A MODEL OF SIGNAL-PROCESSING AT A MAMMALIAN SYMPATHETIC NEURON

A computational model has been developed for the action potential and, more generally, the electrical behaviour of the rat sympathetic neuro ne. The neurone is simulated as a complex system in which five voltage -dependent conductances (g(Na), g(Ca), g(KV), g(A), g(KCa)) one Ca2+-d ependent voltage-independent conductance (g(AHP)) and the activating s ynaptic conductance coexist. The individual currents are mathematicall y described, based on a systematic analysis obtained for the first tim e in a mature and intact mammalian neurone using two-electrode voltage -clamp experiments. The simulation initiates by setting the starting v alues of each variable and by evaluating the holding current required to maintain the imposed membrane potential level. It is then possible to simulate current injection to reproduce either the experimental dir ect stimulation of the neurone or the physiological activation by the synaptic current flow. The subthreshold behaviour and the spiking acti vity, even during long-lasting current application, can be analysed. A t every time step, the program calculates the amplitude of the individ ual currents and the ensuing changes; it also takes into account the a ccompanying K+ accumulation process in the perineuronal space and chan ges in Ca2+ load. It is shown that the computed time course of membran e potential must be filtered, in order to reproduce the limited bandwi dth of the recording instruments, if it is to be compared with experim ental measurements under current-clamp conditions. The membrane potent ial trajectory and single current data are written in files readable b y graphic software. Finally, a screen image is obtained which displays in separate graphs the membrane potential time course, the synaptic c urrent and the six ionic current flows. The simulated action potential s are comparable to the experimental ones as concerns overshoot amplit ude and rising and falling rates. Therefore, this program is potential ly helpful in investigating many aspects of neurone behaviour. (C) 199 8 Elsevier Science B.V. All rights reserved.