Structure Of Circadian Rhythms Flashcards
Why don’t we have a central clock or have all clocks in our body be synced?
Not adaptive
Different cells have different jobs to do. Specialization is important so not all organs have to be using energy to do all jobs at once.
Why are slugs useful for studies?
They have large cells so it’s easy to put electrodes in
Have rhythmic cycles (move at certain times of the day to eat)
Where is the main photoreceptors of aplysia and bulla?
Compound action potentials (CAPs)
What happens when eyes are removed?
Eyes
CAPs found in optic nerve - Low at night, high at dawn
- To signal diurnal aplysia to stop moving
- To signal nocturnal bulla to start moving
Rhythm of CAPs changes, also changes behaviour
What neurons cause CAPs in bulla and aplysia? What differs between them?
Basal retinal neurons (BRNs)
Electrically coupled (because all close together) in bulla retina
Far apart in aplysia retina
How do light pulses and ion concentration cause phase shifts of CAPs in bulla and aplysia?
Ion concentration in sea water:
- Higher K+ causes cells to be excited (depolarization) - Phase shift in subjective night
- Lower Na+ causes cell to hyperpolarize - Phase shift in subjective day
Light pulse: Causes phase delay
- Ca2+ levels are supposed to drop at night but light causes it to release again and delay removal (depolarization)
Low calcium + Light pulse: Phase advance
- Light induces Ca2+ channels to remove Ca2+ earlier
When are the BRNs hyperpolarized and depolarized in the day in bulla?
Hyperpolarized at night - No CAPs
- Ca2+ is being removed
Depolarized in day - CAPs
Where are the photoreceptors of silkmoths located?
Explain the pernyi and cecropia study
In the brain
Pernyi exit pupa late in the day
Cecropia exit pupa early in the day
1) Take brain out - Variable emergence
2) Brain put into abdomen - Emergence went back to normal
3) Brains swapped - Pernyi emergence happens early, Cecropia emergence happens late
Where are the photoreceptors in cockroaches?
Explain the transplant study
Brain (optic lobe)
Cockroaches entrained to different light cycles:
- DD had short period
- LL had long period
When one optic lobe was replaced, the cockroaches displayed both periods
- There are two lobes and two clocks!
How can you prevent a rhythm from occurring in fruit flies?
Where are the photoreceptors in fruit flies?
Knock out PER gene
Dorsal and ventral lateral neurons
- Switching of PER gene here gets rid of rhythm
Eksin
Seasonality in migratory birds
Where is photoreceptor?
Taking out eye causes entrainment for a bit before starting to freerun in DD
- Something was temporary entraining
Feathers removed for surgery grew back later at same time when freerunning happened
- Found that there’s a weak photoreceptor on top of head (pineal gland)
Gaston
Pineal gland
Found that pineal gland is important for expressing rhythm
Sparrow drifts into arrhythmic pattern over a few days w/out light
Zimmerman
Pineal transplant (sparrow)
Intact pineal gland transplanted into sparrow with arhythmic pattern
- Causes rhythmicity to return
Swapping pineal glands of sparrows entrained to different times causes them to reflect each other’s rhythm
Takahashi
Suprachiasmatic nucleus (SCN)
Pineal gland melatonin release in vitro
Found SCN is required for expressing circadian rhythms in avian mammals
Electrical lesion of SCN caused loss of rhythm
Also found that when taking out a pineal gland and putting it in vitro
- Still rhythmic and photosensitive
- Rhythm caused by melatonin output
Cassone
Sympathetic norepinephrine release
Melatonin
Sympathetic norepinephrine release can entrain the pineal rhythm
Melatonin can cause phase shifts in behavioural rhythm
True or false?
The clock in avian mammals is only in the pineal gland
False
Clock is distributed between SCN and pineal gland for some
Some don’t use pineal gland
