Primary afterdischarge in organotypic hippocampal slice cultures: Effects of standard antiepileptic drugs

Abstract

In the hippocampus intense high frequency electrical stimulation induces a long-lasting rhythmic synchronization (primary afterdischarge). In order to examine the suitability of primary afterdischarges (PADs) in organotypic hippocampal slice cultures (OHSCs) as an in vitro model of evoked seizures, we have worked out in detail the sensitivity of PADs to standard antiepileptic drugs (AEDs) and compared the necessary concentrations to those that were effective in animal models of partial and generalized tonic-clonic seizures. OHSCs were prepared according to the interface culture method from 8 to 11-day-old Wistar rats. A PAD in CA1 was elicited by stimulating the stratum radiatum with an intensity of two times that required to elicit a maximal population spike. The effects of carbamazepine, phenytoin, valproic acid, phenobarbital, diazepam, and ethosuximide on the duration and on frequency properties of PADs and the tonic-like and clonic-like subdivisions of PADs were determined, and as a measure of the AEDs potency half maximal effective concentration (EC(50) ) values were calculated from concentration-response curves. Carbamazepine, phenytoin, valproic acid, phenobarbital, and diazepam reduced the durations of PADs and tonic-like and clonic-like subdivisions of PADs. The effects were concentration dependent and reversible. Ethosuximide was ineffective. The effects on subdivisions of PADs differed between AEDs. Carbamazepine and phenytoin shortened the tonic-like and clonic-like subdivisions at similar proportions, whereas phenobarbital, diazepam, and valproic acid preferentially shortened the clonic-like subdivision. Diazepam at low concentrations increased the duration of tonic-like subdivisions, an effect not seen with the other AEDs. The suppressive effects of AEDs on frequency properties of tonic-like and clonic-like subdivisions were variable and observed only at higher concentrations. Carbamazepine and phenytoin were more effective in the PAD test in OHSCs than in the maximal electroshock and kindled seizures tests. The effectiveness of phenobarbital, diazepam, and valproic acid in the PAD test matched their effectiveness in the MES test and-with the exception of valproic acid and diazepam-in kindled seizures tests. Valproic acid was less effective in OHSCs than in the kindled seizure tests, and diazepam was more (generalized seizures) or less (focal seizures and afterdischarge durations) effective in this animal model than in OHSCs. We conclude that the PAD test in OHSCs is a suitable in vitro model of evoked seizures. The model could serve as an initial screen to identify the most promising leads for further evaluation and characterization in in vivo models of efficacy and toxicity.