A White-Noise Approach for Estimating the Passive Electrical Properties of
Wright, W. Neil, Berj L. Bardakjian, Taufik A. Valiante, Jose L. Perez-
Velazquez, and Peter L. Carlen.
Institute of Biomedical Engineering, Department of Electrical and Computer
Engineering, Department of Medicine, University of Toronto, and Playfair
Neuroscience Unit, Toronto Hospital, Toronto, Ontario, Canada.
APStracts 3:0157N, 1996.
SUMMARY AND CONCLUSIONS
1. The passive electrical properties of whole-cell patched dentate granule
(DG) cells were studied using zero-mean Gaussian white-noise (GWN) current
stimuli. Transmembrane voltage responses were used to compute the first-order
Wiener kernels describing the current-voltage relationship at the soma for six
cells. Frequency domain optimization techniques using a gradient method for
function minimization were then employed to identify the optimal electrical
parameter values. Low power white-noise stimuli are presented as a favorable
alternative to the use of short pulse current inputs for investigating
neuronal passive electrical properties. 2. The optimization results
demonstrated that the lumped resistive and capacitive prop- erties of the
recording electrode must be included in the analytic input impedance
expression in order to optimally fit the measured cellular responses. The
addition of the electrode resistance (Re) and capacitance (Ce) to the original
parameters, somatic conductance (GS ), somatic capacitance (CS ), axial
resistance (RA ), dendritic conduc- tance (GM ), and dendritic capacitance (CM
), results in a seven parameter model. The mean Ce value from the six cells
was 5.40.3 (SE) pF while Re following formation of the patch was found to be
202 M . 3. The six dentate granule cells were found to have an input
resistance of 60020 M and a dendritic to somatic conductance ratio of 6.31.1.
The electrotonic length of the equivalent dendritic cylinder was found to be
0.420.03. The membrane time constant in the soma was found to be 133 ms while
the membrane time constant of the den- J209-95RRR 2 drites was 585 ms.
Incorporation of morphological estimations lead to the following distributed
electrical parameters (meanSE): Rms =254 kcm2, Cms =0.480.05 F cm-2, Ri=725
cm, Rmd =594 kcm2, Cmd =0.970.06 F cm-2 . Based on capacitive measurements the
ratio of dendritic surface area to somatic surface area was found to be 342.
4. For comparative purposes hyperpolarizing short pulses were also injected
into each cell. The short pulse input impedance measurements were found to
underestimate the input resistance of the cell and overestimate both the
somatic conductance and the membrane time constants relative to the white-
noise input impedance measurements.
Received 29 March 1995; accepted in final form 25 June 1996.
APS Manuscript Number J209-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996