Intracellular Staining

The principal advantages of simultaneously recording from, and staining of single neurons, buried deep in tissue, is obvious and need not be stressed. Particularly in insects, where most cell somata are electrically silent, there is so far no way to correlate neuronal activity with a particular cell other than to penetrate and to label small fibers simultaneously (Hengstenberg, 1971). Great efforts have been undertaken during the past years to develop methods that would meet the many and often conflicting demands that an ideal intracellular marking procedure has to satisfy by appropriate histochemical and histologic procedures, seem at present to approach most closely the requirements of an ideal marking method. Each of the three has distinct advantages to recommend it for a particular problem and drawbacks that may prohibit its application in other instances. We chose Procion yellow when searching the blowfly's brain for visual interneurons that might be involved in movement perception, because the dye does not seem to interfere with neuronal activity in-acute experiments. It can easily be injected, and the necessary histologic processing 307