The reflex latency and the level of mediation of spinal afferent impulses to the cardiovascular sympathetic neurones

Summary

Studies were carried out to determine the cause of 20–30 msec difference in latency of reflex discharges elicited by electrical stimulation of A fibres of tibial nerve and recorded in inferior cardiac and kidney nerves in anaesthetized cats. Conduction velocity of tonic and reflex induced impulses was measured in these nerves with the cross-correlation method. Cross-correlograms of potentials of both nerves have one maximum corresponding to the mean velocity of approximately 0.6 m/sec. There's no significant activity corresponding to conduction through preganglionic B fibres even after suppressing the C fibres activity with tetraethylammonium. If the recording electrodes on the inferior cardiac nerve are placed 12–18 mm nearer to the ganglion stellatum than the electrodes on the kidney nerve to the aorticorenal ganglion the reflex discharge in the former nerve appears 20–30 msec earlier than in the latter. As this difference depends on non-equal recording conditions it cannot be quoted as an argument of bulbar mediation of spinal afferent impulses to so called cardiovascular neurones.