Abstracts

Rationale: Spontaneous seizures in temporal lobe epilepsy (TLE) occur in part by abnormal neuronal activity within the hippocampus. However, the relationship between the firing properties of hippocampal CA1 pyramidal cells during seizure onset is largely unknown. Here we study the relationship between in vivo firing patterns of CA1 pyramidal cells and interneurons and pre-seizure interictal spikes in a spontaneous seizure animal model of TLE. Methods: Seventy-day-old adult male Sprague-Dawley rats (n=5) were treated with lithium pilocarpine in order to induce status epilepticus. After 2 months, rats developed Racine grade 5 spontaneous epileptic seizures. Single unit recordings were obtained (sampling rate 32 kHz) using 24 channels of 6 microwire tetrode arrays placed in the CA1 region. Eight of these 24 channels were also used to obtain simultaneous CA1 region EEG recordings (sampling rate 2 kHz). A light-emitting diode tracked both head position and locomotion during EEG and tetrode microelectrode recordings. Results: : Rats developed two classes of pre-seizure patterns labeled class 1 and class 2. A total of five class 1 and 14 class 2 pre-seizure patterns were observed. Class 1 pattern showed intermittent polyspike and spike/wave activity concomitant with decreased CA1 pyramidal cells firing rate. Head movement was stationary during class 1 transition to seizures. In contrast, class 2 pre-seizure patterns were accompanied by active movement and high frequency EEG spiking activity. In addition, a transient change in pyramidal cells firing rate was observed, concomitant with head movement. Conclusions: These preliminary findings suggest that during seizure onset 1) characteristic changes in both EEG and single unit CA1 pyramidal cells firing properties may in part be influenced by rat activity, and 2) CA1 pyramidal cells firing properties may contribute in part to the two distinct EEG seizure patterns.