Effects of gamma-aminobutyric acid (GABA) agonists and a GABA uptake inhibitor on pharmacoresistant seizure like events in organotypic hippocampal slice cultures

Purpose: Seizure like events (SLEs) induced by low magnesium or 4-aminopyridine in organotypic hippocampal slice cultures (OHSCs) are resistant to standard antiepileptic drugs including phenobarbital, and 1,4-benzodiazepines [Albus, K., Wahab, A., Heinemann, U., 2008. Standard antiepileptic drugs fail to block epileptiform activity in rat organotypic hippocampal slice cultures. Br. J. Pharmacol. 154, 709-724]. The present study was undertaken in order to test the effects of other compounds on SLEs in OHSCs that enhance GABA-mediated actions.

Methods: Six to 12 days old Wistar rats were used to cultivate OHSCs according to the interface method [Stoppini, L., Buchs, P.A., Muller, D., 1991. A simple method for organotypic cultures of nervous tissue. J. Neurosci. Methods 37, 173-182]. Neuronal activity and extracellular potassium concentration were recorded under submerged conditions. SLEs were induced by lowering the magnesium concentration. The effects of GABA(A) agonists muscimol and isoguvacine, the GABA(B) agonist baclofen, the GABA uptake blocker nipecotic acid and the neurosteroid alfaxalone on induction and ongoing SLEs were analyzed.

Results: Low magnesium induced SLEs were dose dependently suppressed by the GABA(A) receptor agonists muscimol, isoguvacine and alfaxalone and by the GABA uptake inhibitor nipecotic acid whereas the GABA(B) receptor agonist baclofen attenuated but did not suppress SLE.

Discussion: Our findings demonstrate that in OHSCs GABA has an inhibitory effect on SLEs. Proconvulsant effects of GABA agonists on spontaneous neuronal activity and seizure like activity were never observed. Our findings exclude a possible contribution of impaired/altered GABA-ergic mechanisms based on immaturity of receptors and/or low receptor density to seizure susceptibility and pharmacoresistance in OHSCs.