Animals sense odorants and show olfactory preference towards them. It is empirically known that olfactory preference to the same odorant changes depending on the odorant concentration in humans. For example, indole has a pleasant and floral smell at low concentrations, but is putrid at high concentrations. However, little is understood about the neuronal basis of this behavioral phenomenon because of high complexity of neural circuits in higher animals. Therefore, for the analysis of neural and molecular mechanisms of the phenomenon, we use Caenorhabditis elegans in which all neurons and their complete connectivity pattern have been described. Here I introduce the results of analyses of odor concentration-dependent preference change using C. elegans.

In this review, we summarized our studies about the bioactivities of volatile terpenoid components in the trees against harmful organisms. The brine shrimp bioassay was performed as the screening of active components. Anti-termite, anti-mite and anti-tick components were revealed on mono-, sesqui-, and di-terpenoids obtained from several parts of the trees. Some terpenoids in the plant essential oils showed the growth inhibition activities against harmful algae. We also explained the effects of oxidations of the essential oil component on the antifungal activities against wood decay fungi. Finally, we introduced our recent study of antifungal properties of terpenoids against Heterobasidion parviporum.

Plants have a system of ‘priming and trigger’ for the effective defense system with phytoalexin. Attacked plants emit specific volatile compound(s), which have neighboring plants ready for production of phytoalexin. In case of studying tree, the size and hard tissue prevents biochemical and molecular biological research works. In this chapter, proposing a woody plant’s cell culture system as a study model of chemical communication and the primary results are presented.

Most mammals deposit scent marks to advertise territory ownership. When other individuals encounter these marks, they can recognize species, sex, age, and individuals by sniffing the scents. This recognition is essential for individual and species survival because it enables them to avoid encounters with predators and individuals to which they have previously lost contests and to find mating partners, while avoiding inbreeding. Some compounds, called pheromones, are secreted externally and received by a second individual of the same species, triggering specific reactions, such as innate behavior or changes in developmental and reproductive processes. In addition to visual and voice signals, odorants and pheromones are important for interspecies communication because they persist in the environment long after their senders have moved on. This paper reviews how odorants and pheromones are received in mammalian olfactory systems, considering the main olfactory and vomeronasal systems separately. Then, it explains why olfactory sensitivity and discrimination ability are better in mammals other than humans, such as dogs, and reports on mammalian pheromones for which the chemical structures are identified. Finally, I introduce our research on communication in domestic cats via species-specific odorants with characteristic sulfurous odor.

By inhaling scent volatiles (low-concentration) emitted from the leaves of Laurus noblis or the root of Vetiveria zizanioides, the decrease of vigilance performance during a visual display terminal task was prevented. On the other hands, the essential oil of Abies sibirica or (－)－bornyl acetate reduced arousal levels after the visual display terminal task without any influences of task performance in low-dose (scent aroma) condition. These findings suggest that the volatiles emitted from the leaves of L. noblis or the root of V. zizanioides at low concentration could be utilized when a high level of vigilance performance is needed, such as driving a car. Furthermore, the essential oil of A. sibilica or (－)－bornyl acetate might be useful for the prevention of high-arousal related mental health disturbance, such as insomnia.