Abstract: ObjectiveTo observe the projections from respiratory neurons of medulla oblongata to the motor neuron pool of phrenic nerve in rat. MethodsBy using horseradish peroxidase (HRP) retrograde tracing technique after injecting HRP into phrenic nerve, retrograde labelled neurons were found in C₃-C₅ segment. Then, HRP was injected into the area where the phrenic motor neurons occupied, retrograde labelled neurons were found in medulla oblongata. ResultsPhrenic motor neurons locate in the C₃-C₅ segment ipsilaterally, occuping the intermediate portion of anterior horn and appearing typical motor neurons. Retrograde labelled neurons were found bilaterally in medulla oblongata, the neurons were located in nucleus retroambigualis (RNA), ventramedial area to nucleus retrofacialis (NRF). ConclusionThe phrenic motor neurons may receive direct projection of respiratory neuron in medulla oblongata, the projecting neurons are distributed in RNA and NRF area.

Key words: horseradish peroxidase (HRP), rat, phrenic motor neuron, medulla oblongata, respiratory neuron, nucleus retroambigualis (RNA), nucleus retrofacialis (NRF)