title: Effects of sleep-wake state on the genioglossus vs.diaphragm muscle response to CO(2) in rats.
abstract: The effects of sleep on the ventilatory responses to hypercapnia have been well described in animals and in humans. In contrast, there is little information for genioglossus (GG) responses to a range of CO(2) stimuli across all sleep-wake states. Given the notion that sleep, especially rapid eye movement (REM) sleep, may cause greater suppression of muscles with both respiratory and nonrespiratory functions, this study tests the hypothesis that GG activity will be differentially affected by sleep-wake states with major suppression in REM sleep despite excitation by CO(2). Seven rats were chronically implanted with electroencephalogram, neck, GG, and diaphragm electrodes, and responses to 0, 1, 3, 5, 7, and 9% CO(2) were recorded. Diaphragm activity and respiratory rate increased with CO(2) (P < 0.001) across sleep-wake states with significant increases at 3-5% CO(2) compared with 0% CO(2) controls (P < 0.05). Phasic GG activity also increased in hypercapnia but required higher CO(2) (7-9%) for significant activation (P < 0.05). Further studies in 15 urethane-anesthetized rats with the vagi intact (n = 6) and cut (n = 9) showed that intact vagi delayed GG recruitment with hypercapnia but did not affect diaphragm responses. In the naturally sleeping rats, we also showed that GG activity was significantly reduced in non-REM and REM sleep (P < 0.04) and was almost abolished in REM even with stimulation by 9% CO(2) (decrease = 80.4% vs. wakefulness). Such major suppression of GG activity in REM, even with significant respiratory stimulation, may explain why obstructive apneas are more common in REM sleep.
authors.affiliation: Department of Medicine, University of Toronto, Toronto, Canada M5S 1A8. richard.horner@utoronto.ca
authors.forename: Richard L
authors.initials: RL
authors.lastname: Horner
authors.forename: Xia
authors.initials: X
authors.lastname: Liu
authors.forename: Harmeet
authors.initials: H
authors.lastname: Gill
authors.forename: Philip
authors.initials: P
authors.lastname: Nolan
authors.forename: Hattie
authors.initials: H
authors.lastname: Liu
authors.forename: Sandeep
authors.initials: S
authors.lastname: Sood
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000494:pharmacology*; D003964:Diaphragm / Q000187:drug effects*; D004569:Electroencephalography; D008297:Male; D009334:Neck Muscles / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012119:Respiration; D012132:Respiratory Muscles / Q000187:drug effects*; D012890:Sleep / Q000502:physiology*; D012895:Sleep, REM / Q000187:drug effects; D014059:Tongue / Q000187:drug effects*; D014630:Vagus Nerve / Q000502:physiology; D014851:Wakefulness / Q000502:physiology*
chemical_list: D002245:Carbon Dioxide