Hyperthermia induces epileptiform discharges in cultured rat cortical neurons

Febrile seizures (FS), or fever-induced seizures, are the most common form of seizures during childhood. Although simple FS are usually considered benign, prolonged or recurrent FS are proposed to increase the risk for developing subsequent temporal lobe epilepsy (TLE) in adults. The pathophysiology of FS is still largely unknown. In this study, by using whole-cell patch-clamp recording techniques, we demonstrated that hyperthermia (39-40°C) induced a "febrile seizure-like event" expressed as spontaneous, recurrent, epileptiform discharges (SREDs) followed by a series of sustained depolarizations (SDs) in cultured rat cortical neurons (7-14DIV). The SREDs were characterized by abruptly developing, paroxysmal depolarizing shifts (PDS) of membrane potential with high-frequency spike firing characteristic of electrographic seizures. Furthermore, we also found that hyperthermia induced persistent neuronal hyperexcitability as assessed by their intrinsic electrogenic characteristics which include: 1) depolarized resting potential (RP); 2) decreased input resistance (R(in)); 3) a marked decrease in amplitude, duration and afterhyperpolarization (AHP) of spontaneous action potentials; 4) a prominent reduction in action potential (AP) current threshold (I(th)) and potential threshold (TP); and 5) a dramatic shortened duration, decreased inter-spike intervals (ISI), and increased firing frequency of evoked action potentials. Additionally, our present study also revealed that baclofen (100μM), a specific GABA(B) receptor agonist, significantly repressed the hyperthermia-induced neuronal hyperexcitability and epileptiform discharges in cultured cortical neurons. The results suggest that hyperthermia may induce epileptiform activities in cultured cortical neurons by suppression of the GABA(B) receptor-mediated inhibition, in turn leading to the development of persistent neuronal hyperexcitability when the cells suffered from heating insult. This study provides a novel cellular model for studying the pathogenetic mechanisms of febrile seizures in vitro.