More evidence for appetite-regulating roles of the oxytocin system, which is the same as the isotocin system in fish, can be found in studies using higher vertebrates: insatiable appetite and strong obesity have been linked to impaired oxytocin signalling [131,132] and blocking oxytocin neurons can increase the feed intake [133]. Here, OXT is linked to obesity due to melanocortin 4 receptor deficiency.