June 1 PSY397
The Bulla Eye:
Pacemaker is embedded in the retina. They look like ganglion cells. In Bulla, the
pacemaker cells are all clustered at the base of the eye. Basal retinal neurons
(BRNs). Discovered that these cells were able to maintain rhythmicity.
Reduced eye still produces circadian rhythms:
Started cutting out pieces of the eye, first the lens and the retina. Finded that
rhythms persisted without all of the retina.
Rhtyms in the reduced eye preparation:
Rhythm still somewhat remains, but its reliability goes down.
Circadian photoreceptor localization:
To see if the cells were actually responsible for the compound action potential. Took
fibe optics and luminated either the whole eye through the retina, or only the BRNs.
If you illuminate the photoreceptor: asynchronous action potential
If you shine light on the base of the eye: large, synchronous discharges from BRNs.
CAP rhythms and the phase response curve to light
One eye is given the light.
Change in phase shift response from the illuminated eye. The eye can shift, it can be
entrained by light cycles.
Current injection causes phase shift
Mechanism: what is it in that cell that’s creating the rhtyhm. Follow the light input
pathway deeper and deeper into the cell.
Recorded intracellularly from the BRNs. BRNs, even without a retina, are
photosensitive. Underlying the rhythm of action potential was a rhythm of
membrane potential. Light could affect the system by producing depolarization.
So, first they looked at whether or not you could shift the phase of the clock by
electric stimulation, not directly light. Found it actually did. Possibly the action of
depolarization is shifting the clock.
A: injected positive current. Found phase shifts where you would expect them.
Positive current mimics light.
B: instead of injecting positive current, they made the cellular interior more
negative. Got different phase shifts. Negative current seemed to mimic not light, but
something else. Get shifts in the middle of the subjective day. So, it could be
reflecting a dark pulse.
Changes in membrane potential cause phase shifts:
Low Na hyperpolarizes. Not only do you have a rhythm of membrane potential that
appears to produce a circadian rhythm, you now have a mechanism of shifting the
clock. Low calcium blocks light induced phase shifts:
Took a look at what happens if you take Ca out of the seawater. Lack of calcium
negates phase shifting. Whatever light is doing doesn’t get any further when Ca is
Low Ca: blocks the advance
Light + low Ca: significant advance. If you reduce the Ca on the outside so its less
than whats inside. Instead of reducing Ca, you are creating an outward flow of Ca.
Low Calcium lengthens period:
Calcium is being removed from the sea water. Low calcium tends to lengthen the
Low calcium lengthens the period only during the day