This study was initiated to investigate effects of the novel
neuromodulator carisbamate (
RWJ 333369) in the hippocampal neuronal culture model of
status epilepticus and spontaneous epileptiform discharges. Whole-cell current clamp techniques were used to determine the effects of
carisbamate on spontaneous recurrent epileptiform discharges (SREDs, in vitro
epilepsy), depolarization-induced sustained repetitive firing (SRF) and low Mg(2+)-induced continuous high frequency spiking (in vitro
status epilepticus). This in vitro model is an important tool to study the effects of
anticonvulsant drugs (AEDs) on SREDs that occur for the life of the neurons in culture.
Carisbamate dose dependently blocked the expression and reoccurrence of SREDs. The ED(50) value for its
antiepileptic effect was 58.75+/-2.43 microM. Inhibition of SRF is considered a common attribute of many AEDs.
Carisbamate (100 microM) significantly decreased SRF in hippocampal neurons. All these effects of
carisbamate were reversed during a 5 to 30 min
drug washout period. When exposed to low Mg(2+) medium cultured hippocampal neurons exhibit high frequency spiking. This form of in vitro
status epilepticus is not effectively blocked by conventional AEDs that are known to be effective in treating
status epilepticus in humans.
Carisbamate, like
phenytoin and
phenobarbital, had little or no effect on low Mg(2+)-induced continuous high frequency spiking. These results characterize the effects of
carisbamate in the hippocampal neuronal culture model of epileptiform discharges and suggest that the ability of
carisbamate to inhibit depolarization-induced SRF may account in part for some of it's
anticonvulsant effect.