OPTICAL IMAGING OF LOW MG2-INDUCED SPONTANEOUS EPILEPTIFORM ACTIVITY IN COMBINED RAT ENTORHINAL CORTEX-HIPPOCAMPAL SLICES()

A reproducible increase in transmission of infrared light was observed during spontaneous seizure-like events (SLEs) induced by low Mg2+ sol utions in combined rat entorhinal cortex-hippocampal slices. Compariso n of half maxima of transmission change in different regions indicated propagation of SLEs from the medial entorhinal cortex towards the tem poral cortex suggesting spread along existing anatomical pathways. Thu s, optical imaging of spontaneous epileptiform activity is possible an d may improve the assessment of spread patterns. The optical signal ou tlasted both SLEs and associated K+ signals. In contrast, the tetraeth ylammonium signal, indicating changes of the extracellular space (ECS) volume, had a longer time course than the transmission changes. ECS v olume changes are widely held to be responsible for transmission chang e. Our data suggest that other mechanisms may also contribute to incre ased light transmission during epileptiform activity.