brain ribonucleic acid amount substantia nigra molecular composition trait substantia nigra ribonucleic acid amount 2025-10-14T18:10:22Z Trait.ontology substantia nigra RNA amount CMO:0003331 The proportion, quantity, or volume of ribonucleic acid in the substantia nigra of the brain, the layer of grey substance that separates the posterior parts of the cerebral peduncles (tegmentum mesencephali) from the anterior parts; it normally includes a posterior compact part with many pigmented cells (pars compacta) and an anterior reticular part whose cells contain little pigment (pars reticularis). Ribonucleic acid is a high molecular weight, linear polymer composed of nucleotides containing ribose and linked by phosphodiester bonds. VT:0011230