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1Institut für Neurophysiologie and 2Neurologische Klinik und Poliklinik, 3Institut für Experimentelle Neurologie, Charité Universitätsmedizin Berlin, Berlin, Germany
Submitted 22 February 2005; accepted in final form 17 September 2005
Prolonged seizures, e.g., induced by fever, experienced early in life are considered a precipitating injury for the subsequent development of temporal lobe epilepsy. During in vitro epileptiform activity, spreading depressions (SDs) have often been observed. However, their contribution to changes in the properties of juvenile neuronal tissue is unknown. We therefore used the juvenile hippocampal slice culture preparation (JHSC) maintained in normoxia (20% O2-5% CO2-75% N2) to assess the effect of repetitive SD-like events (SDLEs) on fast field potentials and cell damage. Repetitive SDLEs in the CA1 region could be induced in about two-thirds of the investigated JHSCs (n = 61) by repetitive electrical stimulation with 2200 pulses. SDLEs were characterized by a transient large negative field potential shift accompanied by intracellular depolarization, ionic redistribution, slow propagation (assessed by intrinsic optical signals) and glutamate receptor antagonist sensitivity. The term "SDLE" was used because evoked fast field potentials were only incompletely suppressed and superimposed discharges occurred. With 20 ± 1 repetitive SDLEs (interval of 1015 min, n = 7 JHSCs), the events got longer, their amplitude of the first peak declined, while threshold for induction became reduced. Evoked fast field potentials deteriorated and cell damage (assessed by propidium iodide fluorescence) occurred, predominantly in regions CA1 and CA3. As revealed by measurements of tissue partial oxygen pressure during SDLEs repetitive transient anoxia accompanying SDLE might be critical for the observed cell damage. These results, limited so far to the slice culture preparation, suggest SDs to be harmful events in juvenile neuronal tissue in contrast to what is known about their effect on adult neuronal tissue.
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