A sleep study shows episodes of sudden loss of muscle tone triggered by laughter, with brief REM-like intrusions during wakefulness. Which neurotransmitter system is primarily deficient in this condition?
- A Hypocretin (orexin) neurons of the lateral hypothalamus ✓
- B Dopaminergic neurons of substantia nigra
- C Serotonergic neurons of the dorsal raphe nucleus
- D Noradrenergic neurons of the locus coeruleus
Correct answer: A. Hypocretin (orexin) neurons of the lateral hypothalamus
Explanation
The clinical description is narcolepsy with cataplexy (Type 1 narcolepsy), caused by autoimmune destruction of hypocretin/orexin-producing neurons in the lateral hypothalamus. Hypocretin normally promotes wakefulness and suppresses REM sleep; its absence leads to sudden REM intrusions during wakefulness (cataplexy, sleep paralysis, hypnagogic hallucinations). Diagnosis is confirmed by CSF hypocretin-1 < 110 pg/mL. Dopaminergic loss characterizes Parkinson's disease.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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