Neurotransmitter systems is a fundamental concept and area of research in neuroscience focusing on the intricate networks and processes by which neurons communicate chemically through neurotransmitters. This field investigates the molecular mechanisms of neurotransmitter synthesis, release, receptor interaction, and inactivation, as well as the organization and function of neuronal circuits defined by specific neurotransmitter usage, holding critical significance for understanding brain function, behavior, and the pathophysiology of neurological and psychiatric disorders.