Differential effect of sleep-wake states on lingual and dorsal neck muscle activity in rats

Postural tone is reduced during slow-wave sleep (SWS) and absent during rapid eye movement sleep (REMS). In obstructive sleep apnea subjects, upper airway dilating muscles, including those of the tongue, show a similar pattern; this contributes to sleep-related airway obstructions. However, in healthy subjects, state-dependent changes in the activity of pharyngeal muscles are variable. In seven chronically instrumented Sprague-Dawley rats, an animal model used to study sleep and sleep-disordered breathing, we quantified lingual and postural muscle activity across the sleep-wake states by measuring the root mean square levels of the electromyograms (EMG) in successive 10 s intervals collected during 2 h of recording at a constant circadian time (1-3 p.m.). The nuchal EMG was low and steady during SWS and further reduced with occasional twitches during REMS. In contrast, the mean lingual EMG during SWS was only 5.9 ± 1.6% (S.E.) of its mean in wakefulness, and during REMS, it increased to 46 ± 15% (S.E.) (p < 0.03) due to the appearance of phasic bursts, the intensity of which progressively increased. The lingual and nuchal activities also had different time courses during state transitions. In obstructive sleep apnea subjects, the sleep-wake changes in the activity of pharyngeal muscles may become similar to those in postural muscles as a result of pharyngeal tone adaptations to the disorder.