Integrative effects of general anaesthetics: why nerve axons should not be ignored.

The effects of low and clinically relevant concentrations of inhalation anaesthetics and related compounds on the firing behaviour of nerve axons from a number of species are described. The observation of substantial, if sometimes transient, changes in excitability is contrasted with the view that axonal ion channels are insensitive to many general anaesthetics. Taking the squid giant axon as a well-studied example, we show that a full understanding of these effects can only be achieved through a detailed investigation of the actions of a range of compounds on a number of ion channels. Small alterations in the properties of individual channel types can in combination result in major changes in the behaviour of a multi-channel system such as an axon. Finally, as an example of the spectrum of activity of structurally related compounds, we compare the effects of inhalation anaesthetics with those of volatile convulsants.