| Abstract: | The characteristics of 40 C-fibres arising from the aortic arches of 15 normotensive rabbits have been investigated. The conduction velocity of the fibres varied between 0.5-1.8 m/s (0.91±0.05, mean ± S.E.). The activation threshold for all the fibres lay between 70–140 mmHg. 32 medullated fibres from the same animals had thresholds between 35 and 90 mmHg. After correction for the time delay in conduction the firing in the C-fibres occurs in early systole. Pressure response curves were constructed for 10 medullated and 18 C-fibres. The mean activity at 100 mmHg was, for the C-fibres 5.0 Hz and for the medullated fibres 34 Hz. At 130 mmHg the activity in the C-fibres was 13 Hz and in the medullated fibres 68 Hz. Thus C-fibres from the aortic baroreceptor regions are activated at higher pressures than the medullated fibres and have lower discharge frequencies. Noradrenaline did not influence the pressure response curves of the C-fibres. It is concluded that the arterial baroreceptor C-fibres may exert a weak tonic influence on the vasomotor centre at normal pressures but are likely to be of greater importance when the arterial pressure rises acutely. |
