Inhibition of renal nerve discharge by liminal stimulation of non-myelinated aortic afferents

The pattern of inhibitory responses of sympathetic nerve discharge to liminal activation of aortic C-fibres was studied in rabbits. The animals were anaesthetized with urethane and chloralose and vagotomized. Sympathetic postganglionic discharge was recorded from single fibres of the renal nerve. Inhibitory responses were elicited by single shocks or short trains (2-5 shocks at 10 Hz) and assessed from peri-stimulus time histograms. Clear-cut inhibition of the sympathetic discharge was observed in 6 out of 10 fibres. It was evoked by one shock in 5 fibres and by two shocks in 1 fibre. The mean latency of the inhibitory response elicited by one shock was 318 +/- 18 ms and its duration amounted to 196 +/- 22 ms (mean +/- SE). The increase in the number of shocks prolonged the duration of the inhibitory response without markedly affecting their latency.