Non-Visual Photoreception

Lecture 17

2 types of retinal input to the brain?

1. visual input

2. non-visual system

3 components regulated by the non-visual system in retinal input to the brain?

1. pupil size

2. terminate melatonin secretion

3. circadian effects

Non-Visual System

involves light detection, but no images

Visual Input

image forming system

2 main systems in the transfer of visual input from retina to the brain?

1. LGN

2. visual cortex

5 biological processes that light detection is important for (other than seeing)?

1. synchronizing the circadian clock

2. pupil size

3. inhibiting melatonin secretion

4. induction of sleep (in rodents)

5. negative phototaxis

Pupil size is regulated by _____ _____.

light intensity

2 main ways to test which photoreceptor is involved in non-visual responses?

1. spectral sensitivity assays

2. genetic mutations

How are spectral sensitivity assays used to test which photoreceptors are involved in non-visual responses?

see which wavelengths respond the best

3 things some blind people (non conscious light perception) retain?

1. synchronize to a light/dark cycle

2. phase shift to a light/dark cycle

3. suppress nocturnal melatonin levels with light exposure

Which photoreceptors match the spectral sensitivity of the circadian system?

rods

How did we determine that rods were involved in the non-visual responses?

tested phase shifts to different wavelengths & found they had maximal shifts to blue/green light; matches circadian system

In testing which photoreceptors match the spectral sensitivity of the circadian system, researchers found that the maximal shifts were to _____/_____ light, near ___nm. Later research found that this was between ___nm & ___nm.

1. blue/green

2. 500

3. 476

4. 515

Contrary to what was guess using spectral sensitivity assays, research found that phase shifts persist in mice lacking _____ & _____.

1. rods

2. cones

Describe the phase shifts & melatonin levels in mice lacking rods & cods. Describe this in the mice lacking eyes. What does this suggest?

1. phase shifts persist & melatonin decreases when exposed to light

2. no phase shift & melatonin does not respond to light normally

3. suggests that eyes are important for the circadian cycle, but not rods & cones

How do birds & reptiles differ in their photoreceptor anatomy? What does this mean for their ability to synchronize without eyes?

1. pineal glands are photoreceptive (reptile have “parietal eye” that connects to glan); have deep brain photoreceptors

2. can synchronize to light/dark after eyes have been remove

What did researchers find when they applied light to the back of human knees? Has this withstood the test of time?

1. could reset circadian clock

2. no, widely discredited

How does enculeation affect mammalian circadian shifting? What does this tell us?

1. show no response to light exposure with eye removal

2. eyes are necessary

With rods & cones shown not to cause phase shifts, what other photoreceptor has been positioned to be responsible for the non-visual system?

melanopsin

Melanopsin

light-responsive ganglion cells

6 qualities of rods & cones?

1. medium to narrow receptive fields

2. fast responses

3. medium to high sensitivity

4. light hyperpolarizes cells (no APs)

5. adapt to continuous illumination

6. specialized for detail & contrast

6 qualities of melanopsin?

1. huge receptive fields

2. slow “on” & “off” responses

3. low sensitivity

4. light depolarizes cells (APs)

5. do not adapt to illumination

6. specialized for illumination

What is the max wavelength for rods? Cones? Melanopsin?

1. 494

2. 419

3. 484

Mice lacking melanopsin have a diminished _____ _____ in response to bright light, but can still see.

pupillary response

Mice lacking melanopsin have a diminished _____ _____ in their circadian rhythms in response to bright light.

phase shift

2 findings in melanopsin knockout mice in response to bright light?

1. diminished pupillary reflex

2. diminished phase shift in circadian rhythms

Compare responses to light in the following: rodless mice; rodless/coneless mice; melanopsin knockouts. What does this suggest?

1. full response

2. full response

3. smaller response, but there is still a response

4. perhaps there is a redundancy in the system?

3 things we see in response to light in triple knockout mice (i.e., rods, cones, melanopsin)?

1. no pupillary response to light

2. do not show a decrease in melatonin synthesis enzyme AA-NAT

3. do not synchronize to light/dark cycles (non-24)

Given that it takes the triple knockout to remove synchronization abilities, there may be overlap in _____ and _____ function.

1. RGC

2. ipRGC

2 reasons researchers tested the elimination of the ipRGCs?

1. tests if non-ipRGCs participate in non-visual responses

2. tests if ipRGCs participate in normal visual responses

3 findings following the selective elimination of ipRGCs? What does this suggest?

1. loss of pupillary response to light

2. loss of circadian responses to light

3. preservations of visual responses

4. ipRCGs are necessary for non-image forming responses

_____ contain melanopsin & are important for non-image forming photoreception.

ipRGC

_____ _____, _____ _____, and the _____ _____ are all regulated by non-image forming photoreception from the ipRGCs.

1. melatonin levels

2. circadian rhythms

3. pupillary reflex

_____ and _____ can activate ipRGc, compensating for the lack of melanopsin in melanopsin KO animals.

1. rods

2. cones

5 effects of using tablet/eBook at bedtime?

1. longer SOL

2. less REM

3. higher alertness before bed

4. sleepier the next day

5. more difficulty waking up

While effects of using tech before bed are often described in terms of blue light keeping the system awake, most of these effects are likely due to _____.

arousal

3 effects on melatonin secretion from room light?

1. delayed

2. shortened

3. decreased

Given the wavelengths of light impacting the circadian system, what has been suggested to avoid negative effects of tech at bedtime?

blue light blockers/filters

Given the literature as a whole, does blue light vs blue light blockers effect sleep?

no; not well replicated but mixed findings

3 major conclusions from the studies examining blue light at bedtime?

1. any effects are likely minor & will have minimal next-day effects anyways

2. habitual use of the blue filter might diminish any initial benefit

3. probably better to just avoid any significant light at night