CCD IMAGING OF THE ELECTRICAL-ACTIVITY IN THE LEECH NERVOUS-SYSTEM

A single ganglion of the nervous system of the leech Hirudo medicinali s was isolated. One or both roots emerging from each side of the gangl ion were sucked into suction pipettes used either for extracellular st imulation or for recording the gross electrical activity. The ganglion was stained with the fluorescence voltage sensitive dye Di-4-Anepps. The fluorescence was measured with a nitrogen cooled CCD camera. Our r ecording system allowed us to measure in real time slow optical signal s corresponding to changes in light intensity of at least 5 parts per thousand. These signals were caused by the direct polarization of neur onal structures, the afterhyperpolarization or the afterdischarge indu ced by a prolonged stimulation. When images were acquired at fixed tim es, several of them could be averaged and optical signals of at least 2 parts per thousand could be reliably measured. These optical signals originated from well identified neurons, such as T, P and N sensory n eurons. By taking images at different times and at different focal pla nes, electrical events could be followed at a temporal resolution of 5 0 Hz. The three dimensional dynamics of electrical events, initiated b y a specific stimulation, was imaged and the spread of excitation amon g leech neurons was followed. When two roots were selectively stimulat ed, their neuronal interactions could be imaged and the linear and non -linear terms of the interaction could be characterized.