Bipolar electrodes, stereotactically implanted in the hippocampus of adult rats, were used to deliver 10 s trains of suprathreshold tetanic electrical stimuli every few minutes. As indices of seizure intensity, durations of the afterdischarges triggered by these stimuli were measured, and the accompanying behaviors were scored on a 5-point scale. After 2-3 h, prolonged afterdischarges appeared in conjunction with severe limbic seizures, separated by periods of approximately 60 min. After 3-9 h, the stimulation was withheld until the following day. Upon reinstitution of the stimuli, intense seizures were seen at the onset, and the cycle time between them was shortened. Enhanced responsiveness to a fixed stimulus persisted for several months, the longest period tested. In addition, the enhanced epileptogenicity showed transference and was not stimulus-specific. These studies, using stimuli with low intertrain frequency and short interstimulus intervals, establish a robust and rapidly-developing model of epileptogenesis in the hippocampus that is comparable to traditional kindling.
- limbic system