Final Exam Flashcards
What is the temporal relationship between per gene expression and PER protein levels in fruit flies? In mammals?
in both fruit flies and mammals, there’s a cyclic relationship between PER gene expression (making mRNA) and the levels of PER proteins. The gene produces mRNA, which leads to the creation of proteins. These proteins accumulate, inhibit their own gene’s activity, and then break down, allowing the cycle to start again.
In fruit flies, on what clock gene or protein does light act to cause phase shifts, and how does light affect that gene or protein?
In fruit flies, light acts on a clock gene called “period” (per) to cause phase shifts. Light affects this gene by regulating the production of the PER protein. When flies are exposed to light, it can either speed up or slow down the production of the PER protein, causing changes in their internal biological clock.
In mice, on what clock gene or protein does light act to cause phase shifts, and how does light affect that gene or protein?
In mice, light acts on a clock gene called “Clock Protrein” to cause phase shifts. Light exposure impacts the activity of these proteins, which in turn affects the mouse’s internal clock.
Can circadian clocks operate without gene transcription, and if so, what is the evidence?
Yes, circadian clocks can operate without gene transcription. Some evidence comes from experiments using cyanobacteria. These organisms have a clock-like system that functions without gene transcription. Researchers found that even when they halted gene expression, the circadian rhythm continued, indicating that the clock can work independently of gene transcription. This suggests the presence of post-translational processes, such as protein modifications, that sustain the circadian rhythm without new gene activity.
The circadian clock is said to be ‘cell autonomous’ – what does that mean, and what is the evidence?
“Cell autonomous” means that each cell possesses its own independent circadian clock. This clock allows the cell to regulate its functions, like metabolism, independent of signals from other cells or the body. Evidence for this comes from experiments where cells kept in isolation maintain their circadian rhythm, showing that they continue to follow their internal clock without external cues from the body or other cells.
Is there a circadian clock in the olfactory bulb? If so, does it cycle ‘in phase’ with the SCN pacemaker (i.e., showing peaks and troughs at the same time as the SCN). Does it require the SCN circadian pacemaker to cycle?
Yes, the olfactory bulb has its own circadian clock. It does cycle in phase with the master clock in the brain called the suprachiasmatic nucleus (SCN). However, the olfactory bulb’s clock can operate independently, but it can also be influenced by signals from the SCN, suggesting a connection between the two clocks.
Knockout of the gene Bmal1 has what effect on circadian rhythms in mice?
Knocking out the gene Bmal1 leads to having no circadian limits to entrainment of food. These mice don’t rely on the typical daily patterns to know when to eat. They’re not restricted by the usual time cues; they can adapt to eating at any time, without following the usual 24-hour cycle like normal mice do.
Are there circadian clocks in peripheral organs and tissues (e.g., liver, pancreas, etc) and if so, what stimuli are they entrained by, and what role does the SCN pacemaker play?
Yes, there are circadian clocks in peripheral organs like the liver, pancreas, and others. They can be entrained by cues like meal timing, temperature changes, and hormone levels. The SCN pacemaker in the brain acts as the master regulator, coordinating these peripheral clocks to keep them synchronized with the overall day-night cycle and ensuring harmony among different organ rhythms.
Why do circadian activity rhythms damp out in nocturnal rodents maintained in constant light for many weeks? What effect does constant light have on individual circadian clock cells in the SCN?
Constant exposure to light can cause dampening of circadian activity rhythms in nocturnal rodents over time because their internal biological clocks lose their regularity and synchronization. In the SCN, individual circadian clock cells start to desynchronize, affecting their coordination and leading to disrupted rhythms seen in behavior and activity patterns.
In mice, what effect does Per protein have on Bmal1? Does it affect Bmal1 gene expression, or does it affect how Bmal1 protein activates the per and cry genes?
The Per protein in mice affects Bmal1 by inhibiting its activity. Per doesn’t directly affect Bmal1 gene expression but instead interferes with how Bmal1 protein activates the per and cry genes, creating a feedback loop that regulates the circadian clock.
If the SCN pacemaker is made up of several thousand individual circadian clock cells, what happens to circadian activity rhythms if those cells become desynchronized from each other?
This desynchronization can lead to irregular and fragmented activity patterns rather than the usual organized daily rhythms.
Following a shift of the LD cycle, do circadian clocks in different brain and body parts re-entrain at the same rate or at different rates?
The master clock in the brain, the (SCN) plays a crucial role in coordinating these rhythms throughout the body. When there’s a shift in the light-dark cycle, the SCN adjusts to the new timing and helps to re-establish the rhythms in other organs and tissues.
Heart, liver, and other tissues may take a bit longer to fully re-entrain
What role do rods and cones play in entrainment of the circadian clock by light in mammals? Are they necessary (no entrainment without rods and cones)? Are they sufficient (entrainment is possible with only rods and cones)?
Rods and cones in the eyes play a crucial role in entraining the circadian clock by detecting light. They are necessary for entrainment, meaning without rods and cones, you’d lose the ability to see objects or movement. They need ganglion cells to be sufficient
What role does the photopigment melanopsin play in entrainment of the circadian clock by light in mammals? Is it necessary? Is it sufficient? What cells in the retina contain melanopsin?
Melanopsin is crucial for entrainment of the circadian clock in mammals. It’s necessary because it helps transmit light information to the brain’s circadian system, particularly in low-light conditions. While melanopsin is essential, it’s not sufficient on its own for entrainment. It’s primarily found in a specific type of retinal cells These cells contribute significantly to signaling light information to the brain for regulating the circadian rhythm.
What are ‘intrinsically photoreceptive retinal ganglion cells’ and what is their relationship with rods and cones?
Intrinsically photosensitive retinal ganglion cells (ipRGCs) are a unique type of cells in the retina that can directly sense light, unlike rods and cones. While rods and cones are the main visual cells, ipRGCs have their own light-sensitive pigment called melanopsin, allowing them to detect light levels and play a specific role in regulating the body’s internal clock, the circadian rhythm. They work alongside rods and cones but have a distinct function in signaling light information for non-visual processes like regulating sleep-wake cycles.
Intrinsically photoreceptive retinal ganglion cells have many dendrites that form a wide net-like pattern. Form determines function, and sometimes we can infer what a neuron does based on what it looks like. What does the broad, net-like dendritic tree of these neurons imply about what these ganglion cells can communicate about light. Would they be useful for counting photons (signalling daytime) or would they have any use for object recognition?
The broad, net-like dendritic tree of intrinsically photoreceptive retinal ganglion cells suggests they’re specialized for capturing overall ambient light levels rather than details or shapes. This structure implies they’re more suited for signaling changes in overall brightness, like distinguishing between day and night (counting photons), rather than recognizing specific objects or details in the visual environment.
Which wavelength (and associated colour) of light is most effective for inducing phase shifts?
Short-wavelength blue light is the most effective for inducing phase shifts in the circadian rhythm
The direct projection from the retina to the suprachiasmatic nucleus is called the____________
The direct projection from the retina to the suprachiasmatic nucleus is called the “retinohypothalamic tract.”
In the mouse circadian clock, activation of retinal photoreceptors by light causes release of which neurotransmitter in the suprachiasmatic nucleus?
neurotransmitter
The neurotransmitter (answer to previous question) that is released in the SCN in response to light has what effect on SCN neurons?
The neurotransmitter glutamate, released in response to light in the SCN, excites and activates SCN neurons, playing a key role in transmitting light signals to regulate the circadian clock.
Lesions to which of the following structures consistently block phase shifts induced by exercise in Syrian hamsters?
Lesions to the intergeniculate leaflet (IGL) consistently block phase shifts induced by exercise in Syrian hamsters.
A neurotoxin that kills 5HT (serotonin) neurons in the mouse brain has what effect on circadian rhythms
Mice with these lesions failed to entrain to a daily exercise schedule.
Neurons in the intergeniculate leaflet are activated by what type of stimulus, and are important for entrainment to what kind of time cues?
Neurons in the intergeniculate leaflet (IGL) are activated by changes in ambient light levels and are crucial for entrainment to non-image-forming time cues, especially those related to the timing of dawn and dusk.
In hamsters, the phase shifting effect of exercise in the usual sleep period can be mimicked by injection of which neurochemical into the SCN?
Injecting glutamate into the suprachiasmatic nucleus (SCN) of hamsters mimics the phase-shifting effect of exercise during the usual sleep period.
Do neurons in the dorsal and median raphe project directly or indirectly to the SCN pacemaker?
Neurons in the dorsal and median raphe project indirectly to the SCN pacemaker, often connecting through other brain regions before reaching the suprachiasmatic nucleus (SCN).
Does melatonin induce phase shifts in mammals, and if so, is the phase response curve similar to the PRC for light, for exercise, or for neither?
Melatonin can induce phase shifts in mammals, but its phase response curve is different from both light and exercise. It follows its own distinct pattern in influencing the circadian rhythm.
Which of the following is a possible mechanism for ‘radio broadcasting’ of circadian signals from an SCN graft?
One possible mechanism for the ‘radio broadcasting’ of circadian signals from an SCN graft is through its ability to synchronize and communicate with the recipient brain tissue by sending out rhythmic signals that influence the recipient’s circadian rhythms. This synchronization happens via neural connections and chemical signaling between the grafted SCN and the host brain.
Tetrodotoxin blocks sodium channels in neurons. What effect does this have on activity of those neurons? What effect does it have on circadian activity rhythms if infused into the SCN?
Tetrodotoxin stops neurons from firing by blocking their sodium channels. When infused into the SCN, it disrupts the normal functioning of SCN neurons, causing disturbances in circadian activity rhythms.
Cutting SCN axonal outputs by circular knife cuts has what effect on circadian rest-activity rhythms? Are there species differences in the effect?
Cutting SCN axonal outputs through circular knife cuts disrupts circadian rest-activity rhythms. The impact can differ among species, but generally, it causes significant disturbances in the normal sleep-wake cycles.
Can SCN transplants restore circadian rhythms in arrhythmic animals that lack studies tell us that direct axonal projections from the SCN to one or more other hypothalamic areas are necessary for some but not all circadian rhythms.
SCN transplants can restore circadian rhythms in animals that lack their own rhythms. Studies suggest that direct axonal projections from the SCN to specific hypothalamic areas are necessary for certain circadian rhythms, but not all rhythms rely solely on these connections
Do animals with an SCN lesion sleep more, less or the same amount as intact animals? Does it depend on the species? Do lesions affect how much animals sleep after they have been sleep deprived for 24h?
Animals with an SCN lesion can sleep more, less, or the same amount compared to intact animals, depending on the species. Lesions can affect how much sleep animals get after being sleep-deprived for 24 hours, altering their recovery sleep patterns.
After 24h sleep deprivation does the amount of recovery sleep depend on the time of day that the deprivation ends, or is this ‘homeostatic’ response completely independent of time of day (circadian phase)?
Animals with an SCN lesion can sleep more, less, or the same amount compared to intact animals, depending on the species. Lesions can affect how much sleep animals get after being sleep-deprived for 24 hours, altering their recovery sleep patterns.
- What is a ‘tau mutant’ hamster?
A tau mutant hamster is a special type of hamster with a mutation that causes its circadian rhythm to have a different natural cycle length (tau) compared to normal hamsters. This mutation affects the duration of its daily rhythms, altering the timing of its sleep-wake cycle.
If a wildtype Syrian hamster receives a partial SCN lesion and then receives an SCN transplant from a tau mutant hamster, what does its circadian activity rhythm look like? Does it look like a wildtype, a tau mutant, or both? If both, is one phase of the circadian rest-activity cycle dominant, or are they equivalent in strength (which begs the question, is it even possible for both phases of the rest-activity cycle to be equivalent in strength)?
When a wildtype Syrian hamster with a partial SCN lesion receives an SCN transplant from a tau mutant hamster, its circadian activity rhythm can exhibit characteristics of both wildtype and tau mutant rhythms. Sometimes, one phase might dominate, while in rare cases, both phases might appear equally strong, but it’s uncommon for both phases to be entirely equivalent in strength.
