EPILEPTOGENESIS IN IMMATURE NEOCORTICAL SLICES INDUCED BY 4-AMINOPYRIDINE

The laminar site of onset of 4-aminopyridine (4AP)-induced epileptifor m discharges in immature neocortical brain slices was localized to lay er V using conventional extracellular field electrodes, current source -density analysis (CSD), and subdivided slices. Intracellular patch-el ectrode recordings in immature layer V neurons confirmed that intrinsi cally bursting (IB) neurons were not present at the ages studied or wi th bath application of 50-200 mu M 4AP. IB properties were not being m asked in the younger animals by the patch electrodes because typical I B neurons in layer V were seen in older rats when the same intracellul ar techniques were used. These results demonstrate that epileptiform a ctivity can be initiated in the absence of IB neurons, and suggest tha t other factors are responsible for the preferential onset in layer V.