Nitric oxide‐producing microglia mediate thrombin‐induced degeneration of dopaminergic neurons in rat midbrain slice culture

• Published in: Journal of neurochemistry 2006-06, Vol.97 (5), p.1232-1242
• Main Authors: Katsuki, Hiroshi, Okawara, Mitsugi, Shibata, Haruki, Kume, Toshiaki, Akaike, Akinori
• Format: Article
• Language: English
• Subjects: Animals; Animals, Newborn; Antioxidants - pharmacology; Biological and medical sciences; Cell Death - drug effects; Cell Death - physiology; Cell Movement - drug effects; Cell Movement - physiology; Chemistry; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Dopamine - metabolism; dopamine neuron; Enzyme Inhibitors - pharmacology; Gliosis - chemically induced; Gliosis - metabolism; Gliosis - physiopathology; inflammation; L-Lactate Dehydrogenase - metabolism; MAP Kinase Signaling System - drug effects; MAP Kinase Signaling System - physiology; Medical sciences; Mesencephalon - cytology; Mesencephalon - drug effects; Mesencephalon - metabolism; Microglia - drug effects; Microglia - metabolism; mitogen‐activated protein kinase; Nerve Degeneration - chemically induced; Nerve Degeneration - metabolism; Nerve Degeneration - physiopathology; Nervous system (semeiology, syndromes); Nervous system as a whole; neurodegeneration; Neurology; Neurons; Neurons - drug effects; Neurons - metabolism; Neurons - pathology; Neurosciences; Neurotransmitters; Nitric Oxide - metabolism; Nitric Oxide Synthase Type II - drug effects; Nitric Oxide Synthase Type II - metabolism; Organ Culture Techniques; Parkinson's disease; Rats; Rats, Wistar; Rodents; Thrombin - toxicity; Toxicity
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1111/j.1471-4159.2006.03752.x

Activated microglia are considered to play important roles in degenerative processes of midbrain dopaminergic neurons. Here we examined mechanisms of neurotoxicity of thrombin, a protease known to trigger microglial activation, in organotypic midbrain slice cultures. Thrombin induced a progressive decline in the number of dopaminergic neurons, an increase in nitric oxide (NO) production, and whole tissue injury indicated by lactate dehydrogenase release and propidium iodide uptake. Microglia expressed inducible NO synthase (iNOS) in response to thrombin, and inhibition of iNOS rescued dopaminergic neurons without affecting whole tissue injury. Inhibitors of mitogen‐activated protein kinases (MAPKs) such as extracellular signal‐regulated kinase (ERK), p38 MAPK and c‐Jun N‐terminal kinase (JNK) attenuated thrombin‐induced iNOS induction and dopaminergic cell death. Whole tissue injury was also attenuated by inhibition of ERK and p38 MAPK. Moreover, depletion of resident microglia from midbrain slices abrogated thrombin‐induced NO production and dopaminergic cell death, but did not inhibit tissue injury. Finally, antioxidative drugs prevented thrombin‐induced dopaminergic cell death without affecting whole tissue injury. Hence, NO production resulting from MAPK‐dependent microglial iNOS induction is a crucial event in thrombin‐induced dopaminergic neurodegeneration, whereas damage of other midbrain cells is MAPK‐dependent but is NO‐independent.