0200 DIRECT ACTIVATION OF G-PROTEIN-COUPLED INWARD RECTIFYING K+ CHANNELS PROMOTE SLEEP IN RODENTS

Abstract

The most common type of sleep disorder is insomnia which is characterized by difficulty falling asleep and/or maintaining sleep. Chronic insomniacs respond poorly to current treatments including benzodiazepines and non-benzodiazepines. Activation of G-protein-gated inward rectifying K channels (GIRKs) by GABAB agonists baclofen or γ-hydroxybutyric acid (GHB) predominantly promote non-rapid eye movement (NREM) sleep in rodents and humans. GHB especially reduces sleep fragmentation in narcoleptic patients. The present study explored the link between direct GIRK activation and sleep regulation in rodents using our potent and selective GIRK channel activator ML297. Whole-cell patch clamp recordings from hypocretin/orexin-EGFP neurons and extracellular recordings of mouse hippocampal CA1 area in mouse brain slices were made to study cellular and synaptic actions of ML297. Wake activity and locomotion were measured using the noninvasive behavior monitoring system SmartCageTM. Furthermore, wakefulness, REM and NREM sleep were determined using the electroencephalogram/electromyogram (EEG/EMG) in wild type mice (C57BL/C) implanted with electrodes. Bath-application of ML297 (5µM) hyperpolarized resting potential, decreased membrane input resistance and blocked spontaneous firing of action potentials in hypocretin/orexin neurons. These actions were reversed after prolonged washout. ML297 (5–50µM) produced no significant effects on normal synaptic activity measured by input-output of field postsynaptic excitatory potentials and an evoked single population of spikes in the hippocampal CA1 area, suggesting ML297 principally causes long-lasting postsynaptic inhibition. Using our noninvasive SmartCageTM system we observed that ML297 (30mg/kg, i.p.) caused a prolonged inhibition of wake activity and locomotion in mice. The EEG/EMG recordings confirmed that ML297 (30mg/kg, i.p.) significantly decreased wakefulness and revealed an increase in NREM sleep without affecting REM sleep in mice. The present study for the first time has demonstrated that direct action of GIRK produces similar sleep regulation to GABAB receptor-mediated modulation. Since GIRKs channels are predominantly expressed in principal excitatory neurons, inhibition of neuronal excitability and depression of the arousal system may powerfully modulate sleep. Direct GIRK activators may present an innovative approach for treatment of chronic insomnia as well as other sleep disorders. This work was supported by NIH grants: R42 HL084990, R44 AG043203, and R44 NS086343.