Research groups such as Assistant Professor Saori Yokoi of Hokkaido University, Specially Appointed Professor Hideaki Takeuchi of Okayama University (joint appointment with Professor of Tohoku University), and National Institute for Basic Biology control whether or not Medaka prefers intimate opposite sex by a hormone called oxytocin. I made it clear that I was doing it.It is hoped that the mechanism that creates intimate preference for the opposite sex and gender differences will be elucidated.

 While medaka females tend to visually remember "males by their side" and actively accept the male's courtship, males court the female regardless of intimacy.In this study, we focused on oxytocin known as "love hormone", which is important for mother-child relationship and bond formation with partners, and examined the effect of medaka on heterosexual preference.

 We produced medaka (oxytocin-deficient medaka) that cannot synthesize functional oxytocin by genome editing technology, and verified their preference for the opposite sex.As a result, females lost their preference for males and actively accepted strangers, but males were indifferent to females they met for the first time in a tripartite relationship (male, male, female), while to intimate females. It was observed that he was driving away his rival male and was near the female (spousal defense behavior).

 Oxytocin is said to work to strengthen attachment to intimate others in humans, but it has been clarified that it works to reduce attachment in male medaka fish.From this, it is considered that oxytocin has a function other than "love hormone" depending on the animal species and sex.

 There was a marked change in the expression level of some genes in the brain of medaka, which showed behavioral disorders.Since the gene was also present in humans, it is expected that basic research on medaka will elucidate the mechanism by which oxytocin controls attachment to intimate others and the mechanism that causes gender differences.

Paper information:[Proceedings of the National Academy of Sciences] Sexually dimorphic role of oxytocin in medaka mate choice

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