Circadian Rhythms and Neurotransmitters

In the field of neuroscience, neurotransmitters play a crucial role in communicating signals between neurons. Specific neurotransmitters are associated with various psychological conditions and bodily functions. For example, serotonin is known to influence mood regulation, and dopamine is linked to reward and pleasure. However, understanding their pathways and interactions is vital for grasping their full impact on behavior and cognition.

Which of the following neurotransmitters is primarily linked to the regulation of circadian rhythms and sleep-wake cycles?