Steady-state electrotonic analysis of intracellularly stained hippocampal neurons

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Abstract

A series of CA1 hippocampal cells were physiologically characterized as probable pyramidal neurons (n = 12) or interneurons (n = 2) in the in vitro guinea pig hippocampal slice. Subsequent intracellular horseradish peroxidase injection allowed anatomical identification of these same cells. Careful measurements of dendritic diameters and lengths allowed application of finite cable analysis. Specific membrane resistance (Rm) averaged 2,450 and 4,860 Ω x cm2 for the pyramidal cells, assuming sealed-end and infinite cable terminations, respectively. For the interneurons and the same terminal assumptions, Rm averaged 915 and 1,050 Ω x cm2. All of these cells demonstrated a rapid loss of combined dendritic trunk diameter, thus failing to satisfy the equivalent cylinder neuron model. Calculated dendrite-to-soma conductance ratios averaged 3.5 and 7.7 for the pyramidal cells (for sealed-end and infinite cable terminations, respectively) and 1.45 and 1.85 for the interneurons (same termination assumptions). Maximum electrotonic length for the pyramidal cells approached 2.0 length constants, while the mean electrotonic length for dendritic terminations averaged 0.98 for the same group of cells. Voltage transfer to the soma from distal dendritic branches (steady state) was computed to be less than 1% of input voltage (for the pyramidal cells). Current transfer from terminal dendritic branches to the soma, calculated for the pyramidal cells, ranged from 20% for the most distal branches to 90% for electrotonically close branches. Schaffer collateral and commissural input both showed greater than 50% current transfer to the soma, whereas entorhinal input would transfer less than 50% of injected current to the soma. These figures suggest that input from distal synapses results in a significant degree of current transfer to the soma via purely passive conduction. Both current and voltage conduction were approximately identical for either sealed-end or infinite cable termination assumptions, in spite of the differing Rm. However, large changes in Rm would affect current attenuation significantly, changing substantially the role of distal synaptic sites.

Original languageEnglish (US)
Pages (from-to)184-199
Number of pages16
JournalJournal of Neurophysiology
Volume44
Issue number1
StatePublished - 1980
Externally publishedYes

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ASJC Scopus subject areas

  • Physiology
  • Neuroscience(all)

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