Parkinsons disease (PD) is a movement disorder caused by degeneration of the nigrostriatal dopamine (DA) neurons in the substantia nigra pars compacta and the resultant deficiency in the neurotransmitter DA at the nerve terminals in the striatum. We and other investigators found increased levels of pro-inflammatory cytokines such as tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6, and decreased levels of neurotrophins such as brain-derived neurotrophic factor (BDNF) in the nigrostriatal region of postmortem brains and/or in the ventricular or lumbar cerebrospinal fluid (CSF) from patients with sporadic PD, and in animal models, such as 1-methyl-4-phenyl-1, 2, 3, 6- tetrahydropyridine (MPTP)- and 6-hydroxydopamine (6-OHDA)-induced PD. These changes in cytokine and neurotrophin levels may be initiated by activated microglia, which may then promote apoptotic cell death and subsequent phagocytosis of DA neurons. Cytokines as pleiotropic factors, promote signals that either lead to cell death or exert neuroprotective effects. The discovery of toxic changes in trophic microglia by M. Sawada and co-workers is important to this point. Ultimately, microglial cells may regulate cellular changes that cause either harm or benefit by producing cytokines or neurotrophins depending upon the primary cause and the circumstances during the inflammatory process of PD.

Parkinson’s disease (PD) is an aging-related disease and the second most common neurodegenerative disease after Alzheimer’s disease. The main symptoms of PD are movement disorders accompanied with deficiency of neurotransmitter dopamine (DA) in the striatum due to cell death of the nigrostriatal DA neurons. Two main histopathological hallmarks exist in PD: cytosolic inclusion bodies termed Lewy bodies that mainly consist of α-synuclein protein, the oligomers of which produced by misfolding are regarded to be neurotoxic, causing DA cell death; and black pigments termed neuromelanin (NM) that are contained in DA neurons and markedly decrease in PD. The synthesis of human NM is regarded to be similar to that of melanin in melanocytes; melanin synthesis in skin is via DOPAquinone (DQ) by tyrosinase, whereas NM synthesis in DA neurons is via DAquinone (DAQ) by tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC). DA in cytoplasm is highly reactive and is assumed to be oxidized spontaneously or by an unidentified tyrosinase to DAQ and then, synthesized to NM. Intracellular NM accumulation above a specific threshold has been reported to be associated with DA neuron death and PD phenotypes. This review reports recent progress in the biosynthesis and pathophysiology of NM in PD.