Circadian photoreception

Question 1

What does the phase response curve for light - induced shifting of the rodent clock look like?

Answer 1

Note signs of advances/delays and how the graph is continuous

Question 2

What are the effects on Per1 of a light pulse in the early subjective night? subjective day?

Answer 2

Subjective night: Per1 induction, phase shift of behavioural rhythms

Subjective day: no Per1 induction, no phase shift of behavioural rhythms

Question 3

Why does the same light pulse cause a different response depending on when it occurs?

Answer 3

Different cellular pathways depending on subjective time

Question 4

How does the retina project signals to the hypothalamus/SCN?

Answer 4

Via the Retinohypothalamic Tract

Releases PACAP and glutamate

PACAP binds the same receptor as VIP and glutamate binds NMDARs (implicated in causing phase advance/delays)

Question 5

Why do blind people still entrain to light dark cycles?

Answer 5

Because visual blindness is not the same as circadian blindness

Melanopsin in the retina besides rods and cones that perceives light

Retinoganglial cells projecting to the SCN that express melanopsin are intrinsically photosensitive

Question 6

Does knocking out melanopsin cause abolished circadian resetting in mice? What does that imply?

Answer 6

No, it severely reduces sensitivity though

Rods and cones can still sense light

Some level of redundancy

triple KO (rods, cones, melanopsin) cannot percieve light at all