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Sleep-wake cycles: EEG • Wakefulness: fast, low voltage and desynchronized electrical activity (bwaves) • Sleep: progressively slower, higher voltage and more synchronized electrical activity of the cortex (awaves) • REM-sleep: partial arousal without wakefulness characterized by desynchronized electrical cortical activity, rapid eye movement loss of muscle tone, erection and dreaming Sleep –wake cycle: clinical observation 1st World war Encephalitis lethargica (« spanische Grippe ») • Von Economo’s observations – Lesions in the basal forebrain and lateral preoptic area » Prolonged wakefulness, insomnia – Lesion in the posterior, lateral hypothalamus and midbrain » Patients sleep for weeks http://www.youtube.com/watch?v=puJCjUsgq7o&feature=related Sleep-wake cycle: experimental work – Diencephalon basal forebrain and mid-rostral brain stem express two, stable firing states to produce rest or arousal (flip-flop) Lesions and electrical stimulation • Sleeping centers Ventrolateral preoptic nucleus – Sleep active neurons in the lateral preoptic area • VLPO neurons c-FOS positive during sleep – Use the neurotransmitter GABA and galanin – Lesions provoke loss of 70% of non-REM and REM-sleep Initiation of sleep is driven by the VLPO Sleep active neurons (c-FOS) Galanin-positive neurons Sleep-wake cycles: experimental work Most belong to the « ascending reticular activating system » of Moruzzi and Magoun • Wake centers – Wake active neurons in monoaminergic nuclei • Monoaminergic nuclei: locus coeruleus, dorsal raphe • Cholinergic: laterodorsal tegmental nucleus (LDTG) and basal nucleus of Meynert • Histaminergic: tuberomammillary nucleus – Wake promoting peptidergic neurons in LHA • Hypocretin cells in the lateral hypothalamus stimulate the center of the ascending reticular system, thus contributing to wakening – Hypocretin defect – narcolepsy (sudden sleep attacks), fall in REM-sleep Sleep-wake cycle: summary Wakefulness NREM-sleep Sleep-wake cycle: summary REM-sleep Sleep-wake cycles: the hypocretin system a success story of genomic based biology • Gautwick et al. (1996): subtractive hybridization aimed at identifying mRNA’s species that are expressed only in discrete nuclei within the hypothalamus – New hypothalamic mRNA (hypocretin 1 and 2) found by in-situ hybridization to occur in the lateral hypothalamus • Sakurai et al. (1998) transfected cell lines that stably express each of the 50 orphan GPCRs and then measured Ca2 + fluxes – Identified the hypocretin 1 and 2 receptors • Genetic linkage studies in Doberman Pinschers with narcolepsy (1999) – The defective canine gene encodes the hypocretin 2 receptor http://www.youtube.com/watch?v=Jhw6ahl_XaI Sleep-wake cycles: the hypocretin system • Narcolepsy: autoimmune disease, 1:2’000 people • excessive daytime sleepiness • cataplexy (muscle weakness precipitated by strong emotions (laughter or surprise) • sleep paralysis • hypnagogic hallucinations • Hypocretin receptor KO mice – Cataplexic attacks – More time spent in REM-sleep http://www.youtube.com/watch?v=Jhw6ahl_XaI Sleep-wake cycles: the hypocretin system Anatomo-physiological studies • Hypocretin contained in dense core vesicles • Projections from the lateral hypothalamus to various nuclei involved in arousal • Hypocretins are excitatory peptides Sleep-wake cycles: the hypocretin system • Human narcolepsy (2000) – Hypocretin undetectable in 37 of 42 narcoleptic – Few or none hypocretin neurons in the hypothalamus at autopsy – One patient with a mutation in the hypocretin gene Hypocretin opposes REM sleep