Is there electrical coupling between phrenic motoneurons in cats?

The possibility of electrical coupling between phrenic motoneurons was studied in anesthetized cats. In animals with C4-C7 dorsal roots cut (spinal cord intact), no sign of short-latency increase in the firing probability was observed in one phrenic rootlet following stimulation of the other phrenic rootlet. Intracellular recording from 21 phrenic motoneurons, in cats spinalized at the C1 segment, revealed no graded, short-latency antidromic depolarizations, even when the collision technique was used. Conditioning depolarizations of the impaled motoneurons never resulted in an increase of cell firing following test antidromic activation of adjacent motoneurons. It is concluded that the short-term discharge synchronization, observed within the phrenic nucleus by other authors, must be due to the action of chemical synapses.