[Neuromelanin in neurons of substantia nigra lacking tyrosine hydroxylase]

The distribution of tyrosine hydroxylase (TH), a key enzyme of catecholamine synthesis, was studied immunocytochemically in the neurons of substantia nigra in the human brain (n=7), and localization of neuromelanin in these cells was determined. The evidence indicating the existence of three types of neurons in substantia nigra was obtained, including the neurons containing both TH and neuromelanin, neurons containing only neuromelanin, and neurons expressing neither TH, nor neuromelanin. Presence of a population of neuromelanin-containing neurons lacking TH (which make up 7-30% of the cells) is discussed considering the participation of catecholamines and TH in neuromelanin synthesis.