GLUTAMATE RELEASE AND UPTAKE AND KINDLING: REDOX EFFECT ON GLUTAMATE TRANSPORTERS AND NMDA-R
Abstract number :
1.031
Submission category :
Year :
2002
Submission ID :
42
Source :
www.aesnet.org
Presentation date :
12/7/2002 12:00:00 AM
Published date :
Dec 1, 2002, 06:00 AM
Authors :
Yuto Ueda, Jun Tokumaru, Taku Doi, Yoshihito Hayashi, Yoshio Mitsuyama, L. James Willmore. Psychiatry, Miyazaki Medical College, Miyazaki, Japan; St. Louis University, St. Louis, MO; Miyazaki Medical College, Miyazaki, Japan
RATIONALE: Epileptogenesis is associated with receptors and transporters regulating glutamate, especially NMDA-R and glial excitatory amino acid transporters (EAATs). However, these proteins possess regions sensitive to redox, undergoing opposite functional changes in response to oxidation or reduction of sulphydryl groups. This study was designed to examine redox modulation of reactive sulphydryl components of NMDA-R and EAATs on kindling development and glutamate release in rat hippocampus.
METHODS: Male Wistar rats were used in these experiments. Kindling-like phenomena were induced with periodic release of high potassium (K+: 100 mM for 5 min at 40 min intervals) through in vivo microdialysis in the rat ventral hippocampus. Extracellular glutamate ([Glu]o) levels were measured before and after K+ stimulation by on-line enzyme fluorometry. During K+-aCSF infusion [Glu]o was increased and prolonged spike discharges were recorded. Either a disulphide reducing compound, 100 [mu]M dithiothreitol (DTT), or an oxidizing compound, 100 [mu]M 5,5[ssquote]-dithio-bis(2-nitrobenzoic) acid (DTNB) was added to aCSF during the experiment.
RESULTS: Perfusion with DTT was associated with acceleration of kindling with [Glu]o increasing slowly and returning rapidly to basal levels. DTNB perfusion was associated with delayed kindling development with [Glu]o increased rapidly and returned slowly to basal levels, an effect that could be caused by down-regulation of NMDA-R and EAATs from an oxidizing redox reaction with protein thiol groups. Further, these data suggest that seizure-related glutamate release and either protective or destructive effects of glutamate are affected by redox effects on receptor and transporter sulphydryl groups.
CONCLUSIONS: Our data obtained from freely moving rats confirm that the kindling phenomena is dependent not only on extracellular glutamate, but upon the functional state of NMDA-R as well. We propose that redox effects may be of critical importance in the process of epileptogenesis.
[Supported by: This study was 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.).]