Seizure initiation and propagation in the pilocarpine rat model of temporal lobe epilepsy.

Editor's Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see Review of Toyoda et al. Temporal lobe epilepsy (TLE) is the most common type of epilepsy in adulthood. It is characterized by seizures originating from the limbic system, particularly the hippocampus, parahippocampal regions, and amygdala. TLE is frequently associated with an initial precipitating injury such as perinatal hypoxia, febrile seizure, infection, or head trauma. Occasionally the precipitating injury includes status epilepticus (SE), an acute, prolonged seizure typically involving convulsions and loss of consciousness. The precipitating injury is usually followed by a seizure-free latent period, and eventually the appearance of recurrent seizures (French et al., 1993). Animal models of TLE have been instrumental in clarifying the pathophysiol-ogy of epilepsy and in the development of antiepileptic drugs and other treatments. The pilocarpine model of TLE belongs to a group of animal models that replicate the general progression of events as observed in humans, and it has been used frequently since its introduction 30 years ago (Turski et al., 1983). In this model, systemic injection of the convulsant pilo-carpine induces SE, likely through activation of M1 muscarinic receptors, followed by a seizure-free latent period, and eventually the appearance of recurrent seizures that continue for the rest of the animal's life. Seizure initiation and propagation in human TLE has been examined extensively , because this information is crucial for resective surgeries aimed at treating uncontrolled seizures. In contrast and somewhat surprisingly, until recently relatively little was known about seizure initiation and propagation in the pilocarpine rat model of TLE. Toyoda at al. (2013) aimed to address this knowledge gap using simultaneous electrophysiological recordings from several brain regions. These experiments revealed important and interesting aspects of seizure spread in one of the most widely used animal models of epilepsy. Toyoda et al. (2013) examined spontaneous seizures in 10 pilocarpine-treated rats, using local-field-potential recordings and video monitoring. Bipolar recording electrodes were implanted bilaterally in eight brain regions. Target regions were selected in part based on previously reported neuropathological changes in humans and/or rats. Using video monitoring , behavioral severity of each seizure was ranked on a standard 0 –5 Racine scale. Seizure onset in each recording …