Muscarinic cholinergic receptors in human narcolepsy: a PET study.

To investigate the function of the muscarinic cholinergic receptor (mAchR) in narcolepsy and the effects of pharmacotherapy on mAchRs. Muscarinic neural transmission serves as the main executive system in REM sleep. Studies in canine narcolepsy reported an increase in mAchRs in the pons. The mAchRs of 11 drug naive/free patients with narcolepsy and 21 normal controls were investigated using PET with [11C]N-methyl-4-piperidylbenzilate ([11C]NMPB). Measurements were done in the pons, thalamus, striatum, and cerebral cortex. Seven of the 11 patients also underwent additional PET scans after the alleviation of symptoms by pharmacotherapy. There were no differences in [11C]NMPB binding between the control and drug naive/free patients in all areas analyzed. At the time of on-medication PET scan, [11C]NMPB binding in the thalamus was decreased, but only to a small degree compared with that by anticholinergic drugs. The present results do not support the notion that the mAchR is the main site of action of pharmacotherapy in the marked clinical improvement of human cataplexy.