Age-dependent striatal excitotoxic lesions produced by the endogenous mitochondrial inhibitor malonate.

Intrastriatal injection of malonate, a reversible inhibitor of succinate dehydrogenase (SDH), produced age-dependent striatal lesions, which were significantly greater in 4- and 12-month-old animals than in 1-month-old animals. Both histologic and neurochemical studies showed that the lesions were significantly attenuated by administration of the noncompetitive NMDA receptor antagonist MK-801. Water-suppressed chemical shift magnetic resonance imaging showed that malonate produces increased striatal lactate concentrations and striatal lesions on T2-weighted scans that were attenuated by MK-801. Neurochemical characterization of the lesions showed significant decreases in markers of medium-sized spiny neurons (GABA and substance P), whereas a marker of medium-sized aspiny neurons (somatostatin) was not different from control values, consistent with an NMDA receptor-mediated mechanism. The effects of intrastriatal injections of malonate on ATP concentrations were compared with those of the irreversible SDH inhibitor 3-nitropropionic acid (3-NP). The ATP depletions following an equimolar injection of malonate were less marked and more transient than those of 3-NP. These results show that the competitive SDH inhibitor malonate produces more transient and milder bioenergetic defects than 3-NP, which are associated with selective activation of NMDA receptors. The results strengthen the possibility that a subtle impairment of energy metabolism may play a role in the pathogenesis of Huntington's disease.