Parkinson's disease affects differently Met5- and Leu5-enkephalin in the human brain

When measured in post-mortem human control brains, the ratio of Met5-enkephalin levels to those of Leu5-enkephalin varied from 1 to 13 in the 11 areas examined. In parkinsonian brains a significant reduction in the levels of both peptides was found in the pallidum and putamen whereas only Met5-enkephalin levels were decreased in the substantia nigra and ventral tegmental area. Therefore, Met5-enkephalin and Leu5-enkephalin may be located (at least partly) in different neuronal populations in the human brain.