Biochemical aspects of Parkinson-dementia complex

Positron emission tomography of a parkinsonian patient with dementia revealed a decreased cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) in the cerebral cortex and deep gray matter, whereas a parkinsonian patient without dementia showed a decrease in CBF and CMRO2 in the deep gray matter, but not in the cerebral cortex. The ratio of 3,4-dihydroxyphenylacetic acid/L-dopa in the plasma after L-dopa administration was significantly increased in parkinsonian patients with hallucinations, indicating an accelerated metabolism of L-dopa. The concentration of 5-hydroxyindoleacetic acid (5HIAA) was decreased in the cerebrospinal fluid of parkinsonian patients with psychiatric symptoms, especially with visual hallucinations. The serotonin level in mouse striatum was significantly reduced 1 week after methylphenyltetrahydropyridine (MPTP) injection, though returned to normal in 4 weeks. The 5HIAA level increased at both 1 and 4 weeks. The activity of tryptophan hydroxylase was increased in the striatum 1-4 weeks after MPTP injection, but was unchanged in the cerebral cortex. The choline acetyltransferase (ChAT) activity was significantly decreased in the hippocampus 1 week, but not 4 weeks after MPTP. The ChAT activity was not changed in the frontal cortex at either 1 or 4 weeks.