Impairment of mitochondrial energy metabolism may contribute to the se
lective neuronal degeneration observed in Huntington's disease and oth
er neurodegenerative disorders. Intrastriatal injection of the excitot
oxin, quinolinic acid, produces a pattern of neuronal death similar to
that seen in Huntington's disease. However, little is known about the
effects of quinolinic acid on striatal energetics. In the present wor
k, time-dependent changes in energy metabolism caused by injection of
quinolinic acid into rat striatum were examined. Oxygen consumption by
free and synaptic mitochondria was quantified and correlated with the
concentrations of nucleotides and amino acids at different times afte
r injection. Compared with saline-treated controls, a decrease in ADP-
stimulated (state 3)to basal (state 4)oxygen consumption (respiratory
control ratio) by free mitochondria was apparent in quinolinic acid-in
jected striata as early as 6 h after treatment. No significant changes
were seen in nucleotide concentrations at this time. By 12 h after in
jection, the decline in the respiratory control ratio was more pronoun
ced (45%), and reductions in ATP, NAD, aspartate, and glutamate (30-60
%) were also observed. These results show that injection of quinolinic
acid in vivo produces progressive mitochondrial dysfunction, which ma
y be a common and critical event in the cell death cascade initiated i
n Huntington's disease and in animal models of this neurodegenerative
disorder. The indicators of mitochondrial function examined in this st
udy, therefore, may be useful in evaluating the efficacy of neuroprote
ctive agents.