circadian rhythms: lecture 4 proseminar in biological psychology
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Circadian Rhythms: Lecture 4 Proseminar in Biological Psychology. Circadian Rhythms. Circa: "about” Dies: “day" Circadian rhythms are physiological and behavioral characteristics that follow a daily, or circadian, pattern. 24 hour period. Biological Rhythms. - PowerPoint PPT PresentationTRANSCRIPT
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Circadian Rhythms: Lecture 4
Proseminar in Biological Psychology
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Circa: "about” Dies: “day"
Circadian rhythms are physiological and behavioral characteristics that follow a daily, or circadian, pattern
Circadian Rhythms
24 hour period
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Biological Rhythms
Ultradian: cycles lasts shorter than a day- milliseconds it takes for a neuron to fire- 90 minutes sleep cycle (REM and NON REM sleep)- hunger- YOUR ATTENTION SPAN IN CLASS!
Infradian: cycles lasts longer than a day- monthly menstrual cycle- hibernation in animals- bird migration
Circadian: cycles lasting 24 hr- sleep-wake cycle- body temperature- testosterone levels: highest around 6:00 am, low
at 6:00 pm
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What dictates or governs our 24 hr cycle?
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Environmental Cues: the light/dark cycle
Zeitgerbers: German for “Time Giver”
-Meals-Temperature-Social activity-The tide (marine animals)
Entrainment
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Zeitgebers
….no circadian rhythms?
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We Do Not Need Environmental Cues for Circadian Rhythms
• Persistence of rhythm in constant conditions(LL/DD) & (Temp): tend to drift.. Under natural
conditions, the clocks are precise. • Rhythm can be entrained
So CR=daily rhythm is endogenously generated,
but still susceptible to modulation by 24-hour environmental cycles
endogenous "clock
How do we know that these rhythms aren't entirely environmentally induced?
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French Astronomer
Jean Jacques d’Ortous de Mairan (1729)
Heliotrope leaves closed at night
Observed the persistence of leaf movement in plants placed in
constant dark
For 2 centuries nobody cared!!!
First Time Evidence for a Endogenous Clock
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Psychiatrist August Forel
(1910)Noticed bees returning to
the breakfast table at the
same time of day to get jam
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Psychiatrist August Forel
(1910) the bees returned at the same time of the day even when the food was not present
Hey Fred, where’s the jam?
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von Frisch & Beling (1920) First experiment done in the lab setting
1. Used Bees – set out sugar in water for several days
2. Bees came as expected
3. When not offered bees continued to show up
4. Performed the experiment in a salt mine = same result
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1931 – Wiley Post (Aviator)Flew eastward around the
world in 8 1/2 days (208 hrs)
- flying ability adversely affected
- sleep was disrupted- general feeling of
uneasiness- nausea
First person to report JET LAG internal clock not adjusted to
environmental clock
Early Human Evidence of an Endogenous Clock
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•Blind animals still show circadian rhythms
Other Evidence
- Some strains of Mice have virtually no retinabut still have circadian rhythms
- Blind people show circadian cycles
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Put Animals & Humans in “Constant Conditions”
Constant Conditions: LIGHT/LIGHT DARK/DARK
“Free Running” = without cues
How close is the endogenous clock to 24 hr cycle?
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Depends on the Species
Mus musculus (mouse) = 23.5Homo Sapiens (Humans) = 25?24.18Mesocricetus auratus (Hamster) = 24.1
The ‘natural’ period of a biological rhythm free-running in constant conditions:
TAU
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Running Wheel ActivityMeasurement of Tau
Onset of running wheel activity is used
the phase indicator while free Running = CT12
14L/10D
Mouse (23.5) Hamster (24.1)
Actogram
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Measurement of Tau in humans
Actiwatch
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The Clock – Oscillator
Suprachiasmatic Nucleus
SCN
Densely packed collection of small cells(only 20,000) anterior hypothalamus
Midline in a shallow impression of the optic chiasm
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SCN - Biological ClockSCN - Biological Clock
Suprachiasmatic Nucleus (SCN)
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Feeding, sleep, temperature, hormones
SCN neurons project to other hypothalamic regions
Sleep & waking (Ventral)Sub paraventricular Zone
Body Temp (Dorsal)Sub paraventricular Zone
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Retina-Geniculate-Striate Pathway – Ventral View
Anterior Portion of the Hypothalamus (SCN)
Superior to optic chiasm, receives input from optic nerves (RHT); this input synchronizes the “clock” in the SCN to the exterior day-night cycle
Retino-hypothalamic Tract
SCN
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Innervation of the Pineal Gland in
Humans –needs SCN
Dependent on the
Light/Dark Cycle
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Evidence for SCN - Biological Clock
1900’s Simpson & Galbriath
Rectal Temp every 2 hours for 2 months!!!!!
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• Lesions here interfere with circadian rhythms
1967 – C. P. Richter (rats)Hypothalamic Lesions = disrupted eating, drinking, activity
1972
Evidence for SCN - Biological Clock
Moore & Eichler Stephan & Zucker
SCN
Lesions disrupted running wheel activity, drinking, hormones
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•Lesions here interfere with circadian rhythms (rodents, primates)
-Still show rhythms but desynchronized to environment L/D cycles (sleep at inappropriate times)
-Abolishes rhythms completelyfeeding, locomotor activity, sleep, temperature, hormones
Evidence for SCN - Biological Clock
Important! Changed the pattern of sleep not the
amount
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SCN - Biological ClockSCN - Biological Clock
SCN
day night
Increased metabolic activity (Schwartz & Gainer, 1977)
So..SCN keeps track of day or nightBut not whether you are diurnal or nocturnal
Injected 2-DG in rats…same results in squirrel monkeys
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•SCN cells invivo and invitro confer rhythminicity - in tissue culture - transplantation
Electrophysiological studies - electrical activity continues even
after surgical removal from hypothalamus- other brain sites also show this but
need a connection the SCN
•Lesions of visual cortex have no effect on rhythms
•Severing RHT = free running rhythm
Other Major Evidence for SCN - Biological Clock
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SCN neurons (4)All show circadian rhythms
Displaying individual rhythms
…coolio
Tissue Culture
Electrophysiological studies - electrical activity continues even after surgical removal from hypothalamus
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Remove clock from the animal and clock still exhibits a sustained circadian rhythm
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Transplantation Studies – Cooler Stuff
Ralph et al (1990)
Removed SCN from Mutant Hamsters (short tau 22 hrs)
Transplanted SCN into hamsters that had lesioned SCN
Restored….Sleep/Wake Cycle….not regular cycle BUT….the short rhythms!!
VISA VERSA…same results!!!! transplant to Mutants
Ralph, M. R. and Menaker, M. (1989)
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Transplantation Studies – Coolest Stuff
Silver et al (1996)
Lesioned SCN of Hamster = abolished rhythms
Got donor SCN placed in tiny semipermeable capsuletransplanted into III ventricle
Chemicals, nutrients in NO SYNAPTIC TRANSMISSION
Reestablished rhythms!??? Chemical
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What makes the clock tick? Hands of the SCN
“Main Oscillator” (SCN cells)But what about at the molecular level?
GENES (contain the instructions that tells a cell
what its job will be)
Cells contain a newly discovered protein (clock protein)
that regulates gene function and which shows 24-hr
variations in cellular levels that appears to account for
24-hr variations in neuronal activity