Gammahydroxybutyrate (GHB), a product of intermediary metabolism, has profound effects on the activity of the central nervous system (CNS), particularly on consciousness. Because of its soporific effects, GHB has become both a drug of abuse and, paradoxically, a clinically useful therapeutic for treatment of the sleep disorder narcolepsy. Narcolepsy, a Rapid Eye Movement (REM) sleep-related disorder that afflicts approximately 1 in 1000 Americans, is characterized by excessive daytime sleepiness (EDS), cataplexy (a sudden loss of muscle tone triggered by emotional stimulation), and a cluster of other symptoms. Xyrem, the sodium salt of GHB, has been approved by the U.S. Food and Drug Administration for the treatment of both the cataplexy and EDS symptoms of narcolepsy. GHB facilitates slow wave activity (SWA) in the EEG and slow wave sleep (SWS), thereby consolidating nocturnal sleep and resulting in increased alertness on the subsequent day. Despite its clinical utility, the mechanism of action of GHB remains controversial with evidence for action both through GABA-B receptors and through specific GHB binding sites in the CNS. The specific goals of this project are to identify the neural substrates of GHB-induced SWA and understand the mechanism(s) underlying the therapeutic effects of GHB on narcolepsy/cataplexy. To achieve these goals, we will exploit a mouse model of narcolepsy/cataplexy in which the hypocretin (Hcrt) neurons degenerate postnatally as they do in human narcoleptics. We will follow up on our preliminary results using these hcrt/ataxin-3 mice which indicate that GHB can reduce cataplexy-like symptoms as it does in humans and test the hypothesis that these therapeutic effects are mediated through the GABA-B receptor. We will conduct functional neuroanatomical studies to test the hypothesis that GHB differentially affects behavioral state regulatory regions in hcrt/ataxin-3 mice. Based on our preliminary results in which GHB induces Fos expression in the locus coeruleus (LC), we will use the neurotoxin DSP-4 to lesion noradrenergic cells to test the hypothesis that an intact LC is necessary for the therapeutic effect of GHB. We will also conduct cellular electrophysiological studies to determine whether the intrinsic properties of the neurons in the LC or the ventrolateral preoptic area (VLPO) are affected by acute or chronic exposure to GHB. Lastly, we will evaluate whether the therapeutic efficacy of GHB is associated with brain gene expression changes. The results of the studies proposed above will enhance our understanding of the neurobiology that underlies the therapeutic activity of GHB and may also provide insights into the cellular and molecular mechanisms that underlie cataplexy and EEG SWA.
In patients with narcolepsy, a sleep disorder characterized by excessive daytime sleepiness and related symptoms, degeneration of hypocretin (Hcrt) neurons in the brain has been observed. Gammahydroxybutyrate (GHB) is a clinically useful therapeutic for treatment of the sleep disorder narcolepsy but the mechanism of action is unknown. We will exploit a mouse model of narcolepsy in which the Hcrt neurons degenerate postnatally as they do in human narcoleptics to understand how GHB is beneficial in human narcolepsy.
