Studies on the inspiratory generating effect of the dorso-medial area of nucleus facialis.

The responses in phrenic nerve activity resulting from stimulation and successive focal block of the dorso-medial area of nucleus facialis (dmNF) were studied in urethane anaesthetized rabbits. It was found that: (1) Long train stimulation (0.025-0.2 mA, 100 Hz) delivered to the dmNF caused marked prolongation in inspiratory duration and distinct increase in amplitude of phrenic discharge. Continuous inspiration with increased amplitude was usually observed during stimulation. (2) Short train stimulation (10 pulses, 100 Hz, 0.025-0.2 mA) during inspiration increased the duration and amplitude of inspiration. When the short train stimulation was delivered during expiration, inspiration would be initiated prematurely. (3) Microinjection of L-glutamate (0.5 M, 0.5-2 microliters) into the dmNF also increased inspiratory duration and amplitude. (4) Focal block of the dmNF by microinjection of lidocaine (2%, 1-2 microliters) produced strong depression or complete cessation of inspiration. In conclusion, the results of the present study show that the dmNF may play an important role in the neurogenesis of respiratory rhythm.