Comparative Perspectives on the Function of Oxytocin in Fish and Mammals

The central oxytocin (OT) system regulates various behavioral processes, including social recognition, social bonding, and mate preference. In human studies, intranasal administration of OT facilitates the salience of social information mediated by visual information and motivational states in both sexes. Some rodent animal models, such as mice and prairie voles, have been used to investigate the neural/molecular mechanisms underlying central OT function. Elucidating how the OT system modulates visual processing is difficult using rodent models, however, because rodents mainly use chemical communication and olfactory investigation for social interactions. In this review, we propose medaka fish as an advantageous comparative model for investigating this issue. Medaka fish have the ability to visually recognize conspecifics and select the appropriate mate based on familiarity recognition. Medaka fish can use faces (head parts) for familiarity recognition, and may have a special neural system to recognize faces. OT receptors are distributed in homologous areas of the primary visual center in medaka fish and primates (optic tectum and superior colliculus, respectively). In addition, mutations of genes for OT or OT receptors (OTR) in medaka influence mate choice in a sex-specific manner. As human OT administration also has opposite effects depending on the sex, comparative studies between medaka and humans could help to elucidate the evolutionary roots and basic neural mechanisms underlying social salience in face detection, as well as how the OT system contributes to the sexual spectrum and diversity in mating strategies.