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The Journal of Neuroscience, July 15, 1999, 19(14):5875-5888

Supralinear Summation of Synaptic Inputs by an Invertebrate Neuron: Dendritic Gain Is Mediated by an "Inward Rectifier" K⁺ Current

Ralf Wessel¹, William B. Kristan Jr², and David Kleinfeld¹

Departments of ¹ Physics and ² Biology, University of California at San Diego, La Jolla, California 92093

Dendritic processing of glutamatergic synaptic inputs was investigated in the anterior pagoda cell of leech. We observed that below spike threshold, the amplitude of individual EPSPs decreased with hyperpolarization and that simultaneous stimulation of pairs of synaptic inputs leads to the supralinear summation of EPSPs. Voltage-clamp measurements revealed a hyperpolarization-activated, Ba²⁺-sensitive, fast, noninactivating K⁺ conductance that depends on the external [K⁺]. These features are those of an "inward rectifier," Kir. Microsurgery experiments, in combination with electrophysiological measurements, revealed an inhomogeneous spatial distribution of the Kir conductance. Furthermore, on surgical removal of the neurites that contain the Kir conductance, the amplitude of EPSPs from the remaining synaptic inputs increased with hyperpolarization. A model cell, with the Kir conductance as the sole voltage-dependent conductance, reproduced qualitatively the observed voltage dependence of individual EPSPs as well as the supralinear summation of EPSP pairs.

Key words: dendritic processing; leech; inward rectifier; supralinear summation; model; synaptic inputs

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Copyright © 1999 Society for Neuroscience  0270-6474/99/19145875-14$05.00/0

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