Numerical analysis of electrotonus in multicompartmental neuron models.

ABSTRACT

Advances in anatomical and biophysical techniques have produced a wealth of data from certain classes of mammalian central neurons. In order to evaluate quantitatively these data and the hypotheses of neuronal function to which they lead, we have developed LADDER, a computer program for simulating neuronal electrotonus under current- or voltage-clamp conditions. This program models a neuron as an unbranched series of isopotential compartments composed of resistive and capacitive elements, i.e., a ladder network. Synaptic inputs are represented by realistic time-varying conductance changes. LADDER solves the set of simultaneous linear differential equations that describe this model by numerical integration in the time domain. Several tests confirmed the accuracy of LADDER's calculations. Simulated responses to current pulses were quantitatively similar to the charging transients that have been reported in hippocampal CA3 pyramidal neurons. These digital simulations also agreed closely with previously reported results from an analog neuronal model. In addition, transfer of synaptic charge in the model neuron, under both current- and voltage-clamp conditions, equalled theoretical predictions from two-port analyses of linear electrotonus. To illustrate the application of LADDER, we present the results of simulations involving the spread of voltage and current arising from various synaptic inputs.