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 Delta (< 4 Hz) Stage 4 REM 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 Ventral periaqueductal grey (dopamine)

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

11. Mechanisms of REM sleep See Saper lab Nature 2006

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 activates arousal regions ( ) REM-on neurons

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

22. Orexin may stabilize sleep/wake behavior

23. 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

24. Sleep disorders are clinically important • 15% of adults have chronic insomnia • 24% 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

25. 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.

26. Narcolepsy Daytime sleepiness Disrupted 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

27. W REM 1 2 3/4 2000 2000 2400 2400 0400 0400 0800 0800 1200 1200 1600 1600 Polysomnograms in control anduntreated narcolepsy patient MT W REM Control 1 2 3/4 Time of day MT Untreated narcolepsy Time of day Adapted from Rogers et al. Sleep. 1994;17:590.

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

29. 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

30. Cataplexy in orexin knockout mice

31. Probable mechanisms of narcolepsy no orexin LDT/PPT REM-on cells raphe LC motor neurons

32. 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

33. 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

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

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

36. Narcolepsy and Metabolism • People with narcolepsy are mildly obese (BMI=28) but eat less than normal • Thus, metabolic rate may be reduced in narcolepsy Drugs: tricyclic antidepressants Modafinil trazedone Amphetamines Gamma hydroxy butyrate

37. Orexin/ataxin-3 mice

39. Orexin/ataxin-3 mice are overweight but eat less than normal decreased metabolic rate and locomotor activity? less motivation to eat?

40. Orexin and drug addiction • Addiction to amphetamines appears to be quite rare in people with narcolepsy • Orexin neurons activate brain regions implicated in drug-seeking (ventral tegmental area, nucleus accumbens) and makes VTA neurons more excitable • Mice lacking orexin have almost no conditioned place preference to morphine • …Maybe orexin provides the impetus to seek rewarding stimuli like food and drugs

41. orexin Arc VMH VTA Wakefulness, reduced REM sleep raphe LC Feeding Motivation, drug-seeking VLM Increased sympathetic activity

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

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

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

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

46. Why do orexin KO mice run less? • Sleepiness • Imminent cataplexy • Less motivated to keep running (perhaps running is less rewarding)