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Episodic hypoxia evokes long‐term facilitation of genioglossus muscle activity in neonatal rats
Author(s) -
McKay Leanne C.,
Janczewski Wiktor A.,
Feldman Jack L.
Publication year - 2004
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2004.064006
Subject(s) - hypoxia (environmental) , genioglossus , facilitation , medicine , neuroscience , term (time) , cardiology , psychology , chemistry , physical medicine and rehabilitation , electromyography , oxygen , organic chemistry , physics , quantum mechanics
The aim of this study was to determine if episodic hypoxia evokes persistent increases of genioglossus muscle (GG) activity, termed long‐term facilitation (LTF), in neonatal rats in vivo . Experiments were performed on anaesthetized, spontaneously breathing, intubated neonatal rats (postnatal days (P) 3–7), divided into three groups. The first group ( n = 8) was subjected to three 5‐min periods of hypoxia (5% O 2 –95% N 2 ) alternating with 5 min periods of room air. The second group ( n = 8) was exposed to 15 min of continuous hypoxia. The third ( n = 4) group was not exposed to hypoxia and served as a control. GG EMG activity and airflow were recorded before, during and for 60 min after episodic and continuous hypoxic exposure. During hypoxia, GG EMG burst amplitude and tidal volume ( V T ) significantly increased compared to baseline levels (episodic protocol: mean ± s.e.m ; 324 ± 59% of control and 0.13 ± 0.007 versus 0.09 ± 0.005 ml, respectively; continuous protocol: 259 ± 30% of control and 0.16 ± 0.005 versus 0.09 ± 0.007 ml, respectively; P < 0.05). After the episodic protocol, GG EMG burst amplitude transiently returned to baseline; over the next 60 min, burst amplitude progressively increased to levels significantly greater than baseline (238 ± 40% at 60 min; P < 0.05), without any significant increase in V T and respiratory frequency ( P > 0.05). After the continuous protocol, there was no lasting increase in GG EMG burst amplitude. We conclude that LTF of upper airway muscles is an adaptive respiratory behaviour present from birth.