Neurobiology of Sleep and Wakefulness

1. Neurobiology of Sleep and Wakefulness Tom Scammell, MD Neurology, BIDMC

2. Circadian regulation of sleep (Saper) • The neurobiology of sleep • Narcolepsy and other sleep disorders

3. 3 Stages of Behavior • Wakefulness - awareness of self and one’s environment • Rapid Eye Movement (REM) Sleep - unconscious but cortex active, dreaming, paralysis, saccadic eye movements • Non-REM Sleep - unconscious with little cortical activity

4. The electroencephalogram

5. EEG waves differ across behavioral states Alpha (8-13 Hz) Stage 1 Stage 2 NREM Stage 3 Stage 4 REM Delta (< 4 Hz) Theta (4-7 Hz)

6. The Sleep Cycle REM 12 1 2 3 4 5 6 Clock time

7. 2 major determinants of sleep: • Homeostatic component- long sleep compensates for prolonged wakefulness • Circadian component - alertness varies with time of day

8. Sleep homeostasis: adenosine • ATP ADP AMP Adenosine • Dependent on glucose, glycogen, and O2 • Brain glycogen falls with sleep deprivation • Adenosine concentration rises during wake and falls during sleep • Caffeine blocks adenosine receptors • Other somnogens: PGD2, TNFa...

9. Wake-promoting pathways

10. REM sleep • Cortical activation • Dreams are vivid, emotional, and bizarre • Paralysis • Rapid eye movements • Autonomic fluctuations

11. Mechanisms of REM sleep

12. Non-REM sleep • Cortical synchrony • Difficult to wake out of deep NREM sleep • Dreams brief and less vivid • Increased parasympathetic activity

13. Mechanisms of Non-REM sleep

14. VLPO lesions produce insomnia Lu, et al, 2000

15. Amines and carbachol inhibit the VLPO Gallopin, et al, 00

16. The flip-flop and bistability Saper, et al, 01

17. What stabilizes wake and sleep?

18. OrexinHypocretin

19. Brief bouts of wake and sleep with orexin deficiency %wake %wake Mochizuki, et al, 04

20. Orexin innervation of the human locus coeruleus Scammell, 03

21. Orexin activates arousal regions ( ) REM-on neurons

22. Orexin excites orexin neurons Li, et al, 02

23. Orexin may stabilize sleep/wake behavior

24. Activity of state-regulatory nuclei Wake Non-REM REM Amines (locus coeruleus, dorsal raphe, tuberomammillary nucleus) Acetylcholine (LDT/PPT, basal forebr.) Orexin/Hypocretin GABA (ventrolateral preoptic nucleus) O O O O O

25. Sleep disorders are clinically important • 15% of adults have chronic insomnia • 4% of adults have chronic sleepiness • 25% of motor vehicle accidents with loss of consciousness are due to falling asleep • 60% of fatal truck accidents are due to sleepiness

26. A 23 year old woman is referred for excessive sleepiness after having fallen asleep while driving. She reports that her sleepiness has been present since high school, and she often struggles to remain awake. She occasionally feels weak in the knees when laughing. Once, she fell to the ground while laughing during a party and could not get up for 1-2 minutes. If she is sleepy while driving, she may imagine seeing an animal in the road. Once she was terrified to find herself unable to move for a minute after awakening.

27. Narcolepsy Daytime sleepiness Fragmented nighttime sleep Fragments of REM sleep (?) Cataplexy • sudden, brief episodes of muscular weakness, Hypnagogic hallucinations • vivid, dream-like hallucinations at the beginning or end of sleep Sleep paralysis • inability to move upon awakening

28. MT W REM 1 2 3/4 1800 2000 2200 2400 0200 0400 0600 0800 1000 1200 1400 1600 MT W REM 1 2 3/4 1800 2000 2200 2400 0200 0400 0600 0800 1000 1200 1400 1600 Polysomnograms in control anduntreated narcoleptic patient REM Sleep Control Sleep stage Time of day REM Sleep Untreated Patient Sleep stage Time of day Adapted from Rogers et al. Sleep. 1994;17:590.

29. Loss of orexin in human narcolepsy Crocker, et al, 05

30. Impaired orexin signaling and narcolepsy Mice/Rats/Dogs Humans Lack of orexin Loss of orexin neurons Lack of orexin receptors Loss of orexin neurons Narcolepsy Daytime sleepiness Fragmented sleep Cataplexy Sleep paralysis Hypnagogic hallucinations

31. Cataplexy in orexin knockout mice

32. Probable mechanisms of narcolepsy LDT/PPT REM-on cells

33. What causes narcolepsy? • Most narcoleptics do not have mutations in the genes coding for orexin or its receptors • Only 1/3 of monozygotic twins will both develop narcolepsy • 85% of narcoleptics with cataplexy have HLA DQB1* 0602 compared to only about 25% of the general population

34. What causes narcolepsy? • Narcoleptics may have gliosis (scarring) in the orexin neuron region • HLA DQB1* 0602 and other genes may confer a susceptibility for some individuals to develop narcolepsy, possibly through an autoimmune attack on the orexin neurons

35. Narcolepsy and Metabolism • People with narcolepsy are mildly obese (BMI=28) but eat less than normal • Orexin knockout mice only have narcolepsy • Thus, human narcolepsy may be due to more than just orexin deficiency

36. Orexin/ataxin-3 mice

38. Orexin/ataxin-3 mice are overweight but eat less than normal ?decreased sympathetic tone & metabolic rate

39. Orexin neurons contain preprodynorphin mRNA

40. Lateral hypothalamic dynorphin is lost in orexin/ataxin-3 mice WT Orexin KO Orexin/ataxin-3

41. Orexin neurons respond to metabolic factors Yamanaka, et al, 03

42. Hunger-induced wake requires the orexin neurons Yamanaka, et al, 03

43. Orexin and drug addiction • Addiction to amphetamines appears to be quite rare in people with narcolepsy • Orexin neurons innervate brain regions implicated in drug-seeking (ventral tegmental area, nucleus accumbens) • Orexin neurons are activated with conditioned place preference • Orexin antagonist blunts conditioned place preference to morphine or amphetamines • …Maybe orexin provides the impetus to seek rewarding stimuli

44. VTA Motivation, drug-seeking

45. Waking is due to the coordinated action of neurons producing amines, acetylcholine, and orexin • Pontine pathways regulate REM, and preoptic nuclei promote non-REM sleep • Orexin deficiency produces narcolepsy • Orexin may promote many aspects of arousal

46. Orexin KO run less but the diurnal pattern is normal

47. Orexin KO spend less time running Still, orexin KO mice initiate wheel running as often and run as fast as WT mice

48. KO fall asleep or have cataplexy soon after running 28% of running bouts are soon followed by cataplexy

49. Timelines of wheel running