Phrenicotomy alters phrenic long-term facilitation following intermittent hypoxia in anesthetized rats

M. S. Sandhu, K. Z. Lee, Ralph F Fregosi, D. D. Fuller

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

Intermittent hypoxia (IH) can induce a persistent increase in neural drive to the respiratory muscles known as long-term facilitation (LTF). LTF of phrenic inspiratory activity is often studied in anesthetized animals after phrenicotomy (PhrX), with subsequent recordings being made from the proximal stump of the phrenic nerve. However, severing afferent and efferent axons in the phrenic nerve has the potential to alter the excitability of phrenic motoneurons, which has been hypothesized to be an important determinant of phrenic LTF. Here we test the hypothesis that acute PhrX influences immediate and long-term phrenic motor responses to hypoxia. Phrenic neurograms were recorded in anesthetized, ventilated, and vagotomized adult male rats with intact phrenic nerves or bilateral PhrX. Data were obtained before (i.e., baseline), during, and after three 5-min bouts of isocapnic hypoxia. Inspiratory burst amplitude during hypoxia (%baseline) was greater in PhrX than in phrenic nerve-intact rats (P < 0.001). Similarly, burst amplitude 55 min after IH was greater in PhrX than in phrenic nerve-intact rats (175 ± 9 vs. 126 ± 8% baseline, P < 0.001). In separate experiments, phrenic bursting was recorded before and after PhrX in the same animal. Afferent bursting that was clearly observable in phase with lung deflation was immediately abolished by PhrX. The PhrX procedure also induced a form of facilitation as inspiratory burst amplitude was increased at 30 min post-PhrX (P = 0.01 vs. pre-PhrX). We conclude that, after PhrX, axotomy of phrenic motoneurons and, possibly, removal of phrenic afferents result in increased phrenic motoneuron excitability and enhanced LTF following IH.

Original languageEnglish (US)
Pages (from-to)279-287
Number of pages9
JournalJournal of Applied Physiology
Volume109
Issue number2
DOIs
StatePublished - Aug 2010

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Diaphragm
Phrenic Nerve
Motor Neurons
Hypoxia
Axotomy
Respiratory Muscles
Axons
Lung

Keywords

  • Axotomy
  • Phrenic motoneurons
  • Plasticity

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)
  • Medicine(all)

Cite this

Phrenicotomy alters phrenic long-term facilitation following intermittent hypoxia in anesthetized rats. / Sandhu, M. S.; Lee, K. Z.; Fregosi, Ralph F; Fuller, D. D.

In: Journal of Applied Physiology, Vol. 109, No. 2, 08.2010, p. 279-287.

Research output: Contribution to journalArticle

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