON centre and Green OFF surround?

Answer 8

Green cones also respond to red light but by less than red cones - hence AP response is in between that of a normal Red ON only and Green OFF only response.

Question 9

Bigger or smaller than P and M GC?

Answer 9

Bigger

Question 10

What opsin do ipGC contain?

Answer 10

Melanopsin - similar to opsin in flies, it is similar to cone opsins

• evoluntionary older than normal opsins BUT has similar structure
• Also has different second messenger cascade to cone opsins

Question 11

T/F: Placing melanospin into kidney cells (which don’t have any opsin) activates it when stimulated by light

Answer 11

T

Question 12

Melanopsin signalling uses a _ GPCR - opening/closing channels (TRP channel)

Answer 12

Gq - opening channels (TRP channel)

Question 13

Where do ipGCs receive inputs from?

Answer 13

Rods/cones, amacrine cells

Question 14

What do ipGCs do?

Answer 14

Range of activities in the brain that communicate functions such as sleep regulation, circadian rhythm as well as pupil responses, light levels, light allodynia (light making pain worse - photophobia associated with migraine, ocular injury or infection)

Question 15

What area has to be affected for ipGCs to be affected?

Answer 15

Optic nerve - that’s where the GCs are

Question 16

Melanopsin can be used to restore vision - How?

Answer 16

During retinal degen. melanopsin GCs are spared

*Reintroducing functional melanopsin into the eyes of mice with retinal degeneration restores the pupillary light reflex (PLR).

Question 17

How does glaucoma affected GCs?

Answer 17

Due to increased IOP, optic nerve is damaged and causes gradual loss of GC (tends to be large ones first - Parasol/M GC)