Abstracts

RATIONALE: In this study, we wondered whether continuous inhibition of glutamate transporter would be associated with hippocampal neurotoxicity. We studied the interaction between redox and excitotoxicity in the hippocampus following increased glutamate induced by the transporter inhibitor L-trans PDC (L-trans-pyrrolidine-2,4-dicarboxylic acid) using in vivo microdialysis and EPR spectroscopy.
METHODS: Using pentobarbital anesthesia (37.5 mg per kg i.p.) male Wistar rats were stereotaxically implanted in ventral hippocampus with a microdialysis probe connected to a EPR resonator. Freely moving rats received 1mM L-trans PDC through the probe. Free radicals were detected using the spin trap POBN. Antioxidant ability was examined utilizing the principle that an exogenously applied nitroxide radicals (carbamoyl-PROXYL) reduces paramagnetism in the brain, of which the decay rate of ESR signal intensities would reflect the antioxidant ability (i.e. half-life).
RESULTS: Control rats did not form a POBN adduct. However, perfusion with the transporter inhibitor L-trans PDC caused an ESR spectra with hfc of: aN=15.7G and aH=2.5G, corresponding to a lipoxygenase-linoleic acid generated lipid radical. Median half-life of the nitroxide radical was significantly longer in the L-trans PDC group than in control.
CONCLUSIONS: Sustained glutamate increase induced by inhibition of glutamate transport resulted in generation of lipid radicals and reduced antioxidant ability in the hippocampus. Collapse of glutamate transport in chronic focal seizures is associated with redox change and potential for neuronal membrane injury. Our data support the hypothesis that molecular biological perturbations in the regulation of glutamate transporters could play a role in hippocampal injury during epileptogenesis.
Support: This study was partially supported by a Grant-in-Aid for Encouragement of Young Scientists (12770537) from the Ministry of Education, Science, Sport and Culture, Japan. (to Y.U.)