Generation and propagation of epileptiform activity in the hippocampal slice preparation

For the investigation of epileptiform events in the hippo-campal CA1 field, in-vitro slices of the guinea-pig were used. After adding 0.1 mmol 4-aminopyridine to the bathing medium, field potentials were recorded with an electrode array, consisting of 8 semi-microelectrodes at spacings of 0.1 ram. A comparison was made between the spontaneously occurring field potentials (SFP) in CA I and those evoked by different inputs to the CA1 pyramidal cells, namely alveus, str. oriens and Schaffer collaterals. For this purpose the electrode array was placed in CA l, parallel to the axes for the pyramidal cells.
The regularly occurring SEP's presented a similar distribution as the potentials evoked by stimulation of str. oriens or alveus of CAI, but differed from those evoked by stimulation of the chaffer colaterals. This indicates that in CA1 SFP's are generated in a similar way as field potentials evoked by alveus or str. oriens stimulation. It was also found that SFP's are propagated from CA3 and CAI at a velocity of 0.16-0.30 m/sec. Therefore pathways in alveus and str. oriens, connecting CA3 and CA1, may be important in propagating epileptiform activity. This was supported by experiments in which different pathways were sectioned.