Unit 5 - Biological Rhythms

What do Biological Rhythms allow? (slide 3)

• help organisms coordinate internal functions with external environment

• allow one to anticipate predictable changes in environment

Cicadian rhythms (slide 5-6)

• display cycle of 24 houts

• daily rhythm

• body generally releases substances/ make changes internally

What generates circadian rhythms? (slide 7)

• internal and external cues

Zeitgeber (slide 7)

• external cue used by individual to sync eith environment (ex: light)

WHeel running in hamsters (slide 9-10)

• proxy for waking or activity in hamsters

• hamsters generally run at night time

• high activity → lights off, low activity → lights on

What can internal biological clock maintain and how can it be observed? (sldie 10-11)

• in zeitgeber absence → internal biological clock can maintain rhythm

• ex: constant dim light/no light

• observe internal rhythms by removing zeitgebers

What is Free-running? What do hamsters in constant light show?

Free-running - rhythm not synchronized with environment

hamsters in constant light → activity rhythms longer than 24 hours

How does hamster activity change if you shift/ delay light? Constant dim light (no zeitgeber)? (slide 12)

Shifting/delaying light

• Hamsters primarily run in in dark

• delay light by 4 hours → hamsters cahnges activity to match zeitgeber

No light/zeitgeber

• hamsters still maintains internal rhythm, has activity

• wakes up a bit later each day

Absence of zeitgebers in humans

In absence of light

• humans internal rhythm is slightly longer than 24 hours

• time awake shifts forward

Suprachiasmatic nucleus (SCN) (slide 16)

• SCN in the hypothalamus

• crucial brain region controlling endogenous rhythms

• circadian rhythms

Describe neural activity in the SCN (light) (slode 17)

• show high activity rates in light phase (true for nocturnal and diurnal species)

What is unique about the mutant tau hamsters?

• when free-running (constant dim light) → periodicity is 22 hours (instead of WT 24.5 hrs)

Describe the experiment done on mutant tau hamsters to find SCN function (slide 20)

1) Tau hamsters wake up earlier each day in constant dim light (22 hr)

2) Making a lesion to the SCN → hamsters runs on wheel at random times

3) SCN from WT hamster (24.5 hr) is dissected and implanted into tau mutant without SCN (replaced)

4) after implantation → circadian rhythm is restored and wake up shifts to right, matching behavior of wildtype

Describe hwo internal rhythms changes when tau mutant implanted with WT SCN and vice-versa (slide 21)

tau Mutant control → Wild type SCN

• periodicity increases 22→24.5 hours and matches Wild type

WT control → tau SCN

• Periodicity decreases 24.5→22 and matches tau

What is a chronotype and Midpoint of sleep on Free day (MSF) (slide 22)

Chronotypes

• when one’s endogenous circadian clock syncs to 24 hour day

• what time of day clock syncs to (early bird vs. night owl)

MSF

• midpoint of sleep on free days

• larger MSF → night owl, smaller SCF → early bird

• ex: MSF = 4, go to bed at midnight and wake up at 8 AM

• ex: MSF = 7, go to bed at 3 AM and wake up at 11 AM

What trend do you see in MSF at different ages? (slide 23)

• teens and 20s → see a larger MSF value

• older adults → see a smaller MSF value

• increase in teens and 20s, decrease gradually after that point

Social Jetlag

• mismatch between internal “body clock” and social clock (ex: work, school, other obligation)

• less time outdoors associated with increased mismatch

Relationship between chronotype and depression (slide 25)

• later the chronotype → higher reports of depression/symptoms

Observation of ground squirrels with intact or lesioned SCN

• squirrels with intact SCN → less likely to be killed by cat

• squirrels with lesioned SCN → more likely to be killed

Jet lag (slide 29)

• when endogenous rhythms out of sync with zeitgebers

• not only planes

  • rotating shift work

  • night shift → risk factor for breast cancer

Experimental design simulating jetlag in hamsters (slide 31)

• experimental jetlag → 6 hour advance every 3 days

• cause poor results in learning tasks

• hamsters highly motivated to run in wheels → conditioned place preference as learning and memory test

Hamster conditioned place preference test (slide 32)

Condition Place Test

• Phase 1

  • Enclosed place with doorway and two chambers

    • Chamber 1: paired, contains running wheel

    • Chamebr 2: unpaired, no wheel

  • Put hamster in cage and let them run wheel → repeat and hamster will learn where wheel is in space

• Phase 2

  • “Porbe test” , wheel is removed from paired areas, now both cmabers have no wheel

  • see where hamsters end up

• Results

  • Control hamsters (no jet lag) prefer paired chamber where wheel used to be → remember where wheel is

  • Jet lag hamsters don’t show preference for a chamber → don’t remember

BrdU staining and Canaries (slide 34-35)

Canaries

• neurogenesis can persist in parts of brain

BrdU Staining

• answers question , How do we know new adult neurons formed?

• BrdU - marker for cell division

Process

1) Inject animal with BrdU

2) BrdU incorporated in new DNA strands after cell division (replace thymine, pair with adenine)

2) stain brain for BrdU → cells contianing BrdU was formed after injection, only stays if implanted in middle of cell division

What can BrdU tell us about cells? What do we need to do to see if a cell is a neuron? → Neurogenesis in Adults (slide 36)

• BrdU detection in cell tells us cel was born recently, NOT if it is a neuron

• brain must be stained for protein only expressed in neurons → use special microscope to see if stains in same place

Brain staining to determine neurogenesis (slide 37)

Process

• stain parts of brain involved with neurons

• stain parts of brain of glial cells

• Overlap stains of neuron, glial cells, and BrdU → look for overlap of BrdU and neuron to see where in brain produce new neurons

hippocampus region where neurons can be produced in adults

BrdU and Jet Lag effects on Brain (slide 38)

• BrdU can asses effect of Jet lag on brain

• Jet lag reduce number of BrdU cells regardless of hormone status 

Jet lag conslusions

1) Jet lag reduces learning ability for wheel location

2) Jet lag reduces neurogenesis in a part of brain important for learning

Effect of Jet lag in flight crew

Two groups:

• Short-recovery crew: less than 5 days to recover from international flight (>7 time zones)

• Long-recovery crew: more than 15 days to recover from international flight

Results

• Short recovery crew show reduced reaction time and mistakes on tests on average