Combined antagonism of aminergic excitatory and amino acid inhibitory receptors in the XII nucleus abolishes REM sleep-like depression of hypoglossal motoneuronal activity.
It is hypothesized that the suppression of motor activity (atonia) that occurs during REM sleep is caused by the combined inhibition of motoneurons by glycine or GABA and withdrawal of excitation mediated by serotonin and norepinephrine. However, it is not known whether these mechanisms can fully account for the atonia. In urethane-anesthetized, paralyzed and artificially ventilated rats, REM sleep-like episodes can be repeatedly elicited by microinjections of a cholinergic agonist, carbachol, into the dorsomedial pons. We used this model to determine whether microinjections of a combination of antagonists of serotonergic, adrenergic, GABA(A) and glycinergic receptors (methysergide, prazosin, bicuculline and strychnine) into the XII nucleus can abolish the carbachol-induced depression of XII motoneuronal activity. REM sleep-like episodes were elicited prior to, and at different times after, antagonist microinjections. In all six rats studied, the depression of XII motoneuronal activity did not occur when tested 30-60 min after the antagonists, whereas other characteristic features of the response (latency, duration, the appearance of hippocampal theta rhythm, activation of the cortical EEG, slowing of the respiratory rate) remained intact. The carbachol-induced depression partially recovered after 2-3 hours. We conclude that the REM sleep-like depression of XII motoneuronal activity can be fully accounted for by all or some of the following mechanisms: a withdrawal of motoneuronal excitation mediated by norepinephrine and serotonin and increased inhibition mediated by GABA and glycine.
Fenik
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Department of Animal Biology, School of Veterinary Medicine and Center for Sleep and Respiratory Neurobiology, University of Pennsylvania, Philadelphia, PA 19104-6046, USA.
Davies
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Kubin
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D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D018674:Adrenergic Antagonists / Q000494:pharmacology; D000818:Animals; D018679:Cholinergic Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D005998:Glycine / Q000378:metabolism; D018684:Glycine Agents / Q000494:pharmacology; D007002:Hypoglossal Nerve / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009046:Motor Neurons / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D009434:Neural Pathways / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D009638:Norepinephrine / Q000378:metabolism; D011149:Pons / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism; D012702:Serotonin Antagonists / Q000494:pharmacology; D012895:Sleep, REM / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D018674:Adrenergic Antagonists; D018679:Cholinergic Agonists; D018756:GABA Antagonists; D018684:Glycine Agents; D017981:Receptors, Neurotransmitter; D012702:Serotonin Antagonists; D012701:Serotonin; D005680:gamma-Aminobutyric Acid; D005998:Glycine; D009638:Norepinephrine