INTRACELLULAR AND EXTRACELLULAR RESPONSES OF THE SEVERAL REGIONS OF THE MAUTHNER CELL OF THE GOLDFISH

Abstract

A method has been devised for recording from the various regions of the Mauthner neuron. Recordings have been made from perikaryon, axon-hillock, lateral dendrite and axon. The determination of recording position was made by histochemical localization of iron salts deposited from the tips of steel microelectrodes. It was found that the extracellular recordings could be used, in turn, as a good indicator of the cell part being recorded from. The most prominent extracellular response was a very large (up to 45 mV) nearly monophasic negative spike; this arose at the axon hillock region. A diphasic potential change was found at the perikaryon, a smaller monophasic positive potential at the distal part of the lateral dendrite. Associated with the large extracellular negative spike was a small intracellular action potential (30-50 mV; resting potential, 70-80 mV) in the soma and dendrite. The amplitude of the intracellular action potential in the axon was much greater (up to 115 mV). There was no evidence of a special dendritic response. The orthodromic input to the cell by way of the eighth cranial nerves was studied. The preponderant effect of ipsilateral stimulation was excitatory, that of contralateral stimulation, inhibitory. Evidence was obtained that the orthodromic impulse originated at a site more closely associated with the axon than with the cell body. It was concluded that the action potential actively invaded the axon hillock but not the distal part of the lateral dendrite.