CONTRIBUTION OF T-TYPE CALCIUM CHANNELS TO AFTERDISCHARGE GENERATION IN RAT HIPPOCAMPAL SLICES

To clarify the possible involvement of Ca2+ channel subtypes in epilep togenesis, the CA1 region of rat hippocampal slices was examined for t he pharmacological effects of Ca2+ channel blockers on ictal-like afte rdischarges (ADs) observed following the repetition of high-frequency electrical stimulation, as well as on interictal-like bursts of popula tion spikes following single stimuli in the presence of bicuculline. N i2+ and amiloride, which predominantly block T-type Ca2+ channels, sup pressed the number of spikes in ADs at concentrations of these two cha nnel blockers sufficient to eliminate this type of Ca2+ channel in acu tely dissociated and cultured hippocampal neurons. On the other hand, neither the L-type Ca2+ channel blocker nifedipine nor the N-type Ca2 channel blocker, omega-conotoxin GVIA had any effect on the generatio n of ADs. In addition, none of these T-, L- and N-type channel blocker s had any effect on the bicuculline-induced, interictal-like epileptif orm discharges. We therefore conclude that the activation of T-type Ca 2+ channels, which is distinct from the mechanisms involved in interic tal activity, may play a causative role in the generation of ictal-lik e ADs. (C) 1998 Elsevier Science B.V.