neuromelanin

Neuromelanin is a dark pigment found in a subset of neurons in the brain, most prominently in the substantia nigra pars compacta and the locus coeruleus. It is related to melanins found in skin but is chemically distinct and accumulates in specific brain cells with age.

Composition and formation: Neuromelanin is a polymer formed by the oxidation and polymerization of catecholamines, primarily dopamine and norepinephrine, and their related quinones. It binds metals such as iron and copper and is thought to play a role in detoxification by sequestering potentially harmful ions and reactive species. Its accumulation increases with aging, although the exact biosynthetic pathway remains incompletely understood.

Role and significance: The precise function of neuromelanin remains a topic of research. It is proposed to have protective effects, such as metal binding and antioxidant activity, but its presence also coincides with increased vulnerability of pigmented neurons under certain pathological conditions. In Parkinson's disease, loss of neuromelanin-containing neurons in the substantia nigra is a key feature, and pigment-related processes may contribute to neuroinflammatory responses when cells die.

Detection and clinical relevance: Neuromelanin can be observed histologically as brown-to-black pigment within neurons. In clinical imaging, neuromelanin-sensitive MRI sequences are used to visualize and quantify pigment content in the substantia nigra, offering a potential biomarker for aging and neurodegenerative risk.

Species variation: Neuromelanin is present in humans and some other mammals, with notable interspecies differences in its distribution and content.