Paroxysmal depolarization shifts induced by bicuculline in CA3 neurons of hippocampal slices: suppression by the organic calcium antagonist verapamil.

Organic calcium antagonists have been reported to abolish epileptic neuronal discharges elicited by pentylenetetrazol and penicillin. It was tested whether the organic calcium antagonist verapamil is able to suppress also paroxysmal depolarization shifts (PDS) induced by bicuculline. This is of special interest, since bicuculline is assumed to produce PDS by blocking GABAergic synaptic inhibition. The experiments were performed on CA3 neurons of hippocampal slices (guinea pig). Verapamil (40, 60, and 80 microM) reduced amplitude, duration and frequency of appearance of PDS until the generation of PDS failed. The results indicate that calcium currents are also involved in bicuculline PDS, and that bicuculline exerts its epileptogenic action, at least in part, on extrasynaptic sites.