Development of new antiepileptic drugs: challenges, incentives, and recent advances

Stabilizing dendritic structure as a novel therapeutic approach for epilepsy

People with epilepsy often experience long-term cognitive dysfunction and other neurological deficits, including memory loss, learning disabilities and neurobehavioral disorders, which may exhibit a progressive course correlating with worsening seizure control. Furthermore, a third of epilepsy patients have seizures that are intractable to all available treatments. Thus, novel therapies for seizures and the neurological comorbidities of epilepsy are desperately needed. As most current treatments are merely symptomatic therapies that suppress seizures, epilepsy researchers have recently realized the critical need for novel therapeutic strategies targeting the underlying mechanisms of epileptogenesis and seizure-related brain injury. Yet, to date, few such antiepileptogenic therapies have emerged or are even in developmental stages. Although many seizure medications modulate the functional or physiological activity of neurons, the methods for stabilizing the structure of neurons are relatively unexplored therapeutic strategies for epilepsy. Human pathological studies and animal models of epilepsy demonstrate obvious structural abnormalities in dendrites of neurons, which could contribute to neuronal dysfunction, epileptogenesis and cognitive/neurological deficits in epilepsy patients. This dendritic injury may be caused by activity-dependent breakdown of cytoskeletal elements, such as actin. Mechanistically targeted approaches to limit seizure-related structural changes in dendrites may represent a novel therapeutic strategy for treating epilepsy and its complications.

[Animal models to develop surgery of focal epilepsies?]

A model is a simplified preparation that reproduces only the most critical features of a disease. To be considered as a validated animal model, such an experimental preparation must fulfill three criteria: isomorphism or similarities of the symptoms; predictivity or identical pharmacological reactivity; homology or etiological similarity. In epilepsy, the use of animal models helps our understanding of physiological and pathological networks involved in the genesis, maintenance, and propagation of seizures. The animal models of epilepsy are also useful in designing and testing new surgical therapeutical strategies, in particular using deconnection or neuromodulation in drug-resistant focal epilepsies. Here we describe three animal models of focal epilepsy, adapted to addressing experimental surgery issues. Kindling consists in the regular liminar stimulation of a given brain structure in the rodent to develop a focal discharge that is secondarily generalized. The local application of epileptogenic agents such as cobalt, iron, or penicillin leads to focal discharges that do not generalize in the rodent or the primate. It is a model of focal neocortical epilepsy without secondary generalization. The focal application of kainate, an excitotoxic glutamate agonist, in the dorsal hippocampus of the adult mouse results, after a latent period, in spontaneous and recurrent focal discharges, behavioral interictal troubles, drug resistance, and histological anomalies reminiscent of hippocampal sclerosis. This constitutes a model of mesial-temporal epilepsy. Better knowledge, in these models, of the neural networks generating, propagating, and/or controlling the seizures should make it possible to design innovative surgical approaches for the treatment of drug-resistant epilepsies.