Dopamine levels in the striatum, pallidum, and substantia nigra of two patients with Parkinson's disease to whom levodopa had been administered for one year were below that found in control patients; however, the levels were greater than those reported in untreated patients with Parkinson's disease. Moreover, the presence of dihydroxyphenylalanine in the two brains confirmed the drug's cerebral penetration, with the highest concentrations being in the striatum, pallidum, substantia nigra, and hypothalamus. The significant pathological abnormality in one patient (striatonigral degeneration) in contrast with the other could not be correlated with a difference in the clinical course nor the biochemical findings.
Greer M, Collins GH, Anton AH. Cerebral Catecholamines After Levodopa Therapy. Arch Neurol. 1971;25(5):461–467. doi:10.1001/archneur.1971.00490050095008
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