Firing rate may be a determinant of nerve fibre vulnerability in axonopathies.

Analysis of the discharge characteristics and conduction velocities of single vagal nerve fibres innervating slowly adapting mechanoreceptors in the oesophagus and lungs of acrylamide affected dogs has demonstrated that a group of fibres, the fastest conducting fibres to each organ, fail to conduct. The two failed groups have conduction velocities which are grossly different and yet they have a common receptor type, they have a similar fibre length and they have the same central nervous system destination. Amongst the oesophageal fibres, the failed group with conduction velocities in the upper third of the control range had firing rates which were normally higher than those of the surviving slower conducting fibres (P less than 0.01). The same observation applied to the respiratory fibres (P less than 0.05). It is possible that firing rate is also a factor in predicting the vulnerability of axons in axonopathies.