[Role of the medial region of nucleus retrofacialis of the rabbit in the generation of respiratory rhythm].

The medulla of rabbits were exposed from ventral surface. When 1% procaine (0.3-1.0 microliters) was injected bilaterally through a micropipette into the medial region of nucleus retrofacialis (mNRF), the respiratory movement and phrenic rhythmical discharge could be reversibly abolished in all of 20 rabbits tested. The area related is very limited, about 1.0 x 1.0 x 1.0mm. Histological examination has shown that the effective injected area is mNRF. Discharge patterns of the respiratory-related neurons (RRNs) in mNRF of the rabbit were analyzed. The result showed that there were many E and E-I PS neurones in the mNRF. Blockade of mNRF caused continuous firing of most inspiratory and expiratory neurons recorded in the VRG and DRG and abolishment of respiratory rhythm. The minority of respiratory neurons were inactivated during apnea. Stimulation of the caudal portion of VRG and DRG during apnea could evoke only a short cluster of phrenic discharges instead of rhythmical firing, indicating that respiratory neurons located in these areas can not generate rhythmic activity themselves. The results suggest that an important area of the respiratory rhythm generators may be located in the medial region of nucleus retrofacialis.