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DOI: 10.1055/s-2005-920471
Intranasal orexin A reduces activation and food intake in humans
Orexin A is known from animal experiments to influence arousal and food intake behavior. In an exploratory study we assessed effects of intranasal orexin A on food intake and activation in humans. Experiments were conducted in 12 food-deprived subjects who were administered either 100 nmol of orexin or placebo before ingesting 400ml of liquid food. Before and after sessions, subjects rated feelings of tiredness and filled in an adjective check list. They were allowed to eat rolls ad libitum 60min after substance administration. In the placebo condition, rated tiredness declined towards the end of the session, whereas in the orexin condition it remained elevated and exceeded placebo values at the end of the test. Scores of tiredness and deactivation in the check list were likewise increased following orexin. Also, subjects in the orexin condition ate less rolls. Our observations are in line with findings on central nervous effects of orexin A in monkeys and indicate that intranasal orexin A reduces food intake and attenuates activation in humans. In rodents, orexin A has reversed effects, pointing to a species-dependent effect on central nervous pathways.