The Six Major Neurotransmitter Systems

Psychopharmacology focuses on six major neurotransmitter systems. Serotonin—produced in the brainstem’s raphe nuclei—modulates

mood, anxiety, sleep, appetite, and cognition.

Selective serotonin reuptake inhibitors, or SSRIs, enhance serotonergic signaling. Norepinephrine—arising from the

locus coeruleus—drives arousal, attention, and stress responses. Serotonin-norepinephrine reuptake inhibitors target both serotonin

and norepinephrine. Dopamine—released from the substantia nigra and ventral tegmental area—governs motivation,

reward, movement, and salience. Too little dopamine in the nigrostriatal

pathway causes Parkinsonism; excess in mesolimbic circuits contributes to psychosis. Antipsychotics primarily block

D2 receptors. Glutamate is the brain’s major excitatory neurotransmitter, critical for learning