Socially induced sex change regulates forebrain isotocin in Lythrypnus dalli

The neurohypophyseal peptides are evolutionarily conserved and their expression can be socially modulated. Our question was what effect will socially induced sex change have on forebrain isotocin, an oxytocin homologue? We removed males from social groups to induce dominant females to change sex and become males in Lythrypnus dalli. Fish in the late stages of sex change had fewer forebrain isotocin-immunoreactive (-ir) cells than early stage and unchanged females. When groups were consolidated into unequivocal males (control males and sex-changed new males) and unequivocal females (fish prior to courtship as a male), females had significantly more isotocin-ir cells than control males and recently sex-changed fish. This is the first study demonstrating the social regulation of forebrain isotocin.