Retigabine: has the orphan found a home?

Recent and Emerging Anti-seizure Drugs: 2013

OPINION STATEMENT

Recent and emerging pharmacotherapies have become available for use within the last 4 years to enhance our ability to manage people with epilepsy (PWE). More antiseizure drug (ASD) choices allow greater opportunity to match a unique medicine with each patient from the time of first seizure and for drug-resistant epilepsy. Balancing the efficacy, safety, and tolerability of an ASD is unique for each person and epilepsy syndrome. This tailored approach to effectiveness includes seven new ASDs that have become available since 2009 to treat PWE expanding our armamentarium to more than two dozen ASDs in the US that are now available for use. "Which ASD is best?" is still a complex challenge that remains to be answered. Until the ASD is found that is a panacea for everyone, the role of new AEDs in the treatment of epilepsy lies in the hands of the clinician to address the overall needs of the person first and foremost. In this paper, the newest and emerging ASDs in 2013 are reviewed focusing on the pharmacology, efficacy, and adverse effects. Each ASD has benefits and risks and the ultimate role in clinical use will be established over time as experience with each agent grows.

Ezogabine: a new angle on potassium gates

Ezogabine is a new drug for adjunctive therapy of partial-onset seizures with a novel mechanism of action. As a potassium-channel facilitator, it promotes membrane repolarization and thus opposes rapid repetitive discharges. Side effects are typical for antiepileptic drugs and the safety profile is good. Occasional instances of urinary difficulty may require surveillance.

The mechanism of abrupt transition between theta and hyper-excitable spiking activity in medial entorhinal cortex layer II stellate cells

Recent studies have shown that stellate cells (SCs) of the medial entorhinal cortex become hyper-excitable in animal models of temporal lobe epilepsy. These studies have also demonstrated the existence of recurrent connections among SCs, reduced levels of recurrent inhibition in epileptic networks as compared to control ones, and comparable levels of recurrent excitation among SCs in both network types. In this work, we investigate the biophysical and dynamic mechanism of generation of the fast time scale corresponding to hyper-excitable firing and the transition between theta and fast firing frequency activity in SCs. We show that recurrently connected minimal networks of SCs exhibit abrupt, threshold-like transition between theta and hyper-excitable firing frequencies as the result of small changes in the maximal synaptic (AMPAergic) conductance. The threshold required for this transition is modulated by synaptic inhibition. Similar abrupt transition between firing frequency regimes can be observed in single, self-coupled SCs, which represent a network of recurrently coupled neurons synchronized in phase, but not in synaptically isolated SCs as the result of changes in the levels of the tonic drive. Using dynamical systems tools (phase-space analysis), we explain the dynamic mechanism underlying the genesis of the fast time scale and the abrupt transition between firing frequency regimes, their dependence on the intrinsic SC's currents and synaptic excitation. This abrupt transition is mechanistically different from others observed in similar networks with different cell types. Most notably, there is no bistability involved. 'In vitro' experiments using single SCs self-coupled with dynamic clamp show the abrupt transition between firing frequency regimes, and demonstrate that our theoretical predictions are not an artifact of the model. In addition, these experiments show that high-frequency firing is burst-like with a duration modulated by an M-current.