Generalised seizure-induced changes in rat hippocampal glutamate but not GABA release are potentiated by repeated seizures.

The effects of repeated or a single generalised seizure on extracellular glutamate and gamma-aminobutyric acid (GABA) levels in the ventral hippocampus of the freely-moving rat were studied using maximal electroshock-induced seizures in conjunction with in vivo microdialysis. A single seizure resulted in three phases of post-ictal changes in glutamate and GABA levels: during phase I, there were transient increases in both glutamate and GABA whilst in phase II, levels of both amino acids were reduced. In phase III, glutamate levels were elevated above basal whilst the decrease in GABA levels was sustained. Following repeated seizures, the phase I rise in glutamate was increased 3-fold and the phase III rise was significantly potentiated, compared with the changes produced by a single seizure. No differences were observed in the post-ictal changes in GABA levels between a single or repeated seizures.