Abstracts

Kindling is thought to model complex partial seizures. Although the specific mechanism remains unknown, the long-lasting excitatory synaptic transmission efficacy found in pentylenetetrazol (PTZ)-kindled animals that is related to extracellular glutamate concentration is of interest. Glutamate-mediated responses of NMDA receptors combined with collapse of GABA-mediated inhibition suggest both molecular and cellular mechanisms. In these experiments we wondered if altered glutamatergic and GABAergic synaptic transmission in PTZ kindling were associated with changes in glutamate transporter proteins. We used semiquantitative western blotting with antibodies specific to individual excitatory amino acid transporters (EAATs) and GABA transporters (GATs) to test our hypothesis. Using male Wistar rats, we induced kindling with PTZ (16 mg per ml in saline) given i.p. three times a week as a 40 mg per kg injection. Animals were considered kindled after two consecutive stage 5 seizures (generalized tonic-clonic seizure). Twenty-four hours after the last stage 5 seizure animals were killed and both hippocampi were removed and a crude membrane fraction was prepared for western immunoblotting. We found that levels of GLAST, GLT-1 and EAAC-1 glutamate transporters were elevated significantly. However, no change was found in any of the GABA transporters. Chronic seizures induced by amygdalar Fe+++ or kainic acid injection are associated with down-regulation of glial glutamate transporters. While our PTZ-kindled animals have enduring behaviors consistent with chronic kindling, the changes we found in EAATs are more consistent with reports of expression of transporters found in acute models of seizures such as status epilepticus. In fact, administration of glutamatergic receptor agonists or GABAergic receptor antagonists result in increased levels of glutamate transporters. Elevation of expression of EAATs would be important as a molecular regulatory response associated with increased glutamate metabolism in the acute phase of kindling with reverse glutamate transport and re-uptake into the hippocampal neurons. While our preliminary observations are of interest, we believe that observation of EAATs and GATs expression over prolonged periods may provide clues to enduring changes fundamental to kindling. (Supported by a Grant-in-Aid for Encouragement of Young Scientists (10770490) from the Ministry of Education, Science, Sport and Culture, Japan (to Y.U.).)