Synaptic potentials in respiratory neurones during evoked phase switching after NMDA receptor blockade in the cat
Article first published online: 22 SEP 2004
The Journal of Physiology
Volume 508, Issue 2, pages 549–559, April 1998
How to Cite
Pierrefiche, O., Haji, A., Foutz, A. S., Takeda, R., Champagna, J. and Denavit-Saubié, M. (1998), Synaptic potentials in respiratory neurones during evoked phase switching after NMDA receptor blockade in the cat. The Journal of Physiology, 508: 549–559. doi: 10.1111/j.1469-7793.1998.549bq.x
- Issue published online: 22 SEP 2004
- Article first published online: 22 SEP 2004
- (Received 3 February 1997; accepted after revision 5 December 1997)
- 1Blockade of NMDA receptors by dizocilpine impairs the inspiratory off-switch (IOS) of central origin but not the IOS evoked by stimulation of sensory afferents. To investigate whether this difference was due to the effects of different patterns of synaptic interactions on respiratory neurones, we stimulated electrically the superior laryngeal nerve (SLN) or vagus nerve in decerebrate cats before and after i.v. administration of dizocilpine, whilst recording intracellularly.
- 2Phrenic nerve responses to ipsilateral SLN or vagal stimulation were: at mid-inspiration, a transient inhibition often followed by a brief burst of activity; at late inspiration, an IOS; and at mid-expiration, a late burst of activity.
- 3In all neurones (n= 16), SLN stimulation at mid-inspiration evoked an early EPSP during phase 1 (latency to the arrest of phrenic nerve activity), followed by an IPSP in inspiratory (I) neurones (n= 8) and by a wave of EPSPs in post-inspiratory (PI) neurones (n= 8) during phase 2 (inhibition of phrenic activity). An EPSP in I neurones and an IPSP in PI neurones occurred during phase 3 (brief phrenic burst) following phase 2.
- 4Evoked IOS was associated with a fast (phase 1) activation of PI neurones, whereas during spontaneous IOS, a progressive (30-50 ms) depolarization of PI neurones preceded the arrest of phrenic activity.
- 5Phase 3 PSPs were similar to those occurring during the burst of activity seen at the start of spontaneous inspiration.
- 6Dizocilpine did not suppress the evoked phrenic inhibition and the late burst of activity. The shapes and timing of the evoked PSPs and the changes in membrane potential in I and PI neurones during the phase transition were not altered.
- 7We hypothesize that afferent sensory pathways not requiring NMDA receptors (1) terminate inspiration through a premature activation of PI neurones, and (2) evoke a late burst of phrenic activity which might be the first stage of the inspiratory on-switch.