Abstracts

EAAC-1 functions in the re-uptake of extracellular glutamate that then leads to synthesis of GABA. Knockdown of EAAC-1 by anti-sense induces convulsive seizures in rats. GTRAP3-18 suppresses the binding affinity of glutamate with EAAC1 on the GABAergic neuron. The aim in this study was to measure the changes in GTRAP-18 expression induced by PTZ-kindling, and evaluate PTZ-kindling development in rats with knockdown of GTRAP3-18., Exp.1; Male Sprague-Dawley rats were kindled by repetitive i.p. injection of PTZ (16 mg/ml in saline, 40mg/kg) at the rate of three times a week. Control animals were injected at the same rate with an equal volume of saline. Behavior was observed and scored following each injection. Animals were considered fully kindled after having two consecutive stage 5 seizures. Only fully kindled animals were used for the experiment. Six animals in each group were anesthetized with sodium pentobarbital and killed by decapitation on day 14 of the experiment. PTZ animals were sacrificed following a last stage 5 seizure. A crude membrane fraction extracted from both hippocampi was used for western blot followed by hybridized with GTRAP3-18 polyclonal antibody.
Exp. 2; Rats underwent i.c.v. injection of oligonuleotide of anti-sense primer (n=12) and sense primer (n=12) for GTRAP3-18. Following these injections half of the rats in each group were used to measure the knockdown ratio of GTRAP3-18, while the remaining rats were used for PTZ-kindling., Exp.1; In PTZ-kindled rats, GTRAP3-18 was reduced to 89% of control.
Exp.2; GTRAP3-18 was decreased by about 40 % of control in rats receiving the anti-sense oligonuleotide. Further, in these animals, PTZ seizure duration was significantly prolonged, latency more brief and kindling onset earlier when compared to control animals., Prior work with microdialysis from GTRAP3-18 antisense treated rats has shown that extracellular GABA concentration is markedly elevated. In this experiment, PTZ kindling over 14 days caused decrease in GTRAP3-18 protein. This down regulation of GTRAP3-18 may be a fundamental response to kindling to enhance GABA synthesis in compensation for the enduring process of epileptogenesis. However, GTRAP3-18 knockdown was associated with worse responses to PTZ. Our observation suggests that there is a pathological reversal of GABA action between inhibition and excitation that is induced by changes in Cl- gradient with enhanced GABA release., (Supported by Grant-in-Aid for Scientific Research (C) (2) (18591297) from the Ministry of Education, Science, Sport and Culture, Japan (to Y.U.).)