The Sleep Promoting Effect Of Dexmedetomidine And Its Regulation Mechanism On Rapid Eye Movement(REM) Sleep

Dexmedetomidine（DEX）is the dextroisomer of medetomidine,anα₂-adrenergic receptor（α₂-AR）agonist.It works by binding toα₂-AR and activating G protein,which opens K⁺channels,causing hyperpolarization of the cell membrane and producing sedative and analgesic effects.α₂-AR is widely distributed in various neurons in the brain,including cholinergic neurons in the pedunculopontine tegmentum（PPT）that initiate and maintain rapid eye movement（REM）sleep.Our previous exploratory experiments found that DEX differs from most hypnotic drug in that it promotes slow-wave sleep（SWS）and meanwhile reduce REM sleep persistently.This result is consistent with an earlier study that showed mice given oral DEX had the same effect,but the mechanism by which DEX reduces REM sleep is still unclear.Consequently,we propose the hypothesis that DEX may inhibit REM sleep by suppressing cholinergic neurons in the PPT which carryα2-AR.This study aims to reveal the characteristics of DEX sleep-promoting effects and the possible mechanisms for regulating REM sleep.Methods:To test this hypothesis,microinjection of the cholinergic agonist carbachol into the PPT is used to induce a REM sleep model.We constructed a cat sleep-wake recording system,used MRI to determine the stereotaxic parameters of the lateral geniculate nucleus（LGN）,hippocampus（Hipp）,and PPT,and analyzed electroencephalogram（EEG）,LGN and Hipp EEG,electromyogram（EMG）,and electrooculogram（EOG）to assess wakefulness（W）,light slow-wave sleep（SWS1）,deep slow-wave sleep（SWS2）,and REM sleep phases.We analyzed changes in sleep-wake phase,sleep structure,and EEG power spectra after different doses of DEX administered by intramuscular injection（i.m.）over a 24-hour period to explore their effects on different sleep-wake phases.We used immunofluorescence to label cholinergic neurons andα_2A-AR in the PPT and analyzed the distribution of cholinergic neurons carryingα_2A-AR to provide anatomical evidence for DEX’s pharmacological effects.We also used microinjections of DEX,carbachol,and carbachol combined with DEX（i.m.）to explore the possible mechanisms by which DEX inhibits REM sleep.Results:（1）Compared with saline,DEX doses of 2.5,5,and 10μg/kg（i.m.）respectively increased mainly SWS1 by 4.5%（p>0.05）,34.7%（p<0.05）,and 85.3%（p<0.001）and delta（0.5-4 Hz）and alpha（9-14 Hz）frequency range power spectra on EEG,while decreased REM sleep by 40.7%（p<0.001）,60.6%（p<0.001）,and 75.2%（p<0.001）and the theta（4.5-9 Hz）frequency range power spectra.Sleep structure analysis found that the increase in SWS was due to a shorter latency and longer average duration of sleep episodes,while the decrease in REM sleep was due to a longer latency and reduction of REM episodes.（2）Double immunofluorescence labeling and statistical analysis showed that88.5±1.94%of cholinergic neurons in the PPT carryingα_2A-AR.（3）Compared with saline,injection of DEX（4μg/0.5μl）into the PPT caused a33.57%reduction in REM sleep for 6 hours（p<0.01）,and sleep structure analysis showed that DEX prolonged the REM sleep latency and reduced the number of REM episodes.Injection of carbachol（1μg/0.5μl）into the PPT caused a sustained increase in REM sleep for 12 hours and an increase in the theta band power spectrum,but co-administration of DEX and carbachol could inhibit carbachol-induced REM sleep.Conclusion:DEX produces a sleep-promoting effect characterized by an increase in slow wave sleep and a decrease in REM sleep.Most cholinergic neurons in the PPT carryα_2A-AR,and DEX acts on the PPT to inhibit REM sleep and antagonize PPT cholinergic activity-induced REM sleep caused by carbachol,suggesting that DEX can exert its inhibitory effect on REM sleep by suppressing PPT cholinergic neurons.