Brain
There are dozens of other chemical neurotransmitters that are used in more limited areas of the brain, often areas dedicated to a particular function. Serotonin, for example—the primary target of antidepressant drugs and many dietary aids—comes exclusively from a small brainstem area called the raphe nuclei. Norepinephrine, which is involved in arousal, comes exclusively from a nearby small area called the locus coeruleus. Other neurotransmitters such as acetylcholine and dopamine have multiple sources in the brain, but are not as ubiquitously distributed as glutamate and GABA.
Selective serotonin reuptake inhibitor
In the brain, messages are passed from a nerve cell to another via a chemical synapse, a small gap between the cells. The presynaptic cell that sends the information releases neurotransmitters including serotonin into that gap. The neurotransmitters are then recognized by receptors on the surface of the recipient postsynaptic cell, which upon this stimulation, in turn, relays the signal. About 10% of the neurotransmitters are lost in this process; the other 90% are released from the receptors and taken up again by monoamine transporters into the sending presynaptic cell, a process called "reuptake".