Recording of spontaneous activity in cultured superior colliculus slices using microelectrode array

Retino-tectal projection is one of the pathways in visual information processing. During development, spontaneous electrical activity of superior colliculus (SC) probably plays an important role for proper network formation. In this study, SC slices were taken from new-born rats and cultured on microelectrode-array (MEA) substrates. Spontaneous activities of the cultured SC were recorded for four weeks. During the first week, most of the cultured SC slices generated sporadic spikes. These sporadic spikes gradually changed into periodic synchronized bursts. Spatially organized synchronized activity produced low frequency signals (local field potential: LFP). All of the test slices showed clear LFPs within three weeks. Large negative peaks were observed in the middle layer of the slices, while positive signals were obtained around the deep layers. Current source density (CSD) analysis revealed that middle layers acted as a current source and surface and deep layers were the sinks. These results suggested that layered structures of SC were well-maintained under the culture conditions and the cells in the middle layers played dominant roles in generating these periodic synchronized spontaneous activities.