Phrenic-to-phrenic inhibition and excitation in spinal cats

In decerebrate, C2-spinalized cats, stimulation of the C6-phrenic root produces a weak activation of phrenic motoneurons in the adjacent C5 segment in a few animals (23%). When phrenic motoneurons are electrically excited by testing stimulation applied to the spinal cord or internal intercostal nerve, the evoked responses recorded in a cervical phrenic root are partly inhibited by conditioning stimulation applied to another ipsilateral or contralateral cervical phrenic root. We therefore conclude that phrenic fibers exert both inhibitory and excitatory effects on adjacent phrenic motoneurons in the cervical spinal cord.