Circadian Rhythms: Lecture 4
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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.

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Circadian Rhythms: Lecture 4 Proseminar in Biological Psychology

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Circadian rhythms lecture 4 proseminar in biological psychology

Circadian Rhythms: Lecture 4

Proseminar in Biological Psychology


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


Circadian rhythms lecture 4 proseminar in biological psychology

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


Circadian rhythms lecture 4 proseminar in biological psychology

What dictates or governs our 24 hr cycle?


Circadian rhythms lecture 4 proseminar in biological psychology

Environmental Cues: the light/dark cycle

  • Zeitgerbers: German for “Time Giver”

  • Meals

  • Temperature

  • Social activity

  • The tide (marine animals)

Entrainment


Circadian rhythms lecture 4 proseminar in biological psychology

Zeitgebers

….no circadian rhythms?


Circadian rhythms lecture 4 proseminar in biological psychology

  • 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?


Circadian rhythms lecture 4 proseminar in biological psychology

First Time Evidence for a

Endogenous Clock

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!!!


Circadian rhythms lecture 4 proseminar in biological psychology

Psychiatrist August Forel

(1910)

Noticed bees returning to

the breakfast table at the

same time of day to get jam


Circadian rhythms lecture 4 proseminar in biological psychology

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?


Circadian rhythms lecture 4 proseminar in biological psychology

  • von Frisch & Beling (1920)

  • First experiment done in the lab setting

  • Used Bees – set out sugar in water for several days

  • 2. Bees came as expected

  • When not offered bees continued to show up

  • Performed the experiment in a salt mine = same result


Circadian rhythms lecture 4 proseminar in biological psychology

Early Human Evidence of an Endogenous Clock

  • 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


Circadian rhythms lecture 4 proseminar in biological psychology

Other Evidence

  • Blind animals still show circadian rhythms

- Blind people show circadian cycles

- Some strains of Mice have virtually no retina

but still have circadian rhythms


Circadian rhythms lecture 4 proseminar in biological psychology

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?


Circadian rhythms lecture 4 proseminar in biological psychology

The ‘natural’ period of a biological rhythm

free-running in constant conditions:

TAU

Depends on the Species

Mus musculus (mouse) = 23.5

Homo Sapiens (Humans) = 25?24.18

Mesocricetus auratus (Hamster) = 24.1


Circadian rhythms lecture 4 proseminar in biological psychology

Measurement of Tau

Running Wheel Activity

14L/10D

Mouse (23.5) Hamster (24.1)

Onset of running

wheel activity is used

the phase indicator while free

Running = CT12

Actogram


Circadian rhythms lecture 4 proseminar in biological psychology

Measurement of Tau in humans

Actiwatch


Circadian rhythms lecture 4 proseminar in biological psychology

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


Circadian rhythms lecture 4 proseminar in biological psychology

Suprachiasmatic

Nucleus (SCN)


Circadian rhythms lecture 4 proseminar in biological psychology

Body Temp (Dorsal)

Sub paraventricular Zone

Sleep & waking (Ventral)

Sub paraventricular Zone

  • Feeding, sleep, temperature, hormones

SCN neurons project to other hypothalamic regions


Circadian rhythms lecture 4 proseminar in biological psychology

Retina-Geniculate-Striate Pathway – Ventral View

SCN

Retino-hypothalamic

Tract

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


Circadian rhythms lecture 4 proseminar in biological psychology

Innervation of the Pineal Gland in Humans –needs SCN

Dependent on the Light/Dark Cycle


Circadian rhythms lecture 4 proseminar in biological psychology

Evidence for SCN - Biological Clock

1900’s Simpson & Galbriath

Rectal Temp every 2 hours for

2 months!!!!!


Circadian rhythms lecture 4 proseminar in biological psychology

Evidence for SCN - Biological Clock

  • Lesions here interfere with circadian rhythms

    • 1967 – C. P. Richter (rats)

    • Hypothalamic Lesions = disrupted eating

    • , drinking, activity

    • 1972

Moore & Eichler

Stephan & Zucker

SCN

Lesions disrupted running wheel activity, drinking, hormones


Circadian rhythms lecture 4 proseminar in biological psychology

Evidence for SCN - Biological Clock

  • Lesions here interfere with circadian rhythms (rodents, primates)

    • Still show rhythms but desynchronized to environment L/D cycles (sleep at inappropriate times)

    • Abolishes rhythms completely

    • feeding, locomotor activity, sleep, temperature, hormones

  • Important! Changed the pattern of sleep not the amount


Circadian rhythms lecture 4 proseminar in biological psychology

SCN

night

day

Increased metabolic activity (Schwartz & Gainer, 1977)

So..SCN keeps track of day or night

But not whether you are diurnal or nocturnal

Injected 2-DG in rats…same results in squirrel monkeys


Circadian rhythms lecture 4 proseminar in biological psychology

Other Major Evidence for SCN - Biological Clock

  • 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


Circadian rhythms lecture 4 proseminar in biological psychology

  • Tissue Culture

  • Electrophysiological studies - electrical activity continues even after surgical removal from hypothalamus

SCN neurons (4)

All show circadian rhythms

Displaying individual rhythms

…coolio


Circadian rhythms lecture 4 proseminar in biological psychology

Remove clock from the animal and clock still exhibits a sustained circadian rhythm


Circadian rhythms lecture 4 proseminar in biological psychology

Ralph, M. R. and Menaker, M. (1989)

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


Circadian rhythms lecture 4 proseminar in biological psychology

Transplantation Studies – Coolest Stuff

Silver et al (1996)

Lesioned SCN of Hamster = abolished rhythms

Got donor SCN placed in tiny semipermeable capsule

transplanted into III ventricle

Chemicals, nutrients in NO SYNAPTIC TRANSMISSION

Reestablished rhythms!

??? Chemical


Circadian rhythms lecture 4 proseminar in biological psychology

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


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