Self-sustaining Limbic Status Epilepticus Induced by 'continuous' Hippocampal Stimulation: Electrographic and Behavioral Characteristics

A model of status epilepticus centered in the limbic system and elicited by 'continuous' focal electrical stimulation of the hippocampus is presented. Under appropriate conditions, the status epilepticus persisted for many hours after discontinuing the electrical stimulus. The critical determinant for the establishment of this self-sustaining limbic status epilepticus (SSLSE) was the length of stimulation, rather than the side (left vs. right) of stimulation or kindling before stimulation. Observations, obtained from stimulus-free intervals spaced regularly during the stimulus protocol and from the period after stimulation had been completed, revealed a distinct and stereotyped electrographic progression of SSLSE though several stages. Brief monitoring periods throughout the stimulus protocol yielded electrographic criteria that predicted which animals would experience experience SSLSE. The presence of synchronous, stimulus-independent seizure activity bilaterally in the hippocampi during stimulation was necessary to establish SSLSE. Intense motor seizure activity, like that seen with kindled motor seizures, occurred intermittently during SSLSE. However, 'limbic' behavioral seizures identical to those seen after low doses of kainic acid or during the early stages of kindling were nearly continuous. These studies indicate that there is a predictable course to limbic status epilepticus and point to the hippocampus as a key element involved in initiating and maintaining this syndrome.