Locus coeruleus neurons: Cessation of activity during cataplexy

Cataplexy, a symptom of narcolepsy, is a loss of muscle tone usually trigge red by sudden, emotionally significant stimuli. We now report that locus co eruleus neurons cease discharge throughout cataplexy periods in canine narc oleptics. Locus coeruleus discharge rates during cataplexy were as low as o r lower than those seen during rapid-eye-movement sleep. Prazosin, an ct, a ntagonist, and physostigmine, a cholinesterase inhibitor, both of which pre cipitate cataplexy, decreased locus coeruleus discharge rate. Our results are consistent with the hypothesis that locus coeruleus activit y contributes to the maintenance of muscle tone in waking, and that reducti on in locus coeruleus discharge plays a role in the loss of muscle tone in cataplexy and rapid-eye-movement sleep. Our results also show that the comp lete cessation of locus coeruleus activity is not sufficient to trigger rap id-eye-movement sleep in narcoleptics. (C) 1999 IBRO. Published by Elsevier Science Ltd.