Which neurotransmitters are classified as monoamines?

• A. Dopamine, Norepinephrine, Serotonin, Epinephrine
• B. Acetylcholine, GABA, Glutamate, Glycine
• C. Endorphins, Enkephalins, Dynorphin, Substance P
• D. Histamine, Nitric oxide, Carbon monoxide, Adenosine

Answer: (A)

Monoamines are neurotransmitters built from aromatic amino acids with a single amine group, forming the catecholamines and indolamines that regulate mood, arousal, and autonomic functions. The group consisting of dopamine, norepinephrine, epinephrine, and serotonin fits this classification perfectly: dopamine, norepinephrine, and epinephrine are catecholamines derived from tyrosine, while serotonin is an indolamine derived from tryptophan. These transmitters share a common chemical theme and are typically inactivated by reuptake or metabolism via monoamine oxidase and COMT, with signaling largely mediated through G-protein–coupled receptors.

The other options mix neurotransmitter types: acetylcholine is a quaternary amine, not a monoamine; GABA, glutamate, and glycine are amino acid neurotransmitters; neuropeptides like endorphins and substance P are not monoamines; and gases or purines like nitric oxide, carbon monoxide, and adenosine do not fall into the monoamine category.