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1 January 2006 Vasotocin/Isotocin-immunoreactive Neurons in the Medaka Fish Brain Are Sexually Dimorphic and Their Numbers Decrease After Spawning in the Female
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Abstract

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/iso-tocin (VT/IT) neurons in the brains of both male and female medaka (Oryzias latipes) using immu-nohistochemistry. 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.

Tamaki Ohya and Shinji Hayashi "Vasotocin/Isotocin-immunoreactive Neurons in the Medaka Fish Brain Are Sexually Dimorphic and Their Numbers Decrease After Spawning in the Female," Zoological Science 23(1), 23-29, (1 January 2006). https://doi.org/10.2108/zsj.23.23
Received: 8 April 2005; Accepted: 1 November 2005; Published: 1 January 2006
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