N-Acetyl Aspartate

The most prominent signal in the H-1 magnetic resonance spectrum of the human brain and spinal cord arises from N-acetyl aspartate (NAA). NAA is formed by acetylation of aspartate within the neuronal mitochondria, a reaction that helps draw glutamate back into the tricarboxylic acid cycle. Transport of NAA out of neurons is slow, leading to the build-up of a substantial concentration (similar to 20 mM) in the neuronal cytoplasm. NAA is broken down by deacetylation in oligodendrocytes, delivering acetyl groups for myelin formation. NAA levels are decreased in many neurological disorders, including multiple sclerosis, stroke, and Huntington disease. This decrease is loosely interpreted as indicating neuronal dysfunction. In several disorders, NAA reductions are at least partially reversible, indicating that they might arise from a reduced neuronal energy metabolism, and/ or disruption of neuronal membranes, and not simply from neuronal loss.