Neurotransmitters are essential in homeostasisAcetylcholine: important in the brain and at synapses; maybe excitatory or inhibitoryBiogenic amines: a group of nitrogen-containing NTs derived from amino acids, such as epinephrine, norepinephrine, serotonin and dopamine.Amino acids: asparate, glutamate, glycine, and GABA. Asparate and glutamate are excitatory. Glycine and GABA are inhibitors.Peptides: substance P, an excitatory NT; Endorphins in decreasing painNitric oxide (NO):