Neuromelanin

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5,6-Dihydroxyindole, the monomer out of which neuromelanin polymers are formed

Neuromelanin (NM) is a dark

5,6-dihydroxyindole monomers.[1] Neuromelanin is found in large quantities in catecholaminergic cells of the substantia nigra pars compacta and locus coeruleus, giving a dark color to the structures.[2]

Physical properties and structure

Photomicrograph of neuromelanin (brown material) in a neuron of the substantia nigra. Hematoxylin and eosin stain. The scale bar is 20 microns (0.02mm) in length.

Neuromelanin gives specific brain sections, such as the substantia nigra or the locus coeruleus, distinct color. It is a type of melanin and similar to other forms of peripheral melanin. It is insoluble in organic compounds, and can be labeled by

free radical structure and it avidly chelates metals.[3]

Synthetic pathways

Neuromelanin is directly biosynthesized from

mitochondria where it is metabolized by monoamine oxidase. Excess dopamine and DOPA molecules are oxidized by iron catalysis into dopaquinones and semiquinones which are then phagocytosed and are stored as neuromelanin.[4]

Neuromelanin biosynthesis is driven by excess

catecholamines not accumulated by synaptic vesicles.[5]

Function

Neuromelanin is found in higher concentrations in humans than in other

].

Role in disease

Neuromelanin-containing

Neuromelanin has been shown to bind neurotoxic and toxic metals that could promote neurodegeneration.[5]

History

Dark pigments in the substantia nigra were first described in 1838 by Purkyně,[8] and the term neuromelanin was proposed in 1957 by Lillie,[9] though it has been thought to serve no function until recently. It is now believed to play a vital role in preventing cell death in certain parts of the brain. It has been linked to Parkinson's disease and because of this possible connection, neuromelanin has been heavily researched in the last decade.[10]

References