Electrical interaction among large cells in the cardiac ganglion of the lobster,Panulirus japonicus

To investigate electrical interaction among large cells in the lobster cardiac ganglion, electrotonic transmission between the somata of two such cells was observed by applying current pulses of two different durations and recording induced responses in the membrane potential of soma. The brief potential changes induced in one soma were transmitted to an adjacent soma through electrotonic pathways in the same way as the longer potential changes. However attenuation was greater for the shorter pulses. The amplitude of the soma spike markedly decreased compared to that of the axon spike, and the ratio was about 5.5. The soma spike was not a regenerative response of the soma membrane, but it was an electrotonic spread of the axon spike. The attenuation ratio of the soma spike was almost the same as that measured for a brief potential change such as a spike applied to the soma. These findings indicate that the soma spike spreads electrotonically to the adjacent soma through the electrical connections, while the axon spike does not. Such electrical transmission of the spike was extremely weak. The slow potential, electronic transmission of which had been observed between large cells, was restricted to the soma. The results suggest that the electrotonic pathways interconnect the somata of large cells in the anterior part of the ganglionic trunk, but not the axons. Electrical transmission of the spike through the pathways is very weak because of the inexcitable membrane of the somata. The electrotonic pathways are considered to be fibre-like connections between dendrites arising from the somata.