Phrenic reflexes in the decerebrate and spinal rabbit.

Investigations were undertaken to study the characteristics of phrenic reflexes with partial or total elimination of the descending neuronal pathways. Experiments were performed on 17 decerebrate, vagotomized, paralysed and artificially ventilated rabbits. The experimental procedure included a midsagittal section of the medulla or a hemisection followed by a total transection of the spinal cord at C1. The effects of compression of the rostral or caudal parts of the thorax, pressure on the muscles at the lumbar level and passive movements of the hindlimb were studied on the efferent vagal and phrenic neurograms. Partial elimination of the descending pathways evoked an increase in the intensity of the spinal reflexes. Characteristics of the reflexes which we have obtained after lesions of the medulla or spinal cord enable us to search for their central path. After transection of the spinal cord, no sustained phasic phrenic nerve activities were observed. The results suggest that after high cordotomy the phrenic motoneuronal pool has a potential capability for generating phasic bursts and additional inputs are required for their development.