Effects of repetitive activation and changes in external ionic environment on hippocampal CA1 pyramidal cell afterhyperpolarizations

Induction of epileptiform activity by temperature elevation in hippocampal slices from young rats: an in vitro model for febrile seizures?

Extracellular field potential recordings were performed in the CA1 subfield of hippocampal slices obtained from Wistar rats aged 2-38 days. When the brain tissue was maintained at 35 degrees-36 degrees C (values obtained in the tissue chamber well), single-shock orthodromic stimuli elicited a response in the stratum pyramidale that consisted of a single population spike. In contrast, when the temperature in the well was increased to levels greater than 38.2 degrees C for periods of 5-15 min, the same type of stimuli elicited an epileptiform response characterized by a 250- to 600-ms-long, positive-going field potential with superimposed, multiple, negative-going population spikes. This potential resembled the epileptiform response recorded in the hippocampal slice in the presence of convulsants such as penicillin or bicuculline. Once the temperature was restored to control values (i.e., 35 degrees-36 degrees C) after induction of epileptiform activity, the abnormal response could be observed for less than or equal to 2 h. In some experiments (approximately one third of the successful trials), spontaneous epileptiform discharges appeared during and persisted after the increase in temperature. The ability of the hyperthermic period to induce epileptiform changes was age dependent: Epileptiform activity outlasting the period of temperature elevation was not observed in slices obtained from rats aged less than 4 days or greater than 28 days. Our data show that epileptiform activity can be induced by a transient increase in temperature and that the age of the animals from which slices are obtained plays an important role in the appearance of this phenomenon.(ABSTRACT TRUNCATED AT 250 WORDS)