Which neurotransmitter is associated with alertness and arousal, with undersupply potentially leading to depression?

The neurotransmitter associated with alertness and arousal, where an undersupply can potentially lead to depression, is norepinephrine. This chemical plays a crucial role in the body's response to stress and helps to mobilize the brain and body for action. Norepinephrine is involved in regulating mood, and research indicates that low levels of this neurotransmitter can contribute to feelings of apathy and lack of motivation, which are commonly seen in depressive disorders.

While other neurotransmitters like dopamine and serotonin are also important in mood regulation and cognition, norepinephrine is specifically linked to alertness and the regulation of arousal states. It is a key player in the "fight or flight" response, enhancing wakefulness and attentiveness. This distinctive role emphasizes norepinephrine's association with both the physical arousal component and the psychological aspects of mood disorders.