Effects of local nerve cooling on conduction in vagal fibres shed light upon respiratory reflexes in the rabbit

In ten vagus nerves the effect of local cooling on the compound action potential was studied in the temperature range of 34 to 0-degrees-C in spontaneously breathing, anaesthetized rabbits. The mean temperature at which the myelinated (A) fibres were completely blocked, was 10.2 +/- 2.4-degrees-C (mean +/- S.D.). In nine nerves, local vagus cooling to 0-degrees-C failed to block all non-myelinated (C) fibres. In one nerve, total blocking occurred at 2.0-degrees-C. We conclude that in the rabbit, the earlier found increase in tonic activity of the diaphragm following lung inflation or deflation during bilateral local vagus cooling to a temperature between 8 and 0-degrees-C is due to afferent impulses in vagal C fibres.