Which neurotransmitter is closely associated with mood regulation and sleep cycles?

Serotonin is a key neurotransmitter that plays a significant role in mood regulation and the regulation of sleep cycles. It is often referred to as the "feel-good" neurotransmitter due to its influence on mood, emotion, and overall sense of well-being. Low levels of serotonin are often linked to mood disorders such as depression and anxiety. Additionally, serotonin helps modulate various functions in the body, including the sleep-wake cycle, by influencing sleep stages and the onset of sleep. This makes it crucial for maintaining a balanced mood and healthy sleep patterns.

Other neurotransmitters listed have different primary functions: dopamine is mainly involved in reward and motivation, glutamate is the principal excitatory neurotransmitter related to cognitive functions like learning and memory, while norepinephrine is associated with arousal and alertness. Therefore, serotonin is the most relevant neurotransmitter for the context of mood and sleep.