Kainic acid, bicuculline, pentylenetetrazol and pilocarpine elicit maximal dentate activation in the anesthetized rat.

Patterns of epileptiform activity in the hippocampus induced by chemical convulsants were recorded in the urethane-anesthetized rat. Previously, two epileptiform discharges have been recorded in the dentate gyrus after electrical stimulation, one consisting of broad positive potentials and the second consisting of bursts of large amplitude population spikes (termed maximal dentate activation). In the present study, convulsant-induced epileptiform activity was documented and compared to stimulus-evoked activity. Four systemically active convulsants--kainic acid, bicuculline, pentylenetetrazol and pilocarpine--were used in this study. One of the convulsants was administered and the animal was monitored for the development of epileptiform activity in CA1, CA3 and the dentate gyrus. The epileptiform activity that first appeared after each of the convulsants was grouped into four categories. With extended monitoring, or an increase in dose, each of the chemical convulsants produced maximal dentate activation in the majority of the animals tested (72-90%). When maximal dentate activation was present bursts of population spikes were also recorded in CA3 and CA1. These observations suggest that the early discharges are related to the mechanism of action of the convulsant and that the appearance of maximal dentate activation is independent of the mechanism of action. In addition, there does not appear to be a fixed evolution of epileptic discharges in these circuits when comparing seizure induction by different mechanisms.