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This Article Full Text Full Text (PDF) All Versions of this Article: 107/3/686    most recent 00023.2009v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map 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 Google Scholar Articles by St. John, W. M. Articles by Leiter, J. C. PubMed PubMed Citation Articles by St. John, W. M. Articles by Leiter, J. C.

Discharge of the hypoglossal nerve cannot distinguish eupnea from gasping, as defined by phrenic discharge, in the in situ mouse

Department of Physiology, Dartmouth Medical School, Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire

Submitted 12 January 2009 ; accepted in final form 26 May 2009

If normal, eupneic breathing fails, gasping is recruited. Serotonin was proposed as essential for gasping, based on findings using an in vitro mouse preparation. This preparation generates rhythmic activities of the hypoglossal nerve that are considered to be akin to both eupnea and gasping. In previous studies, gasping of in situ rat and mouse preparations continued unabated following blockers of receptors for serotonin. However, hypoglossal activity was not recorded in the mouse, and we hypothesized that its discharge during gasping might be dependent on serotonin. In the in situ mouse preparation, hypoglossal discharge had varying and inconsistent patterns during eupnea, discharging concomitant with the phrenic burst, at varying intervals between phrenic bursts, or was silent in some respiratory cycles. In eupnea, phrenic discharge was incrementing, whereas hypoglossal discharge was decrementing in 15 of 20 preparations. During ischemia-induced gasping, peak phrenic height was reached at 205 ± 17 ms, compared with 282 ± 27.9 ms after the start of the eupneic burst (P < 0.002). In contrast, rates of rise of hypoglossal discharge in gasping (peak at 233 ± 25 ms) and eupnea (peak at 199 ± 19.2 ms) were the same. The uncoupling of hypoglossal from phrenic discharge in eupnea was exacerbated by methysergide, an antagonist of serotonin receptors. These findings demonstrate that hypoglossal discharge alone cannot distinguish eupnea from gasping nor, in eupnea, can hypoglossal activity be used to differentiate neural inspiration from expiration. These findings have significant negative implications for conclusions drawn from the in vitro medullary slice of mouse.

in vitro