Sleep is regulated by a homeostatic process that determines its need and by a circadian process that determines its timing. By using sleep deprivation and transcriptome profiling in inbred mouse strains, we show that genetic background affects susceptibility to sleep loss at the transcriptional level in a tissue-dependent manner. In the brain, Homer1a expression best reflects the response to sleep loss. Timecourse gene expression analysis suggests that 2,032 brain transcripts are under circadian control. However, only 391 remain rhythmic when mice are sleep-deprived at four time points around the clock, suggesting that most diurnal changes in gene transcription are, in fact, sleep-wake-dependent. By generating a transgenic mouse line, we show that in Homer1-expressing cells specifically, apart from Homer1a, three other activity-induced genes (Ptgs2, Jph3, and Nptx2) are overexpressed after sleep loss. All four genes play a role in recovery from glutamate-induced neuronal hyperactivity. The consistent activation of Homer1a suggests a role for sleep in intracellular calcium homeostasis for protecting and recovering from the neuronal activation imposed by wakefulness.homeostasis ͉ microarray ͉ mRNA tagging ͉ sleep deprivation ͉ sleep function T wo main processes regulate sleep. A homeostatic process regulates sleep need and intensity according to the time spent awake or asleep. A circadian process regulates the appropriate timing of sleep and wakefulness across the 24-h day. A highly reliable index of the homeostatic process is provided by the amplitude and prevalence of delta (1-to 4-Hz) oscillations in the electroencephalogram (EEG) of nonrapid eye movement (NREM) sleep (hereafter, ''delta power''). Delta power is high at sleep onset and decreases during sleep, in parallel with sleep depth. Sleep deprivations and naps induce a predictable increase or decrease, respectively, in delta power during subsequent sleep. The interaction between homeostatic and circadian processes is mathematically described in the two-process model of sleep regulation, which provides a framework for prediction and interpretation of a large body of experimental data (1).Among hypotheses concerning the physiological function of waking-induced changes in sleep, the most compelling suggests that sleep plays a key role in synaptic plasticity (2, 3). More specifically, EEG delta power during NREM sleep has been shown to play a critical role in learning-induced plasticity (4-6). In general, the prediction is that local neural activation due to specific behavioral (cognitive) demands imposes a burden on the brain which necessitates sleep and which is reflected by the EEG delta power.On the basis of mathematical modeling and experimental data, we have shown that sleep need, as indexed by the EEG delta power, is under genetic control (7), which is of direct relevance for explaining the interindividual vulnerability to sleep loss in human subjects (8, 9). However, deciphering the molecular bases of sleep need is rendered difficult because the contr...

Our findings indicate that corticosterone contributes to the sleep-deprivation-induced changes in brain transcriptome that have been attributed to wakefulness per se. The study identified 78 transcripts that respond to sleep loss independent of corticosterone and time of day, among which genes involved in neuroprotection prominently feature, pointing to a molecular pathway directly relevant for sleep function.

Narcolepsy is a sleep disorder characterized by excessive daytime sleepiness and attacks of muscle atonia triggered by strong emotions (cataplexy). Narcolepsy is caused by hypocretin (orexin) deficiency, paralleled by a dramatic loss in hypothalamic hypocretin-producing neurons. It is believed that narcolepsy is an autoimmune disorder, although definitive proof of this, such as the presence of autoantibodies, is still lacking. We engineered a transgenic mouse model to identify peptides enriched within hypocretin-producing neurons that could serve as potential autoimmune targets. Initial analysis indicated that the transcript encoding Tribbles homolog 2 (Trib2), previously identified as an autoantigen in autoimmune uveitis, was enriched in hypocretin neurons in these mice. ELISA analysis showed that sera from narcolepsy patients with cataplexy had higher Trib2-specific antibody titers compared with either normal controls or patients with idiopathic hypersomnia, multiple sclerosis, or other inflammatory neurological disorders. Trib2-specific antibody titers were highest early after narcolepsy onset, sharply decreased within 2-3 years, and then stabilized at levels substantially higher than that of controls for up to 30 years. High Trib2-specific antibody titers correlated with the severity of cataplexy. Serum of a patient showed specific immunoreactivity with over 86% of hypocretin neurons in the mouse hypothalamus. Thus, we have identified reactive autoantibodies in human narcolepsy, providing evidence that narcolepsy is an autoimmune disorder.

Maintaining wakefulness is associated with a progressive increase in the need for sleep. This phenomenon has been linked to changes in synaptic function. The synaptic adhesion molecule Neuroligin-1 (NLG1) controls the activity and synaptic localization of N-methyl-Daspartate receptors, which activity is impaired by prolonged wakefulness. We here highlight that this pathway may underlie both the adverse effects of sleep loss on cognition and the subsequent changes in cortical synchrony. We found that the expression of specific Nlg1 transcript variants is changed by sleep deprivation in three mouse strains. These observations were associated with strainspecific changes in synaptic NLG1 protein content. Importantly, we showed that Nlg1 knockout mice are not able to sustain wakefulness and spend more time in nonrapid eye movement sleep than wild-type mice. These changes occurred with modifications in waking quality as exemplified by low theta/alpha activity during wakefulness and poor preference for social novelty, as well as altered delta synchrony during sleep. Finally, we identified a transcriptional pathway that could underlie the sleep/wake-dependent changes in Nlg1 expression and that involves clock transcription factors. We thus suggest that NLG1 is an element that contributes to the coupling of neuronal activity to sleep/wake regulation.ChIP | EEG | gene expression | sleep homeostasis | synaptic plasticity S leep is crucial for learning, memory, and other functions essential for proper functioning of the brain and body (1, 2). These functions have been associated with the sleep recovery process, which defines a level of pressure for sleep that increases with wakefulness and dissipates during sleep and that is reflected by changes in sleep intensity (3, 4). Sleep intensity is indexed by electroencephalographic (EEG) markers of neuronal synchrony in delta frequencies (1-4 Hz) measured during nonrapid eye movement (NREM) sleep (5). During wakefulness, mechanisms favoring desynchrony in the delta range predominate, and the brain can maintain cognition, whereas during sleep, events promoting network synchrony mostly take place with high delta activity thought to be permissive of recovery (3, 6). The sleep recovery process has been hypothesized to originate and contribute to the maintenance of both synaptic and network equilibrium (6-8). This notion is supported by the observation that specific plasticityrelated genes may be directly involved in regulating sleep need (9). Certain clock genes may also directly contribute, in a circadian-independent manner, to the sleep recovery process (5, 9). However, the mechanisms underlying the capacity and requirement of the brain to switch from an alert desynchronized state to an unconscious synchronized state remain elusive.Glutamate, the main excitatory neurotransmitter of the brain, can induce long-term modifications of synaptic transmission and, thus, changes in network connectivity. This is achieved mainly via glutamate's action on two types of receptors: N-methyl-D-aspa...

Curie T; Mongrain V; Dorsaz S; Mang GM; Emmenegger Y; Franken P. Homeostatic and circadian contribution to EEG and molecular state variables of sleep regulation. SLEEP 2013;36(3):311-323.