OPTICAL-RECORDING OF TRISYNAPTIC PATHWAY IN RAT HIPPOCAMPAL SLICES WITH A VOLTAGE-SENSITIVE DYE

Changes in membrane potentials were recorded from rat hippocampal slic es with a voltage-sensitive dye using a real-time optical recording sy stem, which had high spatial resolution of 128 x 128 points with a hig h time resolution of 0.6 ms. Serial excitatory propagation was recorde d in the dentate gyrus, CA3 and CAI after stimulation of the perforant pathway, and the optical signals were clearly divided into two compon ents in the dentate gyrus adjacent to the stimulus site. The slow comp onent was suppressed in Ca2+-free solution, but the fast component in the molecular layer was not affected. However, the application of 1 mu M tetrodotoxin fully abolished both components. These results suggest that the fast and slow components mainly reflect Na+-dependent action potentials and excitatory postsynaptic potentials, respectively. The excitatory response duration in the stratum radiatum of CA3 was signif icantly longer than that in other hippocampal areas. The long-lasting excitation in CA3 is probably related to the CA3 associational project ions, because direct stimulation of CA3 pyramidal cell layer also prod uced similar results. The long-lasting dendritic excitation is probabl y important to integrate synaptic transmission and may be related to e pileptogenesis. When long-term potentiation was induced by a tetanic s timulation (100 Hz for 1 s), the onset latency in the stratum radiatum of CA1 was reduced to as much as 65%, suggesting an increase of excit atory propagation. The analysis of the spatial-temporal optical signal s contributes to understanding information processes in the hippocampu s, related to learning and memory including long-term potentiation. (C ) 1997 IBRO. Published by Elsevier Science Ltd.