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This Article Full Text Full Text (PDF) All Versions of this Article: 89/6/727    most recent expphysiol.2004.028829v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by St.-John, W. M Articles by Leiter, J. C Search for Related Content PubMed PubMed Citation Articles by St.-John, W. M Articles by Leiter, J. C Related Collections Respiratory

¹ Department of Physiology, Dartmouth Medical School, Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756, USA ² Department of Physiology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK

During eupnoea, rhythmic motor activities of the hypoglossal, vagal and phrenic nerves are linked temporally. The inspiratory discharges of the hypoglossal and vagus motor neurones commence before the onset of the phrenic burst. The vagus nerve also discharges in expiration. Upon exposure to hypocapnia or hypothermia, the hypoglossal discharge became uncoupled from that of the phrenic nerve. This uncoupling was evidenced by variable times of onset of hypoglossal discharge before or after the onset of phrenic discharge, extra bursts of hypoglossal activity in neural expiration, or complete absence of any hypoglossal discharge during a respiratory cycle. No such changes were found for vagal discharge, which remained linked to the phrenic bursts. Intracellular recordings in the hypoglossal nucleus revealed that all changes in hypoglossal discharge were due to neuronal depolarization. These results add support to the conclusion that the brainstem control of respiratory-modulated hypoglossal activity differs from control of phrenic and vagal activity. These findings have implications for any studies in which activity of the hypoglossal nerve is used as the sole index of neural inspiration. Indeed, our results establish that hypoglossal discharge alone is an equivocal index of the pattern of overall ventilatory activity and that this is accentuated by hypercapnia and hypothermia.

(Received 16 August 2004; accepted after revision 27 August 2004; first published online 13 September 2004)
Corresponding author W. M. St.-John: Department of Physiology, Dartmouth Medical School, Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756, USA. Email: walter.m.stjohn{at}dartmouth.edu

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