Differential intracellular labelling of identified neurones with two fluorescent dyes

Electrophysiologically characterised rat dorsal root ganglion (DRG) neurones in vitro were injected with a fluorescent dye, either ethidium bromide or Lucifer yellow. Microelectrodes filled with ethidium bromide had lower resistances and were electrically more stable than comparable electrodes filled with Lucifer yellow. Neither dye affected the electrophysiology of these neurones in this study. We have used these dyes to locate and identify unambiguously the electrophysiologically characterised neurones after histological processing. Neurones filled with ethidium bromide could easily be distinguished from those filled with Lucifer yellow, even when they were closely apposed. Preliminary data, using the antibody RT97, indicates the compatibility of ethidium bromide injection with immunocytochemical studies. Ethidium bromide promises to be an important tool for use alone and alongside Lucifer yellow in the correlation of electrophysiology with histology.