NMDA receptor-mediated inspiratory off-switching in pneumotaxic-disconnected cats

The pneumotaxic center is thought to govern inspiratory off-switching (IOS) , and blockade of N-methyl-D-aspartate (NMDA) receptors by dizocilpine impa irs IOS causing apneusis. The present study is to examine whether the NMDA receptor-mediated IOS mechanism functions in the medullary respiratory netw ork after disconnecting the pneumotaxic center. In decerebrate and vagotomi zed cats, the nucleus parabrachialis medialis (NPBM) and vagus nerves were stimulated to evoke IOS and a dorsal pontine transection was performed whil e the central respiratory activity was recorded in phrenic neurogram. The t ransection eliminated the NPBM-stimulated IOS but not the vagally evoked IO S, and developed two types of respiration; eupnea in 12 and apneusis in six out of Is cats. Apneustic respiration was not changed into eupneic one by changing the end-tidal CO2 level. In animals displaying eupnea after the tr ansection, dizocilpine (0.3 mg/kg i.v.) produced apneusis, characterized by a prolonged inspiration, a shortened stage 1 expiration and an unchanged s tage 2 expiration. Dizocilpine caused no further change in the apneustic pa ttern induced by the transection. The present results suggest that the medu llary respiratory network is able to generate a eupneic respiration after d isconnecting the pontine pneumotaxic center, and the NMDA mechanism plays a n important role in the medullary respiratory network. (C) 1998 Elsevier Sc ience Ireland Ltd. ALI rights reserved.