Decrease of hippocampal GABAB receptor-mediated inhibition after hyperthermia-induced seizures in immature rats

Purpose: Whether febrile seizures have detrimental consequences on the brain is still controversial. We hypothesized that neuronal inhibition in the hippocampus is altered after hyperthermia-induced seizures in immature rats. Methods: Rats were given a single seizure by a heat lamp on postnatal day (PND) 15, or repeated seizures by heated air on PND 13 to 15. Fourteen or 30 days after the seizure(s), laminar field potentials were recorded by 16-channel silicon probes in CA1 and the dentate gyrus (DG), in response to the paired-pulse stimulation of the CA3 and medial perforant path, and analyzed as current source density. γ-Aminobutyric acid (GABA)_B-receptor antagonist CGP35348 was injected intracerebroventricularly (icv). Results: At 14 but not at 30 days after a single or after repeated hyperthermia-induced seizures, paired-pulse facilitation (PPF) of the CA1 population spikes at 100 to 200 ms interpulse intervals (IPIs) was significantly increased in seizure as compared with control rats, irrespective of the types of induced seizures. CGP35348 icv also resulted in PPF at 100 to 200 ms IPIs in CA1 of control rats, but CGP35348 had no effect on PPF in seizure rats. At 30 days after repeated seizures, paired-pulse inhibition in the DG was significantly increased at 30-ms IPI, and PPF was increased at 200-ms IPI. CGP35348 increased paired-pulse inhibition in the DG in repeated-seizure rats but not in control rats. Conclusions:We conclude that hyperthermia-induced seizures in immature rats induced a decrease of GABA_B receptor-mediated inhibition in CA1 and DG that lasted ≥14 to 30 days after hyperthermic seizure(s).