| First Author | Vassalli A | Year | 2017 |
| Journal | Proc Natl Acad Sci U S A | Volume | 114 |
| Issue | 27 | Pages | E5464-E5473 |
| PubMed ID | 28630298 | Mgi Jnum | J:244284 |
| Mgi Id | MGI:5913063 | Doi | 10.1073/pnas.1700983114 |
| Citation | Vassalli A, et al. (2017) Hypocretin (orexin) is critical in sustaining theta/gamma-rich waking behaviors that drive sleep need. Proc Natl Acad Sci U S A 114(27):E5464-E5473 |
| abstractText | Hcrt gene inactivation in mice leads to behavioral state instability, abnormal transitions to paradoxical sleep, and cataplexy, hallmarks of narcolepsy. Sleep homeostasis is, however, considered unimpaired in patients and narcoleptic mice. We find that whereas Hcrtko/ko mice respond to 6-h sleep deprivation (SD) with a slow-wave sleep (SWS) EEG delta (1.0 to 4.0 Hz) power rebound like WT littermates, spontaneous waking fails to induce a delta power reflecting prior waking duration. This correlates with impaired theta (6.0 to 9.5 Hz) and fast-gamma (55 to 80 Hz) activity in prior waking. We algorithmically identify a theta-dominated wakefulness (TDW) substate underlying motivated behaviors and typically preceding cataplexy in Hcrtko/ko mice. Hcrtko/ko mice fully implement TDW when waking is enforced, but spontaneous TDW episode duration is greatly reduced. A reformulation of the classic sleep homeostasis model, where homeostatic pressure rises exclusively in TDW rather than all waking, predicts delta power dynamics both in Hcrtko/ko and WT mouse baseline and recovery SWS. The low homeostatic impact of Hcrtko/ko mouse spontaneous waking correlates with decreased cortical expression of neuronal activity-related genes (notably Bdnf, Egr1/Zif268, and Per2). Thus, spontaneous TDW stability relies on Hcrt to sustain theta/fast-gamma network activity and associated plasticity, whereas other arousal circuits sustain TDW during SD. We propose that TDW identifies a discrete global brain activity mode that is regulated by context-dependent neuromodulators and acts as a major driver of sleep homeostasis. Hcrt loss in Hcrtko/ko mice causes impaired TDW maintenance in baseline wake and blunted delta power in SWS, reproducing, respectively, narcolepsy excessive daytime sleepiness and poor sleep quality. |
