Circadian photoreception Flashcards
How can light affect a circadian rhythm?
Either shifting it entirely (new L:D cycle)
Or slight delay/advance (single light pulse)
What is the point of a phase response curve?
To see the effect of a pulse of light on phase shift
Depending on when you flash light you get either a phase delay, advance or no change
Why does the ventral SCN adapt to a a new L:D cycle much faster than the dorsal area?
It receives photic input from the retina
When does a light pulse advance the FRP? When does it delay it?
Advance: mid-late subjective night
Delay: late subjective day-early subjective night
What common pathway do phase shifts have, and when do they diverge?
Both require depolarization of NMDARs, activating CAMKII and NOS
The activation of NOS has differing effects depending on if the light pulse occurred during the early or late subjective night
What connects retinal signalling to the hypothalamus/SCN and how does it do this?
The Retinohypothalamic Tract (RHT)
By PACAP (VIP analog) and Glutamate (binds to NMDAR)
Which photoreceptors mediate circadian light entrainment?
Both rods/cones, and melanopsin-containing cells
Describe protein redundancy and an example of this
When different proteins have similar functions, such that a single KO can be rescued by the other protein
rods/cones and melanopsin can rescue each other’s ability to entrain light cycles
True/False? light reacts with melanopsin
True, Cells containing melanopsin depolarize when light is shone
What happens when just rods/cones or just melanopsin is KOed?
Decreased sensitivity but not total abolition of circadian resetting in response to light
What happens to rod/cone/melanopsin triple KO mice?
Complete FRP even in presence of L:D cycles
What else was noticed in mice with no rods/cones/melanopsin?
No pupillary light reflex (iris contracting in bright light)
True/False? Without rods/cones/melanopsin, there is no way for your body to reset its internal clock
False, there are many other “non-photic” cues that your body can receive (eg activity of a new wheel) that can shift FRP
What is unique about circadian light response in Drosophila?
Drosophila have photoreceptors in almost all cells, not just eyes
CRY has a different effect in drosophila as well, involved in perceiving light (ubiquitinates TIM causing it to be destroyed)
