Serotonin or serotonin system (SERT)

Serotonin / Serotonin System (SERT or 5-Hydroxytryptamine/5-HTT): The serotonin system helps regulate mood, sleep, appetite, and emotional steadiness. Serotonin is one of the brain’s significant chemical messengers (neurotransmitters), carrying signals between neurons (nerve cells). After serotonin is released between brain cells, it’s cleared by a transporter called SERT (also known as 5-HTT), which helps bring the signal to a close and reset the system for what comes next. Serotonin is often described as a “mood chemical,” but this can be misleading. It’s better understood as part of a broader regulatory system that helps stabilize and sustain emotional tone over time. In conditions such as depression, anxiety, and bipolar disorder, serotonin signaling may become slowed, inconsistent, or overly sensitive to stress — especially when sleep and circadian rhythms are disrupted. The problem is not simply “low serotonin,” but a system that has difficulty maintaining steady, well-timed signals. Also see Selective Serotonin Reuptake Inhibitors (SSRIs)