Non-Photic Zeitgebers

Lecture 18 & 19

5 stimuli that can reset the circadian clock (beyond light)?

1. temperature & similar cues

2. social cues

3. feedings

4. sex

5. activity/SD/arousal

Does temperature entrain the clock?

mixed; effects of temperature are variable & species-specific

Invertebrates vs mammals in terms of being entrained by temperature?

1. invertebrates can be entrained by temperature cycles

2. mammals & birds maintain body temperature but can still tell if its is warm vs cold

2 examples of species that can be entrained by temperature? How do we know?

1. pig-tailed monkey

2. pocket mouse

3. they will entrain to a specific hot/cold cycle & will show free-running rhythms when placed in constant temperature

2 examples of species that cannot be entrained to temperature? What do we see instead?

1. flying squirrels

2. squirrel monkeys

3. masking; returns to expected cycles when placed back in constant temperatures

In Utero Entrainment

pregnant mothers can provide time cues to their fetuses

What happens if you raise a pregnant mom & her pups in constant conditions?

pups will free-run, but they will free-run together; show social synchronization

What model is used to determine in utero entrainment effects?

wean pups & determine their activity onset on the day of weaning

What do we see in pups with an SCN lesioned mom? Prior to birth, what does their SCN show? What signals are likely used pre-birth? After birth?

1. pups free-run, but free-run at separate phases

2. SCN is metabolically rhythmic & synchronized

3. mum’s melatonin passing through uterus

4. mum’s melatonin through breast milk

2 qualities of bat lifestyle that suggest they might socially entrain?

1. roost in large colonies in caves that provide complete darkness throughout the day

2. they leave the nest each dusk to forage after a period of “light-sampling” at the cave entrance

Describe the experiment to test social entrainment in bats.

caged individuals were prevented from sampling light; some caged with a colony, other caged alone

2 results from the bat social entrainment study? What conclusion can we draw?

1. bats caged alone for 17 days free-ran with a period > 24 hours

2. bats housed with colony remained synchronized to local time

3. caged bats were entrained by social cues

How did researchers examine social entrainment in beavers?

recorded gnawing sounds over the winter

2 results of the beaver social entrainment study? What does this suggest?

1. colony changed composition over the winter, but while in the lodge, they free-ran

2. gnawing sounds suggested a single circadian period (despite multiple individuals), suggesting all animals were synchronized

3. beavers socially entrain

Did the House Sparrow housed in constant light show social entrainment to recordings of sparrows singing at particular times? What does this suggest about social entrainment?

1. not really; unstable & would start free-running even in presence of song zeitgeber

2. social entrainment is species-specific & birdsong is not a strong zeitgeber in birds

Estrus Cycle

female rats are sexually receptive & fertile for only 10 hours once every 4-5 days

The estrus cycle is induced by a surge in _____ _____ that is gated by the _____ _____.

1. luteinizing hormone

2. circadian clock

Why might the estrus cycle be a social entrainment zeitgeber?

need to time the LH surge so the female is fertile during a time of day when she is likely to find a male; behavioural estrus should synchronize with time male is awake

What 2 entrainment phenomena were found in the estrus cycle? What might this suggest?

1. when males are added to a cage of females the females will begin to cycle with the same phase & period (become synchronized)

2. females alone will synchronize their estrus cycles, but it is less robust without the male

3. entrainment likely mediated by a pheromone

What social entrainment phenomena was suggested in humans? Was this replicated?

1. menstrual synchrony among women

2. no

2 reasons why synchronizing fertility might occur?

1. decreasing overall mortality for prey species

2. animals that live in packs

Lunar Menstrual Synchrony

may be weak synchrony to the lunar phases; may be due to luminance or gravimetric cycles

2 ways time might influence how we eat?

1. types of food

2. quantities of food

2 ways nutrient cravings change across the day?

1. carbs, veggies, fruits: cravings follow hunger

2. salty snacks, sweets, fats: cravings increase throughout the day & don’t follow hunger

How does the circadian rhythm impact speed of eating?

will eat faster during time of day when they are meant to be awake; even when starved, will eat slower during time they are meant to be asleep

How does rat location of eating differ based on the time of day?

1. night: next to food hopper

2. day: take food back to nest (predation risk)

How would you test if time of day or presence of light influences rat eating locations?

turn of the light during day & turn on light during night; if phenomena remains, it suggests that this is a circadian regulated behaviour

Food is the first _____ for baby bunnies. They only feed once a day for 3-5 minutes & will consume up to __% of their body weight.

1. zeitgeber

2. 30

How does food become a zeitgeber for entrainment?

due to anticipation of scheduled feeding

Not only does anticipation for feeding _____ occur, but specific _____ _____ as well.

1. times

2. food types

When studying anticipation, it is often a matter of _____ over _____.

1. clock

2. hourglass

Rats are nocturnal & eat at night, but if food & light are in conflict, _____ wins.

food

When rats are given scheduled feedings during the day, they will wake up for their food. Their activity will match this schedule even when not feed, why?

they wake up due to anticipation of food

2 pieces of evidence that the SCN is not the food clock? What does this suggest?

1. animals lacking an SCN can anticipate a daily meal

2. exercise rhythms & anticipation rhythms can co-exist with different periods

3. 2 clocks

What benefits has time-restricted eating shown in humans?

better sleep, quality of life, & less health issues

Evidence for sexual cues in entrainment? 2 catches to this?

1. exposure to a receptive female will accelerate adjustment to a shifted light/dark cycle

2. dependent on activity

3. doesn’t work if they actually mate

Presenting a female hamster very day can _____ the entrained rhythms. This has a greater effect when females were in _____.

1. advance

2. estrous

What happens when you give a male rat a scheduled daily chance to mate with females? What is the main issue with this study?

1. they will eventually anticipate the mating time

2. right after eating, males will eat; may be food clock entrainment, rather than sexual entrainment

What happens to entrainment if you block post-mating exercise & meals? What does this suggest about sexual entrainment?

1. most rats show no noticeable anticipation

2. more of a function of exercise/food as zeitgebers

Dark Pulses

“flashing” dark during a light period

What was found when exposing animals to dark pulses?

shifts in circadian rhythm phases; circadian phase response curve

How was exercise introduced as a behavioural method for accelerating entrainment to new light/dark cycles?

animals put in a new cage with a new light/dark cycle; would run a lot & wake up on the new time the next day

When comparing different amount of exercise in entrainment, what was the optimal amount of exercise for phase shift? What was the maximum amount of hours that could be shifted due to exercise?

1. 6 hours

2. 3 hours

What happened when examining exercise-induced re-entrainment with dark pulses?

dark pulses elicit activity; when activity is blocked, there are no shifts

Triazolam was a known factor in accelerating re-entrainment in hamsters. How was this re-examined in the context of activity?

blocked activity & found that triazolam did not cause a phase shift; also noted that triazolam elicits activity (activity seems to be the key point)

2 questions to ask in the question of whether exercise is really what is shifting the clock?

1. when does exercise shift the clock?

2. what do “sluggard” hamsters so when locked in a wheel?

When does exercise shift the clock?

exercise only shifts the clock when the animal is normally sleeping

What do “sluggard” hamsters do when locked in a wheel?

they sleep

Given that exercise only retrains when animal would normally be sleeping, what else might be impacting entrainment?

sleep deprivation

How was SD vs exercise in entrainment studied? What did they find? What might this suggest?

1. compared two groups; one had SD & would exercise when SD; the other was SD & had their wheel locked (no exercise)

2. both groups phase shifted

3. SD is more important than exercise in entrainment

What raises concerns that SD might not be the whole story in entrainment?

only ~70% of animals respond to SD

2 things you need to do when sleep depriving a non-responder for phase shift to occur? What does this suggest?

1. intervene sooner

2. intervene more often

3. that wakefulness may be critical

How did researchers examine wakefulness in non-responders? What did these studies find?

1. EEG

2. responders & non-responders do not exhibit the same EEGs; non-responders may not be in alpha wake state

Which systems are the following circadian influences related to: darkness; exercise; SD; arousal?

1. visual system

2. energy use & motor systems

3. homeostatic sleep drive

3 qualities of BF cholinergic cells?

1. input from other arousal cells

2. activation leads to cortical arousal

3. inactivation leads to loss of fast cortical activity

2 regions SCN received cholinergic input from?

1. BF: substantia innominata

2. brainstem: PPT, LDT, PBN

The SCN contains many _____ receptors.

cholinergic

Carbachol

cholinergic agonist

How does carbachol impact the circadian system?

produces non-photic shifts when injected into SCN & IGL

_____ agonists, such as carbachol, can mimic _____ shifts.

1. cholinergic

2. non-photic

How do we know if arousal is involved in cholinergic-induced non-photic shifts? What do we see in practice?

1. examine the BF after non-photic manipulations

2. the BF shows activation by these manipulations; arousal activates SCN-projecting cholinergic cells

4 large roles of cholinergics in non-photic shifts outlined by the research?

1. cholinergics mimic non-photic shifts

2. cholingeric cells in BF that project to SCN are activated following non-photic manipulations

3. ACh acts at the SCN

4. ACh input from BF both necessary & sufficient to reset the clock

3 pieces of evidence for ACh acting at the SCN?

1. intra-SCN atropine blocks non-photic shifts

2. stimulation of BF causes non-photic shifts

3. shifts due to BF stimulation are blocked by atropine

Atropine

agent that blocks ACh receptors

ACh input from the BF is both _____ and _____ to rest the clock.

1. necessary

2. sufficient

Non-photic manipulations appear to produce _____ of SCN activity, which is the effect produced by in-vitro _____ drugs.

1. inhibition

2. cholinergic

Non-photic manipulations suppress SCN _____ _____.

gene expression

Describe the 5 steps of the day portion of the better model of gene expression & non-photic shifts discussed in class.

1. during the day, expression of the period genes is high

2. non-photic pulses eliminate per gene expression

3. premature trough

4. permits an early rise

5. product is a phase advance

Describe the 4 steps of the night portion of the better model of gene expression & non-photic shifts discussed in class

1. during the late night, the per gene is just beginning to be expressed

2. a non-photic pulse knocks it down

3. rise is delayed

4. product is a phase delay

The critical component for non-photic phase shifting may be _____, with _____ _____ simply being a useful tool for achieving sufficient levels of this.

1. arousal

2. physical activity

Actual shift of the clock is likely through inhibition of _____ _____ and _____ of the clock.

1. gene expression

2. activity