Abstracts

To study [italic]in vitro[/italic] electrophysiological responses of human hippocampus obtained from patients with temporal lobe epilepsy and their responsiveness upon antiepileptic drugs. The hippocampus resection has been made in block intending to preserve its structure and vitality. Thus, twenty five specimens were obtained and submitted to [italic]in vitro[/italic] hyperexcitation protocols through the application of artificial cerebral spinal fluid with high potassium concentrations either GABAergic antagonist or magnesium free. Fifteen specimens perfused with Phenytoin and ten with Carbamazepine and Topiramate had their responses recorded for further assessment. Spontaneous epileptic discharges were obtained only in four specimens. Threshold decreasing and the increase of the evoked spikes amplitude were observed after high potassium and bicuculline hyper excitation protocols, promoting the appearance of two groups: one demonstrating few multiple spikes (1 to 2) and another with many multiple spikes (9 to20). After Mg++ free hyperexcitation protocol we also observed a threshold decrease and the increase of the population spike, although the most peculiar fact was an ictal spontaneous discharge during 81,7 seconds. We believe that the different responses are related to epileptogenic variability since we have used three different hyperexcitation protocols. A slight decrease in the number of population spikes after Phenytoin, topiramate and carbamazepine perfusion had no significance. This study presents the characterization of two kinds of responses upon different hyperexcitation protocols. This may be due to the major variability of the tissue obtained from surgical resection therapy since the mechanisms of epileptogenesis are not totally cleared and the absence of the control tissues make this work more difficult. (Supported by CAPES, CNPq, FAPESP, PRONEX.)