The gonadotropin-inhibitory hormone modulates the neurosteroids-synthesizing pathways and aggressive behaviour in male european sea bass

Resumen del trabajo presentado en el 11th International Symposium on Reproductive Physiology of Fish, celebrado en Manaus (Brasil) del 03 al 08 de junio de 2018.Gonadotropin-inhibitory hormone (GnIH) is a neuropeptide that inhibits gonadotropin secretion and regulates vertebrate reproduction. Recent evidences obtained in male quail suggested that GnIH may inhibit aggressive behavior by regulating brain aromatase activity and neuroestrogen synthesis. However, information concerning the role of GnIH in the modulation of brain neurosteroidogenesis and aggressive behavior is lacking in fish. In order to fill this gap, in this study we have analyzed the effects of GnIH in the brain expression of the main neurosteroids-synthesizing enzymes in the European sea bass, Dicentrarchus labrax. Moreover, to understand the behavioral role of GnIH in this species, we have performed a behavioral mirror test as a proxy to measure aggression levels. [Methods]: Sea bass GnIH-1 (sbGnIH-1) and GnIH-2 (sbGnIH-2) were intracerebroventricularly (icv)-administered to the fish (doses 1, 2 and 4 ¿g/fish). Transcript levels of neurosteroid-synthesizing enzymes and steroid receptors were determined in the brain and pituitary of sea bass by quantitative PCR. The effects of GnIH in the aggressive behavior was determined by using a mirror test in pairs of animals. Video recordings started 20 min after the icv injection and extended for 30 min. The video recordings were analyzed using Noldus EthoVision XT software and different parameters related to mobility and mirror interactions were monitored. [Results and Discussion]: Our results showed that both sbGnIH-1 and sbGnIH-2 decreased the brain transcript levels of 17ß-hydroxysteroid dehydrogenase (hsd17b) and 3 ß-hydroxysteroid dehydrogenase (hsd3b) and increased the expression of brain aromatase (cyp19a1b). In the pituitary, sbGnIH-1 also stimulated the cyp19a1b expression whereas sbGnIH-2 reduced hsd17b mRNA levels. Both stimulatory and inhibitory effects of GnIH on the expression of different estrogen receptor subtypes were found. These results suggest that GnIH could reduce the testosterone levels and increase the neuroestrogen synthesis in the brain of sea bass. The behavioral analysis showed that GnIH was able to reduce the relative movement and mirror attack events of sea bass. [Conclusion]: aken together, our results suggest that central administration of GnIH can inhibit the aggressive behavior of sea bass by decreasing the androgen production and increasing the neuroestrogen synthesis in the brain of this species