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