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The electrotonic location of low‐resistance intercellular junctions between a pair of giant neurones in the snail Lymnaea.
Author(s) -
Benjamin P R,
Pilkington J B
Publication year - 1986
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1986.sp015925
Subject(s) - soma , axon , conductance , lymnaea , biophysics , gap junction , time constant , coupling (piping) , electrophysiology , snail , lymnaea stagnalis , membrane potential , anatomy , biology , physics , materials science , intracellular , neuroscience , condensed matter physics , ecology , engineering , microbiology and biotechnology , electrical engineering , metallurgy
The passive electrotonic properties of neurones VD1 and RPD2 in the brain of the snail Lymnaea can be represented by a soma‐finite cable model with closed‐circuit axon termination. There is a considerable individual variation in input resistance, membrane time constant, electrotonic length and axon‐soma conductance ratio, but the average values for these parameters are similar in the two neurones. The cells are tightly coupled by an electrotonic synapse giving an average steady‐state coupling coefficient of 0.68 and an average resistance measured between recording sites in the cell bodies of 20 M omega. Calculations using a model consisting of a symmetrical pair of cells with standard values for the electrotonic parameters show that in this system, for a soma‐soma resistance of 20 M omega, the junction cannot be more than 0.16 length constants from the cell bodies. Reduction in coupling due to membrane current losses in such short proximal axon segments is insignificant. Intra‐axonal recordings indicate that most of the coupling resistance is located at the junction between VD1 and RPD2, which must therefore be closer to the cell bodies than the limiting value of 0.16 length constants assuming an electrical equivalent model which includes the standard electrotonic parameters. If all the soma‐soma resistance is located at the junction, then it could be physically a single array of gap‐junction particles. Despite its low conductance (1/20 M omega = 50 nS) and possibly small physical dimensions, the electrotonic synapse is more than sufficient to ensure spike synchrony in the two cells.