Aberrant light directly impairs mood and learning through melanopsin-expressing neurons
LeGates et al 2012
(presented by colenso) Circadian rhythm
Natural pacemaker controls circadian rhythm.
- 50% of blind individuals experience ‘free running’ – no entrainment to light. about a 25 hr cycle
- Resets to natural environment based on light.
- external signals like social interactions, food etc.
- eye light responsive cells are decoupled from rods and cones — have their own unique opsin (melanopsin).
paper
Prevailing hypothesis: Light impacts circadian photoentrainment and impacts sleep, leading to depression
Question: Are the eye projecting cells related to mood?
- Mouse at 12/12 hour entrain
- Mouse at 3.5/3.5 hour cycle don’t entrain to the cycle, go through free running, ~26 hr cycle, something like 12 awake 14 asleep. Very bright light can disrupt
- aberrant light does not impact gene expression in the brain pace-maker
- aberrant light ‘leads to deprepression’ –less motivated to eat sucrose. -less motivated to try to escape the force swim test. elevated levels of corticosterone (can over express and induce deprepression).
- treat aberrant light exposed animals with fluxetine (Prozac). Do recover motivation to get out of forced swim test. Do reduce corticosterone.
- normal light cycle learn better (finding platform in a water swimming ‘maze’)
- add novel object, animal spends more time with it. T7 light cycle don’t.
- Reduced long-term potentiation (normally associated with learning).
- all these phenotypes fixed by Prozac.
role of light
- Kill the light responsive cells. Aberrant light has no effect on mood or learning.
- (these animals free-run).
Take home message:
- “avoid bright lights at night (computer/TV) leads directly to depression / impaired learning.