Calcium imaging of epileptiform events with single-cell resolution

Epileptic discharges propagate through apparently normal circuits, although it is still unclear how this recruitment takes place. To understand the ro le of different classes of neurons in neocortical epilepsy, we have develop ed a novel imaging assay that detects which neurons participate in epilepti form discharges. Using calcium imaging of neuronal populations during bicuc ulline-induced spontaneous epileptiform events in slices from juvenile mous e somatosensory cortex, we find that fast calcium transients correlate with epileptiform field potentials and intracellular depolarizing shifts and ca n be used as an optical signature that a given neuron has participated in a n epileptiform event. Our results demonstrate a novel method to characteriz e epileptiform events with single-cell resolution. In addition, our data ar e consistent with an important role for layer 5 in generating neocortical s eizures and indicate that subgroups of neurons are particularly prone to ep ileptiform recruitment. (C) 2001 John Wiley & Sons, Inc.