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Passive electrotonic properties of rat hippocampal CA3 interneurones
Author(s) -
Chitwood Raymond A.,
Hubbard Aida,
Jaffe David B.
Publication year - 1999
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 - 10.1111/j.1469-7793.1999.743ab.x
Subject(s) - soma , excitatory postsynaptic potential , biocytin , depolarization , membrane potential , biophysics , neuroscience , conductance , postsynaptic current , chemistry , electrophysiology , biology , physics , inhibitory postsynaptic potential , condensed matter physics
1 The linear membrane responses of CA3 interneurones were determined with the use of whole‐cell patch recording methods. The mean input resistance ( R N ) for all cells in this study was 526 ± 16 MΩ and the slowest membrane time constant (τ 0 ) was 73 ± 3 ms. 2 The three‐dimensional morphology of 63 biocytin‐labelled neurones was used to construct compartmental models. Specific membrane resistivity ( R m ) and specific membrane capacitance ( C m ) were estimated by fitting the linear membrane response. Acceptable fits were obtained for 24 CA3 interneurones. The mean R m was 61.9 ± 34.2 Ω cm 2 and the mean C m was 0.9 ± 0.3 μF cm −2 . Intracellular resistance ( R i ) could not be resolved in this study. 3 Examination of voltage attenuation revealed a significantly low synaptic efficiency from most dendritic synaptic input locations to the soma. 4 Simulations of excitatory postsynaptic potentials (EPSPs) were analysed at both the site of synaptic input and at the soma. There was little variability in the depolarization at the soma from synaptic inputs placed at different locations along the dendritic tree. The EPSP amplitude at the site of synaptic input was progressively larger with distance from the soma, consistent with a progressive increase in input impedance. 5 The ‘iso‐efficiency’ of spatially different synaptic inputs arose from two opposing factors: an increase in EPSP amplitude at the synapse with distance from the soma was opposed by a nearly equivalent increase in voltage attenuation. These simulations suggest that, in these particular neurones, the amplitude of EPSPs measured at the soma will not be significantly affected by the location of synaptic inputs.