Neurotransmitter Associated with Mood Regulation

Neurotransmitters are chemical messengers that transmit signals across synapses in the nervous system. They play a crucial role in regulating various physiological processes and behaviors. Among the many neurotransmitters identified, some are known to influence mood, arousal, and cognitive functions. Each neurotransmitter has a specific role and mechanism of action.

Which of the following neurotransmitters is primarily associated with the regulation of mood and is often linked with depression when present in low levels?