LOCALIZING SITES OF INTRADENDRITIC ELECTROPHYSIOLOGICAL RECORDINGS BYCONFOCAL LIGHT-MICROSCOPY

Studies were undertaken to develop microscopic methods and imaging pro cedures that would permit identification of sites of intradendritic mi croelectrode recordings from pyramidal cells in hippocampal slice prep arations. Intradendritic recordings were obtained with sharp microelec trodes filled with the dye lucifer yellow. Following a recording sessi on a neuron was iontophoretically injected with the dye and imaged by fluorescence videomicroscopy. Images were stored on videotape for late r analysis. They provided a record of the location of the microelectro de recording site. After withdrawal of the microelectrode, slices were processed histologically and imaged a second time with a Bio-Rad 600 confocal attachment on an Olympus BH-2 microscope. Confocal images pro vided detailed anatomical information in three dimensions. In most ins tances, a clear identification of the recording site was achieved by c omparing video images containing the recording electrode and confocal images. Neurophysiological recordings obtained from proximal and dista l apical dendrites were markedly different. Proximal dendritic recordi ngs were similar to those obtained from pyramidal cell soma. However, distal dendrites were not electroresponsive when depolarized by intrac ellular current injection. The techniques described here, or variation s that employ patch electrodes, could provide valuable information tha t should further an understanding of the properties of dendrites in th e central nervous system. (C) 1994 Wiley-Liss, Inc.