The effect of cooling on transmission of impulses in vagal nerve fibres attached to atrial receptors in the dog.

In anaesthetized dogs, the effect of graded cooling on the transmission of the maximum frequency of impulses, evoked by supramaximal stimulation, was studied in myelinated and non-myelinated vagal fibres attached to receptors in the atria. In these fibres, it is shown that first, there is a continuous relation between the maximum frequency of transmission of impulses and vagal temperatures ranging between 37 degrees C and the temperature at complete blockade (no conduction at 0.5 impulses . s-1) for these fibres; second, there is a direct relationship between the maximum frequency of transmission of impulses and the conduction velocity. It is concluded that the maximum frequency of transmission of impulses in vagal fibres attached to atrial receptors in the dogs is related to temperature and conduction velocity. This relationship between maximum frequency of transmission and temperatures provides a quantitative explanation for the previously observed effects of cooling the vagi on the responses to stimulation of atrial receptors which were used to show that the reflex increases in heart rate and reflex reduction in activity in renal nerves involved only atrial receptors attached to myelinated vagal fibres.