Departments of Physiology and Anatomy, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA
Voltage imaging techniques were used to investigate epileptiform
discharges in brain slices containing piriform cortex (PC).
These experiments pinpointed the site of discharge onset in
the endopiriform nucleus (En). Under some conditions, discharge
onset also occurred simultaneously in adjoining neocortex. With
slightly suprathreshold electrical stimulation, discharge generation
was a two-stage process in which onset was preceded by a sustained
spatially localized depolarization denoted as plateau activity.
Plateau activity was seen away from the onset site, in a border
region between En and layer III of PC. A similar two-stage sequence
was seen for slices taken from a variety of planes, using two
different interictal models as well as an ictal model. Plateau
activity was found to be necessary for the generation of both
kinds of discharge. Synaptic transmission at the site of onset
was found to be required for the generation of interictal-like
discharges, but ictal-like discharges were different in that
they could still be generated when synaptic transmission at
this site was impaired. These studies identify specialized regions
with potentially important roles in epileptogenesis and help
to elucidate the neuronal circuitry that can produce epileptiform
activity.
