Intercostal and Cerebellar Influences on Efferent Phrenic Activity in the Decerebrate Cat

The intercostal‐to‐phrenic reflex connections, previously studied only in spinal preparations, have now been further analyzed in decerebrate cats and rabbits. The early excitatory part of the response was of the same nature as the corresponcling response component in spinal preparations. The subsequent inhibitory phase was due both to post‐firing depression, as in the spinal state, and to active inhibition. The responses in decerebrate animals showed marked respiratory variations with almost complete abolishment of the excitatory component in the end‐expiratory phase. In the decerebrate preparation the responses from the different portions of the diaphragm showed qualitative differences which disappeared after spinalization. Further signs of differentiated intercostal‐to‐phrenic relations were obtained by stimulating different intercostal nerves. Stimulation of the anterior lobe of cerebellum exerted pronounced effects both on the respiratory phrenic activity–inhibition, sometimes followed by post‐tetanic facilitation–and on the intercostal‐to‐phrenic reflex–removing the inhibition in the end‐expiratory phase. Some of the features of the synaptic organization of the phrenic nucleus are discussed.