Abstracts

Given appropriate medical treatment, most children [quot]outgrow[quot] their seizure disorders and many will do so after seizure suppression for only 1-2 years. Clearly, for children, epilepsy is not a permanent or irreversible state. Understanding the molecular events that underlie these changes may provide new treatment options. In our tetrodotoxin (TTX) rat hippocampal brain slice model of chronic epilepsy, we have demonstrated and studied just such a resolving period of seizure-like activity.
Hippocampi were prepared from 7 day old Wistar rats according to the method of Niesen and Ge (1999). TTX at 0.5 [mu]M was addded to the culture media for 7 days and then removed. Whole cell patch recordings were performed on CA1 neurons following TTX removal and the microelectrode contained (in mM): 140 KGluc, 10 HEPES, 0.1 CaCl[sub]2[/sub], 1.1 BAPTA, 2 Mg-ATP and 0.1 GTP. GABA[sub]A[/sub]-mediated potentials were studied in the presence of AMPA and NMDA receptor blockers CNQX (50 [mu]M) and APV (30 [mu]M). The day of TTX removal was designated E0 and the days thereafter were numbered accordingly.
On days E0-2, CA1 neurons displayed robust seizure-like activity, including spontaneous and evoked depolarizing bursts (dur: 200-500 msec) with multiple superimposed action potentials and multiple population spikes on evoked field potentials. By E3-5, the duration of the synaptic depolarizing potentials (dur: 100-300 msec) and number of action potentials had decreased. Spontaneous bursts were infrequent. By E6-7, the duration of evoked synaptic potentials decreased to [lt]100 msec and field potentials revealed [lt]4 populaion spikes upon afferent stimulation.
This loss of hyperexcitability was not due to loss of slice viability since the number of pyknotic cells in the region, as measued by hematoxylin-eosin staining, was not increased compared to younger slices. In addition, GABA[sub]A[/sub]- mediated inhibitory potentials recovered gradually, following TTX removal. At E0-2, no inhibitory potentials were observed after blockade of glutamate receptors. By E6-7, normal-looking early IPSPs had reappeared.
Epileptic changes were not permanent in our TTX brain slice model of epilepsy. Normal appearing synaptic properties returned as more and more time passed from the onset of seizure-like activity. This suggests the presence of inherent developmental/homeostatic mechanisms in immature epileptic tissue that may contribute to the resolution of epilepsy observed in most children.
[Supported by: NIH K08-NS01747.]