Maximal dentate activation is produced by amygdala stimulation in unanesthetized rats

In urethane-anesthetized rats, a process termed maximal dentate activation has been shown to be associated with the lengthening of afterdischarges that occurs with repeated hippocampal stimulation. Maximal dentate activation is a unique paroxysmal form of epileptiform discharges consisting of large amplitude population spikes in the dentate gyrus. The current experiments examined the relationship of maximal dentate activation to kindling of motor seizures in the awake animal. Both long duration (5 or 10 s) and short duration (1 s) stimulus trains in either the hippocampus or the amygdala were effective in eliciting maximal dentate activation. Repeated stimulation of the amygdala produced lengthening of afterdischarges and kindling of motor responses, but only after maximal dentate activation had appeared in response to the stimulus. Over the course of amygdala kindling, the duration of maximal dentate activation lengthened with increasing severity of behavioral seizures. This evidence supports the hypothesis that maximal dentate activation is a marker for the presence of seizures distributed throughout limbic circuits. In addition, the data suggest that maximal dentate activation may be an important process involved in the acquisition of kindled responses.