Mechanisms in the development of limbic status epilepticus and hippocampal neuron loss: an experimental study in a model of status epilepticus induced by kindling-like electrical stimulation of the deep prepyriform cortex in rats.

A new model of status epilepticus (SE), which was induced by intermittent electrical stimulation (20 Hz for 20 sec every min for 180 min) of the deep prepyriform cortex, has been developed in the conscious rat. SE was induced in 9 of 16 rats in the drug-free group. The number of stimulation trains required to induce SE in this status subgroup was 125.6 +/- 12.7 (mean +/- SEM) and the mean duration of self-sustained seizure activity (SSSA) occurring after cessation of the stimulation session was 295.4 +/- 111.4 min. Some animals showed secondary generalized seizures. Significant cell loss was observed in the hippocampal CA3 pyramidal cell layer ipsilateral to the stimulation site and bilateral CA1 areas in the status subgroup compared with the group subjected to sham operation. In addition, there was a significant negative correlation between the duration of SSSA subsequent to the stimulation session and the total number of intact pyramidal neurons observed in the bilateral CA1 and ipsilateral CA3 subfields of the status subgroup. There were significant differences between the status and non-status subgroups with respect to the number of afterdischarges (ADs) and the total AD duration during the stimulation session. Pretreatment with phenobarbital (30 mg/kg) prevented the development of SE and hippocampal cell loss completely. Pretreatment with MK-801, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist (0.25 or 1 mg/kg), also prevented hippocampal cell loss, although it did not block SE generation completely, which suggests dissociation of the mechanisms underlying the development of SE and hippocampal damage. These results indicate that prolonged SSSA actually causes hippocampal damage and it is critically dependent upon NMDA receptor participation.