Abstract
Some components of the neural circuits underlying innate odor-evoked responses have recently been elucidated. Odor information detected by the olfactory receptors is transmitted from the olfactory bulb to the cortical amygdala, where physiological and emotional states such as attraction or avoidance are controlled. Thus, activation of specific olfactory receptors can elicit changes in physiological and/or psychological state. Here, we examined on the odorant Hex-Hex Mix, which has been reported to induce anti-fatigue effects. Fatigue is a prevalent condition that is often related to overwork and psychological stress. Various anti-fatigue treatments have been developed, including supplements and odorants. However, the mechanisms underlying the anti-fatigue effects of these substances are currently unclear. In the present study, we analyzed the involvement of the olfactory system in the mechanisms underlying this effect. We identified the human olfactory receptors activated by Hex-Hex Mix, and evaluated whether activation of these olfactory receptors by a newly developed odorant elicited a similar anti-fatigue effect to Hex-Hex Mix. We assessed anti-fatigue effects with behavioral tests, and 17 healthy males performed the 2-back test as a fatigue-inducing task with or without exposure to the new odorant. Immediately before and after the task, participants performed a cognitive task to evaluate their level of mental fatigue. We found that the difference value of the correct response rate on the cognitive task in the evaluation session was significantly different between in the odorant condition and in the without-odorant condition during the fatigue-inducing session suggesting that the new odorant may improve performance in the fatigue-inducing condition. The results indicated that the new odorant activates the same olfactory receptors as Hex-Hex Mix, which has been reported to induce anti-fatigue effects. Our findings suggest that the olfactory receptors in the olfactory system may be involved in the attenuation of fatigue.
Highlights
Odorants are recognized by olfactory receptors (ORs) expressed on the olfactory sensory neurons in the olfactory epithelium
To identify the ORs activated by the anti-fatigue odorant Hex-Hex Mix, the entire range of human ORs were stimulated with 10 ng/ml Hex-Hex Mix, while we evaluated the increase in intracellular cAMP caused by OR activation with a luciferase assay system
The results revealed that the difference value of the correct response rate on non-Stroop trials in Task B in the evaluation session was significantly different between the MCMP condition and the without-MCMP condition during the fatigue-inducing session
Summary
Odorants are recognized by olfactory receptors (ORs) expressed on the olfactory sensory neurons in the olfactory epithelium. Mammalian ORs are seven transmembrane G protein coupled receptors [1]. It was reported that 396 OR genes in humans, and 1035 OR genes in the mouse constitute one of the largest gene families in the mammalian genome [2]. In the mammalian olfactory system, an odorant molecule is recognized by a number of ORs, and an OR can recognize multiple odorant molecules. This mechanism enables us to discriminate hundreds of thousands of odorants [3,4]. The perceptual qualities of an odor are determined by the OR code that is activated
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