Oxygen withdrawal blocks mitochondrial respiration. In rat hippocampal slices, this triggers a massive depolarization of CA1 neurons and a negative shift of the extracellular DC potential, the characteristic sign of
hypoxia-induced spreading depression (HSD). To unveil the contribution of mitochondria to the sensing of
hypoxia and the ignition of HSD, we modified mitochondrial function. Mitochondrial uncoupling by
carbonyl cyanide 4-(trifluoromethoxy)
phenylhydrazone (
FCCP, 1 microM) prior to
hypoxia hastened the onset and shortened the duration of HSD. Blocking mitochondrial
ATP synthesis by
oligomycin (10 microg/ml) was without effect. Inhibition of mitochondrial respiration by
rotenone (20 microM),
diphenyleneiodonium (25 microM), or
antimycin A (20 microM) also hastened HSD onset and shortened HSD duration.
3-nitropropionic acid (1 mM) increased HSD duration.
Cyanide (100 microM) hastened HSD onset and increased HSD duration. At higher concentrations,
cyanide (1 mM),
azide (2 mM), and
FCCP (10 microM) triggered SD episodes on their own. Compared with control HSD, the spatial extent of the intrinsic optical signals of
cyanide- and
azide-induced SDs was more pronounced. Monitoring
NADH (
nicotinamide adenine dinucleotide) and
FAD (
flavin adenine dinucleotide) autofluorescence and mitochondrial membrane potential verified the mitochondrial targeting by the drugs used. Except 1 mM
cyanide, no treatment reduced cellular
ATP levels severely and no correlation was found between
ATP,
NADH, or
FAD levels and the time to HSD onset. Therefore
ATP depletion or a cytosolic reducing shift due to
NADH/
FADH2 accumulation cannot serve as a general explanation for the hastening of HSD onset on mitochondrial inhibition. Additional redox couples (
glutathione) or events downstream of the mitochondrial depolarization need to be considered.