The mechanism(s) of increasing respiratory rate during locomotor‐like activity

It is well known that respiratory rate is affected by afferent inputs from the peripheral chemoreceptors sensing P PO2 through the cranial nerve such as N. IX and X, and that there is a morphological connectivity between the brainstem and lower spinal cord. However, it is unclear whether there is a central pathway that contributes to change respiratory rate during locomotor‐like activity. We employed the decerebrated and arterially perfused in situ preparation to examine it with electrophysiological techniques. It was found that the modulated sympathetic tone, hyperoxia/normocapnea, can activate the locomotor pattern generator via descending pathways and induce locomotor‐like activity in the hindlimb. Although the entrainment of respiratory and locomotor rhythms was observed once locomotor‐like activity is evoked in the hindlimb, we discovered that the locomotor rhythm originating in the lower spinal cord is transmitted to the brainstem via ascending pathways and entrains the respiratory rhythm, indicating that the central mechanism(s) of entrainments of respiratory and locomotor rhythms is the spinal feedback mechanism. From the above, it was suggested that the increase of respiratory rate during locomotor‐like activity is caused by not only the afferent input via the cranial nerve but also the activated spinal cord inducing locomotor‐like activity via ascending pathways. Supported by NINDS/NIH.