Abstracts

The principle of rational pharmacotherapy is based on the assumption that selection of antiepileptic drugs (AED) in the management of epilepsy should be based on choosing drugs with different mechanisms of action. Few studies have addressed the issue of rational pharmacotherapy at the neuronal and network level. The purpose of this study was to determine the effects of 2 AED with similar but different mechanisms of action on the sodium channel. Experiments were performed on mice (P10-14) that were deeply anesthetized with halothane. The cortex was isolated in ice-cold ACSF containing (in mM): 118 NaCl, 3 KCl, 1.5 CaCl[sub]2[/sub], 1 Mg Cl[sub]2[/sub], 25 NaHCO[sub]3[/sub], 1 NaH[sub]2[/sub]PO[sub]4[/sub] and 30 D-glucose, pH of 7.4 bubbled with 95% O[sub]2[/sub] and 5% CO[sub]2[/sub]. Cortical slices (500 [mu]m thick) were sectioned 1500 [mu]m from the frontal pole and were immediately transferred into a recording chamber maintained at a temperature of 32[deg]C. After 20 minutes the potassium concentration was raised from 3 to 5 mM to obtain spontaneous rhythmic activity. Population activity recordings were obtained with suction electrodes positioned onto the surface of the desired cortical layer. Seizure-like activity was induced by the application of 20 [mu]M bicuculline (BIC). Intracellular current-clamp recordings were obtained from cortical neurons using the blind-patch technique. Cell layer and type were identified by staining each neuron with biocytin. Statistical differences between activity patterns were evaluated with the Wilcoxon test. We characterized 44 neurons. Once seizure-like activity was induced with BIC, either 100 [mu]M phenytoin (PHT) or 160 [mu]M lamotrigine (LTG) was added to the ACSF. After 10 min the other AED was added to evaluate combined effects. Intra- and extracellularly recorded burst frequency, amplitude and duration were measured before and after the addition of drugs. Compared to PHT, LTG significantly reduced intracellular burst amplitude (p[lt]0.01), while increasing burst duration (p[lt]0.05). However, neither AED alone significantly altered the amplitude and duration of extracellularly recorded network bursting. Unaffected was also the intra- and extracellularly recorded burst frequency. In contrast, intra- and extracellularly recorded burst frequency and duration were significantly reduced (p[lt]0.01) when both drugs were given in combination. These data demonstrate a significant differential effect on intracellular burst amplitude and duration between LTG and PHT. This result is consistent with our studies in neocortical slices excised from epileptic pediatric patients. In these human slices LTG decreased the amplitude and increased the duration of intracellularly recorded seizure-like bursts. The mechanism underlying the significant combinatory effects of these AED as described here may represent a true synergistic interaction, which can now be studied using this experimental model. (Supported by Falk Foundation (CJM, WvD, JMR)
Brain Research Foundation (CJM, ELD).)