Protective role of hydrogen peroxide in oxygen-deprived dopaminergic neurones of the rat substantia nigra.
Hydrogen peroxide (H2O2) is a reactive oxygen species, responsible for cytotoxic damage through the formation of hydroxyl radicals. Dopamine (DA) neurones of the substantia nigra pars compacta (SNc) are highly sensitive to metabolic stress, and they typically respond to energy deprivation with membrane hyperpolarization, mainly through opening of ATP-dependent K+ channels. Accordingly, H2O2 (3 mM) induced a tolbutamide-sensitive outward current in DA neurones. Conversely, in a hypoxic medium, H2O2 reverted membrane hyperpolarization, which is associated with oxygen deprivation in DA neurones, restored their action potential firing, and reduced the hypoxia-mediated outward current in a concentration-dependent manner, between 0.1 and 3 mM (IC50 0.6+/-0.1 mM). Notably, H2O2 did not counteract membrane hyperpolarization associated with hypoglycaemia, moreover, when catalase was inhibited with 3-amino-1,2,4-triazole (3-AT; 30 mM), H2O2 did not reduce hypoxia-mediated outward current. The counteracting action of H2O2 on hypoxia-mediated effects was further confirmed by single-unit extracellular recordings of presumed DA neurones in acute midbrain slices preparations, using a planar multi-electrode array device. Whilst a prolonged period of hypoxia (40 min) caused firing suppression, which did not recover after perfusion in normoxic conditions, the presence of H2O2 (3 mM) during this prolonged hypoxic period rescued most of the neurones from irreversible firing inhibition. Accordingly, morphological studies showed that H2O2 counteracts the cytochrome c release provoked by prolonged hypoxic treatment. Taken together, our data suggest that H2O2 prevents the metabolic stress of DA neurones induced by hypoxia by serving as a supplementary source of molecular oxygen, through its degradation by catalase.
Geracitano
Raffaella
R
Department of Experimental Neurology, C.E.R.C. - S. Lucia Foundation I.R.C.C.S., Via del Fosso di Fiorano, 65, 00143 Rome, Italy.
Tozzi
Alessandro
A
Berretta
Nicola
N
Florenzano
Fulvio
F
Guatteo
Ezia
E
Viscomi
Maria Teresa
MT
Chiolo
Barbara
B
Molinari
Marco
M
Bernardi
Giorgio
G
Mercuri
Nicola B
NB
D000200:Action Potentials / Q000187:drug effects; D000640:Amitrole / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000502:physiology*; D002374:Catalase / Q000037:antagonists & inhibitors; D015687:Cell Hypoxia / Q000187:drug effects; D045304:Cytochromes c / Q000037:antagonists & inhibitors*; D004298:Dopamine / Q000502:physiology; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D018613:Microscopy, Confocal; D009474:Neurons / Q000187:drug effects / Q000201:enzymology / Q000502:physiology; D018377:Neurotransmitter Agents; D016877:Oxidants / Q000494:pharmacology*; D010100:Oxygen / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D013378:Substantia Nigra / Q000187:drug effects* / Q000502:physiology; D014044:Tolbutamide / Q000494:pharmacology
D007004:Hypoglycemic Agents; D018377:Neurotransmitter Agents; D016877:Oxidants; D015221:Potassium Channels; D045304:Cytochromes c; D014044:Tolbutamide; D006861:Hydrogen Peroxide; D002374:Catalase; D010100:Oxygen; D004298:Dopamine; D000640:Amitrole