monoamines

Monoamines are a class of biologically active amines that function as neurotransmitters, neuromodulators, or hormones. They are derived from aromatic amino acids and typically act in both the central nervous system and the periphery. The major subgroups are the catecholamines—dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline)—and the indoleamines—serotonin (5-hydroxytryptamine) and melatonin. Histamine, derived from histidine, is also commonly classified as a monoamine.

Biosynthesis and storage occur in nerve terminals and various tissues. Dopamine is produced from tyrosine to DOPA and then to dopamine; dopamine beta-hydroxylase converts dopamine to norepinephrine, and phenylethanolamine N-methyltransferase can form epinephrine in the adrenal medulla. Serotonin is synthesized from tryptophan via 5-HTP; melatonin is produced from serotonin in the pineal gland. Histamine is formed by decarboxylation of histidine. Monoamines are stored in synaptic vesicles by vesicular monoamine transporters and released in response to calcium-dependent neuronal activity.

Post-release, monoamines act on specific receptors—primarily G protein-coupled receptors—and effects range from rapid signaling to longer modulation of neuronal circuits. They are cleared from the synapse mainly by reuptake transporters (DAT, NET, SERT) and degraded by enzymes such as monoamine oxidases (MAO) and catechol-O-methyltransferase (COMT).

Functions across systems include regulation of mood, attention, arousal, motor control, autonomic function, and hormonal release. Clinically, monoamine systems are implicated in Parkinson’s disease, depression, anxiety, schizophrenia, and other disorders. Therapies often target monoamine synthesis, reuptake, or degradation, including antidepressants, antipsychotics, and dopaminergic agents. Peripheral monoamines also influence cardiovascular and gastrointestinal physiology.