Monoamine neurotransmitter in brains is
There are three main classes of chemical substances that serve as neurotransmitters and neuromodulators: small molecule transmitters large-molecule transmitters gas transmitters. Small molecule transmitters include amino acids (eg, glutamate, g-aminobutyric acid , and glycine, acetylcholine, monoamines (eg, norepinephrine, epinephrine, dopamine, and serotonin. Large-molecule transmitters include neuropeptides such as substance P, enkephalin, and vasopressin. Neuropeptides are often co-localized with one of the small-molecule neurotransmitters Ref: Ganong's Review of Medical Physiology 26th edition
Serotonin
Glycine
GABA
Dopamine
Nervous system