M05.08.03 Neurotransmitter

Role in Sleep: Serotonin helps to initiate sleep.
Key Points:
- It serves as a precursor to melatonin, which is crucial for regulating the sleep-wake cycle.
- Low levels of serotonin may lead to sleep disturbances.

Role in REM Sleep: Acetylcholine levels are higher during REM (Rapid Eye Movement) sleep.
Key Associations:
- REM sleep is linked with physiological functions like erections in men.
- The ratio of Acetylcholine (ACh) to Norepinephrine (NE) acts as a biochemical trigger for the onset of REM sleep.

Role in Sleep: Norepinephrine levels decrease significantly during REM sleep.
Pathway:
- NE pathways originate in the pons, a brainstem region crucial for REM sleep regulation.

Function: Dopamine plays a role in promoting arousal and wakefulness.
Key Mechanism:
- Dopamine levels rise upon waking, contributing to alertness.

Role in Sleep and Wakefulness: Orexin is a neurotransmitter that regulates arousal, wakefulness, and appetite.
Activation:
- High orexin levels stimulate wakefulness, while low levels help drive sleep, especially at night.
Clinical Connection:
- A deficiency of orexin can result in sleep-state instability, leading to conditions such as narcolepsy.

Conversion: Melatonin is synthesized from serotonin in the pineal gland under the influence of the body’s circadian rhythm.
Key Functions:
- Inhibition: Photoreceptor activation in the retina inhibits melatonin production.
- Sleep-Wake Cycle: Melatonin secretion increases in the evening, causing drowsiness and regulating the circadian alerting system in the suprachiasmatic nucleus (SCN).
Seasonal Affective Disorder (SAD):
- Exposure to bright light can suppress melatonin and alleviate depressive symptoms associated with SAD.

Neurotransmitter	Function	Associated Sleep Phase	Clinical Relevance
Serotonin	Initiates sleep	N/A	Precursor to melatonin
Acetylcholine (ACh)	Higher during REM sleep	REM	Linked with physiological REM functions
Norepinephrine (NE)	Lower during REM sleep	REM	Originates in the pons for REM control
Dopamine	Promotes arousal and wakefulness	Waking	Dopamine levels rise upon waking
Orexin (Hypocretin)	Regulates arousal, wakefulness, appetite	Waking/Sleep	Deficiency leads to narcolepsy
Melatonin	Regulates sleep-wake cycle, promotes sleep	N/A	Involved in SAD treatment

Table: Neurotransmitter Functions in Sleep and Wakefulness

The balance of Acetylcholine and Norepinephrine is essential for triggering REM sleep.
Low levels of serotonin can disrupt sleep, as it is a precursor to melatonin.
Orexin deficiency is associated with narcolepsy, a condition where the brain is unable to regulate sleep-wake cycles.
Melatonin production is influenced by light and is suppressed by bright light, which is used in therapies for SAD.

Neurotransmitter

M05 Behavioral Sciences