HCRT and narcolepsy: Consistently, postmortem studies of human narcolepsy subjects showed an 80–100% reduction in the number of neurons containing detectable prepro-orexin mRNA or orexin-like immunoreactivity in the hypothalamus and undetectable levels of orexin peptides in projection sites (Figures 2A,B) (Peyron et al., 2000; Thannickal et al., 2000).