Lectures 7-9 Flashcards
(134 cards)
What is the general development of circadian rhythms from baby to adult?
For the first few days of life, babies moves throughout day and night with no pattern.
At around day 7 you begin to see a slow move towards a rhythm (less activity at night).
At 4 months old, babies begin to develop a rhythm which is established in light/dark.
Adults show a very strong rhythm.
As we age and get older, our actograms show that we begin to lose our rhythms - we get lower activity during the day and broken sleep during the night (due to naps etc).
Outline briefly the developmental cycle of a rodent.
E0 - embryonic day 0.
Pregnancy in a mouse is 21 days.
Hence, P0/E21 - post natal day zero
Mice pups suckle their mothers for 21 days.
P21 - when they can be weaned (separated from their mother).
5/9 weeks after weaning, the mice reach sexual maturity.
After this they can start mating.
What is the basic anatomy of the mammalian circadian system?
Eyes -> SCN -> Brain -> Peripheral Clocks - Behavioural/Physiological Rhythms (*the brain also projects directly to here).
Detail the development of the visual system in relation to the circadian system in rodents.
Rods and Cones start developing in the embryo of rats and mice.
They carry on developing until around P10 (after birth) and from then they will be fully mature.
This is when mice can begin to detect and process light in the environment like an adult.
Melanopsin retinal ganglion cells develop much faster.
At around P0 mRGCs are present so they can detect light through these RGCs.
The maturation of the mRGCs hit their development peak at around P10.
So before an animal opens its eyes and can see anything, it can still detect light.
The functional retinal output occurs at around P15 in which eyes fully open.
From here all the photoreceptors should be up and ready.
What are the differences between hamsters and rats in their development of the RHT?
In a Hamster, you can see that projections from the RHT to the SCN don’t start to develop until P4.
They develop maximally at P15 to full maturity.
In the Rat, you can see it’s a lot quicker.
They start to project in P1, a day after being born, and develop maximally again at P15.
In both animals, when their eyes fully open they have fully built their RHT projections to the SCN.
Outline the development of the SCN in the circadian system of rodents.
- Neurogenesis: Occurs during the embryonic stage.
- Glial Cells: Appear in the embryo but fully develop by ~P10, later than neurons.
- Synapse Formation: Begins after neurons are in place, from just before birth to ~P10.
- Critical Period: Experiences within 2 weeks after birth can have lasting effects.
- SCN Metabolism: Development of glucose utilization and neuropeptide production starts after birth and completes shortly after P10.
Briefly outline the development of circadian rhythm neuropeptides in rodents.
VIP expression starts happening before birth.
VP is produced only from birth.
GFAP is a marker for glial cells and they take longer to appear; there’s not much until postnatal.
Describe the development of clock genes in Rat SCN and how we discovered it.
You can look in the Rat SCN and look at mRNA levels of key clock genes.
Soon after birth, there is no circadian rhythm of these genes.
At P2, there is starting to be a rhythm forming in Per1 and Per2.
As we get further to P10, there is almost a fully formed rhythm.
BMAL1 and Cry1 take longer but by P10 there is clear expression.
Outline the development of peripheral clock genes in rodents and how we discovered it.
Researchers have been using transgenic mice that you can link a clock gene with luciferase.
So you can take a slice of SCN and look at the expression of the gene over several days.
The current record is that they kept some SCN going for 3 years (as it’s a self-autonomous clock).
Using this method, they looked at different regions in the body and looked for Per1-luc expression to see when the circadian rhythm is expressed.
P7: SCN
P9: Pineal Gland (Melatonin secreted from Pineal Gland).
P10: Adrenal Gland
P10: Lungs
P20: Thyroid
P25: Liver
Why is liver so late in peripheral clock gene development?
The main zeitgeber for the liver is food, until p21, the mothers are suckling but then they start to eat food, providing the zeitgeber needed to get the rhythms started.
What are the proposed maternal effects on the circadian clock of a pup?
Rhythms of a mother will have an influence on a pup.
A mothers rhythms will be established due to eyes being fully functioning and it’s thought that her clock will be able to be translated to the pup.
Thought that melatonin and other hormones can cross the placenta and entrain the rhythms of the pup (whilst still in utero).
Melatonin is key for synchronising the SCN and peripheral clocks.
It’s also thought the peripheral clocks from the mother also influence the rhythm of the pup peripheral rhythms.
What happens to SCN lesioned animals?
They become arrhythmic
What are the maternal effects of arrhythmic mothers on their pups?
Actograms show a locomotor activity of a pup born of a arrhythmic mother.
They do have rhythms but they are all over the place and are not synchronised to each other.
So being an arrhythmic mother doesn’t mean your pups will be but there will be little to no coherence between their rhythms.
Outline the Bellavia et al., (2006) study into maternal melatonin and its effect on drinking behaviour in rat pups.
METHODS:
- Take a WT mouse mother, a Pineal lesioned mouse mother and a Pineal lesioned mouse mother with additional melatonin.
- *Pineal lesion will restrict melatonin production.
- Look at the resulting drinking rhythms found in pups due to the presence or lack of melatonin in breast milk - or supplemented melatonin.
RESULTS:
- In the control, there is a tight rhythm in drinking behaviour around the time of the breast milk with melatonin being drank.
- In the Maternal pinealectomy there was no rhythm.
- In the Maternal pinealectomy + melatonin replacement rhythms were restored to around feeding times.
This shows that melatonin is key for synchronising pups.
What are two hormones are thought to entrain foetal circadian rhythms in rodents?
Melatonin and Corticosterone
Outline the effects of maternal behaviour on pups rhythms.
Rats are nocturnal so spends most of the time in the nest in the day (when resting).
As the pups grows older, the mother stop spending as much time in the nest during the day (as pups can fend for themselves).
For the first 10 days they don’t leave the nest (as you would expect; the eyes are closed and circadian structures are developing).
From P11/12 the pups begin to follow mother at night, this pattern is repeated every day.
This shows that the behavioural rhythm of the mother creates a clear rhythm in the pups.
Describe the development of light sensitivity in mice and how to test it.
Light is the main zeitgeber for the SCN.
This is measured in Labs by flashing a pulse of light at a new born animal and reading the gene expression in the SCN as a response.
c-fos is known as an immediate early gene that gives you an idea of whether a neuron has been activated or not.
If you fire a pulse and it’s expression goes up in SCN, it will increase in the animal.
From P1, the animals can pick up the flash of light (there is already some RGCs that can process light pulses).
Per1: P1
Per2: P3.
From the time of birth (or around it) animals can detect light.
What is clock gating in relation to pups response to light? When do they develop it for c-fos, Per1 and Per3?
If you flash a light in the morning compared to night, will there be a different response (like phase response curves).
You would expect the expression of clock genes to be dependent on the time of day.
Per1: P3
Per2: P5
c-fos: P10
Describe the progression from maternal to photic entrainment in mice pups.
Between P0-P10 most of the structures and key elements of the SCN are not fully formed yet.
So in this period they depend on their mothers rhythms; light doesn’t have too much influence on their rhythms yet.
As they get older there starts to be a joint influence between light and the mother.
Once the animal is weened (no longer getting melatonin milk ~P21) then light begins to drive the infants rhythms.
Here, the mother has no influence and the pup will be fully photo entrained.
Outline the study by Ciarleglio et al., (2011) into photoperiodism in mice pups.
METHODS:
- These experiments look into what would happen if you raised animals in different seasons of light (8:16, 12:12, 16:8)?
- Exposed the animals for the full lactation period (until P21) in these different light conditions.
- Then, put them under the same light conditions 12:12,
- The only difference between the three groups is the light schedule they received after birth.
RESULTS:
- If you look at the period of the neurons, you will see it’s longer for the animals raised in the winter conditions and it was shorter in animals raised in summer conditions.
- So the light environment changed the period of the animal.
Outline the Ameen et al. (2022) study into extreme light environments effects on rodent neuronal development.
METHODS
- Two groups of animals:
- Control 12:12 cycle.
- Disrupted 12:12 - the onset of darkness advanced by 8 hours every 2 days.
- The mice cannot entrain because the rhythm keeps changing.
- They then looked at the neurons in different brain areas:
- PFC
- Hippocampus
- Amygdala.
RESULTS:
- They found that the branching of the neurons was reduced in the animals that had disrupted environments.
- Also, the length of the dendritic projections were shorter.
This demonstrates that disrupting the light an infant is bought up in disrupts the neuronal morphology.
What do experiments show about disrupted light cycles and the effect on the circadian system structures in rats?
It doesn’t have long term effects on photoreception in the retina.
BUT it does have effects on:
- SCN
- Brain
- Peripheral Clocks
- Behavioural/physiological rhythms
What has circadian biology research taught us about how to treat babies in neonatal intensive care units and what are the negative effects of not using this information?
These studies have shown that if the babies are in constant light or dark instead of light/dark cycles, they experience:
- Disturbances to biology rhythms
- Disturbances to sleep states
- Effects postnatal weight gain
- Effects visual development.
One of the main things that decides if a baby goes home or not is how much weight it puts on, another reason using this information is so salient.
Outline the Wakatsuki et al., (2007) study into the consequences of postnatal experience by looking at CLOCK mutant mice.
What are the findings of this study similar to? What does this tell us about it?
METHODS:
- They raised the clock mutant mice in constant darkness (DD), 12:12 light/dark (LD) or constant light (LL).
- Then, after P21, the animals were exposed to normal light dark cycles.
RESULTS:
- The ones in LD or DD were able to synchronise to light/dark and in constant darkness they free run with a 24.5h internal rhythm.
- In the raised in constant light condition, they can entrain to light/dark but the onset is way later than when the lights go off; a couple hours later they start moving (phase delay).
- When you provide constant darkness there is a much larger slope in the cycle when they free run; these animals have 25-26h rhythms.
What does this tell us?
- This is similar to people in Delayed Sleep Phase Syndrome (go to sleep late and wake up late).
- This is important because it DOES matter what the genetics AND environment are that the animal grows up in.
