Variations in nuchal muscle tonus following paradoxical sleep deprivation in the rabbit

Although tonic inhibition of nuchal or facial musculature is considered an intrinsic component of paradoxical sleep (PS) in mammals, this inhibition is either absent or greatly attenuated in the rabbit. To further explore the characteristics of this phenomenon in this species, variations in quantified nuchal muscle activity were examined before, during and following 24 h of PS deprivation. It was postulated that if the substrate for PS-associated tonic electromyogram (EMG) inhibition is present, this procedure--which is known to affect both tonic and phasic components of PS--might enhance such inhibition. For these investigations chronically implanted rabbits (electroencephalographic, eye movement and nuchal muscle placements) were recorded continuously for 5 consecutive days (two day baseline, one day deprivation, two day recovery). Muscle activity was quantified by resetting integration techniques and comparisons made of activity levels before, during and after PS episodes across conditions. The deprivation procedure significantly reduced the amount of PS relative to baseline values, and a significant PS increase (rebound) occurred during postdeprivation recordings. Across-condition EMG-related effects included the corroboration of previous reports of an absence of nuchal atonia during PS, a significant diurnal variation in EMG activity--with greater activity occurring during the dark portion of the light-dark cycle, and enhanced activity immediately following PS episodes relative to either pre-PS or PS levels. Deprivation-related changes in quantified EMG activity included a pre-PS decrease during both the last 12 h of deprivation and the initial 12 h of recovery sleep, and an enhancement of EMG activity during PS.(ABSTRACT TRUNCATED AT 250 WORDS)