Greatly increased numbers of histamine cells in human narcolepsy with cataplexy.

Objective: To determine whether histamine cells are altered in human narcolepsy with cataplexy and in animal models of this disease.

Methods: Immunohistochemistry for histidine decarboxylase (HDC) and quantitative microscopy were used to detect histamine cells in human narcoleptics, hypocretin (Hcrt) receptor-2 mutant dogs, and 3 mouse narcolepsy models: Hcrt (orexin) knockouts, ataxin-3-orexin, and doxycycline-controlled-diphtheria-toxin-A-orexin.

Results: We found an average 64% increase in the number of histamine neurons in human narcolepsy with cataplexy, with no overlap between narcoleptics and controls.