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.
Neurogenomics
The gene expression profile of the central nervous system (CNS) is unique. Eighty percent of all human genes are expressed in the brain; 5,000 of these genes are solely expressed in the CNS. The human brain has the highest amount of gene expression of all studied mammalian brains. In comparison, tissues outside of the brain will have more similar expression levels in comparison to their mammalian counterparts. One source of the increased expression levels in the human brain is from the non-protein coding region of the genome. Numerous studies have indicated that the human brain have a higher level of expression in regulatory regions in comparison to other mammalian brains. There is also notable enrichment for more alternative splicing events in the human brain.