<prompt> Monoamine neurotransmitter in brains isSerotoninGlycineGABADopamine  <response>: 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: Ganongs Review of Medical Physiology 26th edition 