Elsevier

Brain Research

Volume 505, Issue 1, 25 December 1989, Pages 12-22
Brain Research

Research report
Effects of uniform and non-uniform synaptic ‘activation-distributions’ on the cable properties of modeled cortical pyramidal neurons

https://doi.org/10.1016/0006-8993(89)90110-8Get rights and content

Abstract

Knowledge of the resting potential and input resistance reveal little about the electronic structure of nerve cells since that structure is governed by the background distribution of activated conductances. The background distribution of activated conductances (or ‘activation-distribution’) is commonly assumed to be uniform, but there is much evidence to suggest that the ‘activation-distribution’ of cortical pyramidal cells is non-uniform. We investigated effects of uniform and non-uniform activation-distributions with simulations employing passive cable models of an HRP-injected cortical pyramidal neuron. The consequences of 5 different activation-distributions on the effectiveness of synaptic inputs and the electrophysiological properties of the neuron were compared. With non-uniform activation-distributions, (i) the resting membrane potential was non-uniform (with differences of 10–15 mV or more found between soma and distal dendrites), (ii) the electrotonic distances to distal synapses were smaller than with a uniform distribution, and (iii) a two-fold range of variation was seen in the effectiveness of distal synaptic inputs. Differences in time constants, τ0 and τ1, obtained from an analysis of transients and in electrotonic length, L, were also found with different activation-distributions. These differences were difficult to assess due to the inherent difficulty in estimating τ1 (as demonstrated here) and the inappropriateness of the usual formular for L for these cells. Reducing afferent activity (as might happen in tissue slice) increased the effectiveness of distal inputs and reduced the differences in resting potential seen in the neuron. It is concluded that the effectiveness of synaptic inputs and the electrophysiological properties of a neuron can be quite different when the activation-distribution is non-uniform rather than uniform.

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