High Conductance in Dendritic Function

introduction

Most of our understanding of dendritic function has come from studies in isolated preparations like brain slices.This approach has been very successful in defining the basis of dendritic excitability and identifying subunits in neurons. These in vitro recordings have not only shown the diversity of voltage-gated ion channels in dendrites, but have also mapped their distributions and revealed how their densities change during development.However, the baseline conditions in brain slices are often very different from those in the intact brain. In vivo neocortical neurons receive continuous excitatory and inhibitory postsynaptic potentials (EPSPs/IPSPs). Such an intense background activity arises from the cortical presynaptic neurons, spontaneously spiking at low rates, and it induces the postsynaptic membrane voltage to fluctuate, resulting in an irregular spike emission. Under such conditions, the biophysical awake cortical properties of the neurons are substantially altered compared to those of a neuron at rest. So observations in vitro may not directly transfer to the in vivo situations.

In this essay I’m going to argue that the research of Wolfart et al (2005) is compatible with the findings of Destexhe, Rudolph & Pare (2003).

The findings of Destexhe et al (2003)

Destexhe et al (2003) compared the electrophysiological properties of neocortical neurons in vivo and in vitro. Measurements of cortical neurons in virto reveal characteric low input resistance, depolarization, rapid and random membrane potential fluctuations and spontaneous firing (~10Hz). The cerebral cortex is very much interconnected with 5000 to 60000 synaptic contacts per pyramidal neuron. Deshexthe et al reviewed that neuron behaviour can be explained by large opposing excitatory and inhibitory synaptic currents induced by the synaptic bombardment. This intense synaptic bombardment is leading to a 'high-conductance state' that differs markedly from the conditions measured in cortical slices in vitro. Intracellularly, this state is characterized by a high conductance, due to sustained synaptic inputs, and a considerable amount of noise, due to the