Dendrite-to-Soma Input/Output Function of Continuous Time-Varying Signals in Hippocampal CA1 Pyramidal Neurons

1 Department of Physiology, McGill University, Montreal, Quebec, Canada; and 2 Biology and Biochemistry, University of Houston, Houston, Texas Submitted 11 April 2007; accepted in final form 17 September 2007 We examined how hippocamal CA1 neurons process complex time-varying inputs that dendrites are likely to receive in vivo. We propose a functional model of the dendrite-to-soma input/output relationship that combines temporal integration and static-gain control mechanisms. Using simultaneous dual whole cell recordings, we injected 50 s of subthreshold and suprathreshold zero-mean white-noise current into the primary dendritic trunk along the proximal 2/3 of stratum radiatum and measured the membrane potential at the soma. Applying a nonlinear system-identification analysis, we found that a cascade of a linear filter followed by an adapting static-gain term fully accounted for the nonspiking input/output relationship between the dendrite and soma. The estimated filters contained a prominent band-pass region in the 1- to 10-Hz frequency range that remained constant as a function of stimulus variance. The gain of the dendrite-to-soma input/output relationship, in contrast, varied as a function of stimulus variance. When the contribution of the voltage-dependent current I h was eliminated, the estimated filters lost their band-pass properties and the gain regulation was substantially altered. Our findings suggest that the dendrite-to-soma input/output relationship for proximal apical inputs to CA1 pyramidal neurons is well described as a band-pass filter in the theta frequency range followed by a gain-control nonlinearity that dynamically adapts to the statistics of the input signal. Address for reprint requests and other correspondence: E. P. Cook, Dept. of Physiology, McGill University, 3655 Sir William Osler, Montreal, QC H3G 1Y6, Canada (E-mail: erik.cook{at}mcgill.ca )