Neuro3: Circadian Rhythms and Sleep (Dr. Cao - 1 hr)

mTOR activity is regulated by what?

By "clock" and light The activity of mTOR exhibits significant circadian fluctuation in the SCN. And a short light exposure at night time activates the mTOR/S6K signaling cascade in the SCN. But their functions and molecular mechanisms in the clock were not known.

Alterations in circadian rest-activity rhythms in Alzheimer's disease

By knocking out an important clock gene Baml1, the mouse estrous cycle is largely changed. Therefore, clock is important for animal reproduction and should be studied in veterinary medicine.

A 23-year-old woman is seen by her primary care physician. The patient has a several year history of excessive daytime sleepiness. She also reports episodes where she suddenly falls to the floor after her knees become weak, often during a laughing spell. She has no other significant past medical history. Her primary care physician refers her for a sleep study, which confirms the suspected diagnosis. Which of the following laboratory findings would also be expected in this patient? A. Increased serum methoxyhemoglobin B. Reduced serum hemoglobin C. Undetectable CSF hypocretin-1 D. Increased CSF oligoclonal bands E. Increased serum ESR

C. Undetectable CSF hypocretin-1

The master Circadian clock in mammals

***The Suprachiasmatic Nucleus*** (SCN) In the lab we use mice to study the mammalian circadian clock. Similar to humans, the master circadian clock is located in the SCN of the hypothalamus. It receives photic input from the retina and generates molecular rhythms.

Disruptions of Circadian Rhythms

*Circadian Rhythm Disorders* -Jet Lag, Shift Work Sleep Disorder -Advanced Sleep Phase Syndrome (ASPD) -Delayed Sleep Phase Syndrome (DSPS) -Non 24-Hour Sleep Wake Disorder *Circadian clock-related diseases* -Cancer, Neurological and psychiatric disorders -Metabolic syndromes, Cardiovascular diseases While it might not be a matter of life and death for humans, disruption of circadian rhythms do cause health problems. Disruption of circadian rhythms can directly cause circadian rhythm disorders. For example, jet lag and shift work sleep disorder. Point mutations of human clock gene Period 2 and casein kinase I were identified in patients with Familial advanced sleep phase syndrome. Perhaps more importantly, clock malfunction has been linked to a number of common human diseases including cancer, metabolic syndromes, and neurological diseases.

Sleep Stages

*NREM sleep*: a reduction in physiological activity. As sleep deepens, a person's brain waves slow down and gain amplitude, both breathing and the heart rate slow down, and the individual's blood pressure drops. NREM sleep consists of three(or four) stages *Stage 1* is a time of drowsiness or transition from being awake to falling asleep. Brain waves and muscle activity begin slowing down in this stage. People in stage 1 sleep may experience *sudden muscle jerks*, preceded by a falling sensation. *Stage 2* is a period of light sleep during which eye movements stop. Brain waves become slower, with a sudden increase in wave frequency(called *sleep spindles*) , and a sudden increase in wave amplitude (*K complexes*) ; spontaneous periods of muscle tone mixed with periods of muscle relaxation. The heart rate slows and body temperature decreases, when bruxism occurs *Stage 3(and 4)* is called *"slow wave sleep" (SWS)* and is characterized by the presence of slow brain waves called *"delta waves"*(due to synchronized neuronal activities) . Blood pressure falls, breathing slows, and temperatures drops even lower, with the body becoming immobile. Sleep is deeper, with no eye movement and decreased muscle activity, although muscles retain their ability to function. It is most difficult to be awakened during SWS, and people may feel groggy or disoriented for several minutes after they wake up from this stage. During SWS, some children experience *bedwetting, night terrors, or sleepwalking.* The amount of SWS a person gets is directly related to accumulated sleep need — the longer a person has been awake, the more SWS he or she gets when sleep occurs *REM sleep: "paradoxical sleep" or "desynchronized sleep"*; Brain waves are fast and desynchronized, similar to those in the waking state. Extraocular movements during REM due to activity of paramedian pontine reticular formation/conjugate gaze center, PPRF; Breathing becomes more rapid, irregular, and shallow; *eyes move rapidly* in various directions and limb muscles become temporarily paralyzed. Heart rate increases and blood pressure rises. This also is the sleep stage in which most *dreams and penile/clitoral tumescence* occur. REM sleep is thought to play a role in *memory consolidation*, the synthesis and organization of cognition, and mood regulation A) acetylcholine is the principle neurotransmitter B) norepinephrine, serotonin, and histamine suppress REM sleep -Therefore, certain antidepressants (eg, SSRI, SNRI) can pharmacologically suppress REM sleep

The genetic Feedback loop of the molecular clock

*period gene*

Circadian Rhythm disorders

-Jet Lag, Shift Work Sleep Disorder -Advanced Sleep Phase Syndrome (ASPD) -Delayed Sleep Phase Syndrome (DSPS) -Non 24-Hour Sleep Wake Disorder

What is sleep?

A naturally recurring state of mind and body characterized by altered consciousness, relatively inhibited sensory activity, inhibition of nearly all voluntary muscles, and reduced interactions with surroundings

A patient who has not been sleeping well presents to your sleep clinic. During a sleep trial you notice that the patient has multiple hypnic myoclonic episodes, which disrupts the patients sleep. This patient is experiencing difficulty during which sleep stage: A. stage 1 B. stage 2 C. stage 3 D. REM

A. stage 1

REM sleep behavior disorder

Absence of muscle atonia during REM sleep Patients are usually middle aged or older man "Acting out" their dreams Loud and angry vocalizations Antagonistic acts as if receiving an attack Inhibitory interneurons in the medullary reticular formation are not activated Maybe an early sign of neurodegeneration

Circadian Rhythm

Almost all living organisms exhibit circadian rhythms. This figure shows the putative origins of circadian oscillatory systems, from the redox-redux cycles to the PER gene centered genetic feedback loops. The autonomous property is endogenously driven by circadian clocks. It is an evolutionarily conserved property, which confers such an advantage to the organisms that they can predict and prepare for upcoming environmental changes and synchronize their physiology and metabolism to the ambient cycles.

A mother brings her 6-year-old daughter to the pediatrician to discuss her child's sleeping troubles. Three times now in the last month the child has begun screaming and crying in the middle of the night. When the parents rush to the child's room, they find her crying inconsolably. They try to ask her what is wrong, but she does not respond and persists crying for approximately 20 minutes, after which she goes back to sleeping comfortably. Upon awaking the following morning, she has no recollection of the night's events. Which of the following is true about these episodes? A. They will be persistent into adulthood B. They occur only during non-REM sleep C. They can occur any time during the sleep cycle D. They are associated with child abuse E. They are associated with later development of a mood disorder

B. They occur only during non-REM sleep

Cataplexy and Narcolepsy

Caused by the loss of the neuropeptide *hypocretin (orexin)*, which is synthesized by the lateral hypothalamus Characterized by excessive sleepiness, *daytime sleep attacks (transitions from wakefulness directly to REM sleep)*, fragmented night sleep, hallucinations, and *cataplexy* (sudden loss of muscle tone, often triggered by a strong emotion such as laughter) Affects roughly 1 in 2,000 people There is no cure for narcolepsy *Modafinil* (a wakefulness-promoting agent) is currently the preferred first line therapy Cataplexy causes sudden loss of muscle tone that leads to a slack jaw, or weakness of the arms, legs, or trunk. People with narcolepsy can also experience dream-like hallucinations and paralysis as they are falling asleep or waking up, as well as disrupted nighttime sleep and vivid nightmares. Cataplexy video: -https://www.youtube.com/watch?v=1PuvXpv0yDM

An 18-year-old man presents to his primary care physician with a complaint of excessive daytime sleepiness. He denies any substance abuse or major changes in his sleep schedule. He reports frequently dozing off during his regular daily activities. On further review of systems, he endorses falling asleep frequently with the uncomfortable sensation that there is someone in the room, even though he is alone. He also describes that from time to time, he has transient episodes of slurred speech when experiencing heartfelt laughter. Vital signs are stable, and his physical exam is unremarkable. This patient is likely deficient in a neurotransmitter produced in which part of the brain? A. Thalamus B. Pons nucleus C. Hippocampus D. Hypothalamus E. Midbrain

D. Hypothalamus

Circadian sleep/wake cycle in an isolated environment

I understand there are many electrophysiologists in the audience. Here I gave an example of the circadian excitability of SCN neurons. The rest membrane potential exhibits daily variations and spontaneous firing rate also shows significant day/night difference.

Circadian Rhythmicity in Human Physiology

In humans, a variety of physiological functions exhibit daily fluctuations as shown in this figure. For example, our blood pressure and body temperature are highest in the evening. And we have highest alertness in the morning.

The Circadian Clock can be reset by what?

Light! As an important property, the circadian clock is continuously adjusted by the environmental signals such as light. As shown here, the light period during a day is continuously changing throughout the year. To be synchronized with the external light/dark cycles, the circadian clock has to be continuously reset, which is, in some cases, extremely important, for the survival of animals. For example, for the nocturnal rodents, failure to reset their clock and exposure during the day can increase the risk of being killed by their predators.

Insomnia

More than 3 million US cases per year Insomnia may be a symptom of underlying sleep disorders. For example, *restless legs syndrome*—a neurological condition in which a person has an uncomfortable sensation of needing to move his or her legs—can lead to insomnia. An estimated 10 percent of the population has restless legs syndrome. *Sleep apnea* is another sleep disorder linked to insomnia. With sleep apnea, a person's airway becomes partially or completely obstructed during sleep, leading to pauses in breathing and a drop in oxygen levels Insomnia can be caused by psychiatric conditions such as depression, stress and anxiety; medical conditions such as chronic pain, Nasal/sinus allergies, etc Insomnia can be triggered by substances and activities, such as alcohol, caffeine, nicotine; shift work, daytime naps, etc

*Sleep walking*

Most common in children, who usually outgrow it by their teens; usually occurs one to two hours after falling asleep at night. Often, sleepwalking is a random, harmless event. Treatment may be needed if it occurs often or causes injury.

Neural Mechanisms of Sleep

Neurons most critical for sleep and waking are part of the *diffuse modulatory neurotransmitter systems* Involved neurotransmitters include *norepinephrine (locus coeruleus), serotonin(raphe nuclei), acetylcholine(basal forebrain), histamine(midbrain), orexin(hypothalamus)*, etc The diffuse modulatory systems control thalamus rhythms, which in turn control many EEG rhythms Sleep also involves activity in descending branches of the diffuse modulatory systems, such as inhibition of motor neurons during dreaming *Ascending reticular activating system*: reticular core of the brain stem in processes that arouse and awaken the forebrain Sleep-promoting factors: *adenosine*, inhibits awaking diffuse modulatory systems; caffeine is an antagonist of adenosine receptors *Melatonin*: SCN-PVN-Pineal gland, inhibited by light

*Sleep terror disorder*

Night terror, also known as sleep terror, is a sleep disorder, causing feelings of terror or dread, and typically occurs during the first hours of stage 3-4 non-rapid eye movement (NREM) sleep. Sleep terrors begin in children between the ages of 3 and 12, and usually stop during adolescence.

Why do we sleep?

Prolonged sleep deprivation causes death in animals Sleep is not a time when the mind and body shut down It is an *active period* in which a lot of important processing, restoration, and strengthening occurs Exactly how this happens and why our bodies are programmed for such a long period of slumber is not known Our bodies all require long periods of sleep in order to restore and rejuvenate, to grow muscle, repair tissue, and synthesize hormones (*growth hormone*) One of the vital roles of sleep is to help us *consolidate memories* -our brains take in a huge amount of information -Overnight, bits and pieces of information are transferred from short-term memory to long-term memory—a process called "consolidation" -Researchers have also shown that after people sleep, they tend to retain information and perform better on memory tasks

How is sleep studied

Sleep-like states are observed in flies and worms Three fundamental measures to define stages of sleep in mammals Gross brain wave activity, as measured by an electroencephalogram (*EEG*). EEG provides the summary of electrical activity from one area of the brain Muscle tone, electromyogram (*EMG*) Eye movement, electro-oculogram (*EOG*) *EEG reading is the most important measure in differentiating between the stages, while the EMG and EOG are most important in differentiating rapid eye movement (REM) sleep from the other stages*

Tips for better sleep!

Stick to a sleep schedule Pay attention to what you eat and drink Create a bedtime ritual Get comfortable Limit daytime naps Include physical activity in your daily routine Manage stress

***Human Circadian System***

The circadian system is hierarchically organized. The master pacemaker is located in the part of the anterior hypothalamus in the base of our brain called the *suprachiasmatic nucleus (the SCN)*, which is shown here in the framed region. It receives daily light input from the eyes, generates circadian rhythms and in turn sends out output signals to other brain regions as well as the peripheral systems through cyclic neural innervation and hormone secretion. For example, the functions of the autonomic nervous system, endocrine and immune systems are all regulated by the central clock. It is worth noting that each peripheral tissue expresses clock genes and can perform circadian oscillations. However, their local rhythms are always orchestrated by the master pacemaker, of course unless when you are in jet lag, the synchronization in different systems will be disrupted.

mTOR signaling in SCN

The expression of mTOR components including mTOR, phospho-mTOR, phospho-S6 as a readout of S6Ks and phospho-4E-BP1. All these proteins are enriched in the SCN, indicating their significant roles in the clock.

*REM sleep behavior disorder*

The paralysis that normally occurs during REM sleep is incomplete or absent, allowing the person to "act out" his or her dreams that are vivid, intense, and violent.

Sleep Stages, EEG vs EMG, VS EOG

Three functional states of the brain -*Awake* -*Non-REM Sleep* -*REM Sleep*

Physiological and endocrine circadian cycles

To give your more examples of circadian rhythms in our body, this figure shows representative physiological and endocrine circadian cycles in humans held under constant routine conditions. Left panel shows circadian variation in four vital physiological functions, whilst on the right are four endocrine axes subject to circadian control. The shaded area depicts when the subjects would normally have been sleeping but in the constant routine they remained awake.

Sundowning Syndrome

describes a phenomenon when a person habitually becomes confused or disoriented with darkness