Abstracts

Adult Genetic Absence Epilepsy Rats from Strasbourg (GAERS) show a failure to reach stage 3, 4 or 5 during the amygdala kindling process. No spike-and-wave discharges in GAERS are observed in rats younger than 30 days of age. In order to determine whether there is a relationship between the occurrence of spike-and-wave discharges and development of kindling, we examined amygdala kindling rate and spike-and-wave discharges in 20-day (PN20) and 30-day old (PN30) GAERS., Electrodes for stimulation and recording were stereotaxically implanted into basolateral amygdala and cortex of male Wistar (n=12) and GAERS (n=16) pups. After a recovery period of 24 h, animals were stimulated at 400 microA (80 Hz, each 1 msec in duration, for a total duration of 2 sec) every 20 min in PN20 and 90 min in PN30 groups. Animals received kindling stimulations until they achieved three stage 5 or the maximum number of stimulations (35). Seizures were scored by using Racine[apos]s 5-stage scale. EEGs from amygdala and cortex recorded continously before and after each stimulus to analyze spike-and-wave discharges and afterdischarge durations., PN 20 GAERS and non-epileptic Wistar rats show no difference to achieve stage 5 during the kindling progress. Seven out of 9 GAERS animals reached stage 5 and 2 GAERS stayed at stage 2 after application of 35 stimulations in the PN30 GAERS group. The amygdala kindling rate of the 7 kindled animals in the PN30 GAERS group was significantly slower than that seen in non-epileptic animals. Afterdischarge durations of all groups were similar to each other. Spike-and-wave discharges appeared in PN30 GAERS and no spike-and-wave discharge was observed in PN20 GAERS group. The data of cumulative spike-and-wave discharge show a significant increase in post-stimulation 0-10 min period when compared to pre-stimulation period in PN30 GAERS. Kindling-induced increase in spike-and-wave discharges is specifically observed in the 7 kindled PN30 GAERS. In detail, number of spike-and-wave discharges statistically increased whereas mean duration of spike-and-wave complex did not change., These findings suggest that GAERS pups are more prone to develop kindled seizures than adults and resistance to kindling in GAERS is age-related. Ontogenesis of spike-and-wave discharge seems to be involved in the resistance to kindling. The increase in spike-and-wave discharges in postictal state indicates involvement of thalamus and enhanced activity of thalamic nuclei that are responsible for spike-and-wave activity. In addition, the increased spike-and-wave response to kindling stimulations might be a homeostatic mechanism to restore excitatory drive of circuitry involved in kindling progress., (Supported by Marmara University Research Committee.)