Descending respiratory pathways in the medulla oblongata of the cat1

Abstract

Midsagittal sections of the medulla oblongata, extending between levels 3–4 mm caudal to 2–6 mm rostral to the obex, were made in 29 midcollicular decerebrate cats. Respiratory activity was recorded by monitoring spontaneous ventilatory movements in cats breathing air or phrenic nerve potentials in cats immobilized with gallamine and artificially ventilated with 95% O₂-5% CO₂. Midline sections produced definite changes in the rate and depth of respiration and of the phrenic nerve discharge, but cessation of respiratory activity was not usually seen. Despite these alterations in the spontaneous nerve activity, it was possible to elicit, with stimulation of a point in the medullary reticular formation, a marked sustained discharge of the homolateral phrenic nerve. The changes in the spontaneous respiratory pattern probably resulted from disturbances of the neural structures responsible for the genesis of rhythmic respiration rather than of the motor pathways. It is concluded that the efferent respiratory pathways descend from the medulla oblongata into the spinal cord predominantly uncrossed.