Abstracts

Rationale: Expression of spontaneous recurrent epileptiform discharges (SREDs) after a low Mg2+ induced status epilepticus (SE) like injury in cultured hippocampal neurons is a commonly used model to study the mechanisms underlying seizure generation, epileptogenesis, seizure-induced plasticity and development of pharmacoresistant seizures. The present study investigated the antiepileptic and antiepileptogenic effects of novel neuromodulator Carisbamate (RWJ 333369) in this in vitro model of epilepsy.Methods: SREDs were induced into hippocampal neuronal cultures (HNC) by exposing them for 3-h of SE induced by a solution containing no added MgCl2. At the end of the 3-h period, cultures were restored to the physiological concentration (1 mM) of MgCl2. Neurons were tested for the presence of SREDs using patch clamp electrophysiology. Carisbamate was dissolved in recording solution and was applied via gravity feed perfusion.Results: Whole cell current clamp recordings from HNC 1-day after a 3-h, low-Mg2+ treatment demonstrated SREDs or seizure events that occurred spontaneously and lasted for the life of the neurons in cultures. SREDs manifested paroxysmal depolarization shifts, a pathophysiological characteristic of acquired epilepsy. Application of Carisbamate fully inhibited the expression and reoccurrence of SREDs. The anticonvulsant effects of Carisbamate were concentration dependent and maximal inhibition of SREDs was obtained at 100 μM. Carisbamate was applied to neurons during SREDs and it took approx. 15-20 min for it’s antiepileptic effect to be fully manifested. These experiments demonstrated the antiepileptic effects of Carisbamate. In another set of experiments, following a 3-h of low Mg2+ treatment, normal media was restored and the cells were incubated in the presence of 100 μM Carisbamate for 12 h. After this treatment, Carisbamate was removed from the media and at different times after treatment the cultures were studied for epileptiform activity. The cells tolerated Carisbamate without any toxic effects. SREDs were not observed even 12 h after the removal of Carisbamate. These experiments showed the antiepileptogenic effect of Carisbamate following SE in this model.Conclusions: Carisbamate produced inhibition of SREDs in the in vitro model of acquired epilepsy. These results are in line with other in vivo studies that have reported anticonvulsant effects of Carisbamate in different animal models of seizures. Interestingly, cells evaluated the day after treatment with Carisbamate following SE remained seizure-free even in the absence of the drug. This finding demonstrates that Carisbamate was able to prevent the development of epileptiform activity and seizures following SE and indicates that Carisbamate acted as a potent antiepileptogenic agent in the HNC model of acquired epilepsy. Further studies may offer important insights into the therapeutic potential of this agent both as an anticonvulsant and antiepileptogenic drug. (Support: Johnson & Johnson Pharmaceutical Research & Development L.L.C and NINDS grants RO1NS051505, RO1NS052529, UO1NS058213 to RJD).