The Mechanism of Striatal Damage in Mice after Intraperitoneal Injection of 3-nitropropionic Acid

ABSTRACT

BACKGROUND: A newly-found mitochondrial toxin, 3-nitropropionic acid (3-NP), has been proved to induce apoptosis in the striatum. Although striatal lesions produced by 3-NP could develop through an excitotoxic mechanism, the exact relationship between apoptosis induction and excitotoxicity after 3-NP treatment is still not clear. We investigated the role of excitotoxicity and oxidative stress on apoptosis induction within the striatum following intra-peritoneal injection of 3-NP. METHODS: 3-NP was injected for 5 days intra-peritoneally in three month-old mice. One day after the last injection, animals were decapitated. To confirm the presence of apoptosis, we performed in-situ detection of DNA fragmentation by using TUNEL technique and agarose gel elctrophoresis after DNA extraction from striatum. To examine the effect of frontal cortex removal on 3-NP-indeced apoptosis, we removed left frontal cortex by aspiration. For excitotoxicity, NMDA-receptor antagonist-MK 801, non-NMDA antagonist-NBQX, and saline were injected intraperitoneally before 3-NP treatment To detect superoxide, we administered hydroethidium (HEt 200 ul; 1mg/ml) into the jugular vein 2 days after 3-NP, and the density of oxidized HEt in samples were examined under flouscent microscope. We performed caspase staining to test immunoreactivity of caspase 3 in samples. RESULTS: The TUNEL positive cells were not observed in the striatum ipsilateral to the frontal cortex-removed side, but found in the contralateral striatum. Superoxide radicals measured by using HEt and caspase immunoreactivity were also significantly weaker in the striatum ipsilateral to the frontal cortex-removed side than the contralateral striatum. TUNEL staining revealed less apoptotic changes in the striatum of MK801-treated group than NBQX-or saline-treated groups. DNA laddering on agarose gel electrophoresis was observed in the striatum of NBQX- or saline-treated mice, but not found in MK 801-treated group. CONCLUSION: We demonstrated that removal of the corticostriatal glutamate pathway reduced superoxide production as well as apoptosis induced by 3-NP and NMDA receptor antogonist, but not non-NMDA antagonist, prevented 3-NP-induced apoptosis in the striatum. These results suggest that NMDA-mediated glutamatergic excitotokicity plays an important role in 3-NP related striatal damage.