A Parallel Relationship between Parkinson’s Disease and an Excess of S-Adenosylmethionine-Dependent Biological Methylation in the Brain
The primary symptoms of Parkinson’s disease (PD) are resting tremors, bradykinesia and muscular rigidity, due to degeneration of the dopaminergic nigrostriatal pathway. Dopamine (DA) is depleted in the neostriatuml and melanin pigments in the substantia nigra (SN)2. The relative concentration of the DA metabolite, homovanillic acid (HVA) (HVA/DA ratio), also was reported to be increased in the neostriatum3 and urine4,5 of PD patients. An agent that resembles another methylated metabolite of DA, 3,4-dimethoxyphenylethylamine (DIMPEA), was shown to be excreted in the urine of PD patients5,6. The levels of serotonin (5-HT) and norepinephrine (NE) are also decreased and the activity of acetylcholine (Ach) is increased in the brain of PD patients.
KeywordsTyrosine Hydroxylase Substantia Nigra Melanin Pigment Nigrostriatal System Dopaminergic Nigrostriatal Pathway
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