Vasotocin/isotocin-immunoreactive neurons in the medaka fish brain are sexually dimorphic and their numbers decrease after spawning in the female.
In teleosts, the distribution of neurons in the preoptic-hypothalamic region and their associated neurohypophysial hormones, such as vasotocin (VT), appears to be different among species. This differential distribution is thought to reflect the social and/or sexual status of individuals within a species. In the present study, we analyzed the number, size and the distribution of vasotocin/isotocin (VT/IT) neurons in the brains of both male and female medaka (Oryzias latipes) using immunohistochemistry. VT/IT neurons were similarly located in an inverted L-shape in the nucleus preopticus in both gender, as has been already reported in salmonids. However, computer-assisted image analysis revealed sexual dimorphism in the number of VT/IT-immunoreactive (ir) neurons, with greater numbers found in males as compared to females. Further, in the female brain, the number of VT/IT-ir neurons decreased significantly after spawning. In pre-spawning compared to post-spawning females, the small-sized VT/IT-ir neurons dominated. Sexual differentiation of the medaka is fully dependent upon the steroid status during the early developmental stages and steroids are also known to trigger gender-specific behavior in the adult medaka. Our findings strongly suggest that VT and/or IT neurons may be functionally related to ovulation and/or the reproductive axes through connections to their steroidal status.
Ohya
Tamaki
T
Laboratory of Endocrinology, Graduate School of Integrated Science, Yokohama City University, Yokohama 236-0027, Japan.
Hayashi
Shinji
S
D000818:Animals; D001921:Brain / Q000166:cytology; D001923:Brain Chemistry / Q000502:physiology; D005260:Female; D007150:Immunohistochemistry / Q000662:veterinary; D008297:Male; D009474:Neurons / Q000378:metabolism*; D009990:Oryzias / Q000378:metabolism / Q000502:physiology*; D010121:Oxytocin / Q000031:analogs & derivatives* / Q000378:metabolism; D012727:Sex Characteristics; D012726:Sexual Behavior, Animal / Q000502:physiology*; D014668:Vasotocin / Q000378:metabolism*
D010121:Oxytocin; C008215:isotocin; D014668:Vasotocin