Today we know of about 50 neurotransmitters. Undoubtedly there are more waiting to be discovered. Some of the chemical building blocks for neurotransmitters, such as amino acids, come from the foods we eat. Neurons include places to store neurotransmitters. These storage areas, called vesicles , are located close to the ending of each axon.
Neurons synthesize some neurotransmitters right in the vesicle.
Others neurotransmitters are synthesized in the body of the cell and shipped down to the vesicle. Most addictive drugs change the effect of neurotransmitters on neurons. First, the molecule must be present in the brain and distributed unevenly. That is, the molecule must be spread out among different types of neurons, and across regions of the brain that have different functions. Second is a chemical criterion.