The article "The Expanded Biology of Serotonin" by Miles Berger, John A. Gray, and Bryan L. Roth reviews the extensive role of serotonin (5-HT) in various physiological and pathological processes beyond its well-known function as a neurotransmitter. Serotonin is primarily found outside the central nervous system (CNS), regulating cardiovascular function, bowel motility, ejaculatory latency, bladder control, and other processes. The authors highlight recent findings that suggest serotonin may also regulate some processes, such as platelet aggregation, through receptor-independent, transglutaminase-dependent covalent linkage to cellular proteins. They discuss how drugs targeting specific serotonin receptors are being developed to treat a wide range of diseases, including psychiatric and neurological disorders. The review covers serotonin's roles in behavior, vascular biology, cardiac function, pulmonary hypertension, endocrinology, metabolism, gastrointestinal function, pain control, anesthesia, genitourinary function, and reproductive function. The complexity of serotonin's actions and its involvement in multiple physiological processes are emphasized, along with the challenges and opportunities for developing targeted therapies.The article "The Expanded Biology of Serotonin" by Miles Berger, John A. Gray, and Bryan L. Roth reviews the extensive role of serotonin (5-HT) in various physiological and pathological processes beyond its well-known function as a neurotransmitter. Serotonin is primarily found outside the central nervous system (CNS), regulating cardiovascular function, bowel motility, ejaculatory latency, bladder control, and other processes. The authors highlight recent findings that suggest serotonin may also regulate some processes, such as platelet aggregation, through receptor-independent, transglutaminase-dependent covalent linkage to cellular proteins. They discuss how drugs targeting specific serotonin receptors are being developed to treat a wide range of diseases, including psychiatric and neurological disorders. The review covers serotonin's roles in behavior, vascular biology, cardiac function, pulmonary hypertension, endocrinology, metabolism, gastrointestinal function, pain control, anesthesia, genitourinary function, and reproductive function. The complexity of serotonin's actions and its involvement in multiple physiological processes are emphasized, along with the challenges and opportunities for developing targeted therapies.