Odor of Osmanthus fragrans affects orexin level in rats and ingestion behavior in humans

Abstract

Olfactory neural messages are sent to the hypothalamus and induce various autonomic reactions depending on the kind of odor stimulus. Since the hypothalamus is known to produce feeding-related neuropeptides, odors may affect the production of these neuropeptides. In Wistar rats, we examined how the orexin level was affected by odor stimuli. Among several stimuli tested, the odor of Osmanthus fragrans flowers lowered the level of prepro-orexin mRNA in the hypothalamus. Rats fed with food containing the Osmanthus odor showed less food intake and body weight than those fed with non-odor food or food with milk odor used as a comparative odor. In the human experiment, 10 healthy females ranging from 20 to 40 years old were divided into 2 groups with or without exposure to Osmanthus odor and all the subjects were presented with the same menus of meals for 12 days. The results showed that the body weight of the odor group reduced more with better mental and physical status than the control group. Locomotion and rearing were reduced under Osmanthus odor in rats, and the larger contingent negative variance of EEG was observed under Osmanthus odor than under milk odor in humans: both of these results suggest some sedative effects of Osmanthus odor. Collectively, these results suggest that Osmanthus odor affects autonomic, appetitive and mental activities at least through reducing the orexin level. [J Physiol Sci. 2007;57 Suppl:S136]