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Phrenic motoneuron rate‐coding and recruitment during long‐term facilitation
Author(s) -
Lee Kun-Ze,
Fuller David D.
Publication year - 2012
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.26.1_supplement.704.6
Subject(s) - phrenic nerve , hypoxia (environmental) , facilitation , intermittent hypoxia , medicine , anesthesia , respiratory system , neuroscience , biology , chemistry , organic chemistry , oxygen , obstructive sleep apnea
Intermittent hypoxia can elicit a progressive and long‐lasting enhancement of phrenic motor output known as long‐term facilitation (LTF). We hypothesized that phrenic LTF occurs due to rate‐coding of previously active phrenic motoneurons (PMNs) and recruitment of previously silent PMNs. A ″single fiber″ phrenic nerve recording technique was used to characterize PMN firing in anesthetized, vagotomized and mechanically ventilated adult rats. PMNs were classified as early‐inspiratory (Early‐I) or late‐inspiratory (Late‐I) based on their discharge onset relative to contralateral phrenic nerve activity during hyperoxic normocapnic baseline conditions. Consistent with prior reports, acute hypoxia increased the discharge frequency (i.e., rate coding) of both Early‐I and Late‐I PMNs and also caused recruitment of previously silent PMNs. During a 45–60 min period following intermittent hypoxia (3–5 brief hypoxic episodes), Late‐I but not Early‐I PMNs showed a progressive enhancement of discharge frequency. In addition, we noted a previously silent PMN that was recruited at ~45 min post‐episodic hypoxia. These preliminary results are consistent with the hypothesis that phrenic LTF is differentially expressed across phenotypically‐defined PMN subtypes. We suggest that the capacity for plasticity may be greater in Late‐I and silent PMNs compared to those cells activated early in the inspiratory effort.