Factors affecting the cat carotid chemoreceptor and cervical sympathetic activity with special reference to passive hind-limb movements.

1. Recordings have been made of the activity in carotid body chemoreceptor afferent fibres and in the cervical sympathetic of the cat during passive movement of the hind limbs.2. The chemoreceptor activity increases immediately the limbs are moved and is maintained at a raised level with preservation of the chemoreceptor rhythm fluctuations throughout. In some cases, the increase persists for a time after the movements are stopped.3. This early change does not occur if the cervical sympathetic on the same side as the carotid body from which recordings are made is cut, nor does it occur if the femoral and sciatic nerves are cut.4. The carotid artery oxygen tension (P(a, O2)) increases early; in the majority of experiments, there was no significant change in end-tidal P(CO2) although the minute volume of ventilation (V) increased by about 20% of control with passive movement of the hind limbs.5. Passive movement of the hind limbs also causes an immediate rise in cervical sympathetic activity which is sustained, and which is abolished if the femoral and sciatic nerves are cut.6. Electrical stimulation of the cervical sympathetic causes an increase in chemoreceptor afferent discharge.7. Bilateral cervical sympathectomy causes the respiratory lag to increase from approximately 1 sec to some 20 sec and, when passive movements cease, the fall in V is more sluggish than control.8. These results are discussed in the light of the controversy regarding humoral and neurogenic causes for the increase in respiration in exercise.